Impact of body tilt on the central aortic pressure pulse

Abstract

The present work was undertaken to investigate, in young healthy volunteers, the relationships between the forward propagation times of arterial pressure waves and the timing of reflected waves observable on the aortic pulse, in the course of rapid changes in body position. 20 young healthy subjects, 10 men, and 10 women, were examined on a tilt table at two different tilt angles, −10° (Head-down) and + 45° (Head-up). In each position, carotid-femoral (Tcf) and carotid-tibial forward propagation times (Tct) were measured with the Complior device. In each position also, the central aortic pressure pulse was recorded with radial tonometry, using the SphygmoCor device and a generalized transfer function, so as to evaluate the timing of reflected waves reaching the aorta in systole (onset of systolic reflected wave, sT1r) and diastole (mean transit time of diastolic reflected wave, dMTT). The position shift from Head-up to Head-down caused a massive increase in both Tct (women from 130 ± 10 to 185 ± 18 msec P < 0.001, men from 136 ± 9 to 204 ± 18 msec P < 0.001) and dMTT (women from 364 ± 35 to 499 ± 33 msec P < 0.001, men from 406 ± 22 to 553 ± 21 msec P < 0.001). Mixed model regression showed that the changes in Tct and dMTT observed between Head-up and Head-down were tightly coupled (regression coefficient 2.1, 95% confidence interval 1.9–2.3, P < 0.001). These results strongly suggest that the diastolic waves observed on central aortic pulses reconstructed from radial tonometric correspond at least in part to reflections generated in the lower limbs.

The Effect of Body Position on Measures of Arterial Stiffness in Humans

“…BP plays an important role in affecting arterial stiffness, and the effect that gravity has on BP is well documented by regional differences in BP in non-supine positions due to an orthostatic column being created [5], and altering distributions of venous volumes. To combat changes in BP, the baroreceptors must detect the change and activate an auto-DOI: 10.1159/000506351 nomic response to vasoconstrict arterioles and maintain cerebral BP. Acute changes in autonomic activity and increases in BP have each been directly linked to central arterial stiffness [6,7], potentially affecting our understanding of how this measurement should be applied.…”

“…In contrast to common seated BP measurement, cfPWV has been standardized to the supine position for measurement [8]. Little work has been done to investigate the effect of altering body position on the measurement of resting cfPWV [9,10], yet this could be important considering the majority of our waking time is spent in non-supine positions.…”