Heart failure is the inability of your heart to pump enough blood to meet the needs of your body to function normally. One of the tests performed to determine if the amount of blood pumped per minute is adequate is defined as cardiac output. Measurements to identify any deficit of cardiac output are taken at rest most accurately during a cardiac catheterization. During exercise, readings are usually estimated using ultrasound or some type of imaging.
Cardiac Output Defined
Cardiac output, the amount of blood pumped by the heart every minute, is determined by the heart rate and by stroke volume, or the amount of blood leaving the left ventricle after each beat. The stroke volume is measured in milliliters.
The resting heart rate of the average person is 70 beats/minute with a resting stroke volume of 70 mL/beat, reports Biological Sciences. To determine the cardiac output, multiply 70 beats/minute by 70 mL/beat, which equals 4900 mL/minute. Since the average person has about 5,000 mL of blood in the circulatory system, the entire blood supply is pumped through the heart every minute at rest.
Heart Rate
The American Heart Association, or AHA, has established a guideline for target and maximum heart rates during exercise to obtain the most cardiovascular benefit. Your heart rate should go up slowly, beginning with a warm-up period and advancing to more intensity.
The average maximum heart rate, according to the AHA is 220 beats/minute minus your age. The target zone is much lower. For example, the average maximum for a 40-year-old is 180 beats/minute, but the target heart rate is between 90 and 153 beats/minute.
Exercise Benefits
Exercise increases cardiac output by activating the sympathetic nervous system, which increases the heart rate and stroke volume. As the demand for oxygenated blood reaches the muscles, the heart pumps more rapidly and intensely, increasing the stroke volume and causing the heart to fill with more blood.
The Physiology and Psychology Department of Montana State University-Bozeman reports on the distribution differences of cardiac output at rest and during exercise. For instance, at rest, the liver has 27 percent, which is the highest cardiac output and muscle only receives 15 percent; during exercise, the muscles receive 66 percent while the kidneys receive only 3 percent.
Warnings
Before beginning any exercise program, be sure to check with your doctor about any restrictions or conditions. Aim for the lower end of your target heart rate for the first few weeks and build up gradually, or as your doctor advises. You don't have to exercise hard to receive the benefits. The key to exercising and more efficient cardiac output is consistency.
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