Bias and variability in blood pressure measurement with ambulatory recorders.

Abstract

This study sought to determine whether patient characteristics such as age, sex, blood pressure, and pulse pressure differently affect the accuracy of an oscillometric (SpaceLabs 90207) and a microphonic (TM2420 version 7) blood pressure monitor. Blood pressure recorded by two oscillometric and two microphonic ambulatory monitors was compared with simultaneous readings by two pairs of trained, blinded observers using random-zero sphygmomanometry. One hundred and eighteen subjects (53 men and 65 women, aged 17 to 94 years; systolic pressure, 89 to 211 mm Hg; diastolic, 44 to 116 mm Hg) were studied. There were no significant differences within each observer pair or between the two observer pairs as well as no correlation between interobserver differences and patient characteristics. The differences between the monitor and trained observers' readings were 2.8 ±9.9 mm Hg systolic and 3.9 ±6.8 mm Hg diastolic for the SpaceLabs and 5.0±5.2 mm Hg systolic and 3.4±6

Measurement of blood pressure using the auscultatory and oscillometric methods in the same cuff deflation: validation and field trial of the A&D TM2421 monitor

“…The K-sound method also gave reasonable estimates of diastolic BP although some of the recommendations in the AAMI guidelines were not satisfied. The differences from the observers' BP readings were quantitatively similar to those reported by others for this monitor 14 and for other ambulatory monitors using either the K method 4,5,12,15 or the oscillometric technique. 12,13 The accuracy of the oscillometric method in measuring BP, however, was not satisfactory as indicated by the wider distribution of the differences from the observers mean and by the inaccuracies associated with the systolic BP level ( Table 1).…”

“…The oscillometric method, although performing reasonably well for measurements of diastolic BP, failed fully to satisfy the AAMI criteria for the assessment of BP. In view of the tendency of oscillometric monitors to over-read low systolic BP and under-read when the systolic BP is high 12,17 (which was confirmed in the current study), we recommend that the K method continues to be regarded as the 'gold standard'. However, the availability of a monitor capable of recording BP using both methods is of practical value since it allows a reasonably accurate estimate of BP in those subjects where the K technique fails (which it would have done in 33% of cases had oscillometric backup not been available).…”

“…with the TM-2421 monitor compared favourably with another device which records BP using both K and oscillometric methods simultaneously (Colin ABPM 630). 16 Our validation results and those of others, 12,17 however, indicate that the K method is more accurate, and thus in the field use of this monitor should be the method of choice.…”

“…A similar bias has been previously reported with another oscillometric device (Spacelabs 90207: Redmond, WA, USA). 12 This may not be a serious problem in the middle range of systolic BP commonly seen in the clinical setting but it would lead to an underestimation of the proportion of severely hypertensive subjects. This would particularly affect population studies where a wide range of BPs are evaluated and whenever elderly subjects are involved.…”

“…These values were outside the AAMI limits though results similar to ours were found by others with oscillometric devices. 12,13 The level of systolic BP clearly affected the accuracy of the measurement by the oscillometric method ( Figure 1, lower panel). There was a strong positive linear relationship (r = 0.73, P Ͻ 0.0001) between the differences in systolic BP measurements by the two methods (Observer-oscillometric) with higher systolic BPs being under-estimated by the oscillometric method while lower ones tended to be over-estimated.…”