Cardiovascular Responses to Exercise and Stress

Exercise Energetics & O2 - Fueling Up

• O2 Consumption (VO2):
  • Resting VO2: ~3.5 ml/kg/min (1 MET).
  • VO2 max: Maximal O2 uptake; key fitness indicator.
  • Fick Principle: $VO_2 = CO \times (CaO_2 - CvO_2)$.
• Energy Systems Timeline:
  • ATP-PCr (Phosphagen): Immediate, ~10-15s.
  • Anaerobic Glycolysis: Short-term, up to ~1-2 min.
  • Aerobic (Oxidative): Long-term, dominant after ~2 min.
• Fuel Utilization: Carbohydrates for high-intensity; Fats for low-intensity, prolonged exercise.
• O2 Deficit & EPOC (Excess Post-exercise O2 Consumption).

⭐ VO2 max is widely regarded as the single best measure of cardiorespiratory fitness and endurance capacity.

Dynamic Exercise CV Changes - Heart Pumping Hard

Dynamic exercise triggers major CV adaptations:

• Key Adaptations:
  • ↑HR: Sympathetic ↑, parasympathetic ↓; towards max (📌 $220 - age$).
  • ↑SV: ↑Venous return (Frank-Starling), ↑contractility.
  • ↑CO: $CO = HR \times SV$; ↑ significantly (4-8x).
  • ↑SBP (workload-proportional); DBP stable/↓; ↑Pulse Pressure; ↑MAP ($MAP \approx DBP + \frac{1}{3}(SBP-DBP)$).
  • ↓TPR: Dominant muscle vasodilation overrides systemic vasoconstriction.
  • ↑a-vO2 diff: Muscles extract more O2; venous O2 content ↓.

⭐ During dynamic exercise, systolic BP increases proportionally to workload, while diastolic BP typically remains unchanged or slightly decreases due to vasodilation in active muscles, leading to a widened pulse pressure.

Comparison: Rest vs. Max Dynamic Exercise

Dynamic exercise triggers major CV adaptations:

• Key Adaptations:
  • ↑HR: Sympathetic ↑, parasympathetic ↓; towards max (📌 $220 - age$).
  • ↑SV: ↑Venous return (Frank-Starling), ↑contractility.
  • ↑CO: $CO = HR \times SV$; ↑ significantly (4-8x).
  • ↑SBP (workload-proportional); DBP stable/↓; ↑Pulse Pressure; ↑MAP ($MAP \approx DBP + \frac{1}{3}(SBP-DBP)$).
  • ↓TPR: Dominant muscle vasodilation overrides systemic vasoconstriction.
  • ↑a-vO2 diff: Muscles extract more O2; venous O2 content ↓.

⭐ During dynamic exercise, systolic BP increases proportionally to workload, while diastolic BP typically remains unchanged or slightly decreases due to vasodilation in active muscles, leading to a widened pulse pressure.

Comparison: Rest vs. Max Dynamic Exercise ) | | SV (mL) | ~70 | ↑ (100-120+) | | CO (L/min) | ~5 | ↑↑ (20-25+) | | SBP (mmHg) | ~120 | ↑ (180-220) | | DBP (mmHg) | ~80 | ↔ or ↓ | | MAP (mmHg) | ~93 | ↑ (110-130) | | TPR | High | ↓↓ | | a-vO2 diff (mL/dL)| ~5 | ↑↑ (15-18) |

Static Exercise CV Changes - Pressure Challenge

• Nature: Primarily pressure load.
• Mechanisms:
  • Mechanical compression of vessels.
  • Strong sympathetic reflex.
• CV Response:
  • HR: ↑ (moderate)
  • SBP, DBP: ↑↑ (marked)
  • MAP: ↑↑ (significant)
  • CO: ↔ / ↓
  • TPR: ↑↑ (significant)

⭐ Static (isometric) exercise causes a disproportionate rise in both systolic and diastolic blood pressure (pressor response) primarily due to mechanical compression of blood vessels within contracting muscles and a strong reflex sympathetic stimulation.

Training & Stress Response - Adapt & React

• Athlete's Heart (Physiological Adaptation):
  • Long-term endurance training → cardiac remodeling.
  • Key changes: Eccentric Left Ventricular (LV) hypertrophy, ↑ Stroke Volume (SV), ↓ Resting Heart Rate (HR), ↑ cardiac efficiency.
  • 📌 Mnemonic: "SHE" - Stroke volume high, Heart rate low, Eccentric hypertrophy.
  • 

  ⭐ Athlete's heart is a physiological adaptation characterized by eccentric left ventricular hypertrophy, increased stroke volume, and lower resting heart rate, enhancing cardiac efficiency.

• Psychological Stress Response (Acute):
  • Sympathetic activation → ↑ catecholamines.
  • Cardiovascular effects: ↑ HR, ↑ Blood Pressure (BP), ↑ contractility.
  • Regular exercise can attenuate adverse cardiovascular responses to stress, improving resilience.

CV Control Mechanisms - Brain & Body Talk

• Central Command: Anticipatory signals from higher brain centers (motor cortex, limbic system) initiate CV changes.
• Reflex Control:
  • Baroreflex: Modulated (reset) to allow ↑Blood Pressure during exercise.
  • Chemoreflex: Senses blood gas changes ($P_O2$, $P_{CO2}$, pH).
  • Ergoreflex (Muscle work): Mechanoreceptors (contraction) & metaboreceptors (metabolites) signal CNS.
• Hormonal Modulation: Catecholamines (adrenaline, noradrenaline) ↑cardiac output; RAAS influences volume.
• Local Muscle Factors: Autoregulation via vasodilators ($NO$, adenosine, $K^+$) matches blood flow to metabolic demand.

⭐ Central command, originating from higher brain centers, initiates cardiovascular adjustments at the very onset of exercise, often before significant metabolic changes occur in the muscles.

High‑Yield Points - ⚡ Biggest Takeaways

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