Cardiac Function - Introduction
The primary function of the heart is to impart energy to blood in order to generate and sustain an arterial blood pressure necessary to provide adequate perfusion of organs. The heart achieves this by contracting its muscular walls around a closed chamber to generate sufficient pressure to propel blood from the cardiac chamber (e.g., left ventricle), through the aortic valve and into the aorta.
CO = SV × HR
Stroke volume is expressed in ml/beat and heart rate in beats/minute. Therefore, cardiac output is in ml/minute. Cardiac output may also be expressed in liters/minute.
Normal, resting cardiac output differs among individuals of different size. Obviously, the resting cardiac output of someone who weighs 240 lbs is greater than the cardiac output found in a person that weighs 120 lbs. Therefore, in clinical practice, measured values for cardiac output are often expressed as a flow (L/min) per body surface area (m2). When cardiac output is expressed in this way, it is termed "cardiac index" and has the units of L/min/m2. The surface area is estimated from calculations based on body weight and height. Cardiac index normally ranges from 2.6 to 4.2 L/min/m2.
Related topic: Measurement of Cardiac Output