Advanced Exercise Physiology – Cardiovascular Physiology (Lecture 1)

Overview of the Cardiovascular (CV) System

Components

• Heart – pump (≈300–350 g; consumes ≈10 % of resting O₂)

• Vasculature – arteries, arterioles, capillaries, venules, veins

• Blood – formed elements (≈40 %) + plasma (≈60 %)

Core Functions

1. Transport – O₂, CO₂, nutrients, wastes, hormones

2. Homeostatic regulation – fluid balance, BP, pH, thermoregulation (heat transfer via blood)

3. Protection – hemostasis (clotting), immune defense, blood-flow prioritization during loss

Pulmonary vs Systemic Circulation

• Right heart (pulmonary): pumps de-oxygenated blood → lungs → picks up O₂

• Left heart (systemic): pumps oxygenated blood → entire body

Heart Anatomy & Blood Flow (Right → Left)

1. SVC / IVC → Right Atrium (RA)

2. Tricuspid Valve (Right AV) – prevents RA⇆RV backflow

3. Right Ventricle (RV)

4. Pulmonary Semilunar Valve → Pulmonary Artery → Lungs

5. Pulmonary Veins → Left Atrium (LA)

6. Bicuspid / Mitral Valve (Left AV)

7. Left Ventricle (LV) – thickest wall (~3× RV); systemic pump

8. Aortic Semilunar Valve → Aorta → Arterial tree → Capillaries → Veins → (step 1)

• Valves = one-way; disease/leakage alters preload/afterload

• Coronary arteries/veins nourish myocardium (critical in MI)

Cardiac Output (CO / Q̇)

• Definition: volume ejected per minute

• Formula: Q = HR \times SV

• Typical resting values:

  • HR_{rest}\approx 60–80\;\text{b·min}^{-1}

  • SV_{rest}\approx 60–80\;\text{mL·beat}^{-1}

  • Q_{rest}\approx 5\;\text{L·min}^{-1} (♀ slightly lower, ♂ higher)

• Exercise increase: Q_{max}\approx 20–25\;\text{L·min}^{-1} (untrained) → 40+\;\text{L·min}^{-1} (elite endurance)

• Age sets max HR; training mainly augments SV

Blood Vessel Types & Hemodynamics

Structural Layers (inside→out)

1. Endothelium (tunica intima)

2. Smooth muscle (tunica media) – thicker in arteries ⇒ vaso-control

3. Fibrous/elastic connective (tunica adventitia)

Classification

• Elastic (central) arteries – Aorta, iliacs; Windkessel effect dampens pulsatility

• Muscular arteries – named regionals (ulnar, femoral); rich smooth muscle; main site of exercise redistribution

• Arterioles – resistance vessels; greatest pressure drop; SNS & local metabolites dictate dilation/constriction

• Capillaries – single-cell wall; huge cross-sectional area; slow flow for gas exchange; vulnerable to HTN damage

• Venules / Veins – capacitance vessels (≈60 % blood volume at rest); thin wall, valves, low pressure (≈10–30 mmHg); venous return aided by:

  • Skeletal muscle pump

  • Respiratory pump

  • Sympathetic venoconstriction

Pressure & Flow Principles

• Flow follows ΔP / Resistance (Ohm’s law for fluids)

• Blood flows high → low pressure; valve timing hinges on this fact

• Windkessel effect: aortic elasticity stores energy during systole, sustains flow in diastole (prevents zero-flow periods)

• Central (aortic) BP < peripheral (brachial) BP

Blood Composition & Viscosity

• Formed elements (≈40 %)

  • Erythrocytes – carry O₂ via hemoglobin

  • Leukocytes – immune defense

  • Thrombocytes (platelets) – clotting; contribute to athero-plaque

• Plasma (≈60 %) – ≈90 % water + proteins, nutrients, hormones

• Dehydration → ↓plasma → ↑hematocrit → ↑viscosity → ↑resistance → ↑BP & clot risk

Cardiac Cycle (Wiggers Diagram Essentials)

• Duration at HR 75 b·min⁻¹ ≈ 0.8 s (HR 60 → 1 s)

Phases

1. Isovolumetric Contraction (IVC) (all valves closed)

   • LV pressure ↑ steeply (≈5 → 80 mmHg)

   • Volume constant (EDV)

2. Ventricular Ejection

   • Aortic valve opens when P{LV}>P{aorta}

   • Rapid then reduced ejection; volume ↓ to ESV

3. Isovolumetric Relaxation (IVR)

   • Aortic valve closes when P{aorta}>P{LV} (dicrotic notch)

   • All valves closed; LV pressure ↓ rapidly, volume constant (ESV)

4. Ventricular Filling

   • Rapid inflow: Mitral valve opens when P{LA}>P{LV}

   • Diastasis: slower passive filling

   • Atrial systole (A-wave; P-wave on ECG): last ~10 % of filling

Key Relationships

• Valves operate on pressure gradients (no neural trigger)

• Heart sounds: S₁ = AV valve closure (start systole), S₂ = semilunar closure (start diastole)

• Stroke Volume: SV = EDV - ESV

• Ejection Fraction: EF = \dfrac{SV}{EDV}\times100\% (clinical pump metric)

Sample Pressure/Volume Values (approx.)

• EDV\approx 120\;\text{mL}

• ESV\approx 50\;\text{mL}

• SV\approx 70\;\text{mL}

• P{systolic}\approx 120\;\text{mmHg} ; P{diastolic}\approx 80\;\text{mmHg} (aortic)

Clinical & Exercise Relevance

• Left Ventricular Hypertrophy (LVH)

  • Physiologic (endurance training) vs pathologic (HTN, valve disease)

• Blood Pressure refers exclusively to arterial pressure

• High BP end-organ risk: brain (stroke), heart (MI), kidneys (nephropathy), micro-capillary damage

• Hydration status directly modifies plasma volume → influences SV and BP

• Venous return & preload enhanced by active muscle – rationale for cool-down walking

• Post-prandial exercise: splanchnic vasodilation competes with muscle blood flow → GI discomfort/“swim rule”

• Master heart diagram; trace flow w/o notes

• Practice Wiggers diagram interpretation (pressure, volume, ECG, sounds)

• Use Huff “ECG Workout” rhythm strips for self-quizzing (exam source)

• Expect lab practical: setup 12-lead ECG and strip interpretation

• Canvas assignments auto-repeat until 100 %; completion boosts grade

• Review material nightly—fast-paced term!