Purpose and BackgroundBlood Pressure measurementSources or error in blood pressure measurementFaulty TechniqueArterial and Venous Pressure MeasurementsArterial blood pressure measurementMeasuring venous blood pressureDemonstration of valves in veinsResponse to exercise: Design your own experimentLab ReportBlood Pressure and Exercise LabRob MacLeod, Brian Birchler, and Brett BurtonMarch 26, 20121 Purpose and BackgroundPurpose:To learn about external means to measure blood pressure, observe features of venous circulation,and observe the effects of exercise on blood pressure, heart rate, and electrocardiogram (ECG).This lab has the added feature of leaving one piece in need of experimental design by you! Seebelow for more details.BackgroundThis lab will build on the class material we have covered on blood flow and pressure and cardiaccontraction. It will also introduce some ideas we still have to cover on control of the cardiovascularsystem in response to exercise and the electrocardiogram.To prepare, please review the notes and text on the vascular system and blood pressure andalso read the section in your text (or any other good physiology book) on exercise.1.1 Blood Pressure measurementArterial blood pressure is measured by a sphygmomanometer. See the web site www.ktl.fi/publications/ehrm/product2/part iii3.htmfor a nice description of this measurement.The manometer consists of:1. A rubber bag surrounded by a cuff.2. A manometer (usually a mechanical gauge, sometimes electronic, rarely a mercury column).3. An inflating bulb to elevate the pressure.4. A deflating valve.and is team with a stethoscope to better hear the characteristic sounds that will guide you.Figure 1 below shows a schematic diagram from the class notes about the concept behind thismeasurement. For the palpatory measurement technique, after the cuff is placed snugly over thearm, the radial artery is palpated while the pressure is increased until the pulse can no longer befelt, then the pressure is raised an additional 30 mm Hg. As the pressure is slowly released, theartery is palpated until the pulse is felt again. This palpatory method will detect systolic pressureonly.1Figure 1: Schematic diagram of arterial blood pressure measurement by Korotkow sounds.The auscultatory method, in contrast, requires the stethoscope and detects diastolic as well assystolic pressure. The sounds heard when a stethoscope bell (or diaphragm) is applied to the regionbelow the cuff were described by Korotkow in 1905 and are called Korotkow’s sounds. The arteryis compressed as for the palpatory technique and as the pressure is released the first sound heardis a sharp thud which becomes first softer and then louder again. It suddenly becomes muffled andlater disappears. Most people register the first sound as Systolic, the muffled sound as the “firstdiastolic” and the pressure at which the sound disappears as the “second diastolic”. It requirespractice to distinguish the first diastolic, so, for our laboratory, we will record only the first sound(systolic) and the disappearance of the sound (second diastolic). These will not be difficult to elicit,and a little practice will enable you to get almost the same reading on a fellow student three timesin succession.1.2 Sources or error in blood pressure measurement1.2.1 Faulty Technique1. Improper positioning of the extremity. Whether the subject is sitting, standing, or supine,the position of the artery in which the blood pressure is measured must be at the level of the2heart. However, it is not necessary that the sphygmomanometer be at the level of the heart.2. Improper deflation of the compression cuff. The pressure in the cuff should be lowered atabout 2 mm Hg per heartbeat. At rates slower than this venous congestion will develop andthe diastolic reading will be erroneously high. If the cuff is deflated too quickly the manometermay fall 5 or 10 mm Hg between successive Korotkow sounds, resulting in erroneously lowreadings.3. Recording the first blood pressure measurement. Spasm of the artery upon initial compressionand the anxiety and apprehension of the subject can cause the first blood pressure readingto be erroneously high. After the cuff has been applied, wait a few minutes before inflatingthe cuff to record the blood pressure. Make several measurements. Generally the third valuerecorded is the most basal.4. Improper application of the cuff. If the rubber bladder bulges beyond its covering, the pressurewill have to be excessively high to compress the arm effectively. If the cuff is applied tooloosely, central ballooning of the rubber bladder will reduce the effective width, thus creatinga narrow cuff. Both bulging and ballooning result in excessively high readings.2 Arterial and Venous Pressure MeasurementsThe lab is divided into 4 sections, the first 3 of which you should do in parallel in the usual pairedgroups. For the final section, please form groups of 4–5 as this exercise needs this many people tocarry out.2.1 Arterial blood pressure measurementHave the subject relax with both arms resting comfortably at his sides. Wrap the sphygmomanome-ter cuff about the arm so that it is at heart level. The air bag inside the cuff should overlay theanterior portion of the arm about an inch above the antecubital fossa (the interior angle of elbow).The cuff should be wrapped snugly about the arm.Palpatory method: Palpate the radial pulse with the index and middle fingers near the baseof the thumb on the anterior surface of the wrist. While palpating the radial pulse, rapidly inflatethe cuff until there is no detectable pulse and then add another 30 mm Hg, to a value in the rangeof 160–180 mm Hg. Set the valve on the rubber bulb so that the pressure leaks out slowly (about5 mm per second). Continue palpating the radial pulse, and watch the manometer while air leaksout of the cuff. Note the pressure at which the pulse reappears.Record the pressure: mm Hg.This is Systolic pressure as detected by palpation. Allow the pressure to continue to decrease,noticing the changes in the strength of the radial pulse.Auscultatory method: Elevate the pressure in the cuff 20 mm Hg higher than the pressureat which the radial pulse reappeared in the palpatory measurement. Apply the stethoscope belllightly against the skin in the antecubital fossa over the brachial artery. There will be no soundsheard if the cuff pressure is higher than the systolic blood pressure because no blood will flowthrough