• Exhalation clears "dead space" - stale air sitting in your airways (trachea, bronchi) that never reached the alveoli. If you don't fully exhale, your next breath just recirculates that old air.
• A full exhale stretches the diaphragm back to its resting position, allowing a deeper, more efficient next inhale.
• In conditions like asthma or COPD, air gets trapped in the lungs - patients struggle most with getting air out, not in.

1. The lungs want to collapse inward - lung tissue is elastic and, because of its elasticity plus the surface tension of alveolar fluid, it constantly tries to recoil inward (toward the hilum).
2. The chest wall wants to spring outward - the rib cage and thoracic muscles have their own elastic recoil that pulls outward, away from the lungs.

• The negative pressure is what keeps the lungs inflated against their own tendency to collapse
• It couples lung movement to chest wall movement - when the diaphragm contracts and the chest expands, the lungs are pulled open passively
• It also aids venous return to the heart (the great veins in the thorax are also subject to this negative pressure)

Classification of Lung Diseases

I. Functional / Physiological Classification

1. Obstructive Lung Disease

• Definition: Reduced airflow due to airway narrowing or loss of elastic recoil
• PFT pattern: FEV₁/FVC ratio < 0.70 (reduced); TLC normal or increased; air trapping
• Key diseases:
  • COPD (chronic bronchitis + emphysema)
  • Bronchial asthma
  • Bronchiectasis
  • Cystic fibrosis
  • Alpha-1 antitrypsin deficiency
  • Bronchiolitis / bronchiolitis obliterans
  • After lung or stem-cell transplantation

2. Restrictive Lung Disease

• Definition: Reduced lung volumes due to stiff lungs or mechanical constraints on expansion
• PFT pattern: FEV₁/FVC ratio normal or increased; TLC reduced
• Two major subtypes:
  A. Parenchymal (intrinsic) restriction - the lung tissue itself is abnormal:
  • Idiopathic pulmonary fibrosis (IPF)
  • Nonspecific interstitial pneumonitis (NSIP)
  • Sarcoidosis
  • Asbestosis, silicosis, berylliosis (pneumoconioses)
  • Eosinophilic pneumonia
  • Congestive heart failure
  • Drug-induced (amiodarone, methotrexate, nitrofurantoin)
  B. Extra-parenchymal (extrinsic) restriction - the lung is normal but can't expand:
  • Chest wall/skeletal: Obesity, kyphoscoliosis, ankylosing spondylitis, pregnancy
  • Neuromuscular: Guillain-Barre syndrome, myasthenia gravis, ALS, muscular dystrophy, diaphragmatic paralysis, botulism
  • Pleural: Pleural fibrosis (fibrothorax), rheumatoid arthritis, asbestosis
  • Surgical: Lung resection

3. Mixed (Obstructive + Restrictive) Pattern

• Bronchiectasis
• Cystic fibrosis
• Sarcoidosis
• Hypersensitivity pneumonitis
• Pulmonary Langerhans cell histiocytosis
• Lymphangioleiomyomatosis
• Congestive heart failure

II. Anatomical / Structural Classification

III. Aetiological Classification

IV. Acuity Classification

• Acute: Pneumonia, ARDS, pulmonary embolism, acute severe asthma
• Subacute: Hypersensitivity pneumonitis, organizing pneumonia
• Chronic: COPD, IPF, sarcoidosis, bronchiectasis

PFT Summary Table

• Murray & Nadel's Textbook of Respiratory Medicine, Table 32.1
• The Washington Manual of Medical Therapeutics

Obstructive Lung Disease

Classification by Level of Airway Affected

Large Airway Obstruction

Small Airway / Parenchymal Obstruction

COPD is the umbrella term for chronic bronchitis + emphysema combined.

Restrictive Lung Disease

Classification by Location of the Defect

A. Intrinsic (Parenchymal) - Disease within the lung tissue itself

• Rheumatoid arthritis (RA-ILD)
• Systemic sclerosis (most common CTD-ILD)
• SLE, polymyositis/dermatomyositis, Sjogren's

• Sarcoidosis
• Hypersensitivity pneumonitis (extrinsic allergic alveolitis)
• Berylliosis

• Silicosis (silica dust)
• Asbestosis (asbestos fibers)
• Coal worker's pneumoconiosis

• Amiodarone, methotrexate, bleomycin, nitrofurantoin
• Radiation pneumonitis/fibrosis

B. Extrinsic (Extra-parenchymal) - Lungs are normal but cannot expand

• Pleural effusion (large)
• Fibrothorax / pleural fibrosis
• Pneumothorax (tension)

Side-by-Side Comparison

Rheumatic Fever vs. Rheumatic Heart Disease

Core Distinction

Aetiology & Pathogenesis

ARF

• Trigger: Group A Streptococcus (GAS) pharyngitis (S. pyogenes)
• Mechanism: Molecular mimicry - antibodies and CD4+ T cells against streptococcal M protein cross-react with cardiac antigens (myocardium, valves, pericardium)
• The 2-3 week delay after infection = time needed to mount this immune response
• Only 0.3-3% of GAS pharyngitis cases develop ARF - genetic susceptibility plays a role
• Tissue injury via: complement activation, neutrophil/macrophage recruitment, T-cell cytokine release

