Question

The following measurements were made on two individuals (the values recorded remained stable for 1 hour):
Person 1: heart rate, 75 bpm; stroke volume, 60 mL
Person 2: heart rate, 90 bpm; stroke volume, 95 mL
Which person has the greater venous return?
Which person has the longer ventricular filling time?

Accepted Answer

Understand that venous return is the volume of blood returning to the heart per minute, which in a steady state equals cardiac output. Cardiac output (CO) is calculated as the product of heart rate (HR) and stroke volume (SV): $$CO = HR 	imes SV. $$Calculate the cardiac output for each person by multiplying their heart rate (in beats per minute) by their stroke volume (in milliliters). For Person 1: $$CO_1 = 75$$ 	imes 60$$, and for Person 2: CO_2$ = 90 	imes 95. $$Compare the cardiac outputs of both individuals to determine which person has the greater venous return, since venous return must match cardiac output in a steady state. Understand that ventricular filling time is the duration of diastole (the relaxation phase of the heart) during which the ventricles fill with blood. It is inversely related to heart rate because as heart rate increases, the total cardiac cycle duration decreases, shortening diastole. Determine which person has the longer ventricular filling time by comparing their heart rates: the person with the lower heart rate will have a longer ventricular filling time because each cardiac cycle lasts longer.

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Key Concepts

Venous Return

Cardiac Output and Stroke Volume

Ventricular Filling Time