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Respiratory System - Complete Notes (K. Sembulingam & Prema Sembulingam)

Essentials of Medical Physiology - Section 9: Respiratory System and Environmental Physiology Chapters 118-132

CHAPTER 118: PHYSIOLOGICAL ANATOMY OF RESPIRATORY TRACT

Types of Respiration

External respiration - exchange of O2 and CO2 between atmosphere and blood (lungs)
Internal (tissue) respiration - exchange of O2 and CO2 between blood and tissue cells
Cellular respiration - utilization of O2 for oxidative metabolism inside cells

Phases of Respiration

Pulmonary ventilation - movement of air in and out of lungs
Diffusion of gases - O2 and CO2 across the respiratory membrane
Transport of gases - in blood (O2 and CO2)
Tissue gas exchange - between blood and cells

Functional Anatomy of Respiratory Tract

Upper Respiratory Tract:

Nose - filters, warms, humidifies air; contains olfactory receptors
Pharynx - nasopharynx, oropharynx, laryngopharynx; passage for air and food
Larynx - contains vocal cords; voice production; prevents aspiration (epiglottis)

Lower Respiratory Tract:

Trachea - 10-12 cm long, C-shaped cartilage rings; bifurcates at carina (T4/5 level)
Bronchi - right main bronchus wider, shorter, more vertical (foreign body aspiration more common on right)
Bronchioles - no cartilage; terminal bronchioles = last purely conducting airway
Respiratory bronchioles - first site of gas exchange
Alveolar ducts and alveoli - final site of gas exchange

Lungs:

Right lung: 3 lobes (upper, middle, lower), ~625g
Left lung: 2 lobes (upper, lower), ~570g
Total ~700 million alveoli; surface area ~70 m2 (size of tennis court)
Covered by visceral pleura; chest wall by parietal pleura

Respiratory Unit (Acinus)

The terminal respiratory unit consists of:

Respiratory bronchiole
Alveolar duct
Alveolar sac
Alveoli

Respiratory Membrane (Alveolo-capillary membrane)

Layers (from alveolus to blood):

Surfactant layer (type II pneumocytes secrete surfactant)
Alveolar epithelium (type I pneumocytes - thin, for gas exchange)
Basement membrane of alveolar epithelium
Interstitial fluid (thin layer)
Basement membrane of capillary endothelium
Capillary endothelium

Total thickness: 0.2-0.6 micrometers (very thin for efficient diffusion)

Non-Respiratory Functions of Respiratory Tract

Olfaction - smell perception
Vocalization - speech, singing
Prevention of dust particles - nasal hair (vibrissae), mucus, cilia (mucociliary escalator)
Defense mechanism - lysozymes, IgA, macrophages (dust cells)
Maintenance of water balance - expired air is 100% saturated with water vapor
Regulation of body temperature - heat loss through expired air
Regulation of acid-base balance - CO2 excretion regulates pH
Anticoagulant function - mast cells in lungs secrete heparin
Secretion of ACE (Angiotensin-Converting Enzyme) - lungs convert angiotensin I to angiotensin II
Synthesis of hormonal substances - prostaglandins, histamine, serotonin (inactivated by lungs)

Respiratory Protective Reflexes

Cough reflex - irritation in larynx, trachea, bronchi; deep inspiration followed by forceful expiration against closed glottis; expulsion of foreign material
Sneezing reflex - irritation in nasal mucosa; sudden forceful expiration through nose
Swallowing (deglutition reflex) - epiglottis covers larynx during swallowing; prevents aspiration

CHAPTER 119: PULMONARY CIRCULATION

Features of Pulmonary Circulation

Low pressure system: Pulmonary artery pressure = 25/8 mmHg (mean ~15 mmHg)
Systemic circulation: 120/80 mmHg (mean ~100 mmHg)
Low resistance - walls are thin, distensible
Short circuit - blood travels short distance (lung capillaries)
Capillary transit time - 0.75 seconds (at rest), 0.3 sec during exercise
Blood volume in lungs = ~450 mL (~9% of total blood volume)

Pressures

Parameter	Value
Pulmonary arterial systolic	25 mmHg
Pulmonary arterial diastolic	8 mmHg
Mean pulmonary arterial pressure	15 mmHg
Pulmonary capillary pressure	7 mmHg
Pulmonary venous pressure	5 mmHg

Pulmonary Vascular Resistance (PVR)

PVR = (Mean PA pressure - PCWP) / Cardiac output
Normal PVR = 1-2 mmHg/L/min (much lower than systemic)

Factors Affecting Pulmonary Circulation

Hypoxia - causes vasoconstriction (hypoxic pulmonary vasoconstriction - HPV); directs blood away from poorly ventilated alveoli
Cardiac output - increase in CO dilates pulmonary vessels (recruitment and distension)
Gravity - West zones:
- Zone 1 (apex): Pa > Pa > Pv - no flow (theoretical)
- Zone 2 (middle): Pa > PA > Pv - intermittent flow
- Zone 3 (base): Pa > Pv > PA - continuous flow (best perfusion)

Pulmonary Edema

When capillary hydrostatic pressure exceeds oncotic pressure and lymphatic capacity
Normally lymphatics drain ~20 mL/hour; edema occurs when fluid accumulates beyond this
Caused by: left heart failure, mitral stenosis, ARDS, hypoproteinemia

CHAPTER 120: MECHANICS OF RESPIRATION

Inspiration (Active Process)

Primary muscles:

Diaphragm - main muscle; contracts and descends (moves down 1.5 cm quietly, up to 10 cm forcefully)
External intercostal muscles - elevate ribs, increase anteroposterior and transverse diameter

Accessory muscles (during forced inspiration):

Scalene muscles
Sternocleidomastoid
Serratus anterior
Pectoralis minor

Expiration (Passive Process during quiet breathing)

Elastic recoil of lungs and chest wall
Relaxation of inspiratory muscles

Active expiration (forced):

Internal intercostal muscles
Abdominal muscles (rectus abdominis, external and internal obliques, transversus abdominis)

Pressures During Breathing

Phase	Intrapleural Pressure	Intrapulmonary Pressure
End of expiration	-5 mmHg	0 (atmospheric)
During inspiration	-8 mmHg	-3 mmHg
During expiration	-5 mmHg	+3 mmHg

Intrapleural pressure is always negative (sub-atmospheric) - maintains lung inflation.

Compliance

Lung compliance = change in lung volume / change in transpulmonary pressure
Normal lung compliance = 200 mL/cmH2O
Decreased compliance = stiff lungs (fibrosis, pulmonary edema, ARDS)
Increased compliance = emphysema (destruction of alveolar walls)

Surfactant

Produced by Type II pneumocytes (alveolar type II cells)
Composition: Dipalmitoylphosphatidylcholine (DPPC) - major component (~70%)
Function: reduces surface tension; prevents alveolar collapse (atelectasis)
Follows Laplace's Law: P = 2T/r (surfactant lowers T)
Without surfactant: small alveoli collapse; work of breathing increases markedly
Deficiency in: premature babies = Respiratory Distress Syndrome (RDS) / Hyaline Membrane Disease (HMD)

Airway Resistance

Determined mainly by medium-sized bronchi (greatest total resistance)
Normal airway resistance = 1-2 cmH2O/L/sec
Reduced by: bronchodilators (β2 agonists, anticholinergics), deep inspiration
Increased by: bronchoconstriction (asthma), mucus plugging, foreign body

Work of Breathing

Work done to overcome: (1) airway resistance, (2) tissue resistance, (3) elastic resistance (compliance)
Normal work of breathing = ~0.5 joules/breath or ~5% of total body O2 consumption
Increases significantly in asthma, COPD, fibrosis

Restrictive vs Obstructive Disease

Feature	Restrictive	Obstructive
TLC	Decreased	Normal/Increased
FVC	Decreased	Decreased
FEV1	Decreased	Markedly decreased
FEV1/FVC	Normal (>80%)	Decreased (<70%)
Compliance	Decreased	Increased (emphysema)
Examples	Fibrosis, kyphoscoliosis	Asthma, COPD, bronchitis

CHAPTER 121: PULMONARY FUNCTION TESTS (PFTs)

Lung Volumes (4 volumes - cannot be added)

Volume	Definition	Normal Value
Tidal Volume (TV)	Air breathed in/out in one normal breath	500 mL
Inspiratory Reserve Volume (IRV)	Extra air inspired forcefully above TV	3000 mL
Expiratory Reserve Volume (ERV)	Extra air expired forcefully beyond TV	1100 mL
Residual Volume (RV)	Air remaining after maximal expiration	1200 mL

Note: RV cannot be measured by simple spirometry (requires helium dilution or body plethysmography).

Lung Capacities (4 capacities = combination of volumes)

Capacity	Formula	Normal Value
Inspiratory Capacity (IC)	TV + IRV	3500 mL
Functional Residual Capacity (FRC)	ERV + RV	2300 mL
Vital Capacity (VC)	IRV + TV + ERV	4600 mL
Total Lung Capacity (TLC)	All 4 volumes	5800 mL

FRC significance: Stabilizes alveolar O2 and CO2 between breaths; air cushion.