RHD

• Mechanism: Repeated episodes of ARF cause cumulative valve inflammation and healing by fibrosis
• Each attack adds more scarring - even a single severe episode can cause RHD
• Streptococci are completely absent from RHD lesions - it is purely immunological scarring
• Chronic fibrosis is the predictable consequence of repeated healing of acute inflammation

Clinical Features

ARF - Acute, Multisystem Inflammation (lasts 2-4 weeks)

RHD - Chronic Valvular Disease (develops years later)

Diagnosis

ARF - Revised Jones Criteria (2015 AHA)

• Carditis (clinical and/or subclinical echocardiographic valvulitis)
• Arthritis (polyarticular in low-risk; mono or polyarticular in high-risk populations)
• Chorea
• Erythema marginatum
• Subcutaneous nodules

• Polyarthralgia (low-risk) / monoarthralgia (high-risk)
• Fever ≥38.5°C
• ESR ≥60 mm/hr and/or CRP ≥3.0 mg/dL (low-risk); ESR ≥30 mm/hr (high-risk)
• Prolonged PR interval on ECG

RHD - Echocardiography

• Valve thickening, restricted mobility, commissural fusion
• Doppler evidence of stenosis/regurgitation
• No specific blood test - diagnosed by imaging and clinical history

Investigations

Treatment

ARF

• Eradicate GAS: Benzathine penicillin G 1.2 million units IM single dose
• Arthritis: Aspirin 80-100 mg/kg/day OR NSAIDs (rapid symptomatic relief)
• Carditis: Corticosteroids for moderate-severe carditis (no proven long-term benefit on valve outcome)
• Chorea: Haloperidol or carbamazepine if severe
• Hospitalization required

RHD

• Secondary prophylaxis (most important - prevents further ARF attacks): Benzathine penicillin G 1.2 million units IM every 4 weeks for minimum 10 years (often lifelong if carditis occurred)
• Symptomatic heart failure: Diuretics, ACE inhibitors, beta-blockers
• AF: Anticoagulation
• Definitive: Balloon mitral valvuloplasty or valve replacement surgery for significant stenosis

Age Profile & Epidemiology

Key Conceptual Summary

ARF is the fire. RHD is the scar left by the fire.

• ARF = acute, reversible (mostly), multisystem autoimmune response to GAS
• RHD = chronic, irreversible, cardiac-specific fibrotic sequela of recurrent ARF
• The mitral valve bears the brunt in both - acute regurgitation in ARF, chronic stenosis in RHD
• Secondary prophylaxis with penicillin is the single most important intervention to prevent ARF recurrence and thereby halt progression to RHD
• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 525-526
• Goldman-Cecil Medicine, Chapter 269

Specific Proteins Targeted in Rheumatic Fever (Molecular Mimicry)

The Core Concept

Streptococcal Antigens That Trigger Cross-Reactivity

Tissue-Specific Target Proteins

1. Heart Valves (Valvulitis)

• Anti-GlcNAc antibodies cross-react with laminin (a basement membrane/extracellular matrix protein in valve endothelium)
• This initial antibody-mediated damage to the endocardium causes expression of VCAM-1 (vascular cell adhesion molecule-1) on the valve surface

• VCAM-1 upregulation allows T cells to infiltrate the valve substance
• These T cells cross-react with cardiac myosin (the intracellular biomarker antigen)
• Result: granulomatous inflammation, scarring, neovascularization

Autoantibodies against collagen also form secondarily - released from damaged valves, perpetuating the cycle.

2. Joints (Arthritis)

• Mechanism: Immune complex deposition in synovial tissue
• Synovial fluid is sterile with lymphocyte predominance
• The arthritis is transient and non-destructive - unlike valvular disease, joints heal completely
• The specific joint proteins targeted are less well defined compared to cardiac antigens; the damage is primarily from immune complex-mediated inflammation rather than direct molecular mimicry of a single joint protein

3. Brain / Basal Ganglia (Sydenham's Chorea)

• These antibodies activate calcium/calmodulin-dependent kinase II (CaMKII) in neuronal cells
• CaMKII activation leads to dopamine release - explaining the involuntary movements
• Same antibodies seen in PANDAS (Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections)

4. Myocardium (Myocarditis) - Aschoff Bodies

• Anti-M protein antibodies and T cells attack cardiac myosin
• T cells from peripheral blood and heart valves of RHD patients cross-react with both M protein and cardiac myosin
• This forms the Aschoff body - the pathognomonic lesion of rheumatic carditis
  • Central fibrinoid necrosis
  • Surrounded by Anitschkow cells (plump activated histiocytes with "caterpillar" nuclei)
  • Occasional multinucleate giant cells

