Lowering of the cardiac output makes a person suspicious about his deteriorating health. Because a persistent reduction in the cardiac output can be due to numerous factors. It is usually considered to be an indicative of ill health. Cardiac output mainly depends upon two primary factors such as the contraction of the heart ventricles and the frequency of the heart, or the heart rate. Needless to say these are the most obvious factors which effect the pressure or the frequency of heart’s contraction.
Let us look at the different factors which exert a corresponding effect on the cardiac output of every individual.
- The force of contraction of heart: The cardiac output is directly proportional to the force of heart’s contraction. The more powerful the heart contracts, the more is the stroke volume and thus the minute volume. The force of contraction of cardiac muscles in turn depends upon the nutrition, initial length of the muscle fibres, oxygen supply etc. Greater the initial strength of the cardiac muscle fibres, greater will be the force with which the heart contracts. This contraction of muscles is based upon the Frank-Starling law of heart contraction. The intensity of the diastolic filling greatly regulates the initial length of the cardiac muscle fibres.
- Needless to say if a person has leukemia, his cardiac output will be much less than a normal person. Leukemia treatment in India is done with utmost care and by the best doctors. Increase of heart rate increases the minute volume, hence minute volume is directly proportional to the heart rate. But this relationship is restricted within a limit because an excessive increase in the cardiac output reduces the ventricular diastole and its filling. This in turn reduces the stroke volume thereby reducing the minute volume. Low cardiac output can be a symptom of cardiogenic shock,leukemia, acute heart failure, right or left heart failure, congestive cardiac failure, systolic or diastolic heart failure, chronic heart failure, forward and backward heart failure, myocardial dysfunction, myocardial stunning or hibernation etc.
- An extremely fluctuating cardiac output is seen in different cardiomyopathies like,
- Dilated cardiomyopathy
- Restrictive cardiomyopathy
- Hypertrophic cardiomyopathy
- Postpartum cardiomyopathy
- Dysplasia or Arrythmogenic right ventricular cardiomyopathy.
- Pericardial effusion
- Myocardial infarction
- Cardiac tamponade
- Aortic or mitral stenosis
- Pulmonary embolism
- Aortic or mitral regurgitation
- Post cardiac surgical state
- Volume overload
- Hypertension and hypertensive crisis
- End stage renal failure
- Anemia, shunts or even sepsis
Venous return is a determinant of stroke volume. The more is the venous return the greater will be the stroke volume. If the venous return increases, the stroke volume increases in two different ways. Firstly it can supply more blood to the ventricles for being pumped. Secondly it can elevate ventricular filling, which in turn will increase the initial length of the ventricular muscles, due to their over stretching.
As a result of this the force of contraction of the ventricles, as well as the stroke volume are increased. These things if kept in balance constitute a normal healthy cardiac output.