NONINVASIVE METHOD FOR DETERMINATION OF ARTERIAL COMPLIANCE USING DOPPLER-ECHOCARDIOGRAPHY AND SUBCLAVIAN PULSE TRACINGS - VALIDATION AND CLINICAL-APPLICATION OF A PHYSIOLOGICAL MODEL OF THE CIRCULATION

Background The Poiseuillian model of the arterial system currently app lied in clinical physiology does not explain how arterial pressure is maintained during diastole after cessation of pulsatile aortic inflow. Arterial pressure-how relations can be more accurately described by m odels that incorporate arterial viscoelastic properties such as arteri al compliance. Continuous pressure and flow measurements are needed to evaluate these properties. Since the techniques used to date to acqui re such data have been invasive, physiological models of the circulati on that incorporate these properties have not been widely applied in t he clinical setting. The purpose of this study was (1) to validate non invasive methods for continuous measurement of central arterial pressu re and flow and (2) to determine normal reference values for arterial compliance using physiological models of the circulation applied to th e noninvasively acquired pressure and flow data. Methods and Results S imultaneously acquired invasive and noninvasive aortic pressures (30 p atients), flows (8 patients), and arterial mechanical properties (8 pa tients) were compared. Pressure was measured by high-fidelity catheter aortic micromanometer (invasive) and calibrated subclavian pulse trac ing (noninvasive). Aortic inflow was determined from thermodilution-ca librated electromagnetic how velocity data (invasive) and echo-Doppler data (noninvasive). Arterial compliance was determined for two- and t hree-element windkessel models of the circulation using the area metho d and an iterative procedure, respectively. Once validated, the noninv asive methodology was used to determine normal compliance values for a reference population of 70 subjects (age range, 20 to 81 years) with normal 24-hour ambulatory blood pressures and without Doppler-echocard iographic evidence for structural heart disease. The limits of agreeme nt between invasive and noninvasive pressure data, compared at 10% int ervals during ejection and nonejection, were narrow over a wide range of pressures, with no significant differences between methods. Invasiv e and noninvasive instantaneous aortic inflow values differed slightly but significantly at the start of ejection (P<.05), but during the la tter 90% of ejection, values for the two methods were similar, with na rrow limits of agreement. Total vascular resistance and arterial compl iance values derived from invasive and noninvasive data were similar. Arterial compliance values for the normal population using the two-ele ment model (C-2E) ranged from 0.74 to 2.44 cm(3)/mm Hg (mean, 1.57+/-0 .38 cm(3)/mm Hg), with a beat-to-beat variability of 5.2+/-3.9%. C-2E decreased with increasing age (r=-.73, P<.001) and tended to be higher in men (1.67+/-0.41 cm(3)/ mm Hg) than in women (1.51+/-0.35 cm(3)/mm Hg, P=.07). Compliance values for the three-element model (C-3E) were predictably smaller than for the two-element model (mean, 1.23+/-0.30 ; range, 0.59 to 2.16 cm(3)/mm Hg, P<.001 versus C-2E) but correlated with C-2E values (r=.81, P<.001) and were also inversely related to ag e (r=-.56, P<.001). Ridge regression and principal component analyses both showed the compliance value to be a composite function whose vari ation could be best predicted by consideration of simultaneous values for five major hemodynamic determinants: heart rate, mean flow, mean a ortic pressure, minimal diastolic pressure, and end-systolic pressure. Multivariate analysis revealed age and sex to be independent predicto rs of compliance (P<.01 for both). There were no differences in compli ance between black and white subjects.