a. High blood pressure
As the heart exerts more effort to deliver blood to the other parts of the body, high blood pressure causes the arteries to contract. This results in a decrease in cardiac output as afterload rises.
b. Massive bleeding
Massive bleeding stresses the cardiovascular system, which reduces the workload and blood pressure of the heart and, eventually, the perfusion pressure required to deliver blood to the tissues. The heart reacts to this by activating its sympathetic nervous system more and reducing its preload and afterload, both of which lower cardiac output.
c. the drug dopamine
Dopamine lowers blood pressure by preventing the sympathetic neuronal release of norepinephrine, which activates adrenergic and dopaminergic receptors. Its hemodynamic impact depends on the amount of drug dosage; therefore, at low doses, it induces diuresis; at moderate levels, it increases heart rate and cardiac contractility; and at high doses, it elevates afterload because of peripheral vasoconstriction; hence, an increased cardiac output.
d. Running a sprint
During sprinting, the pace and work rate increase, so the muscles require more oxygen to produce energy. The heart increases cardiac output, with an elevated heart rate and stroke volume, to promote oxygen circulation during this exercise.
e. Hyperthyroidism with increased secretion of thyroid hormones
Hyperthyroidism enables the thyroid gland to produce excess thyroxine, which leads to an accelerated metabolism and an increased resting heart rate. In this relation, thyroid hormone has its effects on the heart and peripheral vasculature in terms of decreased systemic vascular resistance and increased left ventricular contractility, blood volume, stroke volume, myocardial contractility, and ejection fraction; overall, an increased cardiac output.
f. Massive myocardial infarction (cardiac tissue death)
A massive myocardial infarction causes a blockage in the arteries, which hinders the blood flow to the heart muscle. This reduces the cardiac pump function, directly affecting myocardial contractility and leading to a decreased cardiac output.
g. Hypothermia
Hypothermia causes the body's core temperature to drop, which causes the skin to constrict reflexively. In this way, hypothermia leads to a reduction in heart rate and arterial pressure, also a rise in ventricular contractile force, which causes a decreased cardiac output as a result.
h. Emotional distress
Experiencing emotional distress causes an increase in heart rate, constriction of blood vessels, elevation of blood pressure, and the release of stress hormones. All of them increase the heart's workload, which raises cardiac output.