A comparison of methods for assessing total arterial compliance

Abstract

There are several methods of assessing total arterial compliance (TAC) based on the two element Windkessel model, which is a ratio of pressure and volume, but the optimal technique is unclear. In this study, three methods of estimating TAC were compared to determine which was the most robust in a large group of patients with and without cardiovascular risk. In all, 320 patients (170 men; age 55+/-10) were studied; TAC was determined by the pulse-pressure method (PPM), the area method (AM) and the stroke volume/pulse-pressure method (SVPP). We obtained arterial waveforms using radial applanation tonometry, dimensions using two-dimensional echocardiography and flow data by Doppler. Clinical data, risk factors, echo parameters and TAC by all three methods were then compared. TAC (ml mm Hg(-1)) by the PPM was 1.24+/-0.51, by the AM 1.84+/-0.90 and by the SVPP 1.96+/-0.76 (P<0.0001 between groups). Correlation was good between all methods: PPM/AM r=0.83, PPM/SVPP r=0.94 and AM/SVPP r=0.80 (all P<0.0001). Subgroup analysis showed significant differences between patients with and those without cardiovascular risk for all three methods; TAC-AM and TAC-SVPP values were similar and significantly higher than TAC-PPM. The only significant relationships observed with TAC and echo parameters were in left ventricular (LV) septal thickness (R(2)=0.07; P<0.0001) and LV mass (R(2)=0.04; P=0.004). Normal and abnormal values of TAC vary according to method, which should be expressed. Each of the techniques shows good correlation with each other, however, values for TAC-PPM are significantly lower. TAC-PPM and TAC-SVPP are comparable in determining differences between groups with and without cardiovascular risk.