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- Due to the narrowing of the arteries in high blood pressure, the afterload will increase causing a decrease in cardiac output.
b. Massive bleeding- The reduced blood flow due to the massive bleeding will cause the preload to decrease since there will be lesser filling that will happen. This will result in a decrease in cardiac output.
c. the drug dopamine- Dopamine is a substance that has an inotropic effect that affects contractility; increases the contractility thereby increasing the stroke volume. This also increases the heart rate thus an increase in cardiac output.
d. Running a sprint- The body uses up oxygen quickly thus the need for faster pumping of the heart to keep up with the body’s need for oxygen and nutrients. This will increase the heart rate thus increasing the cardiac output.
e. Hyperthyroidism with increased secretion of thyroid hormones- Increased secretion of thyroid hormones causes the heart to beat faster as it stimulates the SA node. An increase in heart rate also increases contractility, leading to an increase in cardiac output.
f. Massive myocardial infarction (cardiac tissue death)- Myocardial infarction is caused by the blockage of arteries which will obstruct the blood flow reducing the preload. This also reduces contractility since the damage to the tissue causes its function to weaken.
g. Hypothermia- The decrease in temperature reduces oxygen consumption, as a result, there is also a decrease in the strength of contraction. This will decrease the heart rate.
h. Emotional distress- When experiencing emotional distress, the nervous system will stimulate the release of stress hormones. This causes an increase in heart rate, blood pressure, and contractility, resulting in to increase in cardiac output.