COMPLEX AND FREQUENCY-DEPENDENT COMPLIANCE OF VISCOELASTIC WINDKESSELRESOLVES CONTRADICTIONS IN ELASTIC WINDKESSELS

Based on simulated data, recent studies by others showed that fitting measured pulse pressure with the pulse pressure predicted by the two-e lement windkessel (W2-based pulse pressure method, PPM) yielded estima tes of total arterial compliance closer to simulated values than other estimation methods that use either the W2 model or the three-element windkessel (W3). A later experimental application of the PPM, made by us, however, yielded relatively non pressure dependent estimates of co mpliance that were in contradiction with pressure dependent estimates obtained from the W2 model by fitting to the full aortic pressure wave (full pressure method, FPM). To explain these contradictory findings, in the present study we interpreted the aortic input impedance in ter ms of a viscoelastic windkessel (VW), where total peripheral resistanc e is connected in parallel to a complex and frequency dependent compli ance, C-c(j omega), described by the Voigt cell. Using ascending aorti c pressure and flow taken from four dogs, under a variety of haemodyna mic states, we compared the estimates of compliance obtained from the W3 and VW models and from different W2-based estimation methods: the F PM (C-W2), the PPM (C-pp), the decay time method, DTM (C-dt), and the area method, AM (C-am). The VW-based estimates of complex compliance r esolved contradictions in the W2-based estimates. Static compliance of VW-model, C-VW = C-c(O), showed a good correlation (p = 0.999) with C -W2 Correlation of static compliance with C-am and C-dt estimates was affected by distortions in diastolic pressure decay. The modulus of VW model's dynamic compliance, \C-c(omega(h))\, at the heart pulsation o mega(h) was well correlated (p = 0.975) with C-pp. Analysis of data fi t and compliance estimates indicated that the VW model yields an impro vement over the W3 in the physical interpretation of the overall arter ial properties. (C) 1998 IPEM. Published by Elsevier Science Ltd. All rights reserved.