Summary Table

• Valves: Laminin (surface target) + Myosin (intracellular biomarker)
• Brain: Tubulin (intracellular) + Dopamine receptors (surface target)
• Structural link: M protein's alpha-helical coil mimics the alpha-helical structure of myosin and tropomyosin - this is why cardiac muscle proteins are preferentially targeted
• Fuster & Hurst's The Heart, 15th Ed., p. 861
• Braunwald's Heart Disease, 2 Vol Set

Incidence vs. Prevalence

Core Distinction

Definitions

Incidence

The number of new cases of a disease developing in a population at risk over a specified time period

• Example: 50 new TB cases per 100,000 population per year

Prevalence

The number of all existing cases (new + old) in a population at a given point in time

• Example: 500 diabetics per 100,000 population today

Types

Incidence

Prevalence

The Relationship Between Them

        New cases flowing IN
               ↓↓↓
    ┌─────────────────────────┐
    │   PREVALENCE POOL       │
    │   (all existing cases)  │
    └─────────────────────────┘
               ↓↓↓
       Cases flowing OUT
       (cured, died, emigrated)

• Prevalence increases when: incidence rises, disease duration increases (e.g. better treatment keeps patients alive longer)
• Prevalence decreases when: incidence falls, patients recover/die faster

Practical Examples

HIV/AIDS is the classic exam example: Antiretroviral therapy didn't reduce incidence much, but massively increased prevalence because patients live longer.

Which Measure to Use?

Memory Aid

• Incidence = Incoming new cases (the inflow)
• Prevalence = Pool of all cases present (the pond)

TB Programme Management Indicators

Framework Overview

INPUT → PROCESS → OUTPUT → OUTCOME → IMPACT
(Resources) (Activities) (Coverage) (Results) (TB burden)

I. Input Indicators

II. Process Indicators

III. Output / Diagnostic Indicators

1. Case Notification Rate (CNR)

• Expressed per 100,000 population per year
• Reflects both disease burden AND programme detection capacity

2. TB Treatment Coverage

• WHO End TB target: ≥90% by 2025
• Reflects the gap between estimated and detected cases

3. Case Detection Rate (CDR) - now called TB Treatment Coverage

• Old terminology still used in many exams
• Formula same as treatment coverage above
• Target: ≥70% under original DOTS targets

4. Bacteriological Confirmation Rate

• Measures quality of diagnosis
• Higher rate = more accurate case-finding

5. Drug-Resistant TB Notification Rate

• Number of confirmed RR-TB/MDR-TB cases notified and started on treatment
• % of confirmed RR-TB patients started on appropriate regimens

IV. Treatment Outcome Indicators

Standard WHO Treatment Outcome Definitions

Composite Indicators

Current global TSR: ~85% for drug-susceptible TB; ~76% for HIV-associated TB (WHO 2024) India (NTEP) TSR: ~85.5% (2022)

V. Outcome Indicators (Programme-Level)

VI. Special Population Indicators

VII. RNTCP/NTEP Specific Indicators (India)

Summary: The "3 Key" Programme Indicators for Exams

A programme is considered successful when CDR ≥70% AND TSR ≥85% are achieved simultaneously - this is because you need both high detection AND high treatment success to actually reduce TB burden in the community.

• WHO Global TB Report 2024
• TB DIAH/USAID Navigating TB Indicators Framework
• NTEP (National TB Elimination Programme), India

Mode of Transmission of Dengue + Incubation Period

The Agent

• Virus: Dengue virus (DENV) - a Flavivirus
• 4 serotypes: DENV-1, DENV-2, DENV-3, DENV-4 (all can cause DHF)
• Each serotype gives lifelong immunity to that serotype only - cross-immunity to other serotypes is temporary (weeks to months)

Mode of Transmission

Primary Mode - Vector-Borne (Biological Transmission)

How Transmission Occurs - Step by Step

Viraemic human → Mosquito feeds → Virus in mosquito gut
       ↓
Extrinsic Incubation Period (EIP) in mosquito: 8-12 days
(virus replicates and migrates to salivary glands)
       ↓
Infective mosquito → Bites susceptible human → Injects virus in saliva
       ↓
Intrinsic Incubation Period (IIP) in human: 3-14 days
       ↓
Symptomatic dengue fever

Incubation Periods - The Two Types

Once a mosquito becomes infective after the EIP, it remains infective for life - it can transmit virus with every subsequent bite.

Period of Communicability (Viraemia Window)

This is why mosquito control during the first 5 days of illness is critical - the patient is still viraemic and can infect biting mosquitoes.

