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
Patients with hypertension have increased afterload due to the high force of blood pushing against the walls of the arteries, making the heart require an increased amount of pressure in order to pump blood. In hypertension, high levels of arterial blood pressure is caused by the increase of blood volume and vascular resistance, which can also lead to an increased cardiac output.
b. Massive bleeding
Individuals that experience massive bleeding (hemorrhage) have low levels of arterial pressure and reduced afterload because of the reduction in blood volume, which then results in reduced cardiac output. Severe blood loss is compensated by increased heart rate and contractility.
c. The drug dopamine
Dopamine is a drug that is used to treat low heart rate and low blood pressure. Moderate use of dopamine increases heart rate and contractility, which then results in the enhancement of cardiac output.
d. Running a sprint
During exercises such as running, both heart rate and contractility increase in response to the high demand of oxygen. As the heart rate increases, stroke volume and cardiac output also increase because of the need to supply more oxygen-rich blood to the body when running.
e. Hyperthyroidism with increased secretion of thyroid hormones
Patients with hyperthyroidism have increased heart rate, blood volume, and contractility due to the high levels of thyroid hormone. In this state, preload is increased while afterload is reduced, which leads to a significant increase in cardiac output and stroke volume.
f. Massive myocardial infarction (cardiac tissue death)
A heart attack (myocardial infarction) occurs when the heart doesn’t get a sufficient supply of blood and oxygen, which causes the cardiac output to decrease. Reduced cardiac output is caused by a decrease in contractility and an increase in afterload as the body compensates for heart failure.
g. Hypothermia
Prolonged exposure to very low temperatures causes a significant decrease in heart rate and an increase in contractility.
h. Emotional distress
Individuals who experience emotional stress typically have an increased heart rate and elevated blood pressure due to the presence of cortisol and adrenaline, which also leads to increased cardiac output.
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