Define cardiac output and describe the regulation of cardiac output in normal adults. Add a note on Cardiac Index and Cardiac Reserve.
Cardiac Output (CO) is the amount of blood pumped by each ventricle per minute, calculated as heart rate multiplied by stroke volume.
Regulation in Adults
Heart Rate (HR): Controlled by the autonomic nervous system. Sympathetic activity with norepinephrine and epinephrine accelerates rate, while parasympathetic activity through the vagus nerve and acetylcholine slows it.
Stroke Volume (SV): Determined by preload, afterload, and contractility. Preload depends on venous return; greater stretch produces stronger contractions through the Frank Starling mechanism. Afterload represents resistance faced by the ventricle; higher systemic resistance reduces stroke volume. Contractility reflects myocardial strength independent of preload; sympathetic stimulation and inotropic drugs enhance it.
Cardiac Index (CI): Output adjusted for body surface area, giving a normalized measure of performance. The normal range is about two point five to four liters per minute per square meter.
Cardiac Reserve: The difference between resting output and maximal output during exercise, reflecting functional capacity. It is large in health but reduced in disease.
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