Other (Non-Vector) Routes

Why Aedes aegypti is Such an Efficient Vector

Summary Box

• Park's Textbook of Preventive and Social Medicine, pp. 289-293
• PLOS ONE: The Incubation Periods of Dengue Viruses (mean IIP 5.9 days, EIP 8-12 days at 25°C)

Type of Fever in Dengue

The Pattern: Biphasic (Saddleback / Camelback) Fever

The Fever Curve - Illustrated

How the Fever Progresses

Phase 1 - First Febrile Spike (Days 1-3)

• Sudden onset of high fever: 39°C-40°C
• Accompanied by chills, severe headache, retro-orbital pain, myalgia, arthralgia ("breakbone fever")
• Flushing of face, neck and chest
• Early rash - diffuse flushing or fleeting pin-point eruptions

Defervescence - Brief Remission (Day 3-4)

• Temperature drops for a few hours to 2 days
• Patient feels temporarily better
• Rash appears in 80% of cases during this remission - characteristic maculopapular/scarlatiniform rash starting on chest and trunk
• In DHF - this is the critical phase - plasma leakage, shock, and bleeding risk peaks here

Phase 2 - Second Febrile Spike (Days 4-5)

• Fever returns but is lower and milder than the first peak
• Lasts 1-2 days
• Accompanied by milder versions of the initial symptoms
• Rash may continue with itching and hyperaesthesia

Recovery Phase (Day 6 onwards)

• Fever resolves, usually within 5-7 days total (rarely >7 days)
• Bradycardia common during recovery
• Platelet count rises, haematocrit normalises
• IgM/IgG antibodies become detectable from ~Day 5 onwards

Fever Classification Summary

Why "Breakbone Fever"?

Important Clinical Correlation

• The defervescence (dip) coincides with plasma leakage beginning in DHF
• The patient feels better but is actually entering the most dangerous phase
• Clinicians must not be reassured by the temperature drop - platelet count and haematocrit must be monitored closely between Days 3-6
• Park's Textbook of Preventive and Social Medicine, pp. 291-293

Dengue Fever Type = Biphasic (Saddleback/Camelback) Fever

The Two Peaks

Temperature
    |
40° |  ***
    | *   *                  **
    |*     *                *  *
    |       *              *    *
    |        **          **
    |          **      **
    |            ******
    |_________________________ Days
         1   2   3   4   5   6   7
         [Phase 1] [Dip] [Phase 2]

• Phase 1 (Days 1-3): High fever, headache, myalgia, retro-orbital pain, facial flushing
• Dip (Day 3-4): Brief remission - rash appears in 80% of cases; most dangerous period in DHF (plasma leakage begins)
• Phase 2 (Days 4-5): Milder second fever spike for 1-2 days, then recovery

Also Known As

• "Breakbone fever" - due to the intense bone/joint/muscle pain
• "Three-day fever + two-day fever" - reflecting the biphasic nature

Classification of Haemorrhage - Exam Oriented

1. By Timing (Surgical Classification) ⭐ Most Asked

Memory: P-R-S = Primary (now), Reactionary (24-48 hrs), Secondary (1-2 weeks/infection)

2. By Source of Vessel

3. By Site / Direction of Bleeding

4. By Volume / ATLS Classification of Haemorrhagic Shock ⭐ Very High Yield

Key: BP does not fall until Class III (>30% blood loss). Pulse pressure falls first (Class II). Urine output is the most sensitive indicator of perfusion.

5. By Pathology / Morphological Types (Robbins/Pathology)

6. By Cause (Aetiology)

7. Obstetric Classification (PPH) - Special Category

PPH defined as blood loss >500 mL (vaginal delivery) or >1000 mL (caesarean section)

8. By Intracranial Location (Neurosurgery)

Quick Exam Memory Table

• Bailey & Love's Short Practice of Surgery, 28th Ed., p. 131
• Sabiston Textbook of Surgery - ATLS Classes of Hemorrhagic Shock, Table 33.1

Pathophysiology of Shock - Chart Form

Core Definition

Shock = failure to meet the metabolic needs of the cell Regardless of cause, the final common pathway is decreased tissue perfusion → cellular hypoxia

1. The Vicious Cycle of Shock (from Schwartz's Surgery)

2. Phases of Shock

INCITING EVENT (haemorrhage / sepsis / cardiac failure / neurologic injury)
                         │
                         ▼
           ┌─────────────────────────┐
           │  DECREASED CO / BP      │
           │  Tissue hypoperfusion   │
           └──────────┬──────────────┘
                      │
          ┌───────────▼────────────┐
          │   COMPENSATED PHASE    │  ← Body adapts; BP maintained
          │  (Neuroendocrine kick) │     Tachycardia, vasoconstriction,
          │                        │     oliguria - but BP still normal
          └───────────┬────────────┘
                      │  (if untreated / prolonged)
          ┌───────────▼────────────┐
          │  DECOMPENSATED PHASE   │  ← BP falls, acidosis, cell death
          │  (Cellular injury)     │     Organ dysfunction begins
          └───────────┬────────────┘
                      │  (if further untreated)
          ┌───────────▼────────────┐
          │   IRREVERSIBLE PHASE   │  ← Massive parenchymal + microvascular
          │                        │     damage; resuscitation fails → DEATH
          └────────────────────────┘

