Cardiac output is a term that refers to the amount of blood pumped by the heart during a one-minute period. Cardiac output changes as the demands the body places on the cardiovascular system change. Therefore, the cardiac output during exercise is different from the cardiac output during rest. In addition, the more strenuous the exercise, the higher the cardiac output, but, only up to a certain point. The highest cardiac output possible reflects the functional capacity for the cardiovascular system to meet physical activity demands, according to "Exercise Physiology."
Measuring Cardiac Output
There are three main ways to measure cardiac output: the direct Fick method, indicator dilution and CO2 rebreathing. The direct Fick method uses a mathematic equation to determine cardiac output. It uses measurements of oxygen consumption in the blood, via blood samples, in its calculation. The Indicator dilution method involves injecting inert dye or radioactive materials into the blood and then assessing blood samples. Finally, the CO2 rebreathing method does not require blood sampling or close medical supervision and is non-invasive. It uses a rapid CO2 gas analyzer to make some reasonable assumptions and mathematic calculation to determine cardiac output, notes "Exercise Physiology."
Typical Output?
There is incredible variation of cardiac output from person to person at rest, notes "Exercise Physiology." For the average 155 pound male, the heart pumps 5 liters of blood in a single minute. For the average 123 pound woman, the heart pumps 4 liters of blood per minute. The gender difference observed generally relates more to the size difference that is typical between the sexes, according to "Exercise Physiology."
During Exercise
Systemic blood flow increases as exercise intensity increases. Cardiac output also increases, and rapidly so, in a transition from rest to exercise, notes "Exercise Physiology." However, cardiac output eventually reaches a plateau and that occurs when blood flow meets the metabolic demands of the body during exercise.
Exercise Output?
For average, non-athletic, college-age males, cardiac output during maximal exercise increases to an average of 20 to 22 liters per minute. That is four times greater than the cardiac output at rest, notes "Exercise Physiology." World class endurance athletes can have maximal cardiac outputs, during exercise, of 35 to 40 liters per minute, notes "Exercise Physiology."
Factors that Decrease Cardiac Output
According to Nursing Care Plans, reduced cardiac output can be caused by many things, including heart attacks, high blood pressure, diseases affecting the valves of the heart, congential heart disease, arrhythmias, side effects of some drugs, fluid excess or shortage and an electrolyte imbalance. The elderly are more at risk for decreased cardiac output because aging results in weakened ventricles, which further reduces cardiac output. If the heart cannot pump adequate blood to meet the metabolic demands of the body, treatment is required, notes Nursing Care Plans.
References
- Nursing Care Plans: Decreased Cardiac Output
- "Exercise Physiology"; William McArdle, Frank Katch and Victor Katch; 2001
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