Note: Cardiac output is equal to the product of stroke volume and heart rate (beats/min); thus, increased stroke volume and heart rate pertain to an increase in cardiac output.
a. High blood pressure -High blood pressure can increase the afterload of the cardiac output. Before the opening of semilunar valves, the increased pressure that the blood shall overcome lessens the stroke volume of cardiac output.
b. Massive bleeding - Massive bleeding can lead to lesser stroke volume. Concomitant to this is lesser end-diastolic volume, in which lesser blood volume occupies the right ventricles. Following the Frank-Sterling law of the heart, the duration of diastole shortens when there is less blood that fills the right ventricle. This eventually leads to an increased heart rate.
c. the drug dopamine - The drug dopamine is part of the positive inotropic agents for the heart. Primarily it increases heart rate by promoting Ca2+ inflow during action (cardiac) potentials. In essence, dopamine increases the contractility of the heart’s myocardium which ultimately increases the stroke volume.
d. Running a sprint - When doing an exercise like a sprint, the heart tries to keep up the oxygen demand of involved muscle tissues. Heat is a byproduct of cellular, like muscle cells, activities. The heart rate increases during sprinting which is triggered by the increased body temperature. Ultimately the increased heart rate increases cardiac output.
e. Hyperthryoidism with increased secretion of thyroid hormones - Excess thyroid hormones can cause tachycardia. In such conditions, the heart’s resting rate is elevated. The thyroid hormones heighten heart rate and strengthen cardiac contractility.
f. Massive myocardial infarction (cardiac tissue death) - Massive myocardial infarction (MI) signifies the death of the myocardial tissues. Death to tissues can directly affect the preload of the heart or its ability to stretch before contraction. Consequently, there is a considerable weakening of the heart’s contractility. Altogether, MI decreases stroke volume and cardiac output.
g. Hypothermia - In hypothermia, the body’s temperature is in a lower state than normal. Hypothermia slows down the heart’s rate, which may be beneficial during surgical repairs of heart abnormalities.
h. Emotional distress - Emotional distress triggers the release of hormones by the adrenal medullae as part of homeostasis. The released hormones are epinephrine and norepinephrine hormones. Both hormones magnify the pumping effectiveness of the heart. Consequently, the hormones act like cardiac accelerators, increasing contractility and heart rate.