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 enables our heart to work harder and overcome resistance causing an afterload. Due to narrowed arteries, difficulty in blood flow is present. [1]
b. Massive bleeding
Blood volume is drastically reduced by heavy bleeding, which lowers central venous pressure and lessens heart filling. Consequently, cardiac output is affected as the body increases heart rate and contractility to make up for the decreased blood volume, but the preload also drops along with blood volume. [2]
c. The drug dopamine
Dopamine has positive chronotropic and direct inotropic actions on the myocardium, which raise heart rate and cardiac contractility. [3]
d. Running a sprint
Due to the relatively high heart rates that are attained while running a sprint, cardiac output increases significantly during exercise. Workload-related increases in heart rate cause the heart rate to gradually approach its maximum level. [4]
e. Hyperthryoidism with increased secretion of thyroid hormones
Thyroid hormone most likely causes vasodilatation in the blood vessels supplying the skin and muscle, which results in this high output state. As an outcome of this hormone-induced impact, the heart rate increases by lowering overall peripheral resistance. [5]
f. Massive myocardial infarction (cardiac tissue death)
Muscle hypoxia and necrosis caused by ischemia from reduced coronary perfusion impair myocardial contractility. Whereas, the cardiac output is reduced, which causes the arterial blood pressure to decrease. [6]
g. Hypothermia
Hyperthermia occurs when the temperature climbs too heightened and endangers health. During cold temperatures, there is a reflex adrenergic vasoconstriction (noradrenalin) of the skin. As a result, an increase in stroke volume and a decrease in heart rate. [7]
h. Emotional distress
Experiencing emotional distress can cause an increase in oxygen demand within the body, spasms of the coronary (heart) blood vessels, and electrical instability in the heart's conduction system. It causes an increase in heart rate and yields the heart to pump harder to stimulate blood flow within the body. [7][8]
References:
[7] D.Bachmann, MD. (2019, January 17). Why are there more heart attacks in cold weather? Why Are There More Heart Attacks in Cold Weather? | Ohio State Medical Center. https://wexnermedical.osu.edu/blog/why-are-there-more-heart-attacks-in-cold-weather
[5] deGroot, W. J., & Leonard, J. J. (2004, February 3). Hyperthyroidism as a high cardiac output state. https://www.sciencedirect.com/science/article/abs/pii/0002870370903182
[8] Deussen, A. (2007, September). Hyperthermia and hypothermia. Effects on the cardiovascular system. National Library of Medicine. https://pubmed.ncbi.nlm.nih.gov/17554514/#:~:text=During%20a%20reduction%20of%20the,C%20due%20to%20increasing%20bradycardia.
[3] Dopamine: Uses, Interactions, Mechanism of Action | DrugBank Online. (n.d.). DrugBank. https://go.drugbank.com/drugs/DB00988
[4] Evans, D. L. (n.d.). Cardiovascular adaptations to exercise and training. National Library of Medicine. https://pubmed.ncbi.nlm.nih.gov/3877552/
[1] How High Blood Pressure Can Lead to Heart Failure. (2022, March 4). www.heart.org. https://www.heart.org/en/health-topics/high-blood-pressure/health-threats-from-high-blood-pressure/how-high-blood-pressure-can-lead-to-heart-failure
[6] Khalid, L. ., & Dhakam, S. H. (2008, February 4). A Review of Cardiogenic Shock in Acute Myocardial Infarction. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2774583/#:~:text=Ischemia%20due%20to%20decreased%20coronary,in%20the%20arterial%20blood%20pressure.
[2] Klabunde, R. (n.d.). Hemorrhagic Shock. Cardiovascular Physiology Concept. https://www.cvphysiology.com/Blood%20Pressure/BP031#:~:text=The%20reduction%20in%20blood%20volume,cardiac%20output%20and%20arterial%20pressure.
[9] Torpy, J. M., MD. (2007, October 10). Chronic Stress and the Heart. Cardiology | JAMA | JAMA Network. https://jamanetwork.com/journals/jama/fullarticle/209139