Dynamic Lung Volumes (Spirometry)

Test	Definition	Normal Value
FVC (Forced Vital Capacity)	Max air expelled after full inspiration	4.6 L (males)
FEV1 (Forced Expiratory Vol in 1st sec)	Air expelled in 1 second	3.2 L
FEV1/FVC ratio (Tiffeneau index)	Percentage of FVC expelled in 1 sec	>80%
FEF 25-75%	Mid-expiratory flow rate	Detects small airway disease
PEFR (Peak Expiratory Flow Rate)	Highest flow during forced expiration	400-600 L/min (adults)
MBC/MVV (Max Breathing/Ventilation Capacity)	Max air breathed in/out per minute	125-170 L/min

Measurement of FRC (RV, TLC cannot be measured by spirometry)

Helium dilution method (closed-circuit, most common)
Nitrogen washout method (open circuit)
Body plethysmography (gold standard - measures all gas including trapped air)

FEV1 Graph Interpretation

Normal: FEV1/FVC >80%
Obstructive (asthma, COPD): FEV1↓↓, FVC↓, ratio <70%
Restrictive (fibrosis): FEV1↓, FVC↓↓, ratio normal or >80%

CHAPTER 122: VENTILATION

Pulmonary Ventilation (Minute Ventilation)

Definition: Total volume of air entering or leaving lungs per minute
Formula: Pulmonary Ventilation = Tidal Volume × Respiratory Rate
= 500 mL × 12 breaths/min = 6000 mL/min (6 L/min)

Anatomical Dead Space

Volume of conducting airways where no gas exchange occurs
Includes: nose, pharynx, larynx, trachea, bronchi, bronchioles (up to terminal bronchioles)
Normal = 150 mL (approximately 1 mL/pound body weight or 2.2 mL/kg)

Alveolar Ventilation

Alveolar Ventilation = (TV - Dead space) × RR
= (500 - 150) × 12 = 350 × 12 = 4200 mL/min
This is the volume that actually participates in gas exchange

Physiological Dead Space = Anatomical dead space + Alveolar dead space

Normally: Physiological = Anatomical (alveolar dead space is negligible in health)
In disease (e.g., pulmonary embolism): physiological >> anatomical

Ventilation-Perfusion (V/Q) Ratio

Normal V/Q ratio = 0.8 (alveolar ventilation 4.2 L/min, pulmonary blood flow 5.25 L/min)
At apex (Zone 1): V/Q > 1 (over-ventilated, under-perfused) - acts like dead space
At base (Zone 3): V/Q < 1 (under-ventilated, over-perfused) - shunt-like
V/Q mismatch = most common cause of hypoxemia

CHAPTER 123: INSPIRED AIR, ALVEOLAR AIR AND EXPIRED AIR

Composition of Air

Gas	Inspired Air	Alveolar Air	Expired Air
O2	20.9% (159 mmHg)	13.6% (104 mmHg)	16% (120 mmHg)
CO2	0.04% (0.3 mmHg)	5.3% (40 mmHg)	4.4% (32 mmHg)
N2	79% (600 mmHg)	74.9% (569 mmHg)	75.4% (573 mmHg)
H2O vapor	Variable (47 mmHg in warm air)	6.3% (47 mmHg)	6% (47 mmHg)

Note: Alveolar air has lower O2 and higher CO2 than inspired air because of continuous gas exchange.

Partial Pressures of Gases in Blood

Gas	Alveolar air	Arterial blood	Venous blood
PO2	104 mmHg	95-100 mmHg	40 mmHg
PCO2	40 mmHg	40 mmHg	46 mmHg

CHAPTER 124: EXCHANGE OF RESPIRATORY GASES

Fick's Law of Diffusion

Rate of diffusion ∝ (Surface area × Pressure gradient × Solubility) / (Distance × √Molecular weight)

Factors Affecting Diffusion Across Respiratory Membrane

Thickness of membrane - increased in pulmonary edema, fibrosis (decreases diffusion)
Surface area - decreased in emphysema, pneumonia (decreases diffusion); normal ~70 m2
Pressure gradient - difference in partial pressures between alveoli and blood
Solubility - CO2 is 20x more soluble than O2 in plasma; hence diffuses faster
Molecular weight - CO2 (44) > O2 (32) but solubility compensates

Diffusing Capacity (DL)

= Volume of gas diffusing per mmHg pressure difference per minute
DL for O2 = 21 mL/min/mmHg (at rest); increases to ~65 mL/min/mmHg during exercise
DL for CO = used clinically to measure diffusing capacity (DLCO or TLCO)
Reduced in: emphysema, pulmonary fibrosis, pulmonary hypertension

Gas Exchange in Lungs

O2 diffuses from alveolus (PO2 104 mmHg) → capillary blood (PO2 40 mmHg) → blood equilibrates to 104 mmHg
CO2 diffuses from capillary blood (PCO2 46 mmHg) → alveolus (PCO2 40 mmHg)

Gas Exchange in Tissues

O2 diffuses from arterial blood (PO2 95 mmHg) → cells (PO2 ~20-40 mmHg)
CO2 diffuses from cells (PCO2 ~50 mmHg) → venous blood (PCO2 46 mmHg)

CHAPTER 125: TRANSPORT OF RESPIRATORY GASES

Transport of Oxygen

Two methods:

Dissolved in plasma - 3% (0.3 mL/100 mL blood); PO2 determines this
Combined with hemoglobin as oxyhemoglobin - 97%

Oxygen-hemoglobin dissociation curve:

Sigmoidal (S-shaped) curve - because of cooperative binding (Hb has 4 heme groups)
Each Hb molecule carries 4 O2 molecules
Hb oxygen capacity = 1.34 mL O2/g Hb (Hüfner's constant)
Normal Hb = 15 g/dL → O2 carrying capacity = 15 × 1.34 = 20 mL O2/100 mL blood
At PO2 = 100 mmHg (lungs): Hb is 97.5% saturated
At PO2 = 40 mmHg (tissues): Hb is 75% saturated (Hb gives up 25% of O2)

Bohr Effect (shifts curve to RIGHT):

Increased PCO2
Decreased pH (acidosis)
Increased temperature
Increased 2,3-DPG (2,3-diphosphoglycerate)
Right shift = decreased affinity of Hb for O2 = better O2 unloading to tissues

Haldane Effect:

Deoxygenation of Hb increases CO2 carrying capacity
At tissues: O2 released from Hb allows more CO2 binding to Hb

Transport of Carbon Dioxide

Three methods:

Method	Percentage
Dissolved in plasma	7%
As bicarbonate (HCO3-)	70% (major)
Combined with proteins as carbamino compounds (HbCO2)	23%

Bicarbonate Formation (Chloride Shift / Hamburger Shift):

In RBCs: CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- (catalyzed by carbonic anhydrase)
HCO3- exits RBC in exchange for Cl- entering = Chloride shift
H+ buffered by Hb (Hb-H+, deoxy-Hb is better buffer)

CHAPTER 126: REGULATION OF RESPIRATION

Respiratory Centers (in Brainstem)

Located in the medulla oblongata and pons:

Dorsal Respiratory Group (DRG)
- In nucleus tractus solitarius (NTS), medulla
- Controls inspiration primarily
- Receives input from peripheral chemoreceptors and lung stretch receptors
Ventral Respiratory Group (VRG)
- In nucleus ambiguus and nucleus retroambiguus, medulla
- Controls both inspiration and expiration
- Active during forceful breathing; quiet at rest
Pneumotaxic Center (PTC)
- In upper pons (nucleus parabrachialis)
- Limits duration of inspiration - switches inspiration to expiration
- Increases respiratory rate (shorter inspiratory phase)
Apneustic Center
- In lower pons
- Stimulates DRG → prolonged inspiration (apneusis)
- Normally inhibited by pneumotaxic center and Hering-Breuer reflex

Hering-Breuer Reflex (Inflation Reflex)

Lung stretch receptors (slowly adapting) in bronchial smooth muscle
Activated when lungs are inflated
Signal travels via vagus nerve → inhibits DRG → stops inspiration (prevents over-inflation)
Prevents excessive tidal volume; important in newborns

Chemical Regulation of Respiration

Central Chemoreceptors:

Located on ventral surface of medulla (sensitive to CSF pH/H+)
Respond to CO2 indirectly (CO2 crosses blood-brain barrier → H2CO3 → H+ in CSF)
Most powerful stimulus: increase in PCO2 / decrease in pH
Not directly sensitive to O2

Peripheral Chemoreceptors:

Carotid bodies (at bifurcation of common carotid artery) - main peripheral receptor
Aortic bodies (in aortic arch)
Respond to: ↓PO2 (most important for hypoxic drive), ↑PCO2, ↓pH
Afferent from carotid body: Hering's nerve (branch of IX) → NTS
Hypoxic drive: stimulated when PaO2 < 60 mmHg
Important in COPD patients (hypercapnic patients depend on hypoxic drive)

Normal Values for Respiratory Stimulation

Stimulus	Value	Effect
PCO2 rise by 1 mmHg	PaCO2 > 40 mmHg	Ventilation increases by ~3 L/min
PO2 fall	PaO2 < 60 mmHg	Vigorous stimulation of peripheral chemoreceptors
pH fall	pH < 7.35	Stimulates both central and peripheral chemoreceptors

CHAPTER 127: DISTURBANCES OF RESPIRATION

Abnormal Breathing Patterns

Pattern	Description	Cause
Hyperpnea	Increased depth of breathing	Exercise, fever
Hypopnea	Decreased depth	CNS depression
Tachypnea	Increased rate (>20/min)	Fever, anxiety, pain
Bradypnea	Decreased rate (<12/min)	Opioids, CNS depression
Apnea	Cessation of breathing	Cardiac arrest, severe CNS damage
Dyspnea	Difficult/labored breathing (subjective)	Asthma, heart failure, anemia
Orthopnea	Dyspnea on lying flat	LVF (left ventricular failure)
Cheyne-Stokes breathing	Crescendo-decrescendo with apneic spells	CHF, brain injury, high altitude
Biot's breathing	Irregular breathing with apneic spells	Meningitis, increased ICP
Kussmaul's breathing	Deep, rapid, sighing breaths	Diabetic ketoacidosis (metabolic acidosis)
Apneusis	Prolonged inspiration with short expiration	Pontine lesion (apneustic center)

Common Respiratory Disturbances

Hypoxia (low tissue O2):

Hypoxic hypoxia - low PaO2 (altitude, hypoventilation, V/Q mismatch, diffusion impairment)
Anemic hypoxia - reduced O2 carrying capacity (anemia, CO poisoning)
Stagnant (circulatory) hypoxia - reduced blood flow (heart failure, shock)
Histotoxic hypoxia - cells cannot use O2 (cyanide poisoning)

Hypercapnia - PaCO2 > 45 mmHg; causes respiratory acidosis

Cyanosis - bluish discoloration when deoxygenated Hb > 5 g/dL in capillaries

Central cyanosis: tongue and lips (V/Q mismatch, shunts)
Peripheral cyanosis: fingers/toes (stasis, cold)

Asphyxia - simultaneous hypoxia + hypercapnia; e.g., drowning, strangulation

Carbon Monoxide Poisoning:

CO affinity for Hb is 250x greater than O2
Forms carboxyhemoglobin (HbCO); left-shifts O2-Hb curve (worse O2 delivery)
Cherry-red color of skin/mucous membranes
Treatment: 100% O2, hyperbaric oxygen

Atelectasis - partial or complete lung collapse

Causes: surfactant deficiency, bronchial obstruction, pleural effusion

Pneumothorax - air in pleural space; lung collapses (loss of negative intrapleural pressure)

Open, closed, tension (tension: medical emergency, deviated trachea)

CHAPTER 128: HIGH ALTITUDE AND SPACE PHYSIOLOGY

Effects of High Altitude (Hypobaric Hypoxia)

