IMPACT OF ARTERIAL SITE AND PULSE WAVE ANALYSIS METHOD ON ARTERIAL FORM FACTOR AND MEAN ARTERIAL PRESSURE ESTIMATION.

OBJECTIVE: Mean arterial pressure (MAP) is often estimated from systolic (S) and diastolic (D) blood pressure (BP) using a constant "form factor'' (FF), usually MAP = DBP + 0.33*pulse pressure (PP), yet accurate measurement requires pulse wave analysis (PWA) and waveform integration. MAP is constant across all conduit arteries but PP increases distally [peripheral (p)PP > central ©PP]. Thus, cFF should be higher than pFF; results should also be similar between PWA methods.

DESIGN AND METHOD: We tested these principles in 2 cohorts using 2 transfer function-dependent PWA devices: SphygmoCor (SPG, radial tonometric PWA with integrated MAP) and Mobil-O-Graph (MOB, 24-hour ambulatory brachial oscillometric PWA with proprietary MAP). SPG data (signal-average of 10 PWA) were obtained after 5-10 minutes of rest and MOB values at 20-minute intervals. For direct MAP comparisons, 101 pairs from the SPG and MOB cohorts were matched precisely for pSBP and pDBP (130.9/78.7 mmHg for each, p>.999).

RESULTS: For SPG, n = 376, [mean(SD)]: pBP 140(28)/80(15) and cBP 126(28)/81(15) mmHg, age 48(20) yr, BMI 28(6.6), 54% men, 20% black. SPG-cFF was higher than SPG-pFF [0.44(.049) vs 0.34(.056), p < 0.000] and cFF and pFF were correlated (r2 = 0.23, p < 0.000). On stepwise multiple regression, SPG-pFF was related to MAP > gender > age (multiple-r2 = 0.37, p < 0.000; BMI and race were 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% men, 24% black. MOB-pFF was almost invariate, lower than MOB-cFF [0.46(0.00098) vs 0.57(0.048), p < 0.000], and not correlated with MOB-cFF or any other characteristic. MOB-cFF was higher than SPG-cFF (p < 0.000) with similar variability. In the paired cohorts, mean FF's were similar to the full cohorts but SPG-MAP was much lower than MOB-MAP [96.3 vs 102.6 mmHg (p < 0.000)].

CONCLUSIONS: 1) FF varies within-subjects by arterial location, with cFF > pFF; 2) SPG-pFF varies between-subjects and is affected by MAP, gender, and age; 3) proprietary MOB-pFF is invariate and higher than integrated SPG-pFF; and 4) MOB-MAP is 6% higher than SPG-MAP. These findings may impact studies requiring FF or MAP estimates, especially from proprietary oscillometric devices.