Chapter 4 Lab
Measuring Blood Pressure
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While it is hard to look inside at the components of the body without using expensive techniques (such as MRI or ultrasound imagery sonography), it is possible to witness a basic anatomical function in a different way—through sound.
Blood pressure (BP) is commonly defined as a measurement of the force of the blood acting against the vessel walls during and between heartbeats.1 The pressure exerted against the vessels during a heartbeat (systole) is called the systolic blood pressure, while the pressure recorded between heartbeats (diastole) is called the diastolic blood pressure. Sounds are emitted as a result of the pressure exerted against the vessel walls, and these are called Korotkoff sounds. The detection and disappearance of Korotkoff sounds when external pressure is applied provides the basis of traditional BP assessments.
The BP measurement is a combination of both the systolic and diastolic pressure and is usually written as “systolic / diastolic” (e.g., 120 / 80). BP is usually measured in units of millimeters of mercury (mm Hg). A common, normal BP measurement would be written as 120 / 80 mmHg. Using a sphygmomanometer is the most common and clinically acceptable technique to measure BP.2 It involves an inflatable cuff and a meter to measure pressure.
The BP measurement technique described in this lab focuses on resting BP. It also focuses on using the mercury sphygmomanometry, technique with which you are probably familiar that uses a stethoscope and a manual blood pressure cuff.
- Mercury sphygmomanometer
- Tape measure
- To prepare for a resting BP assessment, the subject should be relaxed and comfortably seated upright with legs uncrossed and back and arms supported. All clothing that covers the location of the cuff should be removed. The room temperature should be comfortable (not hot or cold), the environment should be free from distracting background noises, the subject’s bladder should be relieved prior to the test, and no talking should be allowed by the subject or the tester during the test. Resting BP should always be taken prior to exercise; caffeine, alcohol, and nicotine should be avoided for at least 30 minutes prior to any BP measurement.
- Since various cuff sizes are available, the appropriate cuff size should be determined by measuring the arm circumference with a tape measure at 50% of the distance from the shoulder to the elbow. Once the arm circumference has been recorded, determine the appropriate BP cuff size using the table in this lab.
- Place the cuff around the left or right arm so that the cuff is level with the heart. To do this, it is important to position the subject so that the arm is resting in the same horizontal plane as the heart. BP measurements taken with the arm hanging below or raised above the heart level will be inaccurate.
- In addition, most cuffs have an identification line that is to be placed over the brachial artery. This feature allows the air bladder within the cuff to be positioned directly over the brachial artery. This is important for the occlusion of the artery during cuff inflation. Position the cuff so that the bottom edge of the cuff is approximately one inch (2.5 cm) above the antecubital space (elbow crease).
- Once the subject is seated and relaxed, allow him or her to rest for at least five minutes prior to the first BP measurement.
- With the subject’s palm facing up, place the stethoscope head in the antecubital space firmly but not hard enough to indent the skin. It is recommended that the tester use his or her dominant hand to control the air bulb and the inflation/deflation of the cuff, while the nondominant hand should be used to hold the stethoscope.
- Make sure that the mercury column (or aneroid pressure gauge) is easily readable by the tester. For aneroid pressure gauges, it is recommended that the gauge be placed in the tester’s lap or clip it to the cuff to enable a quick and accurate pressure reading.
- It is important to avoid contacting the stethoscope head with the air tubes connected to the mercury sphygmomanometer. If the air tubes contact the stethoscope head, the sound may be mistaken for a Korotkoff sound and may result in erroneous BP measurements. Therefore, position the air tubes away from the stethoscope head as much as possible.
- Once the cuff, stethoscope, and sphygmomanometer have been properly placed, make sure the air release valve is closed on the air bulb and then quickly inflate the cuff either to 160 mmHg or to 20 mmHg above the anticipated systolic BP.
- Upon reaching the maximum inflation pressure, carefully turn the air release valve counterclockwise to release the cuff pressure. The rate of pressure release should be approximately 2 to 3 mmHg per second.
- While the cuff is deflating, listen carefully for the Korotkoff sounds. Record the systolic BP as an even number to the nearest 2 mmHg where the first Korotkoff sound is heard. Record the diastolic BP as an even number to the nearest 2 mmHg where the last Korotkoff sound is heard. Usually, Korotkoff sounds are described as sharp tapping noises that are similar to tapping the stethoscope head (bell) gently with a finger. After the Korotkoff sounds have disappeared, observe the mercury column for another 10 to 20 mmHg of deflation to confirm the absence of sounds.
- When it is confirmed that no more Korotkoff sounds are audible, rapidly deflate and remove the cuff.
- After a minimum of two minutes of rest, measure BP again using the same technique described above. If the two consecutive measurements of either systolic BP or diastolic BP differ by more than 5 mmHg, take a third BP measurement. After either two or three consecutive BP measurements, calculate the average systolic and diastolic BP. The average systolic and diastolic BP values should be used as the final scores.
Table Cuff size based on arm circumference2
- Adams, G. M. Exercise Physiology: Laboratory Manual, 4th edition. Boston: Mc-Graw Hill, 2002.
- Pickering, T. G., Hall, J. E., Appel, L. J., Falkner, B. E., Graves, J., Hill, M. N., et al. Recommendations for blood pressure measurement in humans and experimental animals. Part 1: Blood pressure measurement in humans: A statement for professionals from the subcommittee of professional and public education of the American Heart Association Council on high blood pressure research. Circulation 111: 697–716, 2005.
- Cramer, J. T., and Coburn, J. W. Fitness testing protocols and norms. In NSCA’s Essentials of Personal Training, eds. R. W. Earle and T. R. Baechle. Champaign, IL: Human Kinetics, 2005, pp. 218–263.
Lab adapted from Housh, T., Cramer, J., Weir, J., Beck, T., & Johnson, G. (2009). Physical Fitness Laboratories on a Budget. (pp. 14–18). Scottsdale, AZ: Holcomb Hathaway, Publishers.