a. High blood pressure
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People with high blood pressure have a higher blood volume. With this, there will be an increase in preload, which would also increase the stroke volume and lead to an increase in cardiac output.
b. Massive bleeding
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A reduction in blood volume occurs during blood loss and in order to compensate for that, the body increases one’s heart rate and contractility, thus, reducing cardiac output.
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People who are experiencing massive bleeding would experience a lower blood volume. With this, there will be less blood to fill the heart during diastole, hence lesser force during the systole (Frank-Starling law of the heart). With this, the stroke volume and cardiac output will decrease.
c. The drug dopamine
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Dopamine is used to increase heart rate and the heart’s contraction force. This is due to positive chronotropic and inotropic effects that dopamine produces. With this, contractility of the heart will increase, hence increasing the stroke volume and blood pressure of the heart.
d. Running a sprint
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When exercising, our muscles work more, hence needing more oxygen. With this muscular activity, the valves are forced to open to allow more blood to go back to the heart (venous return). With an increase in the EDV, there will be an increase in stroke volume and cardiac output.
e. Hyperthyroidism with increased secretion of thyroid hormones
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There will be an increase in production of thyroxine. This hormone is responsible for increasing the heart rate and contractility and lowering resistance. In some cases, hyperthyroidism, with an increased secretion of thyroxine, will lead to irregular heart rate, commonly as tachycardia. With this, there will be an increase in cardiac output.
f. Massive myocardial infarction (cardiac tissue death)
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With the interrupted blood supply, cardiac tissue will die. With this, the heart will not be efficient anymore and its muscle loses some of its strength. With this, there will be a decrease in contractility because infarction reduces the strength of the heart. As a result, there will be a decrease in stroke volume and cardiac output.
g. Hypothermia
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Being in a cold temperature for a prolonged period, it can lead to vasoconstriction. With vasoconstriction, there will be an increase in afterload. In order for the heart to beat the higher pressure, the heart’s preload will also increase to stretch the heart more so that the contraction will be more forceful (Frank-Starling law of the heart). With this there will be a decrease in stroke volume and cardiac output.
h. Emotional distress
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In a stressful environment, our body would react by releasing cortisol. This hormone increases the force of contraction. With this, there will be an increase in heart rate and stroke volume.