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HUMAN KINETICS

Excerpts

Accurate blood pressure measurement critical to exercise prescription

This is an excerpt from Laboratory Manual for Exercise Physiology w/Web Resource by G. Gregory Haff and Charles Dumke.


Receive comprehensive coverage of basic testing procedures in Laboratory Manual for Exercise Physiology.

Blood Pressure Responses to Exercise

In the transition from rest to exercise, systolic blood pressure initially rises rapidly, then levels off once steady state is attained (1, 3). Typical systolic pressures during submaximal exercise range from 140 to 160 mmHg. Graded dynamic exercise normally produces a progressive increase in systolic pressure, and values can reach as high as 250 mmHg during maximal exercise.

Figure 4.1 shows systolic and diastolic blood pressure responses to exercise of increasing intensity. The rise in systolic pressure reflects the increased force of contraction of the ventricles in order to increase cardiac output from sympathetic stimulation. Diastolic pressure may show either no change or a very slight increase or decrease during graded exercise due to a redistribution of blood flow to the capillary beds in the large exercising muscle groups (1, 3).

Following heavy exercise, systolic blood pressure drops rapidly. This rapid drop (hypotension) results from pooling of blood in vessels that were dilated during the heavy exercise. The pooling reduces venous return and thus decreases cardiac output. If the reduction in CO is severe enough, the subject or athlete may experience light-headedness due to insufficient blood flow to the brain. For this reason, a cool-down period is recommended following intense exercise in order to maintain HR and SV and allow the cardiovascular system to readjust gradually.

BP responds differently during isometric exercise (or slow concentric actions). Sustained muscle actions that occlude blood flow can increase resistance tremendously and can result in extremely high systolic and diastolic BP. Thus, even though muscle is contracting and in need of blood flow, continuous muscular contraction surrounding the blood vessels can significantly increase resistance and decrease flow. In an effort to overcome this occlusion, the heart increases pressure.

Accurate Blood Pressure Checks

Measuring blood pressure is a basic skill in exercise physiology since it provides a good indication of the work of the heart; as a result, this skill is critical for properly prescribing exercise for at-risk individuals. Indirect measurement of blood pressure is done with a stethoscope and a sphygmomanometer. The indirect measurement of blood pressure monitors the sounds of blood flow in the brachial artery (Korotkoff phases) that are audible through the stethoscope (for more information about the Korotkoff phases, see the accompanying highlight box). Laminar blood flow makes little or no sound in the arteries, whereas turbulent blood flow due to occlusion from the blood pressure cuff can make a variety of sounds. Although blood pressure can differ slightly in the left and right arms, the difference is minimal; for the purposes of skill acquisition in this lab, students should use the most convenient arm. Note, however, that in clinical assessment both arms should be measured, and the highest recording should be used as the BP measurement (2). When doing serial measurements, the same arm should be used. The arm should be as free of clothing as possible, since clothing can muffle sounds during auscultation; however, simply rolling up or bunching a sleeve can, if done too tightly, mimic a BP cuff and thus occlude blood flow. Different-size cuffs are available for use with different-size arms; specifically, cuffs are available for children, adults, and large adults. Index lines on the cuff should indicate whether the cuff is appropriate for a given subject or patient. The bladder should cover about 80% of the arm to enable it to occlude blood flow effectively when inflated.

BP measurement can be affected by the testing situation and by preparation. Ideally, subjects refrain from using stimulants such as caffeine prior to testing. They should wear loose clothing, be normally hydrated, and avoid strenuous exercise for several hours prior to the test. While being tested, they should not cross their legs, and they should avoid any form of isometric muscle action, such as pressing down on their legs, dangling their feet off the ground, or sitting erect with the back unsupported. In addition, the environment should be free of stimuli such as loud music or unnecessary activity (2).

References

1. Brooks GA, Fahey TD, and Baldwin KM. Exercise Physiology: Human Bioenergetics and Its Applications. 4th ed. New York: McGraw-Hill, 2005.

2. Kenney WL, Wilmore JH, and Costill DL. Physiology of Sport and Exercise. 5th ed. Champaign, IL: Human Kinetics, 2012.

3. Perloff D, Grim C, Flack J, Frohlich ED, Hill M, McDonald M, and Morgenstern BZ. Human Blood Pressure Determination by Sphygmomanometry. Circulation 88: 2460–2470, 1993.




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