Cardiac output, exercise and cardiac hypertrophy.

Cardiac output, exercise and cardiac hypertrophy.

Objectives:
1. Define cardiac output and stroke volume.
2. Describe how heart rate and stroke volume interact to control cardiac output.
3. State the influence of venous return on cardiac output.
4. Define the terms preload, and after load.
5. Measurement of COP.
6. Conditions that cause increase myocardial contractility.
7. Conditions that cause decrease myocardial contractility
8. Physiology of exercise.
9. Cardiac hypertrophy.
Cardiac output:
Cardiac output is amount of blood pumped out of the heart each minute.
Cardiac output = Stroke volume x heart rate.
Cardiac output (COP) is affected by body metabolism, exercise, age and size of the body. In young, healthy men, resting COP average about 5.6 L/minute. For women, this value is 10-20% less
Stroke volume: It is the volume of blood ejected from the ventricle on each beat, is expressed by the following equation:
Stroke volume = End-diastolic volume - End-systolic volume.
Ejection fraction: It is the fraction of end-diastolic volume ejected in one beat. It is normally 55%. It is expressed by the following equation.
Ejection fraction = Stroke volume / End-diastolic volume.
Cardiac index (CI):
Because there is a correlation between resting cardiac output (COP) and surface area of the body, it is important to find some mean by which COP of different sized people can be compared with one another. The COP is frequently stated in term of the cardiac index, which is the cardiac output /minute / m² of body surface. The normal average of cardiac index for adult is about 3.2 L.
The Cardiac index is rapidly rising from 2.5 L/minute/ m2 at infant to a level greater than 4 L/minute/m² at age 10 years, and then declines to about 2.4 L / minute / m² at age 80 years. See figure 15.