The arterial baroreflex and inherent G tolerance.

Sundblad, Patrik; Kölegård, Roger; Migeotte, Pierre-Francois; Delière, Quentin; Eiken, Ola; Kölegård, Roger; Delière, Quentin

Purpose: High G tolerance is based on the capacity to maintain a sufficient level of arterial pressure (AP) during G load; therefore, we hypothesized that subjects with high G tolerance (H group) would have stronger arterial baroreflex responses compared to subjects with low G tolerance (L group). The carotid baroreflex was evaluated using the neck pressure method (NP), which assesses open-loop responses.Methods: The carotid baroreflex was tested in 16 subjects, n = 8 in the H and L group, respectively, in the supine and upright posture. Heart rate and AP were measured.Results: There were no differences between groups in the maximum slopes of the carotid baroreflex curves. However, the H group had a larger systolic and mean AP (SAP, MAP) increase to the initial hypotensive stimuli of the NP sequence in the upright position compared to the L group, 7.5 ± 6.6 vs 2.0 ± 2.4 and 4.1 ± 3.4 vs 1.1 ± 1.1 mmHg for SAP and MAP, respectively. Furthermore, the L group exhibited an increased latency between stimuli and response in AP in the upright compared to supine position, 4.1 ± 1.0 vs 3.1 ± 0.9 and 4.7 ± 1.1 vs 3.6 ± 0.9 s, for SAP and MAP. No differences in chronotropic responses were observed between the groups.Conclusions: It is concluded that the capacity for reflexive vasoconstriction and maintained speed of the vascular baroreflex during orthostatic stress are coupled to a higher relaxed GOR tolerance.

BAROREFLEXES; VASOCONSTRICTION; ORTHOSTATIC hypotension; SYSTOLIC blood pressure; POSTURE; ARTERIAL physiology; CAROTID artery physiology; PHYSIOLOGICAL adaptation; AUTONOMIC nervous system diseases; BLOOD pressure; COMPARATIVE studies; GRAVITATION; RESEARCH methodology; MEDICAL cooperation; RESEARCH; SYMPTOMS; EVALUATION research; RANDOMIZED controlled trials; PHYSIOLOGY

European Journal of Applied Physiology, 2016, Vol 116, Issue 6, p1149

1439-6319

Academic Journal

10.1007/s00421-016-3375-1