Regulation of cardiac output in animals
Heart functions (cardiac output, heart rate) can be regulated by- Intrinsic mechanisms, operating within the myocardium itself and Extrinsic mechanisms (by factors outside the heart). this both will be discussed in later part.
Factors influencing cardiac output
Muscular exercise (4-6 times increase), pregnancy, hypoxia, active digestion, stress and increased body temperature.
Circulation time
Circulation time is the time required for one complete circulation.
This can be measured either by injecting dyes like ferrocyanide or fluorescine or injecting radioactive chemicals.
Cardiac reserve
Cardiac reserve is the maximum percentage that the cardiac output can increase above normal. Cardiac reserve can be measured by exercise test.
It is an adaptive mechanism of the heart by which cardiac output can be increased to maintain a balance between right atrial input and left ventricular output.
This is achieved by
Increase in stroke volume
Increase in heart rate
Hypertrophy of the left ventricle
During exercise the cardiac output can rise up to 400% above normal. If cardiac reserve is inadequate congestive heart failure or cardiac decompensation results which causes stasis of blood in the pulmonary system and right atrium.