FACTORS AFFECTING THE VALIDITY OF THE STANDARD BLOOD-PRESSURE CUFF

Fifty-eight patients, 31 women and 27 men, with a wide range of upper arm circumferences (20-43 cm), ages (16-82 years) and body mass indice s (16-55 kg m-2) were studied. The direct blood pressure was measured in the brachial artery in one arm and simultaneously the indirect pres sure was measured in the other arm using a large standard cuff (rubber bag 12 x 35 cm). The mean intra-arterial blood pressure was (systolic /diastolic) 137 +/- 25 mmHg (SD)/76 +/- 10 mmHg. With the cuff the mea n blood pressure was 134+/- 23 mmHg/85 +/- 11 mmHg. The cuff significa ntly underestimated the systolic blood pressure (3.2 +/- 11.4 mmHg, ra nge -25-30 mmHg) while the diastolic pressure was overestimated signif icantly (8.8 +/- 8.5 mmHg, range -32-14 mmHg). The direct/indirect blo od pressure difference correlated significantly to the intraarterial s ystolic and diastolic pressures (systolic/diastolic; r = 0.44, P = 0.0 006/r = 0.36, P = 0.0062), but only to the auscultatory diastolic pres sure (r = -0.02, P = 0.9/r = -0.45, P = 0.0004). The direct/indirect d ifference correlated significantly to the arm circumference (r= -0.33, P = 0.01/r = -0.30, P = 0.02) as did the diastolic direct/indirect di fference to pulse rate (r = 0.34, P = 0.009). Age did not correlate si gnificantly to the direct/indirect blood pressure difference in this s tudy (r = -0.02, P = 0.9/r = -0.10, P = 0.5). It can be concluded that in addition to the ratio between the arm circumference and the width of the cuff (rubber bag), there are other sources of systematic errors of indirect blood pressure measurement, in particular pulse rate and the level of indirect blood pressure. If corrections could be made wit h regard to these variables, it is obvious that the reliability of the indirect method, especially when used in epidemiological contexts, wo uld increase.