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.
*Numbers written are for the references.
a. High blood pressure
[3] Hypertension (high blood pressure) affects the afterload, since there is a reduced fraction due to constriction of blood vessels and increased blood volumes.
b. Massive bleeding
Massive bleeding (hemorrhage) reduces the blood volume that causes a reduced afterload. To compensate for the blood loss, [4] the contractility of cardiac output and heart rate is increased.
c. the drug dopamine
[9] Dopamine must be used with limitations and moderate doses since it enhances contractility and heart rate, [7] as a treatment of refractory heart failure and shock, which then causes an increase in the cardiac output and stroke volume.
d. Running a sprint
Sprinting raises blood pressure quickly, [11] therefore causing an increase in contractility and heart rate to return the oxygen loss during the exercise. [1] It improves the overall blood circulation since the heart is pumped harder.
e. Hyperthyroidism with increased secretion of thyroid hormones
Hyperthyroidism increases the thyroid hormones count, which targets the heart. [6] The thyroid hormones are known to raise heart rate and cardiac contractility, [5] raising the risk for stroke as its complication.
f. Massive myocardial infarction (cardiac tissue death)
Cardiac tissue death (heart attack) causes a remodeling in the heart structure, [10] therefore increasing the contractility to accommodate for the reduced number of myocardial cells.
g. Hypothermia
[2] At low temperatures, heart rate decreases while increasing contractility. There is an automatic vasoconstriction of blood vessels to accommodate for the low temperatures from the outside.
h. Emotional distress
[8] Stress causes an increase in heart rate since body responses to the environment. The stressors challenge oneself, therefore the body is challenged to respond by greater workload of the heart.
References used:
[1] Adhikari, Anup. (2005). Heart rate response during sprinting and running for short and long distance. RDC - Jakarta Bulletin, 16-19. https://www.researchgate.net/publication/320465248_Heart_rate_response_during_sprinting_and_running_for_short_and_long_distance
[2] Bender, H. W., Austen, G., & Tsunekawa, T. (1963). Effects of Hypothermia on Myocardial Contractile Force. Archives of Surgery, 87(3), 464. https://doi.org/10.1001/archsurg.1963.01310150100023
[3] Froelicher, V. F. (2006). Basic Exercise Physiology. In J. Myers (Ed.), Exercise and the Heart (Fifth Edition) (pp. 1–10). essay, Science Direct. https://doi.org/10.1016/B978-1-4160-0311-3.50004-8
[4] 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
[5] Osuna, P. M., Udovcic, M., & Sharma, M. D. (2017). Hyperthyroidism and the Heart. Methodist DeBakey cardiovascular journal, 13(2), 60–63. https://doi.org/10.14797/mdcj-13-2-60
[6] Rambo, A. M., Peixoto, J. V., Albuquerque, R. A., Silva, I. K., & Fogaça, R. T. (2022). Effects of Hyperthyroidism on Contractility and Na+/Ca2+ Exchanger Activity in the Isolated Papillary Muscle of Rats. International Journal of Cardiovascular Sciences. https://doi.org/10.36660/ijcs.20210023
[7] Reid, P. R., & Thompson, W. L. (1975). The clinical use of dopamine in the treatment of shock. The Johns Hopkins medical journal, 137(6), 276–279.
[8] 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
[9] Truman State University. (n.d.). Dopamine HCl. http://shadwige.sites.truman.edu/cardiac-medications/hemodynamic-medications/dopamine-hcl/#:~:text=Heart%20Failure%3A%20At%20moderate%20doses,additional%20workload%20on%20the%20heart
[10] Zhang, H., Chen, X., Gao, E., MacDonnell, S. M., Wang, W., Kolpakov, M., Nakayama, H., Zhang, X., Jaleel, N., Harris, D. M., Li, Y., Tang, M., Berretta, R., Leri, A., Kajstura, J., Sabri, A., Koch, W. J., Molkentin, J. D., & Houser, S. R. (2010). Increasing Cardiac Contractility After Myocardial Infarction Exacerbates Cardiac Injury and Pump Dysfunction. Circulation Research, 107(6), 800–809. https://doi.org/10.1161/circresaha.110.219220
[11] Zhang, X.-Q., Song, J., Carl, L. L., Shi, W., Qureshi, A., Tian, Q., & Cheung, J. Y. (2002). Effects of sprint training on contractility and [Ca2+]i transients in adult rat myocytes. Journal of Applied Physiology, 93(4), 1310–1317. https://doi.org/10.1152/japplphysiol.01071.2001