Dual Monitor Protocol Comparing the Accuracy of the Oscar 2 & Spacelabs 90207 24-hr Ambulatory Blood Pressure Monitors

V Patteson Lombardi1, Patrick C Reichhold2, Nicholas R Dietz2 & Donald L Pate3

University of Oregon, Biology1 & Human Physiology2 & Institute of Neuroscience3, Eugene, OR USA 97403

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AHA Council on HypertensionAHA Council on the Kidney in Cardiovascular Disease

American Society of HypertensionJoint Scientific Sessions 2017, September 14-17, 2017

Hyatt Regency, San Francisco, CA USA 97411

BackgroundWe developed a Dual Monitor Protocol with labpostural challenges to study the accuracy andreliability of ambulatory blood pressure monitors(ABPMs). First, we studied the Accutracker IIABPM (SunTech Medical) and determined innormotensives (n=29), hypertensives (n=12), andalcohol-dependents (n=11) that the monitorsignificantly underestimated diastolic bloodpressure (DBP) and had the most problems withstanding DBPs. When we used differences betweena mercury (Hg) column and ABPM simultaneous,same arm measurements in the lab to correct for24-hr BPs, we found that several patients weremisclassified. SunTech Medical discontinuedmanufacturing the auscultatory Accutracker II in2010. Here we present our initial studiesexamining the accuracy and reliability of twooscillometric ABPMs, the Oscar 2 (SunTechMedical) and the Spacelabs 90207 (SpacelabsHealthcare).

HypothesesUltimately, proprietary equations developed foroscillometric ABPMs were derived usingauscultatory techniques. Constant pulse pressureassumptions or static equations cannot be appliedto dynamic populations. Though mean arterialpressure (MAP) corresponds to the peak pulsatilepressure in the cuff, it is extremely difficult toproject outward from MAP to estimate pressures,especially DBP . Thus, we predicted thatoscillometric ABPMs also would have difficultiesassessing DBPs and/or exhibit a flashlight effectwith phase-shift inaccuracies at either the systolic-(SBP) or diastolic-end of the continuum .

MethodsWe programmed Oscar 2 and Spacelabs 90207ABPMs to record simultaneous, opposite arm BPsfor 24 hr in a hypertensive male (62 yr). Clockswere synchronized and cuffs were switched every2-3 hr during waking hr. In the lab, observersassessed simultaneous same arm BPs for botharms using an Hg column and Thinklabs digitalstethoscope with 2nd-generation ambient noiserejection and headset output. ABPMs recordedsimultaneous opposite arm BPs interspersed withHg column measurements. To develop correctionsfactors for the 24-hr monitoring, all labmeasurements were made in triplicate anddifferences were calculated between observers’ Hgcolumn mean values and each ABPM’s mean valuesfor supine, seated and standing postures. Inattempt to examine extreme ends of the pressurecontinuum, we also used two Spacelabs ABPMs toassess simultaneous and sequential same andopposite arm pressures over 24-hr in ahypertensive male (52 yr) and a single SpacelabsABPM to assess non-dominant arm pressures in anormotensive male (21 yr). Correction factorsestablished in the lab were applied to 24-hr data.

Summary & Conclusions

1. If patients do not match the subject sample usedto develop specific nomogram-like predictionequations and/or have widely varying pulsepressures, then they may be inappropriatelydiagnosed by 24-hr ABPMs. A flashlight effect orblood pressure phase-shift does appear to existespecially with BPs at either end of the continuum.DBPs and SBPs may be inconsistent andunpredictably inaccurate based on the specificmonitor used and patients’ pressure ranges,postures and activity levels.

2. Initial data implies that the Oscar II andSpacelabs ABPM equations were developed fromsubjects who were seated. This may beresponsible for the significant ABPM measurementerrors relative to observers using an Hg column inthe lab. As with the auscultatory ABPM, standingDBPs may be problematic with hypertensives andsupine DBPs with normotensives. ABPMproprietary equations developed from a singleposture cannot be applied over an entire 24-hrmonitoring period when patients move about andassume a variable % distribution of postures.

3. Though we have examined only a few subjectswith oscillometric monitors, these limited data doprovide some compelling evidence that ABPMs’estimations may be poor and unpredictabledepending upon the specific monitor and patientcircumstances.

4. Prediction equations will not improve unlessABPMs can (a) detect unique postures andmovements and (b) be designed and calibrated tomake sensitivity adjustments based on knownvariations in K-sound and oscillometric-pulsemagnitudes that occur with changes in postureand activity . Both the Oscar and SpacelabsABPMs exhibit run-away inflations with simplemovements like walking or stair climbing . It islikely that motion artifacts are interpreted byABPMs as not having achieved peak systolicpressures. These continuous inflations may bestartling and at times painful for subjects.

5. The Association for the Advancement of MedicalInstrumentation (AAMI) and the European Societyof Hypertension (ESH International) protocolsmust require ABPM validation for a variety ofpostures and activity levels. Additionally,manufacturers should be required to include exactdescriptions of age ranges, genders, races andethnicities examined in developing theirproprietary equations. Until these basic stepsbecome mandatory, ABPMs may provideinaccurate measurements that lead tomisclassification, inappropriate diagnoses andmismanagement of patients.

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Relaxed ArmPost-exercise,

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Relaxed Arm

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Special thanks to Katie Foster and Richard Padgett, MD, of Oregon Heart & Vascular Instituteand John Halliwill, PhD, of U of O Human Physiology for their help with ambulatory monitors.

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