Atmospheric pressure and PO2 fall with altitude (PO2 ∝ barometric pressure)
At sea level: PO2 = 159 mmHg; at 5500m: PO2 ~75 mmHg

Immediate Responses (within minutes-hours)

Hyperventilation - stimulation of peripheral chemoreceptors by low PO2
Increased cardiac output
Polycythemia (later)

Acclimatization (days to weeks)

Hyperventilation continues - causes respiratory alkalosis; kidneys excrete HCO3- (renal compensation)
Polycythemia - EPO released from kidneys → increased RBC production; Hb increases from 15 to ~20 g/dL
Increased 2,3-DPG in RBCs → right shift of O2-Hb curve → better O2 delivery
Increased vascularization in tissues (angiogenesis)
Increased mitochondria in cells

Acute Mountain Sickness (AMS)

Headache, nausea, dizziness, fatigue, insomnia
Caused by cerebral vasodilation and mild cerebral edema
High Altitude Cerebral Edema (HACE) and High Altitude Pulmonary Edema (HAPE) are severe forms
Treatment: descent, O2, acetazolamide (carbonic anhydrase inhibitor - promotes renal HCO3- excretion, stimulates breathing)

Space Physiology

Weightlessness (microgravity): muscle wasting, bone demineralization, fluid shifts to upper body
Space sickness (adaptation to microgravity)
Radiation exposure
No atmospheric pressure outside spacecraft

CHAPTER 129: DEEP SEA PHYSIOLOGY

Hyperbaric Conditions

Atmospheric pressure increases 1 atm per 10 meters depth

Problems in Deep Sea Diving

Oxygen toxicity - breathing 100% O2 at >2 atm causes convulsions (Paul Bert effect); pulmonary toxicity at lower pressures (Lorrain Smith effect)
Nitrogen narcosis (Raptures of the deep)
- Breathing N2 at high pressures (>4 atm)
- Narcotic effect similar to alcohol/anesthesia
- Impairs judgment, causes euphoria
- Prevented by replacing N2 with helium (He-O2 mixtures)
Decompression sickness (Caisson disease / Bends)
- During ascent: dissolved N2 comes out of solution → bubbles in tissues/blood
- Symptoms: joint pain (bends), respiratory distress (chokes), neurological (staggers), skin mottling (creeps)
- Prevention: slow, staged ascent; decompression stops
- Treatment: Hyperbaric oxygen chamber (recompression therapy)

CHAPTER 130: EFFECTS OF EXPOSURE TO COLD AND HEAT

Effects of Cold Exposure

Vasoconstriction of peripheral vessels (conserves heat)
Shivering - involuntary muscle contraction (increases heat production)
Piloerection (goosebumps) - traps air layer (vestigial in humans)
Increased metabolic rate (thyroid hormone, catecholamines)
Hypothermia: core temperature < 35°C; below 28°C → ventricular fibrillation risk

Effects of Heat Exposure

Vasodilation of skin vessels (radiates heat)
Sweating - evaporative heat loss
Reduced metabolic rate
Heat exhaustion - dehydration, salt depletion; treat with salt + water replacement
Heat stroke (sun stroke) - failure of sweating mechanism; core temp >40°C; CNS dysfunction; medical emergency → rapid cooling

CHAPTER 131: ARTIFICIAL RESPIRATION

Methods

Mouth-to-mouth resuscitation (Exhaled air method)
- Most practical method
- Expired air has ~16% O2 (adequate for resuscitation)
- 12-16 breaths/min
Holger-Nielsen method (Arm-lift back pressure)
- Manual method: patient prone, pressure applied to back then arms raised
- Historical method
Silvester method (Chest pressure arm-lift)
- Patient supine, arms raised then chest compressed
Cardiopulmonary Resuscitation (CPR)
- Chest compressions: 30 compressions + 2 breaths (30:2 ratio)
- Rate: 100-120/min
- Depth: 5-6 cm
Mechanical ventilators (IPPV - Intermittent Positive Pressure Ventilation)
- Used in ICU; replaces breathing mechanically

CHAPTER 132: EFFECTS OF EXERCISE ON RESPIRATION

Changes During Exercise

Parameter	Change During Exercise
Respiratory rate	Increases (12 → 20-25/min)
Tidal volume	Increases (500 mL → up to 3000 mL)
Pulmonary ventilation	Increases dramatically (6 → up to 100+ L/min)
PaO2	Maintained (near normal)
PaCO2	Maintained or slightly decreased
Cardiac output	Increases (5 → 20-25 L/min)
V/Q ratio	Becomes more uniform (recruitment of apical capillaries)

Mechanism of Increased Ventilation

Neural factors (rapid onset):
- Cortical irradiation (anticipatory rise before exercise even starts)
- Proprioceptors in muscles/joints (moving limbs stimulate DRG)
Humoral/chemical factors (sustained):
- Rise in K+, CO2, H+ (lactic acid)
- Rise in temperature
- Peripheral chemoreceptors stimulated

Oxygen Debt

Excess post-exercise oxygen consumption (EPOC)
After exercise stops, O2 consumption remains elevated for some time
Used to: repay lactic acid (Cori cycle - converted to glucose in liver), restore ATP/PCr stores, restore O2 in myoglobin and blood
VO2 max = maximum oxygen consumption; index of cardiorespiratory fitness

Fetal Respiration and First Breath

Fetus makes respiratory movements in utero (practice movements)
Lung fluid is present (not air); O2 supplied via placenta
First breath triggers:
- Compression of chest during delivery → sudden recoil expands chest
- Cold exposure stimulates skin receptors → respiratory center
- Rise in PCO2, fall in PO2 at birth → chemoreceptors activated
- Tactile stimulation at birth
Surfactant present from ~34-36 weeks gestation (mature lungs)
Premature babies (<34 weeks): surfactant deficiency → Respiratory Distress Syndrome (RDS)

KEY MEMORY TABLES (Sembulingam Examination Favorites)

Important Normal Values

Parameter	Normal Value
Respiratory rate (RR)	12-16/min (adults)
Tidal volume (TV)	500 mL
Vital capacity (VC)	4600 mL
FRC	2300 mL
RV	1200 mL
TLC	5800 mL
Dead space	150 mL
Alveolar ventilation	4200 mL/min
Minute ventilation	6000 mL/min
PaO2 (arterial)	95-100 mmHg
PaCO2 (arterial)	35-45 mmHg
SpO2 (O2 saturation)	97-100%
Hb-O2 carrying capacity	20 mL O2/100 mL blood
Lung compliance	200 mL/cmH2O
Surface area of lungs	~70 m2
DLO2 (rest)	21 mL/min/mmHg
Pulmonary artery pressure (systolic)	25 mmHg
Normal FEV1/FVC	>80%

Commonly Asked Short Notes

Surfactant - composition, secreted by Type II pneumocytes, DPPC, prevents atelectasis
Oxygen-Hemoglobin dissociation curve - S-shaped, Bohr effect, factors shifting curve
Chloride shift / Hamburger shift - HCO3- out, Cl- in
Hering-Breuer reflex - stretch receptors, vagus, prevents over-inflation
Cheyne-Stokes breathing - causes and pattern
Hypoxia types - hypoxic, anemic, stagnant, histotoxic
Decompression sickness (bends) - cause, treatment
Acclimatization to high altitude - steps
FEV1/FVC ratio - significance in obstructive vs restrictive
Work of breathing - components

These notes cover all chapters in Section 9 of Sembulingam's Essentials of Medical Physiology exactly as organized in the book. The book is authored by K. Sembulingam & Prema Sembulingam (6th/7th edition, Jaypee Brothers). For deep reading, refer to the original text from pages 671-751 (6th ed.).

In flow chart in clear form

Running Command

ls -la /home/daytona/workspace/ 2>/dev/null || echo "workspace ready"

Running Command

mkdir -p /home/daytona/workspace/respiratory-notes

Writing File

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<body>

<div class="page-title">
  <h1>🫁 RESPIRATORY SYSTEM — FLOWCHART NOTES</h1>
  <p>K. Sembulingam &amp; Prema Sembulingam | Essentials of Medical Physiology | Section 9 (Ch. 118–132)</p>
</div>

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<!-- CH 118: PHYSIOLOGICAL ANATOMY -->
<!-- ═══════════════════════════════════════════════════════════ -->
<div class="section">
  <div class="section-title">📌 CH 118 — PHYSIOLOGICAL ANATOMY OF RESPIRATORY TRACT</div>
  <div class="section-body">

    <h3>Types of Respiration</h3>
    <div class="steps">
      <div class="step"><div class="step-num">1</div><strong>External Respiration</strong><br>Atmosphere ↔ Blood<br>(Lungs)</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">2</div><strong>Internal Respiration</strong><br>Blood ↔ Tissue cells</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">3</div><strong>Cellular Respiration</strong><br>O₂ used inside cells<br>for metabolism</div>
    </div>

    <h3>4 Phases of Respiration (Flowchart)</h3>
    <div class="flow-wrap">
      <div class="box header">Atmospheric Air</div>
      <div class="arrow">↓</div>
      <div class="box blue">① PULMONARY VENTILATION<br><small>Air moves in &amp; out of lungs</small></div>
      <div class="arrow">↓</div>
      <div class="box green">② DIFFUSION OF GASES<br><small>O₂/CO₂ across respiratory membrane</small></div>
      <div class="arrow">↓</div>
      <div class="box orange">③ TRANSPORT IN BLOOD<br><small>O₂ &amp; CO₂ carried in circulation</small></div>
      <div class="arrow">↓</div>
      <div class="box teal">④ TISSUE GAS EXCHANGE<br><small>O₂ → cells; CO₂ → blood</small></div>
    </div>

