Q.Define a cardiac cycle and the cardiac output.

The cardiac cycle and cardiac output are two basic measures of the heart's pumping work.

• A cardiac cycle is the orderly, repeating sequence of contraction (systole) and relaxation (diastole) of the atria and ventricles that drives blood through the heart. It includes the systole and diastole of both atria and ventricles.
• In a healthy person about seventy-two such cycles occur each minute, so one cycle lasts about 0.8 seconds.
• Cardiac output is the volume of blood pumped out by each ventricle in one minute. …

The heart works by a rhythmic alternation of squeezing and resting. The cardiac cycle is the name for this orderly, repeating sequence of contraction, called systole, and relaxation, called diastole, of the atria and ventricles that together drive blood through the heart. One complete cycle covers the systole and diastole of both the atria and the ventricles, after which the whole pattern begins again.

Because a healthy heart beats about seventy-two times a minute, seventy-two cardiac cycles occur each minute. Dividing the minute among these beats gives a duration of about 0.8 seconds for a single cycle.

Cardiac output measures the heart's delivery of blood over time. It is defined as the volume of blood pumped out by each ventricle in one minute. Two quantities combine to produce it:

• The stroke volume — the amount of blood each ventricle pumps out in one cycle, roughly 70 mL.
• The heart rate — the number of beats per minute, about seventy-two. …

Method: Defining a Physiological Term and Its Associated Formula

Use this approach for any "define" question that pairs a concept with a quantity that can be calculated.

Steps

Step 1: Give the definition in one precise sentence

Name exactly what event or quantity the term refers to — a cardiac cycle is one complete round of systole and diastole of the atria and ventricles; cardiac output is the volume of blood pumped by one ventricle in one minute.

Step 2: State the typical numeric value with correct units, if one exists

A cardiac cycle takes about 0.8 seconds; a healthy resting cardiac output is about 5000 mL per minute. …