Use of pulse pressure method for estimating total arterial compliance in vivo

Abstract

We determined total arterial compliance from pressure and flow in the ascending aorta of seven anesthetized dogs using the pulse pressure method (PPM) and the decay time method (DTM). Compliance was determined under control and during occlusion of the aorta at four different locations (iliac, renal, diaphragm, and proximal descending thoracic aorta). Compliance of PPM gave consistently lower values (0.893 ± 0.015) compared with the compliance of DTM (means ± SE; r = 0.989). The lower compliance estimates by the PPM can be attributed to the difference in mean pressures at which compliance is determined (mean pressure, 81.0 ± 3.6 mmHg; mean diastolic pressure, over which the DTM applies, 67.0 ± 3.6 mmHg). Total arterial compliance under control conditions was 0.169 ± 0.007 ml/mmHg. Compliance of the proximal aorta, obtained during occlusion of the proximal descending aorta, was 0.100 ± 0.007 ml/mmHg. Mean aortic pressure was 80.4 ± 3.6 mmHg during control and 102 ± 7.7 mmHg during proximal descending aortic occlusion. From these results and assuming that upper limbs and the head contribute as little as the lower limbs, we conclude that 60% of total arterial compliance resides in the proximal aorta. When we take into account the inverse relationship between pressure and compliance, the contribution of the proximal aorta to the total arterial compliance is even more significant.

A comparison of methods for assessing total arterial compliance

“…For both PPM and AM the usual standard units of measurement are ml mm Hg -1 , however, TAC has also been reported in arbitrary units. 16,21 In this study, the normal controls had a TAC of approximately 1.6 ml mm Hg -1 , which correlates well with mean values reported by Stergiopulos et al 5 as well as in a canine model. 6 Similarly, mean values here for AM correlate with those reported by O'Rourke et al 21 but not those reported by Liang et al 16 in similar patients.…”

“…The PPM uses SV (derived from the dimensions and pulsed-wave Doppler velocity of the aortic outflow) and the pressure waveform obtained from tonometry of the radial artery to determine TAC. 5,6,9 Compliance (C) is obtained as dV/dP (V ¼ systemic blood volume; P ¼ pressure and d ¼ change) and resistance (R) represents total resistance. Using the abbreviations j ¼ sqrt(À1), w ¼ 2pf, f being frequency, t is time, Z in is the input impedance and Q is the flow, the equations governing this method in the frequency and time domain are:…”

“…This lack of uniformity among measures of TAC between studies may be hard to interpret, however, most of these studies show the same differences within groups with and without risk. 5,12,16,22 Figure 1 Regression plots for total arterial compliance (TAC) (ml mm Hg -1 ) for the pulse-pressure method ((PPM) upper), area method ((AM) middle) and stroke volume/pulse-pressure method ((SVPP) bottom) between brachial (BPP) and aortic (AoPP) pulse pressure (mm Hg). The regression models were fit using an inverse model fit (Y ¼ b0 þ (b1/t)).…”

“…3,4 Several methods of estimating TAC have been used, all derived from the Windkessel model-a mathematical model based on compliance and resistance, which uses pressure and volume as input. 5,6 The two-element Windkessel model is the simplest one and the most widely used, but still the optimal technique is unclear. This study sought to compare three methods of estimating TAC in a large group of patients with and without cardiovascular risk to determine their correlation and which may be the most robust.…”

Efficient implementation of non-linear valve law and ventricular interaction dynamics in the minimal cardiac model

“…Only a minimal number of parameters, such as chamber elastances and arterial resistances, are required. These models are more suitable for clinical feedback but most are focused on simulating only certain areas of CVS function [5][6][7][8][9][10].…”