    <h3>Functional Anatomy — Airway Tree</h3>
    <div class="flow-wrap">
      <div class="box header">Air Entry</div>
      <div class="arrow">↓</div>
      <div class="box blue">NOSE<br><small>Filters, warms, humidifies</small></div>
      <div class="arrow">↓</div>
      <div class="box blue">PHARYNX<br><small>Naso / Oro / Laryngopharynx</small></div>
      <div class="arrow">↓</div>
      <div class="box blue">LARYNX<br><small>Vocal cords, epiglottis</small></div>
      <div class="arrow">↓</div>
      <div class="box green">TRACHEA<br><small>10–12 cm, C-rings, bifurcates at T4/5 (carina)</small></div>
      <div class="arrow">↓</div>
      <div class="flow-row">
        <div class="box orange">RIGHT MAIN BRONCHUS<br><small>Wider, shorter, more vertical<br>⚠ Foreign body aspiration</small></div>
        <div class="arrow-h">  </div>
        <div class="box teal">LEFT MAIN BRONCHUS<br><small>Narrower, longer,<br>less vertical</small></div>
      </div>
      <div class="arrow">↓</div>
      <div class="box purple">LOBAR → SEGMENTAL BRONCHI</div>
      <div class="arrow">↓</div>
      <div class="box indigo">BRONCHIOLES (no cartilage)<br><small>Terminal bronchiole = last CONDUCTING airway</small></div>
      <div class="arrow">↓</div>
      <div class="box green">RESPIRATORY BRONCHIOLES<br><small>First site of gas exchange</small></div>
      <div class="arrow">↓</div>
      <div class="box orange">ALVEOLAR DUCTS → ALVEOLAR SACS → ALVEOLI<br><small>~700 million alveoli | Surface area ~70 m²</small></div>
    </div>

    <h3>Respiratory Unit (Acinus)</h3>
    <div class="flow-row" style="margin:8px 0;">
      <div class="box teal">Respiratory<br>Bronchiole</div>
      <div class="arrow-h">→</div>
      <div class="box blue">Alveolar<br>Duct</div>
      <div class="arrow-h">→</div>
      <div class="box green">Alveolar<br>Sac</div>
      <div class="arrow-h">→</div>
      <div class="box orange">Alveoli<br>(Gas Exchange)</div>
    </div>

    <h3>Respiratory Membrane — Layers (Alveolus → Blood)</h3>
    <div class="flow-wrap">
      <div class="box yellow">① Surfactant layer<br><small>(Type II pneumocytes)</small></div>
      <div class="arrow">↓</div>
      <div class="box green">② Alveolar epithelium<br><small>(Type I pneumocytes — thin)</small></div>
      <div class="arrow">↓</div>
      <div class="box teal">③ Basement membrane (alveolar)</div>
      <div class="arrow">↓</div>
      <div class="box blue">④ Interstitial space (thin)</div>
      <div class="arrow">↓</div>
      <div class="box indigo">⑤ Basement membrane (capillary)</div>
      <div class="arrow">↓</div>
      <div class="box orange">⑥ Capillary endothelium</div>
      <div class="arrow">↓</div>
      <div class="box red">BLOOD<br><small>Total thickness: 0.2–0.6 μm</small></div>
    </div>

    <h3>Non-Respiratory Functions</h3>
    <div class="grid4">
      <div class="card" style="background:#e8f4fd;border:1.5px solid #2196F3;">
        <h4>🧠 Olfaction</h4>
        <p>Smell perception via olfactory epithelium</p>
      </div>
      <div class="card" style="background:#e8f5e9;border:1.5px solid #4CAF50;">
        <h4>🎵 Vocalization</h4>
        <p>Speech &amp; singing via vocal cords</p>
      </div>
      <div class="card" style="background:#fff3e0;border:1.5px solid #FF9800;">
        <h4>🛡️ Defense</h4>
        <p>Vibrissae, mucus, cilia (mucociliary escalator), IgA, macrophages</p>
      </div>
      <div class="card" style="background:#fce4ec;border:1.5px solid #e91e63;">
        <h4>🌡️ Thermoregulation</h4>
        <p>Heat loss through expired air</p>
      </div>
      <div class="card" style="background:#f3e5f5;border:1.5px solid #9C27B0;">
        <h4>⚖️ Acid-Base</h4>
        <p>CO₂ excretion controls pH</p>
      </div>
      <div class="card" style="background:#e0f2f1;border:1.5px solid #009688;">
        <h4>💧 Water Balance</h4>
        <p>Expired air is 100% saturated with H₂O</p>
      </div>
      <div class="card" style="background:#fffde7;border:1.5px solid #FFC107;">
        <h4>💊 ACE Secretion</h4>
        <p>Lungs convert Angiotensin I → Angiotensin II</p>
      </div>
      <div class="card" style="background:#e8eaf6;border:1.5px solid #3f51b5;">
        <h4>🩸 Anticoagulant</h4>
        <p>Mast cells secrete heparin</p>
      </div>
    </div>

    <h3>Respiratory Protective Reflexes</h3>
    <div class="grid3">
      <div class="flow-wrap">
        <div class="box red">COUGH REFLEX</div>
        <div class="arrow">↓</div>
        <div class="box orange">Irritation in larynx/<br>trachea/bronchi</div>
        <div class="arrow">↓</div>
        <div class="box blue">Deep inspiration</div>
        <div class="arrow">↓</div>
        <div class="box green">Glottis closes</div>
        <div class="arrow">↓</div>
        <div class="box teal">Forceful expiration<br>(expels irritant)</div>
      </div>
      <div class="flow-wrap">
        <div class="box red">SNEEZING REFLEX</div>
        <div class="arrow">↓</div>
        <div class="box orange">Irritation in<br>nasal mucosa</div>
        <div class="arrow">↓</div>
        <div class="box blue">Deep inspiration</div>
        <div class="arrow">↓</div>
        <div class="box green">Forceful expiration<br>through NOSE</div>
      </div>
      <div class="flow-wrap">
        <div class="box red">SWALLOWING REFLEX</div>
        <div class="arrow">↓</div>
        <div class="box orange">Food in pharynx</div>
        <div class="arrow">↓</div>
        <div class="box blue">Epiglottis covers<br>larynx</div>
        <div class="arrow">↓</div>
        <div class="box green">Breathing pauses</div>
        <div class="arrow">↓</div>
        <div class="box teal">Prevents aspiration</div>
      </div>
    </div>

  </div>
</div>

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<!-- CH 119: PULMONARY CIRCULATION -->
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<div class="section">
  <div class="section-title">📌 CH 119 — PULMONARY CIRCULATION</div>
  <div class="section-body">

    <h3>Key Features</h3>
    <div class="grid3">
      <div class="card" style="background:#e8f4fd;border:1.5px solid #2196F3;text-align:center;">
        <h4>Low Pressure</h4>
        <p>PA = 25/8 mmHg<br>Mean = 15 mmHg</p>
        <p style="margin-top:5px;font-size:11px;color:#888;">(vs Systemic 120/80 mmHg)</p>
      </div>
      <div class="card" style="background:#e8f5e9;border:1.5px solid #4CAF50;text-align:center;">
        <h4>Low Resistance</h4>
        <p>Thin, distensible walls<br>PVR = 1–2 mmHg/L/min</p>
      </div>
      <div class="card" style="background:#fff3e0;border:1.5px solid #FF9800;text-align:center;">
        <h4>Transit Time</h4>
        <p>Rest: 0.75 sec<br>Exercise: 0.3 sec</p>
      </div>
    </div>

    <h3>West Zones of Lung (Gravity Effect)</h3>
    <div class="flow-wrap">
      <div class="box red">ZONE 1 — APEX<br><small>PA &gt; Pa &gt; Pv | No / minimal flow<br>(Theoretical dead space)</small></div>
      <div class="arrow">↓ <small style="font-size:10px;">moving downward</small></div>
      <div class="box yellow">ZONE 2 — MIDDLE<br><small>Pa &gt; PA &gt; Pv | Intermittent flow</small></div>
      <div class="arrow">↓</div>
      <div class="box green">ZONE 3 — BASE<br><small>Pa &gt; Pv &gt; PA | Continuous flow (Best perfusion)</small></div>
    </div>
    <div class="note"><strong>PA</strong> = Alveolar pressure | <strong>Pa</strong> = Pulmonary arterial pressure | <strong>Pv</strong> = Pulmonary venous pressure</div>

    <h3>Hypoxic Pulmonary Vasoconstriction (HPV)</h3>
    <div class="steps">
      <div class="step"><div class="step-num">1</div>Low PO₂ in alveoli</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">2</div>Vasoconstriction of pulmonary arterioles</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">3</div>Blood diverted to<br>well-ventilated alveoli</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">4</div>Optimizes<br>V/Q matching</div>
    </div>

  </div>
</div>

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<!-- CH 120: MECHANICS OF RESPIRATION -->
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<div class="section">
  <div class="section-title">📌 CH 120 — MECHANICS OF RESPIRATION</div>
  <div class="section-body">

    <h3>Inspiration vs Expiration</h3>
    <div class="vs-wrap">
      <div class="vs-left">
        <div class="vs-title">INSPIRATION (Active)</div>
        <div class="vs-item"><strong>Primary:</strong> Diaphragm (↓1.5–10 cm)</div>
        <div class="vs-item">External intercostals (↑ribs)</div>
        <div class="vs-item"><strong>Accessory:</strong> Scalene</div>
        <div class="vs-item">Sternocleidomastoid</div>
        <div class="vs-item">Serratus anterior</div>
        <div class="vs-item">Pectoralis minor</div>
      </div>
      <div class="vs-mid">VS</div>
      <div class="vs-right">
        <div class="vs-title">EXPIRATION (Passive/Active)</div>
        <div class="vs-item"><strong>Quiet:</strong> Elastic recoil of lungs</div>
        <div class="vs-item">Relaxation of inspiratory muscles</div>
        <div class="vs-item"><strong>Forced:</strong> Internal intercostals</div>
        <div class="vs-item">Rectus abdominis</div>
        <div class="vs-item">External &amp; internal obliques</div>
        <div class="vs-item">Transversus abdominis</div>
      </div>
    </div>

    <h3>Pressure Changes During Breathing</h3>
    <table>
      <tr><th>Phase</th><th>Intrapleural Pressure</th><th>Intrapulmonary Pressure</th></tr>
      <tr><td>End of expiration (rest)</td><td>−5 mmHg</td><td>0 mmHg (= atmospheric)</td></tr>
      <tr><td>During inspiration</td><td>−8 mmHg</td><td>−3 mmHg (below atm)</td></tr>
      <tr><td>During expiration</td><td>−5 mmHg</td><td>+3 mmHg (above atm)</td></tr>
    </table>
    <div class="important">⚠ Intrapleural pressure is ALWAYS NEGATIVE — maintains lung inflation</div>

