Click on the hyperlink to see the cardiac cycle in motion and what is happening at each phase. This web site has tutorials and much information about the cardiac cycle.
• Amount of blood pumped with each heart beat
• Normal volume is 50ml to 100ml
• Determinants of stroke volume are preload (filling volume), afterload (vascular resistance), and contractility (strength/force of contraction)
• Cardiac output can be directly measured at the bedside with a pulmonary artery catheter (PA catheter) or an external non-invasive device.
• Amount of blood ejected by the heart measured in liters/minute
• Cardiac output is the stroke volume multiplied by the heart rate.
• According to Starling's Law, the greater the end diastolic filling volume, the greater the force of the subsequent contraction of the heart and stroke volume. The stretch of the ventricle causes the increased force of contraction, somewhat like the stretch of a rubber band. The heart rate affects cardiac output. A physiologic response to low cardiac output is tachycardia. It is a compensatory mechanism. Since stroke volume multiplied by the heart rate equals cardiac output, the heart rate will increase to increase cardiac output.
• Pathological tachycardia (i.e. atrial fibrillation, ectopic beats, ventricular tachycardia) will result in decreased cardiac output related to the resulting decreased filling time between contractions. Observe for signs and symptoms of hypoperfusion.
• Pathological bradycardia (i.e. heart block, junctional & ventricular rhythms) may cause decreased cardiac output. This is usually related to the slower heart rate. Sometimes this related loss of the "atrial kick" with certain rhythms. Athletic individuals without pathology and slow heart rates will have normal cardiac outputs.
• Normal CO = 4 to 8 liters/min (relative to body mass index)
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Date last modified: January 7, 2013.
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