Laboratory 16b Blood Pressure

Transcription

1 Laboratory 16b Blood Pressure Objectives: Define pulse, systolic pressure, diastolic pressure, and mean arterial pressure. Determine a subject s pulse, systolic and diastolic blood pressure, and mean arterial pressure. 1. Blood Pressure: The term blood pressure most commonly refers more specifically to arterial blood pressure, or the pressure exerted on the artery walls by the blood. During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure, corresponding to ventricular systole and diastole, respectively. Normal blood pressure is defined by the American Heart Association as a systolic reading of between mmhg. and a diastolic reading of between mmhg. The pulse pressure is defined as the difference between the systolic and diastolic pressures, or the change in pressure that occurs with each heartbeat. Ppulse = Psystolic Pdiastolic The pulse pressure tends to increase with age as the arteries become less compliant. This increase of pulse pressure is a risk factor for heart disease. The mean arterial pressure (MAP) is the average pressure in the arteries over one cardiac cycle. This number reflects the perfusion pressure of the organs and may be the major determinant of vascular damage due to hypertension. It is calculated as: MAP = Pdiastolic + 1/3 Ppulse. Determinants of blood pressure include cardiac output, blood volume, and degree of smooth muscle contraction in the arterioles. Blood pressure is typically measured by the auscultatory method, in the brachial artery of the upper arm. This method uses a sphygmomanometer composed of an inflatable cuff around the upper and a gauge that measures pressure. A stethoscope is used to listen to the different sounds that occur. Units of blood pressure measurement are in mm of HG (millimeters of mercury) and is most accurately measured with a mercury mamometer. Blood pressure is measured by placing the cuff snuggly around the upper arm at roughly the same vertical height as the heart. The cuff is then inflated by repeatedly squeezing a rubber bulb until the artery is completely occluded. A stethescope is placed over the brachial artery at the elbow. Normally, the pulse sound can be felt there. When the blood pressure cuff is Figure 3. A sphygmomanometer in use. 63

2 inflated, the pulse disappears. To determine blood pressure, the examiner listens to the brachial artery with the stethoscope while slowly decreasing the pressure in the cuff. A sound appears once the pressure is low enough to start letting blood flow sporadically through. This sound is called a Korotkoff sound. The pressure at which it is first heard is the systolic blood pressure. This sound will disappear when the pressure in the cuff is less than the diastolic pressure. Activity 1. Place the blood pressure cuff snugly on your patients arm. 2. Have your stethoscope ready around your neck, earpieces pointed up. 3. Pump up the pressure in the cuff, above 200 mm Hg 4. Put the diaphragm of the stethoscope over the brachial artery, which is just in the fold of the arm. 5. Slowly let the pressure out of the cuff, while listening for a heartbeat with your stethoscope. 6. When you first hear the heartbeat, this is the systolic pressure. Keep listening while you let the pressure out. 7. When you stop hearing the heartbeat, this is the diastolic pressure. 8. Record the blood pressure here:. 2. Blood Pressure and Body Position Experiment: Recall the basics of the scientific method, hypothesis development, and the differences between independent and dependent variables from your Biol160 class. Refresh you knowledge from the link here: mdgvtnptscaex- qb778len6kvfwhnszpyxpgvpn12e. Blood pressure is one of the more common measurements taken in a doctor s office. Several factors alter blood pressure over the day including the position of the body. Since blood pressure may be taken with the body in different positions in the medical profession, it is important to understand how the position of the body alters blood pressure. This experiment will determine blood pressure in three body positions: sitting, laying, and standing. The blood pressure standing will be taken immediately upon standing and after standing for at least three minutes. Activity: Write the hypothesis for the experiment on the lab report sheet. Identify both the dependent and Independent variables and record these on the lab report sheet. Identify at least one controlled variable and record this on the lab report sheet. For each lab pair, one person will be the subject and one the data collector. The subject should begin by sitting quietly for at least three minutes. At the end of three minutes, record the subject s blood pressure on the lab report sheet. The subject should then lie down on the lab bench for three minutes. At the end of three minutes, with the subject still lying down, record the subject s blood pressure on the lab report sheet. 64

3 The subject should then stand. Record the subject s blood pressure IMMEDIATELY upon standing. Record the subject s blood pressure after they have been standing for 3 minutes. Write your data on the board to share with the rest of the class. 65

4 Attributions: Figure 3. Pia von Lützau. (2009) [Blood pressure measurement]. Wikimedia Commons. Retrieved Dec 6, 2012 from 66

5 Lab 16b Blood Pressure Name Section 1. Complete this table from the blood pressure taken in the Activity in Section 3. Systolic Blood Pressure Diastolic Blood Pressure Pulse Pressure Mean Arterial Pressure 2. What are the sounds of Korotkoff? Explain why they are only heard between the systolic and diastolic blood pressures. 3. Form a hypothesis for the experiment in Section 2: 4. Identify the dependent variable from the experiment in Section 2: 5. Identify the independent variable from the experiment in Section 2: 6. Identify at least one controlled variable: 67

6 7. Record your blood pressure data in this table: Condition Blood Pressure Seated Supine Standing Immediate Standing after 3 minutes 8. Record the data for the entire class section here: Seated Supine Pair 1 Standing- Immediate Standing- 3 minutes Pair 2 Pair 3 Pair 4 Pair 5 Pair 6 Pair 7 Pair 8 Pair 9 Pair 10 Pair 11 Pair 12 68

7 9. Using the systolic blood pressure, calculate the change from sitting for each condition. Standing- Standing- 3 Seated Supine Immediate minutes Pair 1 0 Pair 2 0 Pair 3 0 Pair 4 0 Pair 5 0 Pair 6 0 Pair 7 0 Pair 8 0 Pair 9 0 Pair 10 0 Pair 11 0 Pair Based on the table in question 11, was your hypothesis supported? YES NO 11. Based on the data, in which condition is the systolic blood pressure lowest? 69

8 12. Did every subject s blood pressure respond the same way to the different positions? If not, discuss this variability in context of how it might relate to a clinical trial of a new antihypertensive medication. 13. Discuss the observed changes in blood pressure in terms of homeostasis. How do the observed changes relate to homeostatic regulation? What exactly is being regulated? 70