    <h3>Surfactant Pathway</h3>
    <div class="flow-wrap">
      <div class="box blue">Type II Pneumocytes<br><small>Alveolar cells</small></div>
      <div class="arrow">↓ secrete</div>
      <div class="box green">SURFACTANT<br><small>DPPC (Dipalmitoyl-phosphatidylcholine) ~70%</small></div>
      <div class="arrow">↓ function</div>
      <div class="box teal">Reduces Surface Tension<br><small>Laplace's law: P = 2T/r</small></div>
      <div class="arrow">↓ result</div>
      <div class="flow-row">
        <div class="box orange">Prevents alveolar collapse<br><small>(atelectasis)</small></div>
        <div class="box green">Reduces work<br>of breathing</div>
        <div class="box blue">Small alveoli don't<br>empty into large ones</div>
      </div>
      <div class="arrow">↓ DEFICIENCY</div>
      <div class="box red">Premature baby (&lt;34 wks)<br>→ RDS / Hyaline Membrane Disease (HMD)</div>
    </div>

    <h3>Compliance</h3>
    <div class="grid3">
      <div class="flow-wrap">
        <div class="box blue">NORMAL<br><small>200 mL/cmH₂O</small></div>
      </div>
      <div class="flow-wrap">
        <div class="box red">DECREASED<br><small>Pulmonary fibrosis<br>Pulmonary edema<br>ARDS<br>(stiff lungs)</small></div>
      </div>
      <div class="flow-wrap">
        <div class="box orange">INCREASED<br><small>Emphysema<br>(destroyed alveolar walls,<br>over-distensible)</small></div>
      </div>
    </div>

    <h3>Work of Breathing — Components</h3>
    <div class="steps">
      <div class="step"><div class="step-num">1</div>Elastic resistance<br>(compliance)</div>
      <div class="step-arrow">+</div>
      <div class="step"><div class="step-num">2</div>Airway resistance<br>(flow resistance)</div>
      <div class="step-arrow">+</div>
      <div class="step"><div class="step-num">3</div>Tissue viscous<br>resistance</div>
      <div class="step-arrow">=</div>
      <div class="step"><div class="step-num">✓</div>Total Work<br>~0.5 J/breath<br>~5% O₂ consumption</div>
    </div>

  </div>
</div>

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<!-- CH 121: PULMONARY FUNCTION TESTS -->
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<div class="section">
  <div class="section-title">📌 CH 121 — PULMONARY FUNCTION TESTS</div>
  <div class="section-body">

    <h3>Lung Volumes (4 VOLUMES — Cannot be added)</h3>
    <table>
      <tr><th>Volume</th><th>Definition</th><th>Normal</th></tr>
      <tr><td><strong>TV</strong> — Tidal Volume</td><td>Air breathed per normal breath</td><td>500 mL</td></tr>
      <tr><td><strong>IRV</strong> — Inspiratory Reserve Volume</td><td>Extra air inspired above TV</td><td>3000 mL</td></tr>
      <tr><td><strong>ERV</strong> — Expiratory Reserve Volume</td><td>Extra air expired beyond TV</td><td>1100 mL</td></tr>
      <tr><td><strong>RV</strong> — Residual Volume</td><td>Air after maximal expiration<br><span class="badge b-red">Cannot be measured by spirometry</span></td><td>1200 mL</td></tr>
    </table>

    <h3>Lung Capacities (4 CAPACITIES = Sum of volumes)</h3>
    <table>
      <tr><th>Capacity</th><th>Formula</th><th>Normal</th></tr>
      <tr><td><strong>IC</strong> — Inspiratory Capacity</td><td>TV + IRV</td><td>3500 mL</td></tr>
      <tr><td><strong>FRC</strong> — Functional Residual Capacity</td><td>ERV + RV</td><td>2300 mL</td></tr>
      <tr><td><strong>VC</strong> — Vital Capacity</td><td>IRV + TV + ERV</td><td>4600 mL</td></tr>
      <tr><td><strong>TLC</strong> — Total Lung Capacity</td><td>All 4 volumes (VC + RV)</td><td>5800 mL</td></tr>
    </table>

    <h3>Dynamic Tests (Spirometry)</h3>
    <table>
      <tr><th>Test</th><th>Definition</th><th>Normal</th></tr>
      <tr><td><strong>FVC</strong></td><td>Max air expelled after full inspiration</td><td>4.6 L (male)</td></tr>
      <tr><td><strong>FEV₁</strong></td><td>Air expelled in first 1 second</td><td>3.2 L</td></tr>
      <tr><td><strong>FEV₁/FVC</strong> (Tiffeneau index)</td><td>% FVC expelled in 1 sec</td><td><strong>&gt;80%</strong></td></tr>
      <tr><td><strong>PEFR</strong></td><td>Peak expiratory flow rate</td><td>400–600 L/min</td></tr>
      <tr><td><strong>MBC/MVV</strong></td><td>Max breathing capacity per min</td><td>125–170 L/min</td></tr>
      <tr><td><strong>FEF 25–75%</strong></td><td>Mid-expiratory flow rate</td><td>Detects small airway disease</td></tr>
    </table>

    <h3>FEV₁/FVC — Interpretation Flowchart</h3>
    <div class="flow-wrap">
      <div class="box header">Spirometry result</div>
      <div class="arrow">↓</div>
      <div class="flow-row">
        <div class="flow-wrap">
          <div class="box green">FEV₁/FVC &gt; 80%<br>FVC normal or ↓</div>
          <div class="arrow">↓</div>
          <div class="box teal">RESTRICTIVE<br><small>Fibrosis, Kyphoscoliosis<br>Obesity, Pleural effusion</small></div>
        </div>
        <div class="arrow-h" style="margin:auto 10px;font-size:24px;">|</div>
        <div class="flow-wrap">
          <div class="box red">FEV₁/FVC &lt; 70%<br>FEV₁ ↓↓</div>
          <div class="arrow">↓</div>
          <div class="box orange">OBSTRUCTIVE<br><small>Asthma, COPD<br>Chronic bronchitis</small></div>
        </div>
      </div>
    </div>

    <h3>Methods to Measure FRC / RV / TLC</h3>
    <div class="steps">
      <div class="step"><div class="step-num">1</div><strong>Helium Dilution</strong><br>Closed circuit<br>(most common)</div>
      <div class="step-arrow">or</div>
      <div class="step"><div class="step-num">2</div><strong>N₂ Washout</strong><br>Open circuit</div>
      <div class="step-arrow">or</div>
      <div class="step"><div class="step-num">★</div><strong>Body Plethysmography</strong><br>Gold standard<br>Measures trapped air too</div>
    </div>

  </div>
</div>

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<!-- CH 122: VENTILATION -->
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<div class="section">
  <div class="section-title">📌 CH 122 — VENTILATION</div>
  <div class="section-body">

    <h3>Ventilation Calculations</h3>
    <div class="flow-wrap">
      <div class="box header">MINUTE VENTILATION (Pulmonary Ventilation)</div>
      <div class="arrow">↓</div>
      <div class="box blue">Tidal Volume × Respiratory Rate<br><strong>500 mL × 12 = 6000 mL/min (6 L/min)</strong></div>
      <div class="arrow">↓ subtract dead space</div>
      <div class="box green">ALVEOLAR VENTILATION<br><strong>(500 − 150) × 12 = 4200 mL/min</strong><br><small>This is what participates in gas exchange</small></div>
    </div>

    <h3>Dead Space Types</h3>
    <div class="grid3">
      <div class="card" style="background:#e8f4fd;border:1.5px solid #2196F3;">
        <h4>Anatomical Dead Space</h4>
        <p>Conducting airways (nose to terminal bronchioles)</p>
        <p><strong>Normal = 150 mL</strong></p>
        <p style="font-size:11px;">(~1 mL/pound body weight)</p>
      </div>
      <div class="card" style="background:#e8f5e9;border:1.5px solid #4CAF50;">
        <h4>Alveolar Dead Space</h4>
        <p>Alveoli ventilated but NOT perfused</p>
        <p><strong>Normally ≈ 0</strong></p>
        <p style="font-size:11px;">↑ in pulmonary embolism</p>
      </div>
      <div class="card" style="background:#fff3e0;border:1.5px solid #FF9800;">
        <h4>Physiological Dead Space</h4>
        <p>Anatomical + Alveolar</p>
        <p><strong>Normal = Anatomical (~150 mL)</strong></p>
        <p style="font-size:11px;">↑ in disease states</p>
      </div>
    </div>

    <h3>V/Q Ratio — Ventilation-Perfusion</h3>
    <div class="flow-wrap">
      <div class="box blue">Normal V/Q = <strong>0.8</strong><br><small>VA = 4.2 L/min; Q = 5.25 L/min</small></div>
      <div class="arrow">↓ Regional variation</div>
      <div class="flow-row">
        <div class="box red">APEX (V/Q &gt; 1)<br><small>Over-ventilated<br>Under-perfused<br>→ Dead space effect</small></div>
        <div class="arrow-h" style="margin:auto 10px;">←→</div>
        <div class="box green">BASE (V/Q &lt; 1)<br><small>Under-ventilated<br>Over-perfused<br>→ Shunt-like effect</small></div>
      </div>
    </div>
    <div class="important">⚠ V/Q mismatch = Most common cause of hypoxemia in clinical practice</div>

  </div>
</div>

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<!-- CH 123: AIR COMPOSITION -->
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<div class="section">
  <div class="section-title">📌 CH 123 — INSPIRED, ALVEOLAR AND EXPIRED AIR</div>
  <div class="section-body">
    <table>
      <tr><th>Gas</th><th>Inspired Air</th><th>Alveolar Air</th><th>Expired Air</th></tr>
      <tr><td><strong>O₂</strong></td><td>20.9% (159 mmHg)</td><td>13.6% (104 mmHg)</td><td>16% (120 mmHg)</td></tr>
      <tr><td><strong>CO₂</strong></td><td>0.04% (0.3 mmHg)</td><td>5.3% (40 mmHg)</td><td>4.4% (32 mmHg)</td></tr>
      <tr><td><strong>N₂</strong></td><td>79% (600 mmHg)</td><td>74.9% (569 mmHg)</td><td>75.4% (573 mmHg)</td></tr>
      <tr><td><strong>H₂O vapor</strong></td><td>Variable</td><td>6.3% (47 mmHg)</td><td>6% (47 mmHg)</td></tr>
    </table>
    <table style="margin-top:12px;">
      <tr><th>Gas</th><th>Alveolar Air</th><th>Arterial Blood</th><th>Venous Blood</th></tr>
      <tr><td><strong>PO₂</strong></td><td>104 mmHg</td><td>95–100 mmHg</td><td>40 mmHg</td></tr>
      <tr><td><strong>PCO₂</strong></td><td>40 mmHg</td><td>40 mmHg</td><td>46 mmHg</td></tr>
    </table>
  </div>
</div>

