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.
Blood pressure
- High blood pressure can cause artery damage by making them less elastic, reducing the flow of blood and oxygen to your heart. With this, it makes it difficult for the heart to function, therefore, it increases your preload, contractility, after load, and heart rate.
Massive bleeding
- Hemorrhage or also known as massive bleeding is a cardiovascular system stress that results in lower cardiac loading but also decreased blood pressure and hence decreased perfusion pressure for tissue blood flow. To compensate, the body raises one's heart rate and contractility, resulting in a decrease in cardiac output.
Drug: Dopamine
- Dopamine is utilized in the medical settings to promote diuresis and support cardiac output and blood pressure. It has both chronotropic and inotropic effects on the myocardium, increasing heart rate and cardiac contractility.
Running a sprint
- Because your muscles require more oxygen when you exercise, your body may require three or four times your typical cardiac output during activity. During exercise, your heart usually beats quicker, allowing more blood to flow to your body.
Hyperthryoidism with increased secretion of thyroid hormones
- Hypothyroidism causes major circulatory changes such as a decrease in cardiac output and contractility (a decrease in heart rate, and an increase in peripheral vascular resistance). With increased thyroxine secretion, there will be an increase in cardiac output due to irregular heart rate, also known as tachycardia.
Massive myocardial infarction (cardiac tissue death)
- A heart attack, also known as a myocardial infarction (MI), occurs when one or more parts of the heart muscle do not receive enough oxygen. Preload and contractility will decrease because the heart will no longer be able to stretch and contract normally, while afterload will increase due to increased blood pressure.
Hypothermia
- Hypothermia is caused by continuous exposure to very cold temperatures, which causes your body temperature to drop and your heart, brain system, and other organs start to malfunction. This reduces heart rate, which the heart attempts to compensate for by increasing contractility and stroke volume.
Emotional distress
- When we are exposed to stressful situations or environments, our bodies begin to secrete cortisols (our body's primary stress hormone) and adrenaline, which causes the heart to beat faster and the blood vessels to constrict to help push blood to the center of the body. This causes an increase in heart rate, an increase in blood pressure, and the release of stress hormones.
References:
A, D. (n.d.). [hyperthermia and hypothermia. effects on the cardiovascular system]. Der Anaesthesist. Retrieved November 15, 2022, from https://pubmed.ncbi.nlm.nih.gov/17554514/#:~:text=During%20a%20reduction%20of%20the,C%20due%20to%20increasing%20bradycardia.
Cardiac output. MyHealth.Alberta.ca Government of Alberta Personal Health Portal. (n.d.). Retrieved November 15, 2022, from https://myhealth.alberta.ca/Health/Pages/conditions.aspx?hwid=tx4080abc
Centers for Disease Control and Prevention. (2021, May 18). High blood pressure symptoms and causes. Centers for Disease Control and Prevention. Retrieved November 15, 2022, from https://www.cdc.gov/bloodpressure/about.htm#:~:text=High%20blood%20pressure%20can%20damage%20your%20arteries%20by%20making%20them,Chest%20pain%2C%20also%20called%20angina.
Heart attack. Heart Attack - Health Encyclopedia - University of Rochester Medical Center. (n.d.). Retrieved November 15, 2022, from https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=85&contentid=P00702
Janet M. Torpy, M. D. (2007, July 18). Acute emotional stress and the heart. JAMA. Retrieved November 15, 2022, from https://jamanetwork.com/journals/jama/fullarticle/208031#:~:text=Experiencing%20emotional%20or%20physical,heart%2C%20which%20can%20be%20dangerous.
McDonough, K. H., Giaimo, M., Quinn, M., & Miller, H. (1999). Intrinsic myocardial function in hemorrhagic shock. Shock, 11(3), 205–210. https://doi.org/10.1097/00024382-199903000-00009
UpToDate. (n.d.). Retrieved November 15, 2022, from https://www.uptodate.com/contents/cardiovascular-effects-of-hypothyroidism#!