Key result
Five-week head-down tilt bed rest is linked to a ~15% lower carotid reservoir pressure integral.
Why the study?
The conventional wave transmission model obscures the Windkessel function of elastic arteries, leading to the reservoir-excess pressure model as a proposed alternative for interpreting arterial blood pressure waveforms.
Does 5-week head down tilt bed rest alter carotid reservoir pressure and left ventricular ejection time in young healthy subjects?
Observational (n=10)
No
Does 5-week head down tilt bed rest alter carotid reservoir pressure and left ventricular ejection time in young healthy subjects?
Prolonged head down tilt bed rest reduces carotid reservoir pressure, which correlates with reductions in left ventricular ejection time and diastolic length, supporting the clinical utility of the reservoir-wave hypothesis.
Bed rest-associated carotid reservoir pressure reductions warrant no practice change; hypothesis-generating for reservoir-wave hypothesis in microgravity research.
Background: The arterial pressure waveform reflects the interaction between the heart and the arterial system and carries potentially relevant information about circulatory status. According to the commonly accepted 'wave transmission model', the net BP waveform results from the super-position of discrete forward and backward pressure waves, with the forward wave in systole determined mainly by the left ventricular (LV) ejection function and the backward by the wave reflection from the periphery, the timing and amplitude of which depend on arterial stiffness, the wave propagation speed and the extent of downstream admittance mismatching. However, this approach obscures the 'Windkessel function' of the elastic arteries. Recently, a 'reservoir-excess pressure' model has been proposed, which interprets the arterial BP waveform as a composite of a volume-related 'reservoir' pressure and a wave-related 'excess' pressure. Methods: In this study we applied the reservoir-excess pressure approach to the analysis of carotid arterial pressure waveforms (applanation tonometry) in 10 young healthy volunteers before and after a 5-week head down tilt bed rest which induced a significant reduction in stroke volume (SV), end-diastolic LV volume and LV longitudinal function without significant changes in central blood pressure, cardiac output, total peripheral resistance and aortic stiffness. Forward and backward pressure components were also determined by wave separation analysis. Results: Compared to the baseline state, bed rest induced a significant reduction in LV ejection time (LVET), diastolic time (DT), backward pressure amplitude (bP) and pressure reservoir integral (INTPR). INTPR correlated directly with LVET, DT, time to the peak of backward wave (bT) and stroke volume, while excess pressure integral (INTXSP) correlated directly with central pressure. Furthermore, Δ.INTPR correlated directly with Δ.LVET, and Δ.DT, and in multivariate analysis INTPR was independently related to LVET and DT and INTXSP to central systolic BP. Conclusion: This is an hypothesis generating paper which adds support to the idea that the reservoir-wave hypothesis applied to non-invasively obtained carotid pressure waveforms is of potential clinical usefulness.
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Palombo et al. (2022) conducted an observational in Healthy volunteers (n=10). Head down tilt bed rest (HDTBR) vs. Baseline (before bed rest) was evaluated on Reservoir pressure integral (INTPR) in kPa*s (p=<0.01). A 5-week head down tilt bed rest in young healthy men significantly reduced the carotid reservoir pressure integral from 10.6 to 9.0 kPa*s.
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