Cardiac Physiology

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Cardiac Physiology
2011-02-04 20:35:44
Cardiac physiology

Cardiac physiology
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  1. What is preload?
    • The amount of blood presented to the VENTRICLE just BEFORE SYSTOLE
    • Major factor that determines preload: VENOUS RETURN (the volume of blood that enters the ventricle during diastole, filling)
    • Second factor: VENTRICULAR COMPLIANCE (the elasticity or 'give' when blood enters the ventricle)
    • Preload increases pressure in ventricle, which stretches the ventricular wall
    • A noncompliant ventricle has a higher intraventricular pressure than a compliant one - higher pressure increases the workload of the heart and thus can lead to HF
  2. What is afterload?
    • The amount of resistance to the ejection of blood from the ventricle
    • When afterload increases - then the heart has to work harder to overcome the resistance and eject the blood
    • Major factors that determines preload: diameter and distensibility of the great vessels (aorta and pulmonary arteries), and the opening and comptency of the semilunar valves (pulmonic and aortic valves - when the valves open easily the resistance is lower)
    • What causes increased afterload: significant vasoconstriction, HTN, or narrowed valvular opening from stenosis
  3. What is contractility?
    • The force of contraction of the heart
    • Catecholamines - sympathetic stimulation/effects can increase contractility (can use positive inotropic effects to increase contractility)
  4. How can you ESTIMATE right ventricular preload status?
    Measure JVD
  5. How can you ESTIMATE left ventricular preload status?
    • Positive hepatojugular test
    • Mean arterial blood pressure
  6. What are cardiac hemodynamics?
    Use of a pulmonary artery catheter to measure intracardiac pressures, pulmonary artery pressures, and cardiac output