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 occurs when there is an elevation of blood volume, which leads to an increased afterload and increased heart rate; therefore increasing cardiac output.
b. Massive bleeding
Massive blood loss leads to decreased central venous pressure and cardiac filling. Since blood pressure and volume decrease during hemorrhage, this results in decreased preload, contractility, and afterload; thereby decreasing cardiac output and arterial pressure.
c. the drug dopamine
Dopamine’s direct inotropic effect on the myocardium links to an increased cardiac output due to increased force of contraction or contractility.
d. Running a sprint
Heart rate increases when running a sprint or exercising in general, which leads to an increased cardiac output.
e. Hyperthyroidism with increased secretion of thyroid hormones
One sign of hyperthyroidism is an elevated resting heart rate, known as tachycardia. This resting heart rate is due to the thyroid hormones which enhance cardiac contractility and increase heart rate, therefore increasing cardiac output.
f. Massive myocardial infarction (cardiac tissue death)
Myocardial infarction can lead to decreased cardiac output due to increased preload and afterload in the heart.
g. Hypothermia
Hypothermia slows down metabolism which leads to the reduction of the oxygen needs of tissues. With this, contractility is decreased, cardiac output is increased, and the heart and brain are able to withstand short periods of interrupted or reduced blood flow.
h. Emotional distress
During emotional distress, heart rate increases due to the presence of epinephrine and norepinephrine, which leads to increased contractility and cardiac output.
References:
Cunha, J. P. (2022, July 18). Dopamine (Dopamine Hydrochloride): Uses, Dosage, Side Effects, Interactions, Warning. RxList. https://www.rxlist.com/dopamine-drug.htm
Klabunde, R. E. (2011). CV Pharmacology | The Pharmacologic Treatment of Myocardial Infarction. Cvpharmacology.com. https://www.cvpharmacology.com/clinical%20topics/myocardial%20infarction
Klabunde, R. E. (2012). CV Physiology |Hypertension - Introduction. Cvphysiology.com. https://www.cvphysiology.com/Blood%20Pressure/BP001
Klabunde, R. E. (2021, February 2). CV Physiology | Hemorrhagic Shock. Www.cvphysiology.com. https://www.cvphysiology.com/Blood%20Pressure/BP031#:~:text=The%20reduction%20in%20blood%20volume
Nall, R. (2022, August 2). Preload and Afterload in Heart Failure. Healthline. https://www.healthline.com/health/heart-failure/preload-and-afterload-in-heart-failure#treatment
Tortora, G. & Derrickson, B.(2012). Principles of anatomy and physiology. John Wiley & Sons