Inaccuracy in determining mean arterial pressure with oscillometric blood pressure techniques

Accurate determination of MAP is important in the calibration of pressure waveforms for calculating central blood pressure (BP). Currently, a precise, individualized measurement of mean arterial pressure (MAP) can be obtained only with intra-arterial measurements of BP or with applanation tonometry. We conducted a study of whether easy-to-use oscillometric devices, validated for systolic and diastolic BP measurements (BHS protocol), give accurate determinations of MAP.

We compared measurements of MAP made with the WatchBP Office oscillometric monitor in 102 subjects with values of MAP assessed by pulse-wave analysis (PWA) (SphygmoCor).

The mean (± SD) oscillometric MAP assessed with the WatchBP Office monitor was 97 ± 12.5 mm Hg, which was equivalent to 23.6 ± 9.1% of the pulse pressure (PP) above diastolic blood pressure (DBP). The MAP as assessed through PWA was 106 ± 14.6 mm Hg (P < 0.01), or 37.7 ± 3.9% of the PP above DBP. In simultaneous measurements made on both arms with the WatchBP Office monitor we observed individual differences in pressure in the left vs. the right arm.

The MAP displayed by the WatchBP Office monitor is too imprecise to be used for calibrations. We suggest that devices for measuring BP not display MAP unless their accuracy is tested.