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<!-- CH 124: EXCHANGE OF GASES -->
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<div class="section">
  <div class="section-title">📌 CH 124 — EXCHANGE OF RESPIRATORY GASES</div>
  <div class="section-body">

    <h3>Fick's Law of Diffusion</h3>
    <div class="box header" style="max-width:600px;margin:0 auto 14px auto;font-size:13px;padding:12px;">
      Rate of Diffusion ∝ (Surface Area × Pressure Gradient × Solubility)<br>
      ────────────────────────────────────────────<br>
      (Distance × √Molecular Weight)
    </div>

    <h3>Factors Affecting Diffusion — Flowchart</h3>
    <div class="grid2">
      <div>
        <h4>Factors that DECREASE diffusion:</h4>
        <div class="flow-wrap">
          <div class="box red">↑ Membrane thickness<br><small>Pulmonary edema, fibrosis</small></div>
          <div class="arrow">+</div>
          <div class="box red">↓ Surface area<br><small>Emphysema, pneumonia, lobectomy</small></div>
          <div class="arrow">+</div>
          <div class="box red">↓ Pressure gradient<br><small>High altitude, V/Q mismatch</small></div>
        </div>
      </div>
      <div>
        <h4>Key comparisons O₂ vs CO₂:</h4>
        <table>
          <tr><th>Property</th><th>O₂</th><th>CO₂</th></tr>
          <tr><td>Solubility</td><td>1×</td><td>20× more soluble</td></tr>
          <tr><td>MW</td><td>32</td><td>44</td></tr>
          <tr><td>DL (rest)</td><td>21 mL/mmHg/min</td><td>Much higher</td></tr>
          <tr><td>Diffusion rate</td><td>Slower</td><td>Faster (solubility dominates)</td></tr>
        </table>
      </div>
    </div>

    <h3>Gas Exchange Flow</h3>
    <div class="grid2">
      <div class="flow-wrap">
        <div class="box header">IN LUNGS</div>
        <div class="box blue">Alveolar PO₂ = 104 mmHg<br>Capillary PO₂ = 40 mmHg</div>
        <div class="arrow">↓ O₂ diffuses INTO blood</div>
        <div class="box green">Blood PO₂ equilibrates<br>to 104 mmHg</div>
        <div class="arrow">↓ simultaneously</div>
        <div class="box orange">Capillary PCO₂ = 46 mmHg<br>Alveolar PCO₂ = 40 mmHg</div>
        <div class="arrow">↓ CO₂ diffuses OUT</div>
        <div class="box teal">Blood PCO₂ equilibrates<br>to 40 mmHg</div>
      </div>
      <div class="flow-wrap">
        <div class="box header">IN TISSUES</div>
        <div class="box blue">Arterial PO₂ = 95 mmHg<br>Cell PO₂ = 20–40 mmHg</div>
        <div class="arrow">↓ O₂ diffuses INTO cells</div>
        <div class="box green">O₂ used for<br>cellular metabolism</div>
        <div class="arrow">↓ simultaneously</div>
        <div class="box orange">Cell PCO₂ = ~50 mmHg<br>Arterial PCO₂ = 40 mmHg</div>
        <div class="arrow">↓ CO₂ diffuses into blood</div>
        <div class="box teal">Venous PCO₂ = 46 mmHg</div>
      </div>
    </div>

  </div>
</div>

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<!-- CH 125: TRANSPORT OF GASES -->
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<div class="section">
  <div class="section-title">📌 CH 125 — TRANSPORT OF RESPIRATORY GASES</div>
  <div class="section-body">

    <h3>Transport of Oxygen</h3>
    <div class="flow-wrap">
      <div class="box header">O₂ in Blood (Total = 20 mL/100 mL)</div>
      <div class="arrow">↓</div>
      <div class="flow-row">
        <div class="flow-wrap">
          <div class="box blue">Dissolved in Plasma<br><strong>3%</strong><br><small>0.3 mL/100 mL</small></div>
        </div>
        <div class="arrow-h" style="margin:auto 10px;font-size:20px;">+</div>
        <div class="flow-wrap">
          <div class="box green">Bound to Hb<br><strong>97%</strong><br><small>As OxyHaemoglobin (HbO₂)</small></div>
        </div>
      </div>
    </div>

    <h3>O₂-Haemoglobin Dissociation Curve</h3>
    <div class="grid2">
      <div class="card" style="background:#e8f4fd;border:1.5px solid #2196F3;">
        <h4>Shape: S-Shaped (Sigmoidal)</h4>
        <ul>
          <li>Cooperative binding (4 heme groups per Hb)</li>
          <li>Hüfner's constant: 1.34 mL O₂/g Hb</li>
          <li>At PO₂ 100 mmHg (lungs): <strong>97.5% saturated</strong></li>
          <li>At PO₂ 40 mmHg (tissues): <strong>75% saturated</strong></li>
          <li>O₂ delivered = ~5 mL/100 mL blood</li>
        </ul>
      </div>
      <div>
        <h4>BOHR EFFECT — Shifts curve RIGHT (↓ O₂ affinity)</h4>
        <div class="steps">
          <div class="step"><div class="step-num">→</div>↑ PCO₂</div>
          <div class="step"><div class="step-num">→</div>↓ pH<br>(Acidosis)</div>
          <div class="step"><div class="step-num">→</div>↑ Temp</div>
          <div class="step"><div class="step-num">→</div>↑ 2,3-DPG</div>
        </div>
        <div class="note" style="margin-top:8px;">Right shift = Better O₂ UNLOADING to tissues<br>Left shift = Better O₂ LOADING in lungs (e.g. fetal Hb, CO)</div>
      </div>
    </div>

    <h3>Transport of CO₂</h3>
    <div class="flow-wrap">
      <div class="box header">CO₂ Produced in Tissues</div>
      <div class="arrow">↓ Enters blood in 3 forms</div>
      <div class="flow-row">
        <div class="flow-wrap">
          <div class="box blue">Dissolved in Plasma<br><strong>7%</strong></div>
        </div>
        <div class="flow-wrap">
          <div class="box green">As HCO₃⁻ (Bicarbonate)<br><strong>70% (MAJOR)</strong></div>
        </div>
        <div class="flow-wrap">
          <div class="box orange">Carbamino compounds<br><strong>23%</strong><br><small>(CO₂ + Hb → HbCO₂)</small></div>
        </div>
      </div>
    </div>

    <h3>Chloride Shift (Hamburger Shift) — Bicarbonate Formation</h3>
    <div class="steps">
      <div class="step"><div class="step-num">1</div>CO₂ enters RBC<br>from tissues</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">2</div>CO₂ + H₂O<br><small>(carbonic anhydrase)</small><br>→ H₂CO₃</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">3</div>H₂CO₃ →<br>H⁺ + HCO₃⁻</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">4</div>HCO₃⁻ leaves RBC<br>Cl⁻ enters RBC<br><strong>(Chloride shift)</strong></div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">5</div>H⁺ buffered<br>by Hb<br>(Hb-H⁺)</div>
    </div>
    <div class="note">Reverse happens in lungs — HCO₃⁻ re-enters RBC, CO₂ released and expired</div>

  </div>
</div>

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<!-- CH 126: REGULATION OF RESPIRATION -->
<!-- ═══════════════════════════════════════════════════════════ -->
<div class="section">
  <div class="section-title">📌 CH 126 — REGULATION OF RESPIRATION</div>
  <div class="section-body">

    <h3>Respiratory Centers (Brainstem)</h3>
    <div class="flow-wrap">
      <div class="box header">BRAINSTEM RESPIRATORY CENTERS</div>
      <div class="arrow">↓</div>
      <div class="flow-row">
        <div class="flow-wrap">
          <div class="box blue">PONS<br>(Upper)</div>
          <div class="arrow">↓</div>
          <div class="box green"><strong>PNEUMOTAXIC CENTER</strong><br><small>Nucleus parabrachialis<br>Limits inspiration duration<br>↑ Respiratory rate</small></div>
        </div>
        <div class="flow-wrap">
          <div class="box blue">PONS<br>(Lower)</div>
          <div class="arrow">↓</div>
          <div class="box yellow"><strong>APNEUSTIC CENTER</strong><br><small>Prolongs inspiration<br>(normally inhibited)</small></div>
        </div>
        <div class="flow-wrap">
          <div class="box blue">MEDULLA<br>(Dorsal)</div>
          <div class="arrow">↓</div>
          <div class="box teal"><strong>DRG — Dorsal Resp. Group</strong><br><small>Nucleus tractus solitarius<br>Controls INSPIRATION<br>Receives vagal inputs</small></div>
        </div>
        <div class="flow-wrap">
          <div class="box blue">MEDULLA<br>(Ventral)</div>
          <div class="arrow">↓</div>
          <div class="box orange"><strong>VRG — Ventral Resp. Group</strong><br><small>Nucleus ambiguus +<br>Nucleus retroambiguus<br>Inspiration &amp; Expiration<br>Active during forced breathing</small></div>
        </div>
      </div>
    </div>

    <h3>Hering-Breuer Reflex (Inflation Reflex)</h3>
    <div class="steps">
      <div class="step"><div class="step-num">1</div>Lung inflates<br>during inspiration</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">2</div>Stretch receptors<br>in bronchi activated<br><small>(slowly adapting)</small></div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">3</div>Signal via<br><strong>Vagus nerve</strong></div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">4</div>Inhibits DRG<br>(inspiration stops)</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">5</div>Prevents<br>over-inflation<br>of lungs</div>
    </div>

    <h3>Chemical Regulation — Chemoreceptors</h3>
    <div class="vs-wrap">
      <div class="vs-left">
        <div class="vs-title">CENTRAL CHEMORECEPTORS</div>
        <div class="vs-item">Location: Ventral surface of medulla</div>
        <div class="vs-item">Respond to: CSF H⁺ / pH</div>
        <div class="vs-item">CO₂ crosses BBB → H₂CO₃ → H⁺ in CSF</div>
        <div class="vs-item"><strong>Most powerful stimulus = ↑PCO₂</strong></div>
        <div class="vs-item">NOT directly sensitive to O₂</div>
        <div class="vs-item">Slow response</div>
      </div>
      <div class="vs-mid">VS</div>
      <div class="vs-right">
        <div class="vs-title">PERIPHERAL CHEMORECEPTORS</div>
        <div class="vs-item"><strong>Carotid bodies</strong> (main) — Hering's nerve (IX)</div>
        <div class="vs-item"><strong>Aortic bodies</strong> — vagus nerve (X)</div>
        <div class="vs-item">Respond to: ↓PO₂, ↑PCO₂, ↓pH</div>
        <div class="vs-item"><strong>Hypoxic drive: PaO₂ &lt; 60 mmHg</strong></div>
        <div class="vs-item">Fast response</div>
        <div class="vs-item">⚠ Critical in COPD patients!</div>
      </div>
    </div>

