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
Hypertension causes bkood vessels to constrict and make it difficult for the blood to freely flow throughout the body. This will lead for the heart to produce more work, increasing its afterload.
B. Massive bleeding
Excessive bleeding leads to the reduction of central venous pressure and cardiac filling. Thererefore, will be a decrease in preload and afterload due to the sarcomere decreasing in length.
C. The drug Dopamine
Dopamine gives rise to a beneficial chronotropic and inotropic effects on the myocardium, thus, there will be an increase on the heart rate and its contractility, also causing the cardiac output to rise.
D. Running a sprint
When running a sprint, our body uses more oxygen therefore there is a need for the heart to work harder, increasing the heart rate. Thus, when there is an increase in the venous return, the end-diastolic pressure and the ventricles' volume also rises, causing the increase in the preload.
E. Hyperthyroidism with increased secretion of thyroid hormones
Triidothyronine or the T3 plays a role of increasing the erythropoietin synthesis, leading to an increase in the mass of the red blood cell. These chemical changes increase the cardiac output due to the increase in blood volume and preload.
F. Massive myocardial infarction (cardiac tissue death)
Cardiac tissue death leads to inadequate supply of blood to a specific part of the body (Ischemia) which leads to muscle hypoxia, which is means there is an insufficient oxygen supplied in the tissues. These changes decreases the myocardial contractility, which decreases the cardiac output.
G. Hypothermia
Hypothermia, or the decrease of the body's temperature, causes vasoconstriction which leads to an increase bradycardia or decrease in heart rate. With these changes, oxygen will be more difficult to reach tissues and its contractility will be reduced.
H. Emotional distress
When faced with stress, the endocrine glands release adrenaline or epinephrine, and cortisol, thus increasing your heart rate and narrowing your blood vessels. This, then, increases the cardiac output.
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
Klabunde, R. E. (2015, July 7). Cardiac preload. Image for Cardiovascular Physiology Concepts, Richard E Klabunde PhD. Retrieved November 11, 2022, from https://cvphysiology.com/Cardiac%20Function/CF007
Dopamine: Uses, Interactions, Mechanism of Action | DrugBank Online. (n.d.). DrugBank. https://go.drugbank.com/drugs/DB00988
Klabunde, R. E. (n.d.). Cardiac preload. Image for Cardiovascular Physiology Concepts, Richard E Klabunde PhD. Retrieved November 11, 2022, from https://cvphysiology.com/Cardiac%20Function/CF007
Klein, I., Danzi, S., & Klein, C. to D. I. (2007, October 9). Thyroid disease and the heart. Circulation. Retrieved November 11, 2022, from https://www.ahajournals.org/doi/10.1161/circulationaha.106.678326
Khalid, L., & Dhakam, S. H. (2008, February). A review of cardiogenic shock in acute myocardial infarction. Current cardiology reviews. Retrieved November 11, 2022, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2774583/