FISDAP Cardiology Practice Test

A decrease in cardiac output can trigger several compensatory mechanisms aimed at maintaining blood flow to vital organs. Among these, an increased heart rate plays a critical role. When cardiac output decreases, the body responds by increasing the heart rate to enhance the volume of blood being pumped with each minute, thus offsetting the reduced stroke volume and striving to stabilize blood pressure and perfusion to essential organs.

The heart rate increase is a physiological response initiated by the autonomic nervous system, particularly through sympathetic stimulation. This mechanism ensures that even though each contraction may be less effective (due to decreased stroke volume), the overall output can be improved by the frequency of contractions.

The other options are not as directly related to compensating for decreased cardiac output. A decreased respiratory rate would typically not support improved oxygenation and could contribute to further issues. Reduced vascular resistance generally helps to lower blood pressure, which is counterproductive in situations where cardiac output is compromised. Finally, a decreased blood volume would further reduce preload, leading to an even greater decline in cardiac output, rather than compensating for it. Thus, increased heart rate is the most effective and immediate response to a decrease in cardiac output.