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
- High blood pressure takes place when the blood flows through the arteries at a higher pressure than normal. An increased afterload can be observed with chronic hypertension, which could result in a reduced ejection fraction and increased end-diastolic and end-systolic volumes.
b. Massive bleeding
- The body’s blood volume decreases during massive bleeding, leading to an increased heart rate and contractility to compensate for the loss. This is followed by baroreceptor activation resulting in sympathetic nervous system activation and peripheral vasoconstriction.
c. The drug dopamine
- Moderate doses of dopamine intensify cardiac contractility and heart rate as it produces positive chronotropic and inotropic effects on the myocardium, while significant intake of the drug increases the afterload as a result of peripheral vasoconstriction. The right amount of dopamine can serve as a medication for very low blood pressure or to cause vasodilation.
d. Running a sprint
- When running a sprint, the muscles order more oxygenated blood delivered to them, thus the body may need three or four times the normal cardiac output. To meet the demands, the muscles signal an increase in the cardiac stroke volume and heart rate, which will raise the cardiac output.
e. Hyperthryoidism with increased secretion of thyroid hormones
- Increased secretion of thyroid hormones in cases of hyperthyroidism gives rise to myocardial inotropy and heart rate. An excessive amount of this hormone also dilates the peripheral arteries, which increases cardiac output.
f. Massive myocardial infarction (cardiac tissue death)
- Myocardial infarction is caused by a blocked blood supply to an area of the heart muscle, which leads to decreased cardiac output and subsequent drop in arterial blood pressure.
g. Hypothermia
- When a patient experiences moderate to severe hypothermia, a drop in the heart rate, blood pressure, and cardiac output can be observed. This is due to the vessels’ response to cold temperatures, wherein they constrict, which limits the blood supply.
h. Emotional distress
- Emotional distress can cause abnormal heart rhythm, an increase in heart rate, elevation of blood pressure, and release of stress hormones, which all require a significant effort from the heart. These are the result of increased oxygen demand, spasms, and electrical instability in the heart that are attributed to prolonged stress.
References:
Armstrong, T.J. & Hooper, N. (2022, September 26). Hemorrhagic Shock. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK470382/
(n.d.).
Dopamine HCl. http://shadwige.sites.truman.edu/cardiac-medications/hemodynamic-medications/dopamine-hcl/
Bhatnagar, A. & Nystoriak, M.A. (2018, September 28). Cardiovascular Effects and Benefits of Exercise. Front Cardiovasc Med. doi: 10.3389/fcvm.2018.00135. PMID: 30324108; PMCID: PMC6172294.
Frishman, W.H. & Gomberg-Maitland, M. (1998). Thyroid hormone and cardiovascular disease. Am Heart J. doi: 10.1016/s0002-8703(98)70081-x. PMID: 9489964.
Dhakam, S.H. & Khalid, L. (2008). A review of cardiogenic shock in acute myocardial infarction. Curr Cardiol Rev. doi: 10.2174/157340308783565456. PMID: 19924275; PMCID: PMC2774583.
Carron, P.N., et al. (2021, June 23). Vital Signs in Accidental Hypothermia. High Altitude Medicine & Biology. https://doi.org/10.1089/ham.2020.0179
Glass, R.M., et al. (2007). Chronic Stress and the Heart. JAMA Network. doi:10.1001/jama.298.14.1722