Adequate cardiac output is necessary in order to supply oxygen and other nutrients to all body tissues. Cardiac output is influenced by stroke volume and heart rate. Factors affecting the stroke volume includes PRELOAD, CONTRACTILITY and AFTERLOAD.
In the following conditions, indicate what factor/s influence the cardiac output: PRELOAD, CONTRACTILITY, AFTERLOAD, HEART RATE. Explain the why the factor/s affects cardiac output in 1 to 2 sentences.
a. High blood pressure
- High blood pressure increases the left ventricular afterload due to the left ventricle having to work harder to eject blood into the aorta.
b. Massive bleeding
- Severe blood loss leads to a decrease in circulating blood volume and consequently decreases the amount of blood returning to the heart, which accounts for the reduction in stroke work and cardiac output; hence, decreasing preload and afterload.
c. the drug dopamine
- Dopamine produces positive chronotropic and inotropic effects on the myocardium, resulting in increased heart rate and cardiac contractility; which is why it is used for treatment of shock and refractory heart failure.
d. Running a sprint
- When running, the heart beats faster so more blood gets out of the body; increasing the heart’s stroke volume by pumping more forcefully, also increasing the contractility.
e. Hyperthryoidism with increased secretion of thyroid hormones
- Hyperthyroidism cardiac effects include increased preload with low systemic vascular resistance, high heart rate, and increased cardiac muscle oxygen consumption. In short term hyperthyroidism, effects result to increased heart rate and high cardiac output.
f. Massive myocardial infarction (cardiac tissue death)
- Myocardial infarction results in the thinning and dilatation of the cardiac wall, which increases the systolic wall stress and the contractile demands on a heart with a diminished number of functional myocardial cells. This results in a decreased cardiac output.
g. Hypothermia
- A significant increase in stroke volume and a significant decrease in heart rate are both caused by hypothermia, yet there is no change in the amount of cardiac output.
h. Emotional distress
- An increase in cardiac output, an increase in contractility, an increase in stroke volume, and an increase in heart rate may all result from experiencing emotional distress.