Determination of age-related increases in large artery stiffness by digital pulse contour analysis.

The stiffness of the aorta can be determined by measuring carotid-femoral pulse wave velocity (PWV(cf)). PWV may also influence the contour of the peripheral pulse, suggesting that contour analysis might be used to assess large artery stiffness. An index of large artery stiffness (SI(DVP)) derived from the digital volume pulse (DVP) measured by transmission of IR light (photoplethysmography) was examined. SI(DVP) was obtained from subject height and from the time delay between direct and reflected waves in the DVP. The timing of these components of the DVP is determined by PWV in the aorta and large arteries. SI(DVP) was, therefore, expected to provide a measure of stiffness similar to PWV. SI(DVP) was compared with PWV(cf) obtained by applanation tonometry in 87 asymptomatic subjects (21-68 years; 29 women). The reproducibility of SI(DVP) and PWV(cf) and the response of SI(DVP) to glyceryl trinitrate were assessed in subsets of subjects. The mean within-subject coefficient of variation of SI(DVP), for measurements at weekly intervals, was 9.6%. SI(DVP) was correlated with PWV(cf) ( r =0.65, P <0.0001). SI(DVP) and PWV(cf) were each independently correlated with age and mean arterial blood pressure (MAP) with similar regression coefficients: SI(DVP)=0.63+0.086 x age+0.042 x MAP ( r =0.69, P <0.0001); PWV(cf)=0.76+0.080 x age+0.053 x MAP ( r =0.71, P <0.0001). Administration of glyceryl trinitrate (3, 30 and 300 microg/min intravenous; each dose for 15 min) in nine healthy men produced similar changes in SI(DVP) and PWV(cf). Thus contour analysis of the DVP provides a simple, reproducible, non-invasive measure of large artery stiffness.