Differences in Orthostatic Blood Pressure Changes Measured with an Oscillometric Blood Pressure Monitor and a Mercury Sphygmomanometer

Aims: To compare orthostatic blood pressure (BP) changes recorded with the SpaceLabs 90207 BP monitor (SL) and the standard mercury sphygmomanometer (HgS).Methods: 85 hospital in-patients aged 60–90 years had nine BP measurements recorded by both instruments using the same arm sequential measurement technique in supine and standing position by two observers. Supine BP was taken as the final set of three supine measurements, ie, one made with the SL, and the mean of the two HgS readings immediately before and after the monitor reading. From the SL supine reading was subtracted the three standing SL monitor readings and from the mean of the 2 supine HgS readings was subtracted the six standing measurements taken by the HgS. The orthostatic BP changes recorded by the HgS immediately before and after each SL monitor reading were averaged and compared with the corresponding orthostatic change recorded by the monitor.Results: The monitor underestimated orthostatic SBP changes at all 3 comparisons compared to the HgS; i) -0.9 ± 14.9 vs 2.7 ± 10.3 mmHg, p < 0.05; ii) 0.3 ± 15.4 vs 4.5 ˙ 12.1 mmHg, p < 0.05; iii) 3.5 ± 16.9 vs 7.5 ± 14.9 mmHg, p < 0.05, respectively. These differences were more pronounced in males than females. Orthostatic hypotension (defined as SBP fall on standing of ≥ 20 mmHg) was recorded in males by the monitor in four (8%) and by the HgS in 12 (25%), p < 0.05. Mean orthostatic DBP changes were similarly recorded by the monitor and HgS. On average only 60% and 77% of orthostatic SBP measurements taken by both instruments agreed within 10 and 15 mmHg respectively while 75% and 88% respectively of orthostatic DBP changes agreed within these limits.Conclusion: Orthostatic BP falls measured by an automatic oscillometric BP monitor may not be equivalent to those taken with a HgS and their use adds a further variable to the comparison of orthostatic BP changes between studies.