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.
- High blood pressure
- High blood pressure or hypertension increases the afterload, which forces the ventricles to work harder in order to eject blood. When blood pressure rises, cardiac output also increases.
- A decrease in circulating blood volume causes the central venous pressure and cardiac filling to fall, which leads to a decrease in cardiac output.
- Dopamine is used to increase myocardial contractility so it is usually given to those who are experiencing low blood pressure.
Running a sprint
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When running a sprint, the skeletal muscles need more oxygenated blood. This causes the heart rate to increase due to an increase in cardiac output.
Hyperthyroidism with increased secretion of thyroid hormones
- Thyroid hormones cause increased preload and contractility, and decreased systemic vascular resistance which results in an increased cardiac output.
Massive myocardial infarction (cardiac tissue death)
- Massive myocardial infarction impairs cardiac function which can lead to reduced cardiac output since preload and heart contractility are reduced.
Hypothermia
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Hypothermia causes the heart rate to slow down due to a decreased time for ventral filling during contraction-relaxation cycle.
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Emotional distress causes an increase in heart rate and blood pressure while hormones, such as cortisol and adrenaline, are released.