1. 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 include PRELOAD, CONTRACTILITY and AFTERLOAD.
In the following conditions, indicate what factor/s influence the cardiac output: PRELOAD, CONTRACTILITY, AFTERLOAD, HEART RATE. Explain why the factor/s affects cardiac output in 1 to 2 sentences.
a. High blood pressure - Increased afterload is observed in hypertension. The higher the pressure is in the blood vessels, the harder it will be to overcome the resistance, therefore cardiac output is compromised.
b. Massive bleeding - Blood volume is reduced when there is bleeding, therefore there is a decrease in preload and afterload. An increased heart rate and contractility allows the body to compensate for this volume loss.
c. the drug dopamine - Dopamine is an inotropic agent that produces positive inotropic effects which results in increased heart rate and contractility = increased cardiac output. This is why it is used to treat low blood pressure and low cardiac output.
d. Running a sprint - During exercise, heart rate is increased to supply the increasing demands of the body for oxygen. This elevates the cardiac output.
e. Hyperthyroidism with increased secretion of thyroid hormones - Increased preload = increased cardiac work. Heart rate increases when there is an increased secretion of thyroid hormones and due to this, there is a lesser time for the heart to pump blood.
f. Massive myocardial infarction (cardiac tissue death) - Due to poor or decreased contractility, the heart may not be able to pump blood efficiently, resulting in less cardiac output or failure.
g. Hypothermia - Hypothermia slows metabolism and this reduces the oxygen demands of the body. This results in bradycardia and despite reduced heart rate, it causes an increased cardiac output.
h. Emotional distress - Stress causes an increased demand for oxygen which leads to an increase in the heart rate, blood pressure, and cardiac output.
References
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