    <h3>Stimulus → Ventilatory Response Flowchart</h3>
    <div class="flow-wrap">
      <div class="flow-row">
        <div class="box red">↑PCO₂ (>40 mmHg)<br><small>+1 mmHg = +3 L/min ventilation</small></div>
        <div class="box orange">↓PaO₂ (&lt;60 mmHg)<br><small>Peripheral chemoreceptors</small></div>
        <div class="box purple">↓pH (&lt;7.35)<br><small>Both central &amp; peripheral</small></div>
      </div>
      <div class="arrow">↓ All stimulate</div>
      <div class="box green">Respiratory Centers (DRG)</div>
      <div class="arrow">↓</div>
      <div class="box blue">↑ Rate and depth<br>of breathing</div>
      <div class="arrow">↓</div>
      <div class="box teal">↑ CO₂ excretion / ↑ O₂ intake<br>→ Homeostasis restored</div>
    </div>

  </div>
</div>

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<!-- CH 127: DISTURBANCES -->
<!-- ═══════════════════════════════════════════════════════════ -->
<div class="section">
  <div class="section-title">📌 CH 127 — DISTURBANCES OF RESPIRATION</div>
  <div class="section-body">

    <h3>Abnormal Breathing Patterns</h3>
    <table>
      <tr><th>Pattern</th><th>Description</th><th>Cause</th></tr>
      <tr><td><strong>Hyperpnea</strong></td><td>↑ depth of breathing</td><td>Exercise, fever</td></tr>
      <tr><td><strong>Tachypnea</strong></td><td>↑ rate (&gt;20/min)</td><td>Fever, anxiety, pain</td></tr>
      <tr><td><strong>Bradypnea</strong></td><td>↓ rate (&lt;12/min)</td><td>Opioids, CNS depression</td></tr>
      <tr><td><strong>Apnea</strong></td><td>Cessation of breathing</td><td>Cardiac arrest</td></tr>
      <tr><td><strong>Dyspnea</strong></td><td>Difficult/labored breathing (subjective)</td><td>Asthma, heart failure, anemia</td></tr>
      <tr><td><strong>Orthopnea</strong></td><td>Dyspnea on lying flat</td><td>Left ventricular failure</td></tr>
      <tr><td><span class="badge b-orange">Cheyne-Stokes</span></td><td>Crescendo-decrescendo + apnea</td><td>CHF, brain injury, high altitude</td></tr>
      <tr><td><span class="badge b-red">Biot's breathing</span></td><td>Irregular + apneic spells</td><td>Meningitis, ↑ ICP</td></tr>
      <tr><td><span class="badge b-purple">Kussmaul's</span></td><td>Deep, rapid, sighing</td><td>DKA (metabolic acidosis)</td></tr>
      <tr><td><strong>Apneusis</strong></td><td>Prolonged inspiration + short expiration</td><td>Pontine lesion</td></tr>
    </table>

    <h3>Types of Hypoxia — Flowchart</h3>
    <div class="flow-wrap">
      <div class="box header">HYPOXIA (Low tissue O₂)</div>
      <div class="arrow">↓</div>
      <div class="flow-row">
        <div class="flow-wrap">
          <div class="box blue"><strong>HYPOXIC</strong><br><small>↓ PaO₂<br>High altitude<br>Hypoventilation<br>V/Q mismatch</small></div>
        </div>
        <div class="flow-wrap">
          <div class="box red"><strong>ANEMIC</strong><br><small>↓ O₂ capacity<br>Anemia<br>CO poisoning<br>Methemoglobinemia</small></div>
        </div>
        <div class="flow-wrap">
          <div class="box orange"><strong>STAGNANT</strong><br>(Circulatory)<br><small>↓ Blood flow<br>Heart failure<br>Shock</small></div>
        </div>
        <div class="flow-wrap">
          <div class="box purple"><strong>HISTOTOXIC</strong><br><small>Cells cannot use O₂<br>Cyanide poisoning</small></div>
        </div>
      </div>
    </div>

    <h3>CO Poisoning — Pathway</h3>
    <div class="steps">
      <div class="step"><div class="step-num">1</div>CO inhaled<br>(affinity 250× O₂)</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">2</div>Forms HbCO<br>(carboxyhemoglobin)</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">3</div>Left shift of<br>O₂-Hb curve<br>(worse O₂ delivery)</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">4</div>Cherry-red<br>skin/mucosa</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">Rx</div>100% O₂<br>Hyperbaric<br>O₂</div>
    </div>

    <h3>Cyanosis</h3>
    <div class="box important" style="background:#fce4ec;border:2px solid #F44336;color:#b71c1c;padding:12px;border-radius:8px;margin:8px 0;">
      Cyanosis appears when Deoxygenated Hb &gt; <strong>5 g/dL</strong> in capillaries
    </div>
    <div class="grid2">
      <div class="card" style="background:#e8f4fd;border:1.5px solid #2196F3;">
        <h4>Central Cyanosis</h4>
        <ul>
          <li>Tongue and lips are blue</li>
          <li>Causes: V/Q mismatch, right-to-left shunt, respiratory failure</li>
        </ul>
      </div>
      <div class="card" style="background:#fce4ec;border:1.5px solid #F44336;">
        <h4>Peripheral Cyanosis</h4>
        <ul>
          <li>Fingers and toes only</li>
          <li>Causes: stasis, cold, peripheral vascular disease</li>
        </ul>
      </div>
    </div>

  </div>
</div>

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<!-- CH 128: HIGH ALTITUDE -->
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<div class="section">
  <div class="section-title">📌 CH 128 — HIGH ALTITUDE AND SPACE PHYSIOLOGY</div>
  <div class="section-body">

    <h3>Acclimatization to High Altitude (Step-by-Step)</h3>
    <div class="flow-wrap">
      <div class="box header">Ascend to HIGH ALTITUDE<br><small>↓ Barometric pressure → ↓ PO₂</small></div>
      <div class="arrow">↓ IMMEDIATE (min–hours)</div>
      <div class="flow-row">
        <div class="box orange">↑ Hyperventilation<br><small>(peripheral chemoreceptors stimulated)</small></div>
        <div class="box blue">↑ Heart rate<br>&amp; Cardiac output</div>
        <div class="box red">Respiratory alkalosis<br>(CO₂ blown off)</div>
      </div>
      <div class="arrow">↓ DAYS TO WEEKS (Acclimatization)</div>
      <div class="flow-row">
        <div class="flow-wrap">
          <div class="box green">Kidneys excrete HCO₃⁻<br><small>(Renal compensation for alkalosis)</small></div>
        </div>
        <div class="flow-wrap">
          <div class="box blue">↑ EPO from kidneys<br>→ ↑ RBC production<br>→ Hb: 15 → 20 g/dL</div>
        </div>
        <div class="flow-wrap">
          <div class="box orange">↑ 2,3-DPG in RBCs<br>→ Right shift O₂ curve<br>→ Better O₂ delivery</div>
        </div>
        <div class="flow-wrap">
          <div class="box purple">↑ Tissue vascularization<br>↑ Mitochondria in cells</div>
        </div>
      </div>
    </div>

    <h3>Acute Mountain Sickness (AMS)</h3>
    <div class="steps">
      <div class="step"><div class="step-num">Sx</div>Headache<br>Nausea<br>Dizziness<br>Insomnia</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">!</div>HACE<br>High Altitude<br>Cerebral Edema</div>
      <div class="step-arrow">or</div>
      <div class="step"><div class="step-num">!</div>HAPE<br>High Altitude<br>Pulmonary Edema</div>
      <div class="step-arrow">Rx</div>
      <div class="step"><div class="step-num">Rx</div>Descent + O₂<br>Acetazolamide<br><small>(inhibits CA → stimulates breathing)</small></div>
    </div>

  </div>
</div>

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<!-- CH 129: DEEP SEA -->
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<div class="section">
  <div class="section-title">📌 CH 129 — DEEP SEA PHYSIOLOGY</div>
  <div class="section-body">
    <h3>Hazards of Deep Sea Diving</h3>
    <div class="grid3">
      <div class="flow-wrap">
        <div class="box red">O₂ TOXICITY</div>
        <div class="arrow">↓</div>
        <div class="box orange">100% O₂ at &gt;2 atm<br><small>Paul Bert effect → convulsions</small></div>
        <div class="arrow">↓</div>
        <div class="box yellow">Lorrain Smith effect<br><small>(pulmonary toxicity at lower pressure)</small></div>
      </div>
      <div class="flow-wrap">
        <div class="box red">NITROGEN NARCOSIS<br><small>"Raptures of the Deep"</small></div>
        <div class="arrow">↓</div>
        <div class="box orange">N₂ at high pressure (&gt;4 atm)</div>
        <div class="arrow">↓</div>
        <div class="box yellow">Narcotic effect<br>Impaired judgment, euphoria</div>
        <div class="arrow">↓ Prevention</div>
        <div class="box green">Replace N₂ with<br>Helium (He–O₂ mix)</div>
      </div>
      <div class="flow-wrap">
        <div class="box red">DECOMPRESSION SICKNESS<br><small>Bends / Caisson Disease</small></div>
        <div class="arrow">↓</div>
        <div class="box orange">Rapid ascent → N₂ bubbles<br>in tissues and blood</div>
        <div class="arrow">↓</div>
        <div class="box yellow">Bends (joints)<br>Chokes (lungs)<br>Staggers (brain)<br>Creeps (skin)</div>
        <div class="arrow">↓ Treatment</div>
        <div class="box green">Hyperbaric O₂ chamber<br><small>(Recompression therapy)</small></div>
      </div>
    </div>
  </div>
</div>

