Office Blood Pressure Variability: Within Session Stability Across Consecutive Measurements Using Oscillometric Devices

Abstract

Objective: Blood pressure (BP) is routinely monitored by healthcare providers and during drug development. For improvement in accuracy, several oscillometric devices perform multiple sequential inflations, rather than relying on a single inflation, to determine a mean systolic and diastolic blood pressure (SBP, DBP). Blood pressure is known to vary physiologically throughout a day, and over the course of days and weeks, due to intrinsic and extrinsic factors. Little data has been published describing the variability of SBP and DBP recorded minutes apart using oscillometric methods (i.e. within session variability). Design and method: We investigated the stability of within session SBP and DBP across 4 datasets by evaluating differences between 3 consecutive inflations recorded 1-2 minutes apart using a clinically validated oscillometric BP monitor that passed the ANSI/AAMI/ISO 2013, ESH-IP 2002 and BHS 1993 protocols (Table 1). These datasets included patients with controlled or uncontrolled hypertension. Results: Data were available from over 10.000 measurement pairs. The differences between inflation 1 and 2 were within ±10, 20 and 30 mmHg for 78.1, 94.4 and 97.9% of the SBP measurements, respectively. For the DBP, 90.7, 95.5 and 97.3 % of the differences between inflation 1 and 2 were within ±10, 15 and 20 mmHg, respectively. A similar trend was seen between inflation 2 and 3. Table 1: Categorical Analysis of BP changes between consecutive inflations. Conclusions: Our data demonstrate substantial variability between consecutive oscillometric BP measurements performed a few minutes apart. Over 20% of the time, consecutive inflations show an absolute change in SBP of at least 10 mmHg. It is unclear whether this represents true physiologic changes in BP or is partly artefactual due to failure of a device's algorithm to determine BP accurately from the oscillometric waveform. These data suggest that criteria for within session variability for automated oscillometric blood pressure devices should be established, including a threshold for repeating the session after 10 minutes of rest.