POST-LECTURE ACTIVITY
THE CARDIOVASCULAR SYSTEM
WEEK 10
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, often known as hypertension, occurs when blood volume increases, causing an increase in heart rate, an increase in preload that causes an increase in stroke volume, and at the same time an increase in afterload that might boost cardiac output.
b. Massive bleeding
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Massive bleeding, or hemorrhage, is described as blood loss that decreases central venous pressure. During massive bleeding, volume decreases, which may result in decreased preload and afterload, an increased heart rate, and decreased contractility, all of which reduce cardiac output.
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c. The Drug Dopamine
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Dopamine is a drug that is frequently used to treat cardiac arrest, low blood pressure, and a low heart rate. When consumed, it raises the heart rate and the force of contraction, or contractility, which leads to an increase in cardiac output and stroke volume.
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d. Running a sprint
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The heart rate increases during physical exercise, such as running a sprint, since more oxygen must be provided as we run more quickly. Therefore, changes in the components, including an increased preload, decreased afterload, and increased contractility, also cause the heart's cardiac output to increase.
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e. Hyperthyroidism with increased secretion of thyroid hormones
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Hyperthyroidism, or increased thyroid hormone secretion, can also lead to increased cardiac output, wherein one of its sign is tachycardia (tak′-i-KAR-d-a), which has an accelerated resting heart rate and enhances cardiac contractility.
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f. Massive myocardial infarction (cardiac tissue death)
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- Myocardial infarction, or more commonly known as heart attack occurs when the heart's muscles are deprived of oxygen due to reduced blood supply or it has completely stopped. Therefore, there may be a decrease in cardiac output as a result of the heart's increased preload and afterload.
g. Hypothermia
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Hypothermia decreases metabolism, which reduces the oxygen requirements of the tissues. This results in an increase in cardiac output, wherein there is a decrease in heart rate, and an increase in contractility, which enables our heart and brain to endure brief interruptions or reductions in blood supply, particularly during a surgical or medical procedure.
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h. Emotional distress
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When we experience emotional distress, our body responds by releasing catecholamines (such as adrenaline and norepinephrine), which increase the heart rate while simultaneously increasing contractility, which can result in an increased cardiac output and increased stroke volume.
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References:
Alila Medical Media. (2017, September 18). Cardiac Output, Stroke volume, EDV, ESV, Ejection Fraction [Video]. YouTube. https://www.youtube.com/watch?v=vFRkSB46bl8
Crestani, C. C. (2016). Emotional Stress and Cardiovascular Complications in Animal Models: A Review of the Influence of Stress Type. Frontiers. https://www.frontiersin.org/articles/10.3389/fphys.2016.00251/full
Holmes, J. C., & Fowler, N. O. (1962). Direct cardiac effects of dopamine. Circulation Research, 10(1), 68–72. https://doi.org/10.1161/01.res.10.1.68
Klabunde, R. (2021, February 2). Hemorrhagic Shock. Cardiovascular Physiology Concepts. https://www.cvphysiology.com/Blood%20Pressure/BP031
Tortora, G. & Derrickson, B. (2014). Principles of Anatomy and Physiology (14th ed.). New Jersey, NJ: Wiley
Wolfe, L. A., & Cunningham, D. A. (1982). Effects of chronic exercise on cardiac output and its determinants. Canadian Journal of Physiology and Pharmacology, 60(8), 1089–1097. https://doi.org/10.1139/y82-157