3. Neuroendocrine Response to Shock (Compensatory Mechanisms)

↓ Blood Volume / ↓ BP
        │
        ├──────────────────────────────────────────┐
        ▼                                          ▼
BARORECEPTORS                              CHEMORECEPTORS
(aortic arch, carotid sinus,               (aorta, carotid bodies)
 atrial volume receptors)                  sense ↓O₂, ↑CO₂, ↑H⁺
        │                                          │
        └────────────────┬─────────────────────────┘
                         ▼
              HYPOTHALAMUS / CNS ACTIVATION
                         │
          ┌──────────────┼──────────────┐
          ▼              ▼              ▼
   SYMPATHETIC      HPA AXIS       ADH (AVP)
   ACTIVATION       ACTIVATION     RELEASE
          │              │              │
          ▼              ▼              ▼
  ↑Catecholamines   ↑Cortisol      ↑Water retention
  (Epi, Norepi)     ↑ACTH          by kidneys
          │
    ┌─────┼──────┐
    ▼     ▼      ▼
↑HR  ↑Contractility  Vasoconstriction
                     (skin, gut, kidneys)
                         │
                         ▼
              BLOOD REDISTRIBUTED to
              Brain + Heart (vital organs)

• RAAS: ↓Renal perfusion → ↑Renin → ↑Angiotensin II → ↑Aldosterone → Na⁺ + H₂O retention
• ADH/AVP: Released from posterior pituitary → ↑water reabsorption in collecting duct

4. Cellular Pathophysiology

↓ Tissue O₂ Delivery
        │
        ▼
AEROBIC METABOLISM FAILS
        │
        ▼
ANAEROBIC GLYCOLYSIS begins
        │
        ▼
↑ Lactic acid → METABOLIC ACIDOSIS (↓pH)
        │
        ▼
Na⁺-K⁺-ATPase PUMP FAILS (needs ATP)
        │
        ├─────────────────────────────────┐
        ▼                                 ▼
Na⁺ + H₂O enter cell          K⁺ leaks OUT of cell
CELLULAR OEDEMA                  HYPERKALAEMIA
        │
        ▼
↑ Intracellular Ca²⁺
(activates proteases, phospholipases)
        │
        ▼
LYSOSOMAL MEMBRANE RUPTURE
        │
        ▼
CELL DEATH (necrosis)
        │
        ▼
INFLAMMATORY MEDIATOR RELEASE
(DAMPs, cytokines, ROS)
        │
        ▼
SYSTEMIC INFLAMMATORY RESPONSE (SIRS)
→ MODS (Multi-Organ Dysfunction Syndrome)

5. Microcirculatory Changes

Initial shock
    │
    ▼
Arteriolar VASOCONSTRICTION (catecholamines)
    │
    ▼
↑ Pre-capillary resistance
    │
    ▼
↓ Capillary hydrostatic pressure
    │
    ▼
Fluid shifts FROM interstitium INTO vasculature
(auto-transfusion / transcapillary refill)
    │
    ▼
Prolonged shock:
    │
    ▼
Endothelial activation + damage
    │
    ├──────────────────────────┐
    ▼                          ▼
↑ Capillary permeability    Cellular aggregation
(fluid leaks OUT of vessels)  (WBCs, platelets plug
→ oedema, hypovolaemia worsens  microcirculation)
    │
    ▼
"No-reflow phenomenon"
(microvascular occlusion persists
even after resuscitation)

6. Organ-Specific Consequences

7. Shock by Type - Haemodynamic Fingerprint

Summary Flowchart - One Page

CAUSE
  │
  ▼
↓ Effective Circulating Volume OR ↓ Cardiac Output OR ↓ SVR
  │
  ▼
↓ MEAN ARTERIAL PRESSURE
  │
  ▼
↓ TISSUE PERFUSION (all organs)
  │
  ├── COMPENSATED → ↑HR, ↑SVR, RAAS, ADH → BP maintained
  │
  ├── DECOMPENSATED → ↓BP, Lactic acidosis, Oliguria, Confusion
  │
  └── IRREVERSIBLE → Cell death, MODS, Death

The gut is the "motor" of MOF - splanchnic ischaemia allows bacterial translocation which drives the systemic inflammatory response that culminates in multi-organ failure.

