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 forces our heart to work harder since it is more difficult than normal for blood to travel efficiently, throughout our bodies, which increases the afterload and ultimately reduces the 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.
c. the drug dopamine
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A result of increased heart rate and contractility occurs due to the positive chronotropic and inotropic effects that dopamine produces which increases the cardiac output and blood pressure as well.
d. Running a sprint
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Our muscles need more oxygen when running a sprint, thereby increasing the heart rate in order for blood to be transported throughout the body quickly. This, then, increases the cardiac output.
e. Hyperthyroidism with increased secretion of thyroid hormones
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Hyperthyroidism occurs when there is an increased production of thyroxine. Due to this, it increases cardiac contractility and heart rate and lowers peripheral resistance which causes an increased cardiac output.
f. Massive myocardial infarction (cardiac tissue death)
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Myocardial infarction is caused by a lack of blood flow to the myocardium which leads to a decreased cardiac output.
g. Hypothermia
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Hypothermia occurs when our body is exposed to very cold temperatures for a prolonged period of time and this can lead to vasoconstriction, the tightening of the arteries, ultimately decreasing cardiac output.
h. Emotional distress
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Experiencing emotional distress would make your body release cortisol and adrenaline; these of which cause constriction of blood vessels and an increased heart rate and blood pressure. As a result, an increase in contractility and cardiac output.
SOURCES:
Berne, R. (1954). The effect of immersion hypothermia on coronary blood flow. Circulation Research, 11. https://www.ahajournals.org/doi/pdf/10.1161/01.RES.2.3.236
Cunha, J. (2022). Dopamine. https://www.rxlist.com/dopamine-drug.htm#description
Dhamoon, A. & Ojha, N. (2022). StatPearls. StatPearls Publishing
Hooper, N. & Armstrong, T. (2022). Hemorrhagic Shock. https://www.ncbi.nlm.nih.gov/books/NBK470382/
University of Rochester Medical Center. (2019). Emotions and heart health. https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=134&ContentID=165