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

Abstract

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° (supine), 30°, and 60°. 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 β0, 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°, 9.5 ± 3.2 m/s at 60°, 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 (R2 for quadratic trend = 0.38, P < 0.01, P vs. linear = 0.04). This result was unaffected by HR tilt-related variations (R2 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.

Keywords: arterial function; arterial stiffness; blood pressure; early vascular aging; hypertension; pressure dependence.

Figure 1.

Measurement protocol. Participants were placed supine on a tilt table placed horizontally (0°). After at least 10 minutes’ resting, blood pressure (BP) and radial tonometry were measured at the upper arm, always kept at the heart level. Then, carotid–femoral pulse wave velocity (PWV) was performed by applanation tonometry. Afterwards, participants were head-up tilted to 30° and 60° and the same set of measurement was repeated at each position after 10 minutes resting.

Figure 2.

Correlation between β₀ and age. Stiffness index β₀ is the constant (exponent) of the exponential pressure–diameter relationship, named “stiffness index,” and was measured in each patient at 0°, using data from measured carotid–femoral pulse wave velocity and central diastolic blood pressure. See equation (1) in the methods session for further details. Solid line: prediction line. Dashed lines: 95% confidence intervals of the prediction line.

Figure 3.

Association between age and the difference of measured (by arterial tonometry) vs. predicted (by equation (7)) pulse wave velocity (PWV) at each tilt angle (30° = circles, 60° = squares), expressed as observed-vs.-predicted PWV and adjusted for tilt-related heart rate changes. Solid line: prediction line. Dashed lines: 95% confidence intervals of the prediction line.