Which two variables determine cardiac output?

Which two variables determine cardiac output?

• A. Heart Rate and Stroke Volume.
• B. End-diastolic volume and afterload.
• C. Pulse pressure and mean arterial pressure.
• D. Venous return and contractility.

Answer: (A)

Cardiac output is determined by how often the heart beats and how much blood it ejects with each beat. The direct relationship is CO = heart rate × stroke volume. So the two variables that determine CO are heart rate (how many times the heart beats per minute) and stroke volume (how much blood is pumped out with each beat). Stroke volume is itself influenced by preload (related to end-diastolic volume), afterload, and contractility, but those factors modify how much blood is ejected per beat rather than setting CO by themselves. Other options point to related pressures or preload factors, which affect the heart's pumping in downstream ways, not the two primary, independent determinants of CO. For example, a typical resting CO results from a certain heart rate and stroke volume, and during exercise both can rise to increase CO.

Cardiac output is determined by how often the heart beats and how much blood it ejects with each beat. The direct relationship is CO = heart rate × stroke volume. So the two variables that determine CO are heart rate (how many times the heart beats per minute) and stroke volume (how much blood is pumped out with each beat).

Stroke volume is itself influenced by preload (related to end-diastolic volume), afterload, and contractility, but those factors modify how much blood is ejected per beat rather than setting CO by themselves. Other options point to related pressures or preload factors, which affect the heart's pumping in downstream ways, not the two primary, independent determinants of CO. For example, a typical resting CO results from a certain heart rate and stroke volume, and during exercise both can rise to increase CO.