Abstract P113: IMPACT OF ARTERIAL SITE AND PRESSURE WAVE ACQUISITION METHOD ON ARTERIAL FORM FACTOR AND MEAN AND CENTRAL ARTERIAL PRESSURE

Abstract

Accurate mean arterial pressure (MAP) measurement requires an integrated arterial pressure waveform but MAP is often estimated from systolic (S) and diastolic (D) BP using a fixed form factor (FF, usually 0.33): MAP = DBP + FF*pulse pressure (PP), also solvable for FF if MAP is known. MAP is constant in the arterial tree but central (c) PP is lower than peripheral (p) PP, so cFF should be higher than pFF, and MAP and FF values should be similar among devices. We tested these principles for 2 transfer function-dependent devices: SphygmoCor (SPG), which generates high fidelity radial arterial tonometry waveforms and integrates MAP, and Mobil-O-Graph (MOB), a 24-hour ambulatory oscillometric brachial pulse wave analysis system that reports a proprietary MAP. SPG data were obtained after 5-10 minutes of rest and MOB values were obtained at 20 min intervals. For SPG (n =371) [mean(SD)]: pBP 140(28)/80(15) and cBP 126(28)/81(15) mmHg, age 48(20) yr, BMI 28(6.6), 54% women, 17% black. SPG-pFF was lower than cFF [0.34(.056) vs 0.44(.049), p<0.000]; SPG-pFF and cFF were correlated (r 2 = 0.23, p<0.000); and on stepwise multiple regression, pFF was related to MAP > gender > age (multiple-r 2 = 0.37, p<0.000; BMI and race excluded). For MOB (n = 157): pBP 135(18)/81(12) and cBP 123(16)/83(12) mmHg, age 59(16) yr, BMI 30(6), 52% women, 24% black. MOB-pFF was a fixed value [0.46(0.00098)] that was lower than cFF [0.57(0.048), p<0.000] and MOB-cFF was not correlated with MAP or any other characteristic. To compare SPG and MOB directly, 101 pairs were matched precisely (SPSS software) for pSBP and pDBP (130.9/78.7 mmHg for each device group); SPG-MAP was lower than MOB-MAP [96.3 vs 102.6 mmHg (p<0.000)] and SPG-cSBP was lower than MOB-cSBP [117.5 (18.0) vs 119.7(14.6), p=.015], with respective FF’s similar to the full groups. We conclude that: 1) FF varies within-subjects by arterial location and (at constant MAP) cFF > pFF; 2) SPG-pFF (but not MOB-pFF) varies between-subjects and is affected by MAP, gender, and age; 3) the proprietary MOB-pFF is fixed and much higher than traditional FF or SPG-pFF; and 4) compared to SPG, MOB overestimates MAP by about 5% and underestimates cSBP by about 2%. These findings have implications for FF methods and proprietary devices such as Mobil-O-Graph.