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.
Highlights
Physiologists have had a very long-standing interest in the mechanisms governing the shape of the arterial pressure pulse
All of these values were quite similar between M1 and M2, indicating that, in each position subjects were hemodynamically stable
The major new finding is that the former and the latter are closely correlated, at least in young subjects in the course of an orthostatic stress test. This result supports the validity of interpreting morphologic features of the central aortic pressure waveform in terms of superimposed forward and reflected waves, even when approximately reconstructed from the noninvasive recording of the radial pulse
Summary
Physiologists have had a very long-standing interest in the mechanisms governing the shape of the arterial pressure pulse. (Frank 1905), he linked these deviations to the finite propagation velocity of pressure waves along arteries in the forward (from heart to periphery) and backward directions (reflections from the periphery toward the heart), never quite resolving the inherent contradiction of a lumped model (Windkessel) that would possess transmission line properties (Parker 2009; Nichols et al 2011a) It was for the generations of physiologists (Dow and Hamilton 1939; McDonald 1955; Taylor 1957; Wormersley 1958; O’Rourke 1967; Nichols et al 1977) to solve this issue, providing a consistent framework for explaining the oscillatory behavior of the arterial system, both in the time and frequency domain, across age groups, genders, health conditions, and species (reviewed in Nichols et al 2011a; O’Rourke and Yaginuma 1984; Parker 2009).
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