Cardiac Output (CO) is primarily determined by which variables?

Cardiac Output (CO) is defined as the volume of blood the heart pumps per minute and is a crucial parameter in assessing cardiovascular health. The primary equation for calculating cardiac output is the product of stroke volume— the amount of blood ejected by the heart with each beat— and heart rate, which is the number of times the heart beats in one minute.

This means that if either stroke volume or heart rate increases, cardiac output will also increase, assuming the other factor remains constant. Stroke volume is influenced by factors such as ventricular filling (preload), myocardial contractility (the heart's ability to contract), and afterload (the resistance the heart must overcome to eject blood). Heart rate is influenced by autonomic nervous system control and hormonal factors.

In contrast, other combinations presented in the options focus on variables that do not directly define cardiac output. While systemic vascular resistance and blood pressure are important in the circulatory system, they do not factor into the direct calculation of CO in this context. Therefore, the correct relationship emphasizing stroke volume and heart rate effectively highlights the core elements that determine cardiac output.