📚 MBBS Final Exam Study Guide

Cardiovascular Physiology: Arterial Pressure, Veins & Blood Reservoirs

SECTION 1: ARTERIAL PRESSURE PULSATIONS

Core Concept

Normal Aortic Pressures (memorize these numbers)

Determinants of Pulse Pressure (2 key factors)

1. Stroke Volume - ↑ SV → ↑ pulse pressure
2. Arterial Compliance - ↓ compliance (stiffer arteries) → ↑ pulse pressure
   • Classic example: arteriosclerosis in elderly

Exam tip: Pulse pressure = SV / arterial compliance. Any condition increasing SV or decreasing compliance will widen the pulse pressure.

SECTION 2: ABNORMAL PRESSURE PULSE CONTOURS ⭐ (High-yield)

Aortic Regurgitation - Key Features

• Diastolic pressure may fall near zero
• Very large pulse pressure
• No dicrotic notch (incisura) - this is a classic exam MCQ point
• Classic eponymous signs (water-hammer pulse, Corrigan's pulse)

SECTION 3: BLOOD PRESSURE MEASUREMENT METHODS

Method 1: Auscultatory (Korotkoff) Method

• Uses BP cuff + stethoscope over brachial artery
• Korotkoff sounds = turbulent flow through partially compressed artery

1. Cuff > systolic → artery fully occluded → no sound
2. Cuff just below systolic → blood flows → first Korotkoff sound = SYSTOLIC pressure
3. Cuff falling → sounds change: tapping → harsh → muffled
4. Cuff ≈ diastolic → sounds disappear → last sound = DIASTOLIC pressure

• Error margin: ~±10% vs direct arterial measurement
• Sounds may persist (go below diastolic) in: AV fistulas, Aortic regurgitation

Method 2: Automated Oscillometric Method

• Uses cuff + electronic pressure sensor
• Detects arterial wall oscillations
• Maximum oscillation amplitude = Mean Arterial Pressure (MAP)
• Automatically calculates: Systolic, Diastolic, MAP, Heart rate

Exam tip: Oscillometric method detects MAP directly (point of maximum oscillation), then calculates systolic and diastolic algorithmically. Auscultatory method directly measures systolic and diastolic.

SECTION 4: NORMAL ARTERIAL PRESSURES & AGE-RELATED CHANGES

Exam tip: "Isolated systolic hypertension" in the elderly is a classic exam scenario explained by decreased arterial compliance.

SECTION 5: VEINS AND VENOUS PRESSURES ⭐

Functions of Veins (5 key roles)

1. Return blood to the heart
2. Capacitance vessels - blood reservoir (hold >60% of total blood volume)
3. Constrict or dilate to regulate stored blood volume
4. Help maintain cardiac output
5. Assist venous return via venous pump (muscle contraction + valves)

Central Venous Pressure (CVP) = Right Atrial Pressure

• Normal = 0 mmHg
• Determined by balance: heart pumping ability vs venous return

• Normal: 0 mmHg
• High (pathology): +20 to +30 mmHg
• Low limit: -3 to -5 mmHg

SECTION 6: GRAVITATIONAL/HYDROSTATIC PRESSURE

Basic Principle

• Pressure increases with depth in fluids
• ≈ 1 mmHg per 13.6 mm vertical distance

In a Standing Human

Danger: Intracranial Veins

• Skull is non-collapsible → can develop negative pressure (~-10 mmHg)
• Risk: air embolism during surgery (air enters negative-pressure sinus)

Effect on Arterial Pressure

• MAP at heart = 100 mmHg
• MAP at feet = ~190 mmHg
• All BP measurements are referenced to heart level - this is why

SECTION 7: VENOUS VALVES & MUSCLE PUMP ⭐

Why Valves Matter

• Without valves: gravity keeps foot venous pressure at ~+90 mmHg constantly
• One-way valves ensure blood flows only toward the heart

Venous (Muscle) Pump Mechanism

1. Muscle contraction → vein compression
2. Valves prevent backflow → blood moves only forward (upward)
3. During walking: foot venous pressure drops to <+20 mmHg

Standing Still vs Walking

SECTION 8: CLINICAL CONSEQUENCES OF VENOUS STASIS

Prolonged Standing

• ↓ Venous return → ↓ blood volume (up to 10-20%)
• Possible fainting (syncope)
• Prevention: leg movement, knee flexion, muscle activation

Varicose Veins

• ↑ venous + capillary pressure
• Chronic leg edema
• Impaired O₂/nutrient delivery
• Skin ulcers, possibly gangrene

• Leg elevation (above heart level)
• Compression stockings

SECTION 9: BLOOD RESERVOIR FUNCTION ⭐

Overview

• Veins hold >60% of total blood volume
• Highly compliant → excellent blood reservoir

During Blood Loss (Hemorrhage Response)

1. ↓ Arterial pressure → baroreceptors activated
2. ↑ Sympathetic stimulation → venoconstriction
3. Blood shifts from veins → arteries
4. Circulation maintained even after ~20% blood loss

Specific Blood Reservoir Capacities (memorize!)

SECTION 10: THE SPLEEN - SPECIAL FOCUS ⭐

As a Blood Reservoir

• Stores RBCs in red pulp, plasma in venous sinuses
• Can release ~50 mL concentrated RBCs → ↑ hematocrit by 1-2%

Blood-Cleansing Function

• Filters blood through narrow splenic channels
• Old/fragile RBCs destroyed by mechanical stress + reticuloendothelial cells
• Hemoglobin breakdown products recycled for new blood cell production

Immune Function

• White pulp produces lymphoid (immune) cells
• Reticuloendothelial cells remove bacteria, debris, parasites
• Works with liver macrophages
• During infection: spleen enlarges → ↑ immune activity

QUICK REVISION: HIGH-YIELD EXAM POINTS 🔑

1. Pulse pressure = Systolic - Diastolic = normally 40 mmHg
2. Aortic regurgitation → absent dicrotic notch + near-zero diastolic = very wide pulse pressure
3. First Korotkoff sound = systolic BP; disappearance = diastolic BP
4. Oscillometric method detects MAP at peak oscillation amplitude
5. CVP = 0 mmHg normally; rises in heart failure and hypervolemia
6. Foot venous pressure = +90 mmHg standing still; <+20 mmHg walking
7. Intracranial dural sinuses = negative pressure → air embolism risk in surgery
8. >60% blood volume is in veins
9. Circulation maintained after ~20% blood loss by venoconstriction
10. Spleen releases 50 mL RBCs during stress → hematocrit ↑ 1-2%
11. Varicose veins: dilation → valve leaflet gap → incompetence (not valve destruction)
12. Arteriosclerosis = decreased compliance → widened pulse pressure in elderly

EXAM MCQ MNEMONICS

• Stenosis (aortic) = Small/weak pulse
• Aortic regurgitation = Absent dicrotic notch, huge pulse pressure
• Ductus arteriosus (patent) = Diastolic dip, bounding pulse

• Cardiac failure
• Hypervolemia (transfusion)
• Inflow increase (arteriolar dilation)
• Excessive venous return
• Failure of heart to empty