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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
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
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)
How can you ESTIMATE right ventricular preload status?
How can you ESTIMATE left ventricular preload status?
Positive hepatojugular test
Mean arterial blood pressure
What are cardiac hemodynamics?
Use of a pulmonary artery catheter to measure intracardiac pressures, pulmonary artery pressures, and cardiac output