Objective: PWV(m/s), a gold-standard measure of arterial stiffness, depends on both age and arterial pressure P(mmHg). We evaluated a model-derived expression that enables to separate between these factors.

Design and method: A previously reported model assumed that P varies exponentially with the arterial volume V (in relative units): P=−α+ϒexp(βV) [Eq.1], where α, β and ϒ are pressure-independent constants that may depend on age. Arterial stiffness (in mmHg) is defined as the local slope of the P-V curve, i.e. dP/dV [Eq.2] and can be expressed by the Bramwell-Hill equation 7.85•PWV² [Eq.3]. Eqs.1−3 provide the model prediction PWV²=0.127β(P+α) [Eq.4], for which β (‘stiffness index’) quantifies the stiffness pressure-dependence and α is the model-based internal pressure. In 68 healthy subjects (59% men, age 54±17 years, BP 133±20 /76±11 mmHg), we measured brachial BP and carotid-radial PWV in supine position with arm supported at 3 postures: below-, at- and above the heart level to obtain PWV at different DBP levels (the relevant pressure for foot-by-foot analysis method). Parameters β and α were best-fitted to Eq.4 using symmetric regression.

Results: PWV² highly correlated with DBP for individuals (mean R=0.95). β was 10.6±7.8 (Mean±SD), and was greater for age ≥53 yr (median) than youngers: 14.0±9.0 vs. 7.3±4.3 (P=0.0002). Similarly, α (−3±57 mmHg) was −14±65 vs. 20±41 mmHg (P=0.01). β and α were highly correlated nonlinearly (R=0.94).

Conclusions: PWV² is superior to PWV for data analysis for its direct association with stiffness and linear dependence on DBP with age- and disease-dependent but pressure-independent coefficients β and α.