Tolerability of the Oscar 2 ambulatory blood pressure monitor among research participants: a cross-sectional repeated measures study

The evidence for the clinical utility of ambulatory blood pressure monitoring (ABPM) continues to accumulate. Blood pressure (BP) measured by this technique is more closely associated with prognosis and is considered to be the current gold standard method for determining an individual's true BP [1, 2]. Clinically, ambulatory BP monitoring is valuable for confirming suspected white-coat hypertension or evaluating white-coat effect in patients with apparently difficult-to-control hypertension, for detecting masked hypertension, and for gaining a better estimate of BP control among treated patients [2‐4]. Additionally, ABPM is useful when evaluating symptoms possibly due to hypotension and is the only technique currently available to assess night-time (sleep) BP [2]. In addition to its clinical usefulness, ambulatory BP monitoring is now recognized as critical in studies of BP-lowering treatments [5].

An obvious downside of ambulatory BP monitoring is the potential inconvenience, related to the need to keep the cuff on the arm during the entire measurement period (usually 24 hours) as well as having to wear the monitor unit on the waist (by a belt or strap) during the day and keep it at the bedside at night. It is thus important to have some sense of the individual's experience when undergoing ambulatory BP monitoring. The Oscar 2 (SunTech Medical, Morrisville, NC) ambulatory BP monitor, in addition to being light and compact, uses motion tolerant algorithms to reduce re-inflates and failed readings. It has an additional feature (auto-intelligent inflation pressure) designed to reduce measurement time and reduce patient discomfort by controlling cuff inflation. A special cuff (the Orbit cuff) has a stretch-sleeve designed to maintain cuff placement and promote patient comfort. We assessed tolerability of wearing the Oscar 2 ambulatory BP monitor among a group of adults not yet diagnosed with hypertension who participated in a research project. A unique feature of our study is that participants wore the monitors on two occasions and they reported on their experiences after each monitoring session.

This study was part of a project conducted to assess the reproducibility of classifications of blood pressure based on pairings of office and out-of-office measurements for purposes of informing the design of a larger study. We recruited sixty adults via signs inviting participation in a study of people with a recent clinic BP measurement that was "borderline" or "a little high." Signs were posted in an academic family medicine center, two community family medicine practices and in a clinical research center. Individuals interested in participating contacted a study coordinator to confirm eligibility and schedule their study visits. To be eligible, a person had to be 30 years of age or older (although one person who was actually 29 years old ended up being enrolled), have no diagnosis of hypertension and be on no medications to lower BP. Exclusion criteria included pregnancy, dementia, any condition that would preclude wearing the monitor (including an arm circumference >46 cm), and persistent atrial fibrillation or other arrhythmia. As an incentive, participants were offered $150 for completion of the study.

Informed consent was obtained prior to any study procedures. Participants underwent two 24-hour ambulatory BP monitoring sessions one week apart using the Oscar 2 oscillometric monitor. The Oscar 2 has been validated for use in adults by both the British Hypertension Society protocol and the International Protocol for the validation of blood pressure measuring devices [6, 7]. The monitors were programmed to measure BP at 30 minute intervals during the daytime (6 am to 11 pm) and at 1 hour intervals during the nighttime (11 pm to 6 am). Maximum BP measurement time was limited to less than 140 seconds, and the monitors were set for a maximum pressure of 220 mm Hg. Participants were given verbal instructions on wearing the monitor, including that that they should try to leave the cuff on during the entire monitoring period, that they should try to hold their cuffed arm as still as possible during a reading to ensure that the monitor would get an accurate reading, that cuff inflation would cause a tight feeling around the arm, and that faulty readings would trigger a repeat measurement. Following each monitoring session, participants completed a questionnaire to assess tolerability of wearing the monitor (Appendix). This questionnaire was adapted from one used in a previous study designed to assess patient satisfaction with wearing an ambulatory BP monitor [8].

We report responses to Likert-scaled questions as means with standard deviations and responses to categorical questions as percentages. We created an overall tolerability score as the sum of the responses to questions 1 and 4 through 8 minus the responses to questions 2 and 3. We defined poor tolerability as a total score of Likert-scaled responses at or above the 75th percentile of the sample. We examined agreement on poor tolerability between the first and second sessions of wearing the monitor and calculated the kappa coefficient and its p-value. We then examined bivariate associations of demographic and general health characteristics with poor tolerability at first wearing of the monitor and tested for significance using chi-square. Finally, we examined whether poor tolerability was associated with reported removal of the monitor and inadequate number of BP measurements. Inadequate number of measurements was defined as <14 usable readings for daytime and <7 usable readings fro nighttime. This study was approved by the Office of Human Research Ethics at the University of North Carolina.

