Cardiovascular System During Exercise

Cardiovascular System During Exercise

• Heart Function:

  • The heart acts as a pump, composed of epicardium (outer), myocardium (middle), and endocardium (inner).
  • Utilizes actin/myosin sliding filament mechanism and ATP for contraction.
  • Intercalated discs enable cells to depolarize as a unit, crucial for coordinated pumping.
  • Heart's pumping action is coordinated by an electrical conduction system (SA node, AV node, bundle of His, bundle branches, Purkinje fibers).
  • Electrical activity produces a characteristic P-QRS-T pattern on an ECG, reflecting atrial (P wave), ventricular depolarization (QRS complex), and ventricular repolarization (T wave).

• Myocardial Oxygen Uptake (MVO2):

  • MVO2 is determined by myocardial tension, contractility, and heart rate.
  • Rate Pressure Product (RPP) is an index of relative cardiac work (HR x SBP).
  • RPP monitoring assists in identifying reproducible angina patterns.
  • Exercise increases coronary blood flow 4-6 fold, due to increased metabolism.
  • The heart receives 200-250ml blood/minute (5% of resting cardiac output).
  • Coronary flow is higher during diastole than systole, important for exercise and cardiac health.
  • The heart is primarily aerobic but has a limited anaerobic capability.

• Cardiac Output (CO):

  • CO = Stroke Volume (SV) x Heart Rate (HR)
  • Stroke Volume is calculated as end-diastolic volume (EDV) minus end-systolic volume (ESV) and depends on preload and afterload.
  • Preload is the load on the ventricle at end diastole (EDV).
  • Afterload is the mechanical load on the ventricle during ejection (aortic pressure).
  • Heart rate is highly influenced by sympathetic/parasympathetic nervous systems and hormones like catecholamines.
  • Ejection Fraction (EF) is a global measure of heart efficiency (SV/EDV).

• Heart Rate (HR) and Exercise:

  • Maximal heart rate is predicted as 220 minus age +/- 10 bpm.
  • Aerobic fitness levels influence maximum HR.
  • Heart rate typically increases linearly with exercise intensity. HR increase of 10 +/- 2 bpm per MET is normal.
  • An inadequate increase in HR with exercise intensity is concerning.
  • Recovery heart rate should decrease by 10 bpm within 1 minute post-exercise.
  • Chronotropic incompetence is a decreased heart rate response to exercise (more than 2 standard deviations below predicted max HR).

• Stroke Volume (SV):

  • SV correlates with increased venous return (preload), contractility, and reduced afterload.
  • SV is influenced by venous return, diastolic filling pressure, blood volume, and systemic blood pressure.
  • SV is normally lower in females and smaller individuals.

• Ejection Fraction (EF):

  • EF is a measure of LV ejection efficiency (SV/EDV).
  • A normal EF is approximately 50%, with lower values indicative of heart failure.

• Arterial Blood Pressure:

  • Normal resting blood pressure is typically 100-139/60-89 mmHg.
  • Blood pressure generally increases with age.
  • Elevated blood pressure (hypertension) stages and hypotension will be mentioned.
  • Systolic blood pressure might plateau or remain steady during steady state exercise.
  • Exercise-induced hypotension (SBP fails to rise, falls by >10mmHg)) is a concern for MI.
  • Diastolic blood pressure typically doesn't change or decreases during graded exercise.

• Exercise Types (Dynamic vs. Static):

  • Dynamic exercise involves continuous movement; SV and EDV increase, and afterload decreases.
  • Static exercise (isometric contractions) has decreased SV, increased afterload, and increased DBP.
  • Valsalva maneuver (forced exhalation against a closed glottis) increases BP and workload on heart.

• Myocardial Ischemia during Exercise:

  • Ischemia is a mismatch of oxygen supply and demand due to increasing exercise intensity.
  • Signs of ischemia (angina) during exercise should be addressed promptly.
  • Static exercise might increase myocardial oxygen demand through the Valsalva maneuver.

• Drug Therapy and Exercise:

  • Beta-blockers, diuretics, and anti-coagulants frequently used in treatment of cardiovascular issues.

• Guidelines for Independent Exercise:

  • Individuals with heart issues should be assessed for suitability for independent exercise. Considerations are functional aerobic capacity, hemodynamic response, symptom stability, knowledge of management, & appropriate supervision.