Cardiac+Outut

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. Each time the heart beats, a volume of blood is ejected. This [|stroke volume] (SV), times the number of beats per minute ([|heart rate], HR), equals the cardiac output (CO). Stroke volume is expressed in ml/beat and heart rate in beats/minute. Therefore, cardiac output is in ml/minute. Sometimes, cardiac output is expressed in liters/minute.
 * Cardiac Output**
 * CO = SV · HR**


 * Measurement of Cardiac Output**

Several direct and indirect techniques for measurement of [|cardiac output] are available. The thermodilution technique uses a special thermistor-tipped catheter (Swan-Ganz) that is inserted from a peripheral vein into the pulmonary artery. Cold saline of known temperature and volume is injected into the right atrium from a proximal catheter port. The saline mixes with the blood as it passes through the ventricle and into the pulmonary artery, thus cooling the blood. The blood temperature is measured at the catheter tip lying within the pulmonary artery and a computer is used to acquired the thermodilution profile and compute flow. Echocardiographic techniques and radionuclide imaging techniques can be used to estimate real-time changes in ventricular dimensions, thus computing stroke volume, which when multiplied by heart rate, gives cardiac output. An old technique based upon the [|__Fick Principle__] can be used to compute cardiac output (CO) indirectly from whole body oxygen consumption (VO2) and the mixed venous (O2ven) and arterial oxygen contents (O2art): To calculate CO, the oxygen contents of arterial and venous blood samples are measured, and at the same time, whole body oxygen consumption is measured by analyzing expired air. The blood contents of oxygen are expressed as ml O2/ml blood, and the VO2 is expressed in units of ml O2/min. If O2art and O2ven contents are 0.2 ml and 0.15 ml O2/ml blood, respectively, and VO2 is 250 ml O2/minute, then CO = 5000 ml/min, or 5 L/min. Ventricular stroke volume would simply be the cardiac output divided by the heart rate.
 * CO = VO2/(O2art – O2ven)**