Overall, participants in this study seemed to have little difficulty with using the Oscar 2 ambulatory BP monitor. As has been found in other studies of tolerability of ambulatory BP monitoring, the greatest disturbance from wearing the monitor was interference with sleep [9‐11]. Two-thirds of wearers reported that the monitor awakened them from sleep. Nonetheless, most participants continued to wear the monitor at night. We found no studies with which to make a direct comparison about the proportion of participants who reported actually removing the monitor. Our questions about monitor removal were modified from a prior study's questionnaire [8], and we found no other study containing similar items. In that study of pregnant women undergoing ABPM using a SpaceLabs 90207 (SpaceLabs Medical, Inc, Redmond, WA) monitor, 15% discontinued their monitoring session [8]. However, the results may not be comparable to ours due to the different population and the slightly different questions used.

We found that the most commonly reported adverse physical effects were pain and skin irritation. Bruising was also reported, although less frequently. It is possible that the second monitoring session resulted in more bruising because it occurred so shortly after the first session. The proportion of participants with inadequate ambulatory BP data was also higher data at the second monitoring. While there may be a need for ambulatory BP monitoring on consecutive weeks in research studies, it is less likely to be used in this manner for clinical care. Other studies have found that approximately 90 to 95% of patients undergoing ambulatory BP monitoring for clinical reasons would be willing to have a repeat monitoring session if so advised [10, 12].

Not surprisingly, we found that people with poor tolerability to wearing the monitor were more likely to remove it, particularly during sleep. However, at the first monitoring session, 24-hour data acquisition was adequate in nearly three-fourths of the participants regardless of whether classified as having poor tolerability or not. This information can be useful for investigators planning research studies. It may be difficult to know who will tolerate the monitor poorly, but we did find that people whose self-reported health status was fair or poor were more likely to be categorized as having poor tolerability. However, this may simply reflect a "rating bias" whereby people who rate their health negatively may rate everything negatively. Our study also may overestimate true tolerability since our sample consisted of voluntary participants in a research study who received monetary incentive for wearing the monitor on two occasions.

To our knowledge, this is the first study to examine the tolerability of ambulatory BP monitoring using the Oscar 2 monitor with its specially designed Orbit cuff. Adverse effects of wearing this monitor seem similar to those described with other monitors. In a study of acceptability of wearing the Mobil-O-Graph (IEM GmbH, Stolberg, Germany) oscillometric ambulatory BP monitor, 55% of patients reported interference with sleep, 41% reported pain, and 17% had a local skin reaction [12]. In an examination of acceptance of ambulatory monitoring using a SpaceLabs 90207 device, 20% of patients reported that the session was uncomfortable [13]. Other studies of the SpaceLab 90202 device found that 30% to 36% reported disturbed sleep, up to 20% reported pain, and 19% to 34% reported that monitoring disturbed their activities [9, 14].

Another strength of this study is its assessment of tolerability on two occasions, providing some estimate of the reproducibility of a questionnaire designed to measure people's experience with wearing an ambulatory BP monitor. We are aware of no other study that has done this type of evaluation. Perhaps most importantly, we analyzed the effects of tolerability on the number of measurements one can expect to obtain from studies of participants in which ambulatory BP monitoring is used. We believe this is useful information for researchers as well as clinicians who use ambulatory BP monitoring.

Our study is limited by a small sample size. It is likely that some of the factors we examined (e.g., elevated BP, greater arm circumference) would be statistically significant with a larger sample. Additionally, because this study was of research participants who volunteered (and were paid) to participate, the findings may not be generalizable outside the research setting. Tolerability was also based on people's self reports, and reported side effects (e.g., bruising) were not verified objectively.

Despite the above limitations, it is clear that ambulatory BP monitoring using current devices, including the Oscar 2 monitor, is not a procedure without some inconveniences and some minor transient adverse effects. It thus does not come as a surprise that ambulatory monitoring has been found to be the least patient-preferred method of measuring BP (after home monitoring and office measurement) [15]. However, studies show that patients also can appreciate the value of the information provided by ambulatory BP monitoring [13]. The data on potential adverse effects as well as the likelihood of disturbances of activities (especially sleep) should be explained to research subjects (or patients) along with the importance of the blood pressure information to be obtained from ambulatory BP monitoring so that people undergoing monitoring understand both the risks and benefits.

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Please circle your response to the next questions .

Yes   No   Sleep was not disturbed

Yes   No   Sleep was not disturbed

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