Milwaukee School of Engineering Case Study: Factors that Affect Blood Pressure Instructor Version

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1 Case Study: Factors that Affect Blood Pressure Instructor Version Goal This activity (case study and its associated questions) is designed to be a student-centered learning activity relating to the factors that can affect blood pressure. The associated handout is designed as a reference for students to refer to as they study the systems that regulate blood pressure. Background This activity is ideally designed for those students who have already covered the following topics in their Physiology or Anatomy and Physiology course(s): a. Sympathetic nervous system b. Medical physics (relationships between pressure, flow and resistance) c. Smooth muscle d. Cardiac muscle e. Membrane potentials and action potentials This activity was designed assuming that the students have not covered the topics of endocrinology, renal physiology, and/or the control of blood pressure. It is also assumed that students know what the word diuretic means. If they do not, they will need to be given this information. The function of ACE inhibitors and beta blockers may also need to be explained to the students, depending on usage of this activity. For example, an instructor may want to talk about the effects of beta blockers both on the heart and on the kidney, depending on the level of detail the instructor is trying to present. This activity may also be appropriate for a summary of integrated function toward the end of a physiology course. Questions can/should be adjusted to fit the specific need of the instructor and situation. Instructions This activity can be used at any point in the class period, preferably before the topics of blood pressure regulation are covered. It is suggested that students work in teams of 2-4. The activity can either be taken on a question by question basis, or students can be asked to complete the entire activity prior to discussion. It is expected that the activity and related discussion will take approximately minutes, depending on the amount of time the instructor allows the students to develop answers to the questions. It is suggested that after the students have been given time to answer the questions, but before the discussion, the attached handout be given to the students. This should aid them in understanding how the factors that they deduced relate to one another for the control of blood pressure.

2 Case Study and Answers (Answers to questions are in italics) Harry Hypertensive is a 68 year old male who has been treated for high blood pressure for the last 8 years. Besides being encouraged to implement lifestyle modifications (such as decreased salt intake and increased exercise), Harry has also been treated with a variety of drugs. The specific drugs have sometimes varied over the years, but they have all been from the following general categories: a. Diuretics b. Beta-blockers (Beta 1 receptor antagonist) c. Calcium channel blocking drugs d. Angiotensin Converting Enzyme (ACE) inhibitors Based on this information, and what you already know from this class, answer the following questions: 1. What is the importance of blood pressure? Why is having high blood pressure of medical concern? Blood pressure, or arterial pressure, is the pressure in the large arteries. Pressure is often measured by looking at how high the pressure will raise a column of liquid. For blood pressure, the standard units are millimeters of mercury, abbreviated as mmhg and it is pressure difference (arterial pressure central venous pressure) across the circulation that is responsible for moving blood through the system. Therefore an appropriate amount of arterial pressure is necessary to move blood at an appropriate rate through the circulation. High blood pressure (hypertension) is a risk factor for atherosclerosis and causes damage to small blood vessels, such as those in the retina and kidneys. It can also lead to hypertrophy of the left ventricle, among other problems. In short, the circulatory system is not designed to handle pressure higher than normal. 2. What is (are) the effect(s) of diuretics on the body? Based on your answer, predict a factor that can affect blood pressure. Diuretics increase water (or saline) loss from the body, by forcing the kidneys to make more urine. Blood is part of the body fluid compartment, so a decrease in body fluid can cause a drop in blood pressure because it causes a decrease in venous return (the amount of blood returning to the heart). 3. Where are beta 1 receptors found in high concentration? What hormone(s) typically binds beta 1 receptors? What is (are) the effect(s) that these hormones induce when they bind to beta 1 receptors? Based on your answer, predict a factor that can affect blood pressure.

3 Beta 1 receptors are found in high concentrations in the heart, where they are typically bound by norepinephrine or epinephrine released from the sympathetic nervous system. When beta 1 receptors are activated, the heart increases in both rate and inotropic state (contractility). Therefore rate and inotropic state can affect blood pressure. 4. Name 2 cell types where the plasma membrane calcium channels contribute either to the action potential, or the resting membrane potential of the cell? a. Cardiac muscle cells b. Smooth muscle cells When calcium enters the cell type in (a.) what do these cells do? Contract When calcium enters the cell types in (b.) what do these cells do? Contract What would be the effect of preventing some calcium from entering both of these cell types? Cardiac muscle cells would not contract as strongly (decreased inotropic state) and smooth muscle cells would relax (decreased vascular resistance). Based on your answers, predict 2 factors that can affect blood pressure. Inotropic state and vascular resistance 5. Angiotensin Converting Enzyme converts the molecule Angioensin I into the active hormone Angiotensin II. The formation of Angiotensin II typically occurs when blood pressure is low. Based on your previous answers, predict the factors that Angiotensin II might have on the body as a way of increasing blood pressure. Although all of the factors that student might list would include, heart rate, vascular volume, vascular resistance or inotropic state, it should be explained to students that the effects of Angiotensin II s are on vascular resistance and vascular volume. Summary There are several factors that affect blood pressure, and they need to work in conjunction to one another for appropriate regulation to take place. For example, an increase in inotropic state will need to be coupled with an increase in venous return in order to create large and sustained increases in arterial pressure. Using the attached diagram students should be able to see how the various factors are related to one another.

