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
Hypertension or high blood pressure involves the constriction of blood vessels, which result in chronic elevations in the afterload, due to a high systemic vascular resistance and aortic pressure increase. With this, an increased afterload leads to a decreased stroke volume, which then affects the cardiac output (LaCombe et al., 2022).
b. Massive bleeding
Significant blood loss due to massive bleeding or hemorrhage results into a decrease in venous return, leading into a diminished stroke volume, and further resulting into an inadequate cardiac output (Haas et al., 2020). Moreover, as there is a decrease in stroke volume, it can be observed that there is a decreased preload, contractility, and afterload of the heart.
c. The drug dopamine
Dopamine is often used as a peripheral vasostimulant to treat low blood pressure and heart rate, and cardiac arrest. Infusion of the drug stimulates and increases myocardial contractility and electrical conductivity (Sonne et al., 2022), resulting in increased stroke volume and cardiac output.
d. Running a sprint
Running a sprint is an exercise, which requires the heart to pump blood quickly in order to supply oxygen to the body. The physical activity contributes to an increased venous return, end-diastolic volume and preload, and force of contraction; hence, there is an increment in stroke volume, heart rate, and cardiac output (Tortora & Derrickson, 2020).
e. Hyperthyroidism with increased secretion of thyroid hormones
With the increased secretion of thyroid hormones in hyperthyroidism, there is an increased preload and contractility, and decreased systemic vascular resistance. This increase leads to the increase of both the stroke volume and heart rate, further leading to the increment in cardiac output (Osuna et al., 2017).
f. Massive myocardial infarction (cardiac tissue death)
Massive myocardial infarction leads to an inadequate cardiac output, due to impaired contractility of heart muscle fibers, and increased preload or afterload, as well as the decrease or stop in blood flow in the heart (Tortora & Derrickson, 2020).
g. Hypothermia
In the case of hypothermia, the metabolism is slowed down, which also slows down the needs for oxygen, to allow the heart and brain to withstand uninterrupted and reduced blood flow, leading to a slower heart rate (Tortora & Derrickson, 2020). Decrease in heart rate was also revealed by the study of Chen et al. (2019), as well as decrease in mean arterial pressure, and increase in stroke volume and contractility.
h. Emotional distress
The response of the body to emotional distress includes an elevation in blood pressure and decrease in peripheral resistance. Furthermore, there is an increased sympathetic stimulation, resulting in greater contractility and heart rate, further resulting in increased stroke volume, as well as cardiac output (Jiang, 2008).