Which factor does NOT affect cardiac output?

Cardiac output is influenced by several key factors that are essential for understanding heart function and physiology. The factors that directly impact cardiac output include preload, contractility, and heart rate.

Preload refers to the volume of blood in the ventricles at the end of diastole, which is critically important because it determines how much blood will be ejected during systole. An increase in preload typically leads to an increase in stroke volume and consequently cardiac output, since the heart pumps more effectively when filled with a greater volume of blood.

Contractility, or the inherent strength of the cardiac muscle contractions, is another significant determinant of cardiac output. When contractility is enhanced, the heart is able to eject a greater volume of blood with each beat, thereby increasing cardiac output. Various factors, such as sympathetic nervous stimulation and certain medications, can modify contractility.

Heart rate, or the number of beats per minute, also directly affects cardiac output. An increase in heart rate leads to a higher number of beats per minute, which can increase cardiac output, provided that there isn't a disproportionate decrease in stroke volume due to reduced filling time.

End-systolic volume (ESV), on the other hand, does not directly affect cardiac output in the same way