A comparison of methods for assessing total arterial compliance

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 (mlmmHg^–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 (R²=0.07; P<0.0001) and LV mass (R²=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.