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
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High blood pressure is when there is an ejection of blood from the heart because of the the higher pressure in the ventricles that causes blood to push the semilunar valves open. This results in an increase in afterload which causes stroke volume to decrease, so that more blood remains in the ventricles at the end of systole (Tortora & Derrickson, 2014).
b. Massive bleeding
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The reduction in blood volume during blood loss causes a fall in central venous pressure and cardiac filling. This leads to reduced cardiac output and arterial pressure, as well as increase in heart rate to make up for blood loss (Klabunde, 2021).
c. the drug dopamine
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Dopamine produces positive chronotropic and inotropic effects on the myocardium, resulting in increased heart rate and cardiac contractility (Rxlist, 2022).
d. Running a sprint
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During exercise, like running, our muscles need more oxygen when we exert ourselves, so our heart typically beats faster so that more blood gets out to our body. This increases our heart rate as we may need three or four times our normal cardiac output, which results in an increase in contractility (Healthwise Staff, 2022).
e. Hyperthryoidism with increased secretion of thyroid hormones
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Hyperthyroidism causes hemodynamic changes, such as increased preload and contractility, as well as decreased systemic vascular resistance, which then causes increased cardiac output (Ertek & Cicero, 2013).
f. Massive myocardial infarction (cardiac tissue death)
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Massive myocardial infarction is a damage to the myocardium caused by subsequent reduced blood flow. This damage is usually irreversible and can affect the normal pumping capacity of the heart, resulting in decreased stroke volume and cardiac output as well as less contractility and more afterload (Hope for Hearts, 2020).
g. Hypothermia
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Hypothermia is when our body has a lower temperature than normal. Since there is a decrease in arterial pressure, bradycardia increases that results in decrease of heart rate and increase in contractilityv (Ishikawa et al., 2021).
h. Emotional distress
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Emotional distress causes the adrenal medullae to release hormones (epinephrine and norepinephrine) which enhances the sympathetic stimulation and increases the heart rate. The said hormones help the heart to beat more rapidly and your blood vessels to narrow to help push blood to the center of the body, resulting in increased heart rate and contractility, as well as the cardiac output (University of Rochester Medical Center, n.d.).
References:
Ertek S & Cicero AF. (2013). Hyperthyroidism and cardiovascular complications: a narrative review on the basis of pathophysiology. Arch Med Sci, 9(5), 944-52. doi:10.5114/aoms.2013.38685.
Healthwise Staff. (January 10, 2022). Cardiac Output. Retrieved from https://myhealth.alberta.ca/Health/Pages/conditions.aspx?hwid=tx4080abc
Hope for Hearts. (September 22, 2020). About Coronary Artery Disease. Retrieved from https://hopeforhearts.com.au/cardiovascular-disease/coronary-artery-disease/
Ishikawa et al. (2021). Effects of Therapeutic Hypothermia on Normal and Ischemic Heart. Front. Cardiovasc.Med. 8:642843. doi:10.3389/fcvm.2021.642843
Klabunde, R. (February 2, 2021). Hemorrhagic Shock. Retrieved frm https://www.cvphysiology.com/Blood%20Pressure/BP031
Rxlist. (July 18, 2022). Dopamine. Retrieved from https://www.rxlist.com/dopamine-drug.htm
Tortora, G. & Derrickson, B. (2014). Principles of Anatomy and Physiology (14th ed.). New Jersey, NJ: Wiley
University of Rochester Medical Center. (n.d.). Emotions and Heart Health. Retrieved from https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=134&ContentID=165