• Schwartz's Principles of Surgery, 11th Ed., Chapter 5 (pp. 133-152)

Mechanism of Labour (Cardinal Movements) - According to Williams Obstetrics

Preliminary Concepts

Most common presentation: Vertex (occiput anterior) in 97% of term pregnancies

The 7 Cardinal Movements of Labour

1. ENGAGEMENT

BPD passes through pelvic inlet
         │
         ▼
Presenting part reaches Station 0
         │
Primiparae: 2 weeks before labour (lightening)
Multiparae: at onset of labour
         │
Head usually enters in TRANSVERSE diameter of inlet
(Left Occiput Transverse - LOT is most common)

• What engages: Biparietal diameter (BPD) = 9.5 cm
• Denominator: Occiput
• Clinical sign: Fundal height decreases, patient says "baby dropped"

2. FLEXION

Head meets resistance of pelvic floor/walls
         │
         ▼
Chin brought to chest (passive movement)
         │
         ▼
Presenting diameter changes:
Occipito-frontal (11.5 cm) → Sub-occipito-bregmatic (9.5 cm)

• Why it matters: Reduces the presenting diameter by ~2 cm, allowing easier descent
• Mechanism: Lever action - longer occiput arm + shorter face arm → flexion
• Passive movement - driven by uterine contractions and pelvic resistance

3. DESCENT

Downward passage of fetal presenting part through birth canal
         │
Forces driving descent:
├── Uterine contractions
├── Abdominal muscle contractions (bearing down)
└── Straightening/extension of fetal body
         │
         ▼
Gradual and progressive (not always continuous)

• Occurs throughout labour but most rapid in 2nd stage
• Assessed by station (-5 to +5 relative to ischial spines)
• Descent occurs simultaneously with all other movements

4. INTERNAL ROTATION

Head in transverse position (LOT/ROT)
         │
         ▼
Occiput rotates ANTERIORLY (45°)
to face symphysis pubis
         │
         ▼
Head now in ANTERO-POSTERIOR diameter of outlet
(Occiput Anterior position)

• Why it occurs: Pelvic floor muscles (levator ani) act like a gutter - sloping anteriorly - and guide the occiput forward
• Normal rotation: 45° from LOT → OA (occiput anterior)
• Abnormal: Rotation to OP (occiput posterior) = "persistent OP" → longer, more painful labour
• Occurs at level of ischial spines as head traverses mid-pelvis

5. EXTENSION

Flexed head reaches pelvic outlet / vaginal introitus
         │
         ▼
Occiput reaches inferior margin of pubic symphysis
         │
         ▼
Head EXTENDS around pubic symphysis (pivot point)
         │
         ▼
Parts delivered in sequence:
Occiput → Bregma → Forehead → Nose → Mouth → Chin
         │
         ▼
Head is born; immediately drops - chin over anus

• Mechanism: Two forces act on the head: uterine contractions push downward; pelvic floor resistance directs anteriorly → resultant force = extension
• Suboccipital region acts as the hypomochlion (fulcrum) against the pubic arch

6. RESTITUTION (External Rotation)

Head delivered; untwists to correct anatomical alignment
         │
         ▼
Occiput rotates back to TRANSVERSE position
(same side it came from - e.g. LOT if was LOA)
         │
         ▼
Now aligns with fetal shoulders
(shoulders are still in oblique diameter of pelvis)

• Passive movement - simple recoil of the neck twist
• Restitution = first 45° rotation back to transverse
• External rotation = further rotation as shoulders undergo internal rotation inside

7. EXPULSION

After external rotation:
Shoulders internally rotate → A-P diameter of outlet
         │
         ▼
ANTERIOR SHOULDER delivered first
(slips under pubic symphysis)
         │
         ▼
POSTERIOR SHOULDER delivered
(passes over perineum)
         │
         ▼
REST OF BODY delivered by lateral flexion
(follows path of least resistance)

Summary Flow Chart

HEAD IN TRANSVERSE (LOT)
        ↓
    ENGAGEMENT
(BPD through inlet, Station 0)
        ↓
     FLEXION
(chin to chest, SOM → SOB diameter)
        ↓
     DESCENT
(downward through birth canal)
        ↓
  INTERNAL ROTATION
(OT → OA, 45° anterior rotation)
        ↓
    EXTENSION
(head pivots under symphysis pubis)
HEAD BORN (occiput → bregma → face → chin)
        ↓
RESTITUTION / EXTERNAL ROTATION
(head realigns with shoulders)
        ↓
    EXPULSION
(anterior shoulder → posterior shoulder → body)

Diameters Involved - Key Numbers

Memory Aid

"Every Fetus Deserves Internal Rotation; External Rotation Expels"

Engagement → Flexion → Descent → Internal Rotation → (Extension) → External Rotation → Expulsion

• Roberts & Hedges' Clinical Procedures in Emergency Medicine, p. 1351
• Cardinal movements illustrated from Gabbe's Obstetrics: Normal and Problem Pregnancies

Protein-Energy Malnutrition (PEM)

Definition

PEM is a spectrum of clinical conditions resulting from inadequate intake of both protein and calories (macronutrients), leading to impaired growth, wasting of body tissues, impaired immunity, and organ dysfunction.

