The BHS protocol requires that a device must give at least 50% of readings within 5 mm Hg and 75% within 10 mm Hg with the two methods (grade B), and the AAMI requires that the average difference between the two methods not exceed 5 mm Hg with a standard deviation of less than 8 mm Hg. 2 Both require the taking of three blood pressure readings in 85 subjects (chosen to have a variety of ages and blood pressures) by trained observers and the device being tested. The two most widely used have been developed by the BHS 52 and Association for the Advancement of Medical Instrumentation (AAMI) in the United States. The increasing use of electronic monitors for both self-and ambulatory monitoring has necessitated the development of standard protocols for testing them. 61, 84 The Portapres enables readings to be taken over 24 hours while the subjects are ambulatory, although it is somewhat cumbersome. It is now commercially available as the Finometer and Portapres recorders and has been validated in several studies against intra-arterial pressures. This method gives an accurate estimate of the changes of systolic and diastolic pressure when compared to brachial artery pressures 63 the cuff can be kept inflated for up to 2 hours. The oscillations of pressure in the cuff are measured and have been found to resemble the intra-arterial pressure wave in most subjects ( Fig. The output of the plethysmograph is used to drive a servo-loop, which rapidly changes the cuff pressure to keep the output constant, so that the artery is held in a partially opened state. This interesting method was first developed by Penaz 63 and works on the principle of the “unloaded arterial wall.” Arterial pulsation in a finger is detected by a photo-plethysmograph under a pressure cuff. Comparisons of several different commercial models with intra-arterial and Korotkoff sound measurements, however, have shown generally good agreement. It should be pointed out that different brands of oscillometric recorders use different algorithms, and there is no generic oscillometric technique. The oscillometric technique has been used successfully in ambulatory blood pressure monitors and home monitors. The main disadvantage is that such recorders do not work well during physical activity when there may be considerable movement artifact. This method is advantageous in that no transducer need be placed over the brachial artery, and it is less susceptible to external noise (but not to low frequency mechanical vibration), and that the cuff can be removed and replaced by the patient during ambulatory monitoring, for example, to take a shower. 1), so that systolic and diastolic pressure can only be estimated indirectly according to some empirically derived algorithm. 32, 39, 97 The oscillations begin at approximately systolic pressure and continue below diastolic ( Fig. This was first demonstrated by Marey in 1876, 38 and it was subsequently shown that when the oscillations of pressure in a sphygmomanometer cuff are recorded during gradual deflation, the point of maximal oscillation corresponds to the mean intra-arterial pressure. Blood pressure measurements in different circumstances and in special populations such as infants, children, pregnant women, elderly persons, and obese subjects are discussed.
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Practical advice is given on how the different devices and measurement techniques should be used.
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The devices currently available for hospital and clinic measurements and their important sources of error are presented. In this article, the basic techniques of blood pressure measurement and the technical issues associated with measurements in clinical practice are discussed. This has led to the proliferation of non-mercury devices and has changed (probably for ever) the preferable modality of blood pressure measurement in clinic and hospital settings. To date, mercury devices have largely been phased out in US hospitals. Although the mercury sphygmomanometer is widely regarded as the “gold standard” for office blood pressure measurement, the ban on use of mercury devices continues to diminish their role in office and hospital settings.