1. 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
Hypertension (high blood pressure) increases aortic pressure that must be exceeded by pressure in the left ventricle in order to eject blood. Because of this, the heart has to work harder for ventricular pressure to exceed aortic pressure, causing afterload to increase and stroke volume to become lower.
b. Massive bleeding
Massive bleeding implies the decrease of blood volume, which affects venous return, one of the factors of preload. This causes a reduction in the preload as well as increase in heart rate and contractility to compensate for volume loss.
c. the drug dopamine
Dopamine is a drug used to treat low blood pressure and low cardiac output. It increases one's heart rate, contractility, and afterload depending on dosage.
d. Running a sprint
Greater cardiac output is required during exercise due to the body's muscles working harder and requiring more blood supply as the exercise goes on. In order to achieve this output, contractility increases, with afterload also increasing due to (temporary) higher blood pressure.
e. Hyperthryoidism with increased secretion of thyroid hormones
The excess thyroid hormones secreted due to hyperthroidism can cause an increase in resting heart rate, left venticular contractility, and blood volume. Hyperthyroidism's cardiac effects also increase preload.
f. Massive myocardial infarction (cardiac tissue death)
Cardiac tissue death occurs when certain parts or areas of the heart's muscles do not get enough oxygen due to an insufficient blood flow--the heart's muscles and the cardiac tissues start to die. Both preload and contractility will decrease because the heart is no longer able to stretch and contract as normal, while afterload increases due to increased blood pressure.
g. Hypothermia
Hypothermia is caused by exposure to prolonged exposure to very cold temperatures--this leads to a decrease in heart rate, which the heart tries to compensate with by increasing contractility and stroke volume. There is also a possibility for an increase in arterial blood pressure, which may result in an increase in afterload.
h. Emotional distress
When experiencing emotional distress, hormones such as epinephrine and norepinephrine are released in response to the negative emotions being felt. These catecholamines cause both heart rate and blood pressure to rise because of increased contractility, all these leading to increased stroke volume and cardiac output.
References
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Homework Clinic. (2020, February 21). Stroke volume - afterload definition & hypertension [Video]. https://www.youtube.com/watch?v=UYkLb5tbBoU
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Mayo Clinic Staff. (2021, March 18). Stress and high blood pressure: What's the connection? Mayo Clinic. Retrieved November 11, 2022, from https://www.mayoclinic.org/diseases-conditions/high-blood-pressure/in-depth/stress-and-high-blood-pressure/art-20044190#:~:text=Your%20body%20produces%20a%20surge,long%2Dterm%20high%20blood%20pressure.
Motloch, L. J., Ishikawa, K., Xie, C., Hu, J., Aguero, J., Fish, K. M., Hajjar, R. J., & Akar, F. G. (2017). Increased afterload following myocardial infarction promotes conduction-dependent arrhythmias that are unmasked by hypokalemia. JACC: Basic to Translational Science, 2(3), 258–269. https://doi.org/10.1016/j.jacbts.2017.02.002
Sonne, J., Goyal, A., & Lopez-Ojeda, W. (2022). Dopamine . National Library of Medicine. Retrieved November 11, 2022, from https://www.ncbi.nlm.nih.gov/books/NBK535451/