• Also called Protein-Energy Undernutrition (PEU) by WHO
• Represents a spectrum from mild (subclinical) to extreme forms
• The two extreme poles are Kwashiorkor and Marasmus

Classification of PEM

A. By Aetiology

B. By Clinical Syndrome (Most Important for Exams)

C. By Severity (Wellcome Classification)

D. By WHO/MUAC (Mid-Upper Arm Circumference)

Clinical Photographs

Pathophysiology (Why the Two Forms Differ)

KWASHIORKOR                          MARASMUS
(Protein deficiency > Calories)      (All macronutrients deficient)

Carbohydrate intake adequate          Severe caloric restriction
       ↓                                     ↓
Insulin secreted                    Cortisol + Glucagon rise
       ↓                                     ↓
Lipolysis suppressed               Fat + Protein mobilized
Proteolysis suppressed               (body adapts)
       ↓                                     ↓
Visceral protein ↓↓                  Wasting of all compartments
Albumin ↓↓                          Albumin relatively spared
       ↓                                     ↓
Oedema (↓ oncotic pressure)          NO oedema
Fatty liver (↓ lipoprotein carrier)  NO fatty liver

Complications of PEM

1. Immune System

• Depressed cell-mediated immunity (T-lymphocyte dysfunction)
• Thymic atrophy and lymphoid depletion
• Impaired complement function
• Increased susceptibility to infections - measles, TB, pneumonia, gastroenteritis
• Secondary infections can be fatal and perpetuate the catabolic state

2. Gastrointestinal

• Villous atrophy of small intestinal mucosa
• Malabsorption - fat, carbohydrate, protein all affected
• Reduced digestive enzyme secretion (lactase deficiency common)
• Bacterial overgrowth
• Impaired gut barrier → bacterial translocation

3. Cardiovascular

• Reduced cardiac muscle mass → reduced cardiac output
• Bradycardia and hypotension
• Susceptibility to cardiac failure during refeeding

4. Liver

• Fatty liver (steatosis) in kwashiorkor - due to reduced VLDL/lipoprotein synthesis
• Impaired drug metabolism
• Reduced coagulation factor synthesis → bleeding tendency

5. Endocrine

• Growth hormone resistance (↑GH but ↓IGF-1)
• Stunted growth - if chronic (height-for-age below -2 SD)
• Hypothyroidism features
• Adrenal and gonadal dysfunction

6. Haematological

• Anaemia - iron, folate, B12 deficiency; also from protein deficiency itself
• Leukopenia
• Thrombocytopenia

7. Neurological / Developmental

• Apathy, listlessness, irritability
• Impaired cognitive development and intellectual capacity
• Permanent neurodevelopmental delay if severe PEM occurs in first 2 years of life ("critical window")
• Peripheral neuropathy

8. Renal

• Reduced GFR and concentrating ability
• Electrolyte imbalances - hypokalaemia, hyponatraemia, hypophosphataemia

9. Refeeding Syndrome (a complication of treatment)

• Rapid refeeding causes sudden shift of phosphate into cells
• Hypophosphataemia → cardiac arrhythmias, respiratory failure, seizures
• Prevention: start feeding slowly, supplement electrolytes

10. Long-term Consequences

• Stunting (chronic malnutrition)
• Obesity and metabolic syndrome in adulthood (Barker hypothesis - fetal programming)
• Reduced adult height and work capacity
• Cognitive deficits and poor school performance

Summary Table - Key Points for Exam

• Robbins, Cotran & Kumar Pathologic Basis of Disease, pp. 412-413
• Lippincott's Illustrated Reviews: Biochemistry, 8th Ed., Table 27.1
• Park's Textbook of Preventive and Social Medicine, p. 737

Black/Dark Patches on Skin - Possible Causes

⚠️ Important First

• Are the patches flat or raised/rough?
• Are they itchy, painful, or completely symptomless?
• Did they appear suddenly or gradually over months/years?
• Are there any other symptoms - fatigue, weight loss, joint pain?
• Do you have diabetes, thyroid issues, or take any medications?

Common Causes of Black/Dark Patches on Legs and Hands

1. Post-Inflammatory Hyperpigmentation (PIH) - Most Common

• What: Darkening left behind after skin inflammation heals (old insect bites, scratches, eczema, acne)
• Looks like: Flat, dark brown-black patches at sites of old injury
• Common in: Darker skin tones (South Asian, African skin)
• Treatment: Sunscreen, vitamin C, niacinamide, hydroquinone creams

2. Acanthosis Nigricans

• What: Velvety, dark, thickened patches in body folds
• Location: Typically neck, armpits, groin - but also backs of hands and knuckles
• Cause: Insulin resistance, diabetes, obesity, hormonal disorders (PCOS, thyroid)
• Key sign: Texture is rough/velvety, not just a colour change
• Why important: It is a marker of underlying metabolic disease - needs blood sugar testing

3. Venous Stasis / Haemosiderin Deposition (Legs specifically)

• What: Iron deposits from leaking blood vessels stain the skin dark
• Location: Lower legs, ankles especially
• Associated with: Chronic venous insufficiency, varicose veins, leg swelling, standing for long periods
• Other signs: Leg swelling, varicose veins, skin hardening (lipodermatosclerosis)

