Week 10
Post-Lecture Activity
THE CARDIOVASCULAR SYSTEM
by GEORGETTE E. ZALDIVAR
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.
1. High blood pressure
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- High blood pressure increases the stress on the heart or aortic pressure due to the narrowed, less elastic arteries that make it more difficult for blood to circulate effectively throughout the body. Because of the increased blood volume, heart rate is also increased; increased preload results in stroke volume and afterload, thus boosting cardiac output.
2. Massive bleeding
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- Massive bleeding, otherwise known as a hemorrhage, involves a decreased blood volume caused by blood loss, external or internal, due to certain injuries, which may consequently result in reduced preload, afterload, and contractility. This ensues in decreased cardiac output.
3. The drug dopamine
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- Dopamine is used to treat hypotension and low cardiac output because it has beneficial chronotropic and inotropic effects on the myocardium, improving cardiac contractility and increasing cardiac output and stroke volume. High doses, however, result in peripheral vasoconstriction, which raises afterload.
4. Running a sprint
- Sprinting causes the heart rate to rise as the muscles require more oxygen and more blood flow to the rest of the body, causing the stroke volume to rise as a result of greater myocardial contractility and increased venous return to the heart. A higher preload, lower afterload, and higher contractility change increase the cardiac output.
5. Hyperthyroidism with increased secretion of thyroid hormones
- Due to an increase in preload and contractile force of the heart muscle caused by hyperthyroidism, cardiac output increases. The drop in end-systolic volume caused by the greater force of contraction leads to an increase in stroke volume, which, coupled with an increased heart rate, improves cardiac output.
6. Massive myocardial infarction (cardiac tissue death)
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- Myocardial infarction—otherwise known as a heart attack—happen when the blood flow to the heart's muscles is deprived of oxygen due to reduced blood supply or complete cessation thereof. As a result of the heart's higher preload and afterload and lower contractility, there may be a broad proliferation of diffuse fibrosis throughout the ventricle, which results in decreased cardiac output.
7. Hypothermia
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- Hypothermia, or a drop in body temperature below 35°C, causes a fall in heart rate and an increase in contractility, allowing the heart and brain to withstand brief interruptions or reductions in blood supply. This raises the stroke volume, which then increases cardiac output.
8. Emotional distress
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- In times of emotional distress, the body secretes adrenaline, raising blood pressure and speeding up the heart rate. This increase in sympathetic stimulation, which coincides with increased epinephrine and norepinephrine secretion as a result of emotions, causes an increase in heart rate and contractility, increasing stroke volume and, ultimately, cardiac output.
REFERENCES:
Ertek, S., & Cicero, A. F. (2013). Hyperthyroidism and cardiovascular complications: a narrative review on the basis of pathophysiology. Archives of medical science : AMS, 9(5), 944–952. https://doi.org/10.5114/aoms.2013.38685
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
Lapum, J. M. L. V. (n.d.). Factors That Influence Blood Pressure – Vital Sign Measurement Across the Lifespan – 1st Canadian edition. Pressbooks. https://pressbooks.library.torontomu.ca/vitalsign/chapter/factors-that-influence-blood-pressure/
McDonough, K. H., Giaimo, M., Quinn, M., & Miller, H. (1999). Intrinsic myocardial function in hemorrhagic shock. Shock (Augusta, Ga.), 11(3), 205–210. https://doi.org/10.1097/00024382-199903000-00009
Reddi, B., Shanmugam, N., & Fletcher, N. (2017, May 1). Heart failure—pathophysiology and inpatient management. BJA Education, 17(5), 151-160. https://doi.org/10.1093/bjaed/mkw067
Tortora, G. J., & Derrickson, B. H. (2020). Principles of Anatomy and Physiology (14th ed.). Wiley.