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 include PRELOAD, CONTRACTILITY, and AFTERLOAD.
In the following conditions, indicate what factor/s influence the cardiac output: PRELOAD, CONTRACTILITY, AFTERLOAD, HEART RATE. Explain why the factor/s affects cardiac output in 1 to 2 sentences.
a. High blood pressure
High blood pressure, or hypertension, increases afterload because higher vascular pressure makes it more difficult for the valves to open, thus increasing afterload. This leads to a reduced amount of ejected blood (Alila Medical Media, 2017).
b. Massive bleeding
During massive bleeding or a hemorrhage, blood volume decreases, thus decreasing preload, and influencing the cardiac output (NURSINGcom, 2019).
c. The drug dopamine
Dopamine is used to treat low blood pressure. It is considered a positive inotropic agent and is used to correct low blood pressure by increasing contractility; however, high doses exacerbate heart failure by increasing afterload due to peripheral vasoconstriction (Cardiogenic Pulmonary Edema Medication: Preload Reducers, Afterload Reducers, Inotropic Agents, n.d.).
d. Running a sprint
Heart rate increases in exercise from epinephrine and norepinephrine enhancement of the heart's pumping effectiveness, thus increasing cardiac output (Tortora & Derrickson, 2017).
e. Hyperthyroidism with increased secretion of thyroid hormones
Excessive thyroid hormones such as that of hyperthyroidism increase cardiac contractility and heart rate thereby increasing cardiac output. This leads to tachycardia, which is an elevated resting heart rate (Tortora & Derrickson, 2017).
f. Massive myocardial infarction (cardiac tissue death)
Cardiac tissue death is usually irreversible and results in reduced cardiac output due to decreased contractility and increased afterload in the heart (Nall, n.d.).
g. Hypothermia
Contractility is decreased by hypothermia as it slows metabolism which reduces oxygen needed by tissues, thereby allowing the heart and brain to withstand short periods of interrupted or reduced blood flow (Tortora & Derrickson, 2017).
h. Emotional distress
During emotional distress, catecholamines such as epinephrine and norepinephrine, cause the heart rate and blood pressure to increase (Torpy et al., 2007). Thus causing a greater cardiac output.
REFERENCES:
Cardiogenic Pulmonary Edema Medication: Preload Reducers, Afterload Reducers, Inotropic Agents. (n.d.). Retrieved November 10, 2022, from https://emedicine.medscape.com/article/157452-medication
Dopamine HCl |. (n.d.). Retrieved November 10, 2022, from http://shadwige.sites.truman.edu/cardiac-medications/hemodynamic-medications/dopamine-hcl/
Torpy, J. M., Burke, A. E., & Glass, R. M. (2007). Acute Emotional Stress and the Heart. JAMA, 298(3), 360. https://doi.org/10.1001/jama.286.3.374
Alila Medical Media (Director). (2017, September 18). Cardiac Output, Stroke volume, EDV, ESV, Ejection Fraction. https://www.youtube.com/watch?v=vFRkSB46bl8
NURSINGcom (Director). (2019, November 7). Understanding Preload and Afterload for Nurses. https://www.youtube.com/watch?v=HeUjO5DC2rA
Nall, R. (n.d.). What Happens to Preload and Afterload in Heart Failure? Retrieved November 10, 2022, from https://www.healthline.com/health/heart-failure/preload-and-afterload-in-heart-failure#treatment
Tortora, G. J., & Derrickson, B. (2017). Principles of anatomy and physiology (14th ed.). Wiley Custom Learning Solutions.