Alterations in Cardiac Output

Exercise:

In normal individuals the greatest change in cardiac output occurs during intensive exercise. During such intensive exercise both heart rate and stroke volume increase. During exercise, the cardiac output varies linearly with oxygen consumption and can increase several fold.

Postural Changes:

On rising to an upright position the cardiac output decreases by about 20%. This is caused by the fact that such a postural change leads to venous pooling in the lower extremities and a decrease in the effective circulating blood volume.

Blood Volume Changes:

In hemorrhagic and traumatic shock there is a pronounced decrease in cardiac output because of decreased blood volume and lessened venous return. Conversely, conditions such as anemia tend to increase cardiac output as a compensatory response to the circulatory hypoxia and to the decreased resistance to flow.

Metabolic Changes:

The most important determinant of blood flow is the metabolic rate of an organ or organism. Thus, metabolic alterations lead to marked changes in cardiac output. During fever and in hyperthyroidism, an increased cardiac output is due to circulatory hypoxia induced by the increased oxygen demand.