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<!-- CH 131: ARTIFICIAL RESPIRATION -->
<!-- ═══════════════════════════════════════════════════════════ -->
<div class="section">
  <div class="section-title">📌 CH 131 — ARTIFICIAL RESPIRATION</div>
  <div class="section-body">
    <h3>Methods</h3>
    <div class="grid3">
      <div class="card" style="background:#e8f4fd;border:1.5px solid #2196F3;">
        <h4>Mouth-to-Mouth</h4>
        <ul><li>Most practical</li><li>16% O₂ in expired air (adequate)</li><li>12–16 breaths/min</li></ul>
      </div>
      <div class="card" style="background:#e8f5e9;border:1.5px solid #4CAF50;">
        <h4>CPR (30:2)</h4>
        <ul><li>30 compressions : 2 breaths</li><li>Rate: 100–120/min</li><li>Depth: 5–6 cm</li></ul>
      </div>
      <div class="card" style="background:#fff3e0;border:1.5px solid #FF9800;">
        <h4>Mechanical Ventilator (IPPV)</h4>
        <ul><li>Intermittent Positive Pressure Ventilation</li><li>Used in ICU</li></ul>
      </div>
    </div>
  </div>
</div>

<!-- ═══════════════════════════════════════════════════════════ -->
<!-- CH 132: EXERCISE -->
<!-- ═══════════════════════════════════════════════════════════ -->
<div class="section">
  <div class="section-title">📌 CH 132 — EFFECTS OF EXERCISE ON RESPIRATION</div>
  <div class="section-body">

    <h3>Changes During Exercise</h3>
    <table>
      <tr><th>Parameter</th><th>Rest</th><th>During Exercise</th></tr>
      <tr><td>Respiratory rate</td><td>12–16/min</td><td>20–50/min</td></tr>
      <tr><td>Tidal volume</td><td>500 mL</td><td>Up to 3000 mL</td></tr>
      <tr><td>Pulmonary ventilation</td><td>6 L/min</td><td>Up to 100–120 L/min</td></tr>
      <tr><td>PaO₂</td><td>95–100 mmHg</td><td>Maintained near normal</td></tr>
      <tr><td>PaCO₂</td><td>40 mmHg</td><td>Maintained / slightly ↓</td></tr>
      <tr><td>Cardiac output</td><td>5 L/min</td><td>20–25 L/min</td></tr>
    </table>

    <h3>Mechanism — ↑ Ventilation During Exercise</h3>
    <div class="grid2">
      <div class="flow-wrap">
        <div class="box green">NEURAL (Rapid onset)</div>
        <div class="arrow">↓</div>
        <div class="box blue">Cortical irradiation<br><small>(anticipatory — before exercise starts)</small></div>
        <div class="arrow">↓ +</div>
        <div class="box teal">Proprioceptors in muscles/joints<br><small>(limb movement → DRG)</small></div>
      </div>
      <div class="flow-wrap">
        <div class="box orange">HUMORAL/CHEMICAL (Sustained)</div>
        <div class="arrow">↓</div>
        <div class="box red">↑ K⁺, CO₂, H⁺ (lactic acid)<br>↑ Temperature</div>
        <div class="arrow">↓</div>
        <div class="box purple">Peripheral chemoreceptors<br>stimulated → ↑ ventilation</div>
      </div>
    </div>

    <h3>Oxygen Debt (EPOC)</h3>
    <div class="steps">
      <div class="step"><div class="step-num">1</div>Exercise ends</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">2</div>O₂ consumption<br>remains elevated</div>
      <div class="step-arrow">→</div>
      <div class="step"><div class="step-num">3</div>Repay lactic acid<br>(Cori cycle in liver)</div>
      <div class="step-arrow">+</div>
      <div class="step"><div class="step-num">4</div>Restore ATP/PCr<br>stores</div>
      <div class="step-arrow">+</div>
      <div class="step"><div class="step-num">5</div>Restore O₂ in<br>myoglobin &amp; blood</div>
    </div>

    <h3>First Breath (Fetal → Neonatal)</h3>
    <div class="flow-wrap">
      <div class="box header">FETUS (In Utero)<br>O₂ via placenta; lung fluid present</div>
      <div class="arrow">↓ At birth</div>
      <div class="flow-row">
        <div class="box blue">Chest compression<br>during delivery<br>→ recoil expands chest</div>
        <div class="box orange">Cold stimulates<br>skin receptors<br>→ resp. center</div>
        <div class="box green">↑PCO₂ / ↓PO₂<br>at birth<br>→ chemoreceptors</div>
        <div class="box teal">Tactile stimulation<br>(slapping)</div>
      </div>
      <div class="arrow">↓ All trigger</div>
      <div class="box green">FIRST BREATH<br><small>Surfactant must be mature (≥34 weeks gestation)</small></div>
      <div class="arrow">↓ If premature (&lt;34 wks)</div>
      <div class="box red">Surfactant deficiency<br>→ RDS (Respiratory Distress Syndrome)<br>= Hyaline Membrane Disease (HMD)</div>
    </div>

  </div>
</div>

<!-- ═══════════════════════════════════════════════════════════ -->
<!-- QUICK REFERENCE TABLE -->
<!-- ═══════════════════════════════════════════════════════════ -->
<div class="section">
  <div class="section-title">⭐ QUICK REFERENCE — IMPORTANT NORMAL VALUES</div>
  <div class="section-body">
    <div class="grid2">
      <table>
        <tr><th colspan="2">Lung Volumes &amp; Capacities</th></tr>
        <tr><td>Tidal Volume (TV)</td><td><strong>500 mL</strong></td></tr>
        <tr><td>IRV</td><td><strong>3000 mL</strong></td></tr>
        <tr><td>ERV</td><td><strong>1100 mL</strong></td></tr>
        <tr><td>RV</td><td><strong>1200 mL</strong></td></tr>
        <tr><td>Vital Capacity (VC)</td><td><strong>4600 mL</strong></td></tr>
        <tr><td>TLC</td><td><strong>5800 mL</strong></td></tr>
        <tr><td>FRC</td><td><strong>2300 mL</strong></td></tr>
        <tr><td>Dead space</td><td><strong>150 mL</strong></td></tr>
        <tr><td>Alveolar ventilation</td><td><strong>4200 mL/min</strong></td></tr>
        <tr><td>Minute ventilation</td><td><strong>6000 mL/min</strong></td></tr>
        <tr><td>FEV₁/FVC</td><td><strong>&gt;80%</strong></td></tr>
        <tr><td>PEFR</td><td><strong>400–600 L/min</strong></td></tr>
        <tr><td>MBC/MVV</td><td><strong>125–170 L/min</strong></td></tr>
      </table>
      <table>
        <tr><th colspan="2">Blood Gas &amp; Misc Values</th></tr>
        <tr><td>PaO₂ (arterial)</td><td><strong>95–100 mmHg</strong></td></tr>
        <tr><td>PaCO₂ (arterial)</td><td><strong>35–45 mmHg</strong></td></tr>
        <tr><td>SpO₂</td><td><strong>97–100%</strong></td></tr>
        <tr><td>Normal RR</td><td><strong>12–16/min</strong></td></tr>
        <tr><td>Respiratory membrane thickness</td><td><strong>0.2–0.6 μm</strong></td></tr>
        <tr><td>Lung surface area</td><td><strong>~70 m²</strong></td></tr>
        <tr><td>DLO₂ (rest)</td><td><strong>21 mL/min/mmHg</strong></td></tr>
        <tr><td>Hüfner's constant</td><td><strong>1.34 mL O₂/g Hb</strong></td></tr>
        <tr><td>O₂ carrying capacity (Hb)</td><td><strong>20 mL/100 mL</strong></td></tr>
        <tr><td>V/Q ratio (normal)</td><td><strong>0.8</strong></td></tr>
        <tr><td>Lung compliance</td><td><strong>200 mL/cmH₂O</strong></td></tr>
        <tr><td>Pulmonary artery (systolic)</td><td><strong>25 mmHg</strong></td></tr>
        <tr><td>Cyanosis threshold (deoxyHb)</td><td><strong>&gt;5 g/dL</strong></td></tr>
        <tr><td>CO affinity vs O₂</td><td><strong>250×</strong></td></tr>
      </table>
    </div>
  </div>
</div>

<div style="text-align:center;padding:20px;color:#888;font-size:11px;background:#263238;color:#cfd8dc;margin-top:20px;">
  Sembulingam Essentials of Medical Physiology | Section 9: Respiratory System &amp; Environmental Physiology | Chapters 118–132
  <br>Prepared for examination use — Flowchart format
</div>

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Here is a summary of what is inside the file - all chapters in flowchart format:

What's Included (Ch. 118-132)

Chapter	Flowcharts Inside
Ch 118 - Anatomy	Airway tree (nose → alveoli), Respiratory membrane layers (6 steps), 4 Phases of respiration, Protective reflexes (3 separate flows), Non-respiratory functions (8 cards)
Ch 119 - Pulmonary Circulation	West zones (3 zones), HPV pathway, Pressure table
Ch 120 - Mechanics	Inspiration vs Expiration (VS comparison), Pressure changes table, Surfactant pathway (full flow), Compliance (3 types), Work of breathing steps
Ch 121 - PFTs	Lung volumes table, Lung capacities table, Dynamic tests table, FEV₁/FVC interpretation flow, Methods for FRC measurement
Ch 122 - Ventilation	Minute → Alveolar ventilation flow, Dead space types (3 cards), V/Q ratio flowchart
Ch 123 - Air Composition	Inspired/Alveolar/Expired air table, Partial pressures table
Ch 124 - Gas Exchange	Fick's law formula box, Factors affecting diffusion, Lung and tissue gas exchange (2 flows)
Ch 125 - Gas Transport	O₂ transport flow (97% Hb + 3% dissolved), O₂-Hb dissociation curve (Bohr effect), CO₂ transport (70% HCO₃⁻), Chloride shift (5 steps)
Ch 126 - Regulation	4 Respiratory centers (DRG, VRG, Pneumotaxic, Apneustic), Hering-Breuer reflex (5 steps), Central vs Peripheral chemoreceptors (VS layout), Stimulus → Response flowchart
Ch 127 - Disturbances	Abnormal patterns table, 4 Types of hypoxia, CO poisoning pathway, Cyanosis (central vs peripheral)
Ch 128 - High Altitude	Acclimatization step-by-step (immediate + long-term), AMS/HACE/HAPE flow
Ch 129 - Deep Sea	O₂ toxicity, N₂ narcosis, Decompression sickness (3 separate flows)
Ch 131 - Artificial Respiration	3 methods (mouth-to-mouth, CPR 30:2, IPPV)
Ch 132 - Exercise	Changes table, Neural + Humoral mechanism, O₂ debt flow, First breath triggers flow
Quick Reference	All important normal values in 2 tables

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