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
High blood pressure, also known as hypertension, makes the aortic valve harder to open because the pressure in left ventricle needs to exceed the elevated blood pressure. Thus, it increases the afterload in the left ventricle, reducing the cardiac output.
b. Massive bleeding
Massive bleeding reduces the blood volume which cause the venous pressure and cardiac filling. This makes the preload lower, decreasing the cardiac output.
c. the drug dopamine
Dopamine is a positive inotropic agent and a vasopressor – constricts the blood vessels. Moderate doses of dopamine increase the myocardial contractility, increasing cardiac output while high doses increase afterload, therefore, decreasing the cardiac output.
d. Running a sprint
Exercises like running a sprint increases the heart’s workload to compensate for the energy and oxygen used by the muscles. As a result, there is an increase in heart rate also increasing the cardiac output.
e. Hyperthryoidism with increased secretion of thyroid hormones
Hyperthyroidism causes increased heart rate and contractility, resulting in increased cardiac output.
f. Massive myocardial infarction (cardiac tissue death)
Massive myocardial infarction, also called heart attack, causes an impair in contractility, reducing the cardiac output.
g. Hypothermia
Hypothermia which is a lower-than-normal body temperature causes vasoconstriction of the blood vessels – increasing preload – leading to increased cardiac output.
h. Emotional distress
The sympathetic nervous system is activated in conditions of stress, releasing epinephrine and norepinephrine which have positive inotropic effects. Thus, there is an increase in contractility and heart rate, resulting in increased cardiac output.
References:
Afterload. (2022). Retrieved November 14, 2022, from Bionity.com website: https://www.bionity.com/en/encyclopedia/Afterload.html#:~:text=Hypertension%20(Increased%20blood%20pressure)%20increases,than%20the%20elevated%20blood%20pressure
CV Physiology | Hemorrhagic Shock. (2021). Retrieved November 14, 2022, from Cvphysiology.com website: https://www.cvphysiology.com/Blood%20Pressure/BP031#:~:text=The%20reduction%20in%20blood%20volume,cardiac%20output%20and%20arterial%20pressure.
Sovari, A. A. (2021, October 17). Cardiogenic Pulmonary Edema Medication: Preload Reducers, Afterload Reducers, Inotropic Agents. Retrieved November 14, 2022, from Medscape.com website: https://emedicine.medscape.com/article/157452-medication
Ertek, S., & Cicero, A. F. (2013). State of the art paper Hyperthyroidism and cardiovascular complications: a narrative review on the basis of pathophysiology. Archives of Medical Science, 5, 944–952. https://doi.org/10.5114/aoms.2013.38685