Gravitational Dose‐Response Curves for Acute Cardiovascular Hemodynamics and Autonomic Responses in a Tilt Paradigm

Abstract

Background The cardiovascular system is strongly dependent on the gravitational environment. Gravitational changes cause mechanical fluid shifts and, in turn, autonomic effectors influence systemic circulation and cardiac control. We implemented a tilt paradigm to (1) investigate the acute hemodynamic response across a range of directions of the gravitational vector, and (2) to generate specific dose‐response relationships of this gravitational dependency. Methods and Results Twelve male subjects were tilted from 45° head‐up tilt to 45° head‐down tilt in 15° increments, in both supine and prone postures. We measured the steady‐state hemodynamic response in a range of variables including heart rate, stroke volume, cardiac output, oxygen consumption, total peripheral resistance, blood pressure, and autonomic indices derived from heart rate variability analysis. There is a strong gravitational dependence in almost all variables considered, with the exception of oxygen consumption, whereas systolic blood pressure remained controlled to within ≈3% across the tilt range. Hemodynamic responses are primarily driven by differential loading on the baroreflex receptors, combined with differences in venous return to the heart. Thorax compression in the prone position leads to reduced venous return and increased sympathetic nervous activity, raising heart rate, and systemic vascular resistance while lowering cardiac output and stroke volume. Conclusions Gravitational dose‐response curves generated from these data provide a comprehensive baseline from which to assess the efficacy of potential spaceflight countermeasures. Results also assist clinical management of terrestrial surgery in prone posture or head‐down tilt positions.

Detection of Preclinical Orthostatic Disorders in Young African and European Adults Using the Head-Up Tilt Test with a Standardized Hydrostatic Column Height: A Pilot Study

“…During the HUTT, the orthostatic changes in the hemodynamic parameters were identical to those presented in the literature [ 43 , 44 , 45 ]. A graded increase or decrease in tilt angle was accompanied by a proportional change in hemodynamic indices (except SBP) and the autonomic nervous system [ 46 ].…”

Effects of trunk posture on cardiovascular and autonomic nervous systems: A pilot study

“…Among them, the gravitational factor is a key factor in cardiac preload and myocardial contractility. Changes in body position can cause cardiovascular reflexes, causing orthostatic venous return obstruction, which leads to reduced cardiac output ( Bergenwald et al, 1977 ; Matzen et al, 1991 ; Harms et al, 2003 ; Dorogovtsev et al, 2021 ; Whittle et al, 2022 ). During supine head-up tilt (HUT), a reduction in SV is associated with a drop in pleural fluid content, cardiac volume, central blood pressure, and hemodynamic changes ( Van Lieshout et al, 2005 ; Cheung et al, 2020 ; Dorogovtsev et al, 2021 ).…”

Linking cerebral hemodynamics and ocular microgravity-induced alterations through an in silico-in vivo head-down tilt framework

“…Additional information regarding the employed instrumentation, usage of devices, and environmental calibration procedure can be found in refs. 12 , 30 .…”