What factors influence cardiac output?

Cardiac output (CO) is the volume of blood pumped out by the heart per minute. It is determined by the following factors:

1. Heart rate (HR): HR is the number of heartbeats per minute. The faster the HR, the greater the CO.

2. Stroke volume (SV): SV is the volume of blood pumped out by the heart per beat. The greater the SV, the greater the CO.

3. Preload: Preload is the force that stretches the heart muscle before contraction. It is determined by the volume of blood in the ventricles at the end of diastole (ventricular end-diastolic volume, VEDV). The greater the preload, the greater the SV and CO.

4. Afterload: Afterload is the force that the heart muscle must overcome to eject blood from the ventricles. It is determined by the pressure in the aorta and pulmonary artery. The greater the afterload, the lower the SV and CO.

5. Contractility: Contractility is the force of contraction of the heart muscle. It is determined by the inotropic state of the heart, which is influenced by factors such as hormones, drugs, and disease. The greater the contractility, the greater the SV and CO.

6. Heart valves: The proper function of the heart valves is essential for maintaining CO. Stenosis (narrowing) or insufficiency (leaking) of the valves can reduce CO.