Not infrequently, blood pressure measurement by the standard auscultatory technique yields a normal systolic pressure with an elevated diastolic pressure. The relatively narrow pulse pressure of such a measurement raises concern about the accuracy of the blood pressure measurement. The purpose of this study was to assess the accuracy of auscultatory blood pressure measurements in patients with an uncommonly narrow pulse pressure, particularly patients with an elevated diastolic but normal systolic pressure, Auscultatory blood pressure measurements were compared with an objective noninvasive standard, called K2 analysis, which has been shown to be more accurate than the auscultatory technique. Blood pressure was measured simultaneously by auscultatory and K2 techniques in 175 subjects. Comparisons were performed (1) in the group as a whole, (2) in four clinical subgroups (normotensive [<140/<90 mm Hg, n=69], hypertensive [greater than or equal to 140/greater than or equal to 90 mm Hg, n=53], isolated systolic hypertensive [greater than or equal to 140/<90 mm Hg, n=38], and isolated diastolic hypertensive [<140/greater than or equal to 90 mm Hg, n=15]), and (3) in two subgroups whose ratio of pulse pressure to diastolic hypertensive group and in the group with a pulse pressure ratio less than 0.45 were considered to have a narrow pulse pressure. In the group as a whole, consistent with previous auscultatory-K2 comparisons, systolic pressure was slightly higher and diastolic pressure slightly lower when measured by K2 versus the auscultatory technique (auscultatory, 145/85 mm Hg; K2, 147/83 mm Hg). For diastolic pressure auscultatory measurements averaged 7 mm Ng greater than K2 in the isolated diastolic hypertensive group (94+/-4 versus 87+/-5 mm Hg) but were less than 3 mm Hg (greater) in the other three groups (P<.0004). For systolic pressure, differences were less than 3 mm Hg in all four clinical groups. Auscultatory-K2 differences of diastolic pressure exceeding 5 mm Hg (and 10 mm Hg) were seen in 73.3% (and 40.0%) of isolated diastolic ic hypertensive subjects versus only 14.5% (2.9%) of normotensive subjects, 22.6% (1.9%) of hypertensive subjects, and 7.9% (2.6%) of isolated systolic hypertensive subjects (P<.0001). Similarly, the auscultated diastolic pressure exceeded the K2 measurement by at least 5 mm Hg (and 10 mm Hg) in 62.5% (29.2%) of subjects with a pulse pressure ratio less than 0.45 versus 13.9% (2.0%) in subjects with a ratio greater than or equal to 0.45 (P<.0001). Auscultatory-K2 differences of diastolic pressure were strongly and inversely related to the pulse pressure ratio (r=-.68, P<.0001) independent of sex, race, or body weight. In conclusion, when the pulse pressure is particularly narrow, auscultation frequently overestimates the true diastolic pressure by 5 mm Hg or more. The treatment implications of this finding, particularly in patients with elevated diastolic but normal systolic pressure, merit further study.
