The elegance of simplicity

Everything should be made as simple as possible, but not simpler. Albert Einstein Oscillometric blood pressure (BP) measurement is increasingly being used and recommended for BP measurement in hospital, in clinic, for 24-hour ambulatory measurements, and at home.1-3 Many aspects of oscillometric BP measurement have been adopted and perpetuated by convention, as opposed to being evidence-informed.4, 5 Historical recommendations for cuff placement used in auscultation, for instance, have been applied to oscillometric measurement by convention.6 In their excellent paper, Li et al7 have challenged cuff placement, as it pertains to oscillometric blood pressure measurement, and whether cuff bladder placement in apposition to the brachial artery affects measurement accuracy. There were two arms to this study. One compared radial intra-arterial BP to oscillometric BP measurement in 104 patients admitted to the intensive care unit. In this study arm, the cuff was systematically rotated through four positions at 90° intervals (standard, medial, lateral, and contralateral). The invasive and noninvasive measurements were taken in opposite arms with the invasive measurements taken before and after each oscillometric measurement (therefore at similar times but not identical). The difference in mean oscillometric BP for all 104 patients from the standard position was, at maximum, 4.99 (systolic)/1.82 (diastolic) mm Hg (CI for mean differences not reported). None of the BP differences from the standard position were statistically significant. In this study arm, comparisons were also made between invasive and noninvasive BP measurements. The differences between invasive and noninvasive measurement in the rotated positions did not significantly exceed the difference in the standard position. The second arm of the study compared the three rotated cuff positions (medial, lateral, and contralateral) to the standard cuff position in 799 patients admitted to an acute care ward. In the second study arm, mean difference in BP between incorrectly positioned cuffs and the standard cuff position was at maximum 0.51 (−1.23, 2.24) systolic (95% CI)/ 0.30 (−1.27, 0.66) diastolic (95% CI) mm Hg. These findings corroborate previous work where rotations of an oscillometric, semi-rigid, wide range cuff in 57 participants, did not significantly alter BP measurements.6 In this previous study, differences between the standard cuff position (with marker over the brachial artery) and rotated cuff positions (lateral 90° and 180°) did not exceed the differences between mercury auscultation and the oscillometric measurement. The Li et al study measured all four cuff positions, whereas the previous study omitted the medial 90° rotation. This result of artery marker rotation not affecting oscillometric BP measurement aligns with how an oscillometric BP is generated. In oscillometry, when the cuff is inflated, the artery is occluded. As the cuff deflates and the artery transitions from an occluded to open state, oscillations occurring with each arterial pulse are sensed by the cuff in a three-dimensional manner and transferred to a device pressure transducer, a two-dimensional sensor. Systolic and diastolic blood pressures are calculated using a proprietary algorithm from an oscillometric waveform envelope generated by the pressure transducer output after filtering and amplification.8 One might predict that, because these arterial oscillations spread outwards in a circumferential manner and then are converted to a two-dimensional output, they will be independent of brachial artery position. In Figure 1, we show single-reading oscillometric waveforms generated in our laboratory in each of the four cuff positions described in the study by Li et al In Figure 2, we show the single-reading oscillometric waveform envelopes from which BPs are derived. The standard deviation of the mean pulse amplitude is 0.0197. The standard error of the mean is 0.0098 highlighting the very similar oscillometric waveforms and envelopes created in the four cuff positions. Further, we also measured variability of oscillometric waveforms measured in the standard cuff position four times (Figure 3). The standard deviation of the mean pulse amplitude for these measurements is 0.051, and the standard error of the mean is 0.025. These results comparing measurements at four different cuff positions and measurements at the standard cuff position are visual confirmation that rotating the cuff does not significantly affect oscillometric BP measurement. One of the main advantages of automated blood pressure measurement is the reduction in observer error inherent to clinical auscultatory blood pressure measurement. The findings in the present study indicated that it is possible to further simplify the automated BP measurement technique because we do not have to worry about cuff position. As we are increasingly recommending automated blood pressure measurement both in clinic and at home, simplification of the process will therefore allow us to focus on those factors that have the greatest effect on the accuracy automated BP measurement (using a validated device, applying a cuff appropriately sized for arm circumference, taking multiple readings, observing antecedent rest, not talking during measurement).9, 10 Previous work has shown that, even in the research setting, most patients do not adopt all of the features of proper home BP technique.11 Passive interventions (those interventions that do not require interaction between the clinician and patient, eg, posters and educational materials) aimed at improving home blood pressure measurement are not effective.11 If active intervention (individual or group interaction between patient and caregiver) is required, simplifying instructions will likely improve adoption. Automated BP measurement has many advantages over auscultation in the clinical setting. This technique allows for out-of-office measurement which is a superior predictor of cardiovascular events,12 it is superior at detecting white coat hypertension,13 and allows for nocturnal readings.14 Home blood pressure monitoring has the added advantage of being cost effective, practical, and uniquely able to provide multiple readings over many days.15, 16 Consequently, home BP measurements are increasingly being used to guide and monitor treatment decisions. With a validated device, home BP measurement can be a reliable and accurate estimate of BP. This is particularly important during these times of social distancing and virtual health care. Clinicians are working to connect with patients in new ways in order to achieve BP targets. The findings of the study by Li et al allow us to further simplify the automated measurement process, making this adoption of this technique even more essential. JR and SS are both shareholders of mmHg Inc, a university-based digital health company.