4 Case Study: Factors that Affect Blood Pressure Student Version Harry Hypertensive is a 68 year old male who has been treated for high blood pressure for the last 8 years. Besides being encouraged to implement lifestyle modifications (such as decreased salt intake and increased exercise), Harry has also been treated with a variety of drugs. The specific drugs have sometimes varied over the years, but they have all been from the following general categories: a. Diuretics b. Beta-blockers (Beta 1 receptor antagonist) c. Calcium channel blocking drugs d. Angiotensin Converting Enzyme (ACE) inhibitors Based on this information, and what you already know from this class, answer the following questions: 1. What is the importance of blood pressure? Why is having high blood pressure of medical concern? 2. What is (are) the effect(s) of diuretics on the body? Based on your answer, predict a factor that can affect blood pressure. 3. Where are beta 1 receptors found in high concentration? What hormone(s) typically binds beta 1 receptors? What is (are) the effect(s) that these hormones induce when they bind to beta 1 receptors? Based on your answer, predict a factor that can affect blood pressure.

5 4. Name 2 cell types where the plasma membrane calcium channels contribute either to the action potential, or the resting membrane potential of the cell? a. b. When calcium enters the cell type in (a.) what do these cells do? When calcium enters the cell types in (b.) what do these cells do? What would be the effect of preventing calcium from entering both of these cell types? Based on your answers, predict 2 factors that can affect blood pressure. 5. Angiotensin Converting Enzyme converts the molecule Angioensin I into the active hormone Angiotensin II. The formation of Angiotensin II typically occurs when blood pressure is low. Based on your previous answers, predict the factors that Angiotensin II might have on the body as a way of increasing blood pressure.

6 Factors Affecting Arterial Blood Pressure The importance of Blood Pressure: Arterial pressure is necessary to push blood through the circulation so that oxygen and nutrients can be delivered to the tissues. Therefore, if blood pressure is too low, the organs will not be adequately perfused and will show signs of hypoxia (fatigue, confusion, cyanosis, etc.). If blood pressure is too high, it can cause damage to blood vessels (leading to strokes, blindness, kidney failure, heart failure, etc.). Therefore, arterial pressure (commonly referred to as blood pressure ) must be carefully regulated. This occurs via several mechanisms, but all mechanisms ultimately affect the factors that can affect blood pressure, which are TPR, HR, blood volume, and inotropic state. The factors that control arterial pressure are cardiac output and vascular resistance. This is often written in equation form, where MAP = mean arterial pressure, which is the average pressure over time in the aorta, and is usually about 100 mmhg, CO = cardiac output, which is normally about 5 liters/minute and TPR = total peripheral p resistance, which is determined by the diameters of the arterioles of the body. If the body is going to affect MAP it must do so by affecting either CO or TPR. MAP = CO x TPR Heart Rate (normal is 72 bpm) Affected by the sympathetic nervous system. Epinephrine and norepi will bind to β 1 receptors to increase HR. Stimulated by the baroreceptor reflex. Preload: Amount of blood in the heart at the end of diastole (end of filling). Indicated by end-diastolic volume. Preload is determined by venous return (amount of blood flowing into the heart) which is usually determined by the amount of blood in the circulation and the tone of venous vessels. CO = HR x SV Total Peripheral Resistance Affected by anything that affects the diameter of the arterioles. This includes a variety of neurotransmitters and hormones as well as molecules released during allergies, infections, etc. Stroke Volume (normal is 65 ml): Amount of blood ejected from the heart in each beat. Can be affected by Neurotransmitters: Epinephrine p and norepinephrine p are released as molecules of the sympathetic nervous system. They cause a constriction of arterioles via α 1 receptors. These hormones are normally released when blood pressure is low (baroreceptor reflex). preload and inotropic state (contractility) of the heart. Both of these can be adjusted through different mechanisms. Inotropic State: The strength of the contraction of the heart. Leads to an increase in SV even at the same preload. Affected by epinephrine and norepinephrine binding to β 1 receptors on the heart. Hormones: Hormones such as angiotensin II and anti-diuretic hormone can cause constriction of blood vessels when they are released/formed at high levels. This normally occurs when blood pressure is very low. Other molecules: 1. Histamine: Released in large amounts in severe allergic reactions. Vasodilates blood vessels after binding to H1 receptor. 2. Endotoxin: Released from Gram negative cell membranes. Potent vasodilator that can lead to a large decrease in blood pressure (septic shock).