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Abstract P363: Dual Monitor Protocol Comparing the Accuracy of the Oscar 2 & Spacelabs 90207 24-hr Ambulatory Blood Pressure Monitors


 Background:
 Our dual monitor protocol enables simultaneous blood pressures (BPs) using two ambulatory monitors (ABPMs) and two observers with a mercury (Hg) column. In normotensives, hypertensives and alcoholics, an
 auscultatory
 ABPM underestimated diastolic BP (DBP) progressively from supine to seated to standing. Our goal was to test the accuracy and reliability of
 oscillometric
 ABPMs.
 
 
 Methods:
 We programmed an Oscar 2 and Spacelabs 90207 to record simultaneous, opposite arm measurements for 24 hr in a hypertensive male (62 yr). Clocks were synchronized and cuffs were switched every 2-3 hr during waking hr. In the lab observers assessed simultaneous same arm BPs using an Hg column and ABPMs recorded simultaneous opposite arm BPs. Lab techniques were repeated in two young (21 yr) male normotensives.
 
 
 Results:
 The monitors’ SBP, DPB and mean arterial pressure differed significantly (all p < 0.001) for 109 simultaneous 24-hr measures. The Oscar averaged 154/101 ± 12/9 mm Hg (Stage II), while the Spacelabs 146/98 ± 10/8 (Stage I), differing by 8/3 ± 7/9 mmHg. Both machines exhibited troubling run-away inflations during walking and stair climbing as sustained motion artifacts were interpreted as not achieving MAP or peak SBP. The ABPMs common variance for SBP was 63% (R = 0.79) and for DBP was 48% (R = 0.69), significantly lower than BPs for trained clinicians using an Hg column (SBP 97%, DBP 95%). In the lab, for SBP the Oscar (151 ± 3 mm Hg) was significantly (P<0.05) higher than the Spacelabs (143 ± 3 mm Hg) and observers (144 ± 4 mm Hg). For DBP, the Spacelabs (88 ± 3 mm Hg) tended (P=0.051) to be lower than the Oscar (90 ± 3 mm Hg) and observers (92 ± 4 mm Hg).
 
 
 Conclusions:
 Subjects can be classified differently based on the ABPM model used. The Oscar and Spacelabs ABPMs demonstrate greater variability estimating DBP. If results from multiple ABPMs are pooled in meta-analyses, interpretations may be muddled especially if one is overestimating and another underestimating 24-hr pressures. Though our dual monitor protocol is challenging to implement, we hope to conduct studies in a large, diverse group. US and international protocols should require postural and exercise testing to ensure that devices truly can be classified as ambulatory and are more consistently accurate and reliable.
