Background: The increase of arterial stiffness with blood pressure (BP) reflects the nonlinear increase of arterial pressure with volume. Stiffness can be represented by the square of the pulse wave velocity (PWV), and is currently measured for diastolic BP (DBP). By analyzing the changes in DBP and diastolic PWV (PWVd) induced by changing arm position, we evaluated a linear relation between stiffness and DBP in an individual subject.

Methods: In 27 healthy subjects (66% men, age 51±17 years, BP 134/78±17/12 mmHg), we measured brachial BP and carotid-radial PWVd in supine position with arm supported at 3 postures: below-, at- and above the heart level. PWVd² was expressed by the model 0.127×β(DBP - α), where β and α were best fitted for each subject, and then used for determining the systolic stiffness PWVs² from the SBP, according to the model 0.127×β(SBP - α). β (“stiffness constant”) expresses the steepness of the pressure-volume exponential curve.

Results: PWVd² highly correlated with DBP for individual subjects (r=0.95±0.03). The mean β was 13.1±11.7 and increased significantly at older age (r=0.49). While diastolic PWV increased linearly with age with r=0.64, calculated systolic PWV increased with age exponentially with r=0.65 that became steep over age 50 years (Figure; all p<0.001).

Conclusions: (1) The gravity effect on brachial DBP induces linear changes in diastolic PWV, which increase with age. (2) The dynamic changes of PWV and DBP may provide a novel and simple determination of systolic PWV, which shows greater age sensitivity than diastolic PWV.