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 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
Increased aortic pressure causes an increase in ventricular preload as a byproduct of increasing the afterload on the ventricle, decreasing stroke volume by increasing end-systolic volume, and increasing the afterload on the ventricle. An increase in afterload generally causes a decrease in stroke volume.
b. Massive bleeding
A pattern of increased heart rate is involved in the circulatory response to bleeding, which provides redistribution of the decreased cardiac output. The reduction in blood volume during blood loss leads to reduced stroke volume, arterial pressure, and overall cardiac output.
c. The drug dopamine
Dopamine dosages that were raised caused an increase in cardiac output and contractility as well as a redistribution of the decreased cardiac output. With the increase in cardiac output due to dopamine caused by increased contractility, stroke volume and heart rate also increases as a result.
d. Running a sprint
While running a sprint, our body needs to increase normal cardiac output caused by preload and contractility because we need more oxygen as we exert ourselves. During exercise, our heart beats more forcefully and faster to increase cardiac output.
e. Hyperthyroidism with increased secretion of thyroid hormones
Hyperthyroidism, which consists of thyroid hormone lowers the total peripheral resistance which increases cardiac output due to an increase in contractility. The drop in end-systolic volume caused by the greater force of contraction leads to an increase in stroke volume, which is associated with an increased heart rate and increased cardiac output.
f. Massive myocardial infarction (cardiac tissue death)
Cardiac function is compromised by the loss of viable myocardium, which can result in decreased cardiac output and, in severe cases, cardiogenic shock. Ischemic myocardium is linked to systolic and diastolic dysfunction as well as myocardial contractility.
g. Hypothermia
Hypothermia decreases heart rate because of low temperature and causes an increase in stroke volume. It is associated with the increased contractility, and resistance in the coronary vascular bed is reduced and flow continues despite very low aortic pressure.
h. Emotional distress
The hormones cortisol and adrenaline prepare our body to deal with stress increasing our heart rate, contractility, and blood pressure. Studies found that the effects of this to the cardiac output and stroke volume may be dependent to the cognition of an individual.
References:
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Brooks, D. P., Chapman, B. J., & Munday, K. A. (1984). The effect of hypothermia on the cardiovascular system and the pressor actions of angiotensin II. Journal of Thermal Biology, 9(4), 243–246. https://doi.org/10.1016/0306-4565(84)90003-2
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