4. Addison's Disease (Adrenal Insufficiency)

• What: Generalised hyperpigmentation, particularly on pressure areas, skin folds, knuckles, lips, scars
• Cause: Low cortisol → high ACTH → stimulates melanocytes
• Other symptoms: Extreme fatigue, weight loss, low blood pressure, nausea, salt craving
• Important: This needs urgent medical attention if suspected

5. Lichen Planus Pigmentosus

• What: Dark grey-brown patches, especially on sun-exposed areas (face, neck, arms) and flexures
• Common in: South Asians and Middle Easterners
• Associated with: Hepatitis C infection sometimes

6. Diabetic Dermopathy

• What: Round or oval brownish, slightly depressed patches
• Location: Specifically on the shins (lower legs)
• Cause: Small vessel disease in diabetes
• Key: Very common in diabetics, often ignored

7. Sun/UV Damage (Solar Lentigines)

• What: Flat, well-defined dark spots ("age spots", "liver spots")
• Location: Sun-exposed areas - backs of hands, face, forearms
• Cause: Chronic sun exposure → melanocyte proliferation

8. Drug-Induced Pigmentation

• Some medications cause skin darkening: minocycline (antibiotic), amiodarone, hydroxychloroquine, chemotherapy agents, oral contraceptives

9. Tinea Nigra (Fungal)

• What: Black/brown macular patch, usually on palm (rarely sole)
• Cause: Fungal infection (Hortaea werneckii)
• Treatment: Simple antifungal cream

Red Flags - See a Doctor Urgently If:

What to Do

1. See a dermatologist - they can often diagnose by examination alone
2. Take a photo of the patches in good lighting to show progression over time
3. Get basic blood tests: fasting blood sugar, HbA1c, thyroid function, cortisol (if fatigue present)
4. Avoid self-treating with strong bleaching creams without diagnosis - some contain steroids or mercury which can worsen the skin

Ichthyosis - Your Likely Condition

What Does It Look Like?

What is Ichthyosis?

Types - Which One Might You Have?

Why Does It Happen? (Simple Explanation)

Gene mutation (FLG / STS gene)
        ↓
Skin protein (filaggrin / steroid sulfatase) abnormal
        ↓
Dead skin cells cannot shed properly
        ↓
They pile up on the surface
        ↓
Dry, thick, dark, scaly patches

• In Ichthyosis Vulgaris: The filaggrin protein that holds the skin barrier together is defective → skin loses moisture + can't shed dead cells
• In X-linked Ichthyosis: Enzyme steroid sulfatase is missing → dead cells stick together instead of shedding

Key Features That Help Confirm It

• Worst on lower legs (shins) - classic location
• Also outer arms, back, abdomen
• Usually spares armpits, groin (flexures) in vulgaris
• Palms may have extra skin lines (hyperlinear palms)

• Dry, rough, dark or grey-brown scales
• Skin feels like sandpaper or fish scales
• Worse in cold/dry weather, better in summer/humid weather
• No redness or oozing (unless infected)

Management - What You Can Do

Daily Routine

Medications (prescribed by doctor)

• Retinoids (vitamin A derivatives) - acitretin or isotretinoin for severe cases
• Keratolytics - salicylic acid, alpha-hydroxy acids to help shed scales
• Topical steroid sulfatase replacements being studied for X-linked type

Things That Worsen It

• Cold, dry weather
• Hot showers
• Harsh soaps/detergents
• Not moisturising after bathing

Reassurance

• It is not contagious - no one can catch it from you
• It is not dangerous to your overall health in most forms
• It does not spread to other people
• The skin condition is lifelong but very manageable with consistent skincare
• Associated with atopic eczema and asthma in some cases (ichthyosis vulgaris)

What to Ask Your Doctor

1. "Which type of ichthyosis do I have?"
2. "Should I have a genetic test?"
3. "What moisturiser do you recommend for my skin type?"
4. "Are there any triggers I should avoid?"

• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 1063
• Fitzpatrick's Dermatology (Ichthyosis Vulgaris section)

Obstructive vs. Restrictive Lung Disease

Core Difference in One Line

PFT (Spirometry) - The Key Distinguishing Tool

The FEV₁/FVC ratio is the single most important distinguishing test.

• Low = obstructive
• Normal/high = restrictive

Pathophysiology

Examples

Obstructive

Restrictive - Intrinsic (parenchymal)

Restrictive - Extrinsic (extra-parenchymal)

Clinical Features Compared

Flow-Volume Loop (Exam Favourite)

Obstructive:                    Restrictive:
    Flow                            Flow
     |  ***                          |   ***
     | *   *                         |  *   *
     |*     *____                    | *     *
     |____________ Volume            |_________ Volume
   (scooped out expiratory          (normal shape but
    curve; low peak flow)            smaller loop overall)

• Obstructive = scooped/concave expiratory limb, reduced peak expiratory flow
• Restrictive = normal shape but proportionally smaller loop

One-Line Memory Aid

"Obstructive = Out problem (can't breathe out); Restrictive = Room problem (no room to breathe in)"