Age-Specific Acute Changes in Carotid-Femoral Pulse Wave Velocity With Head-up Tilt

BACKGROUND

Aortic stiffness as measured by carotid-femoral pulse wave velocity (cfPWV) is known to depend on blood pressure (BP), and this dependency may change with age. Therefore, the hydrostatic BP gradient resulting from a change in body posture may elicit a cfPWV change that is age-dependent. We aimed to analyze the relationship between BP gradient-induced by head-up body tilting-and related changes in cfPWV in individuals of varying age.

METHODS

cfPWV and other hemodynamic parameters were measured in 30 healthy individuals at a head-up tilt of 0 degrees (supine), 30 degrees, and 60 degrees. At each angle, the PWV gradient and resulting cfPWV were also estimated (predicted) by assuming a global nonlinear, exponential, pressure-diameter relationship characterized by a constant ss(0), and taking into account that (diastolic) foot-to-foot cfPWV acutely depends on diastolic BP.

RESULTS

cfPWV significantly increased upon body tilting (8.0 +/- 2.0 m/s supine, 9.1 +/- 2.6 m/ s at 30 degrees, 9.5 +/- 3.2 m/s at 60 degrees, P for trend <0.01); a positive trend was also observed for heart rate (HR; P <0.01). When the observed, tilt-induced cfPWV change measured by applanation tonometry was compared with that predicted from the estimated BP hydrostatic gradient, the difference in observed-vs.-predicted PWV change increased nonlinearly as a function of age (R-2 for quadratic trend = 0.38, P <0.01, P vs. linear = 0.04). This result was unaffected by HR tilt-related variations (R-2 for quadratic trend = 0.37, P <0.01, P vs. linear = 0.04).

CONCLUSIONS

Under a hydrostatic pressure gradient, the pulse wave traveling along the aorta undergoes an age-related, nonlinear PWV increase exceeding the increase predicted from BP dependency.