Comparison of Autonomic Control of Blood Pressure During Standing and Artificial Gravity Induced via Short-Arm Human Centrifuge

Abstract

Autonomic control of blood pressure is essential toward maintenance of cerebral perfusion during standing, failure of which could lead to fainting. Long-term exposure to microgravity deteriorates autonomic control of blood pressure. Consequently, astronauts experience orthostatic intolerance on their return to gravitational environment. Ground-based studies suggest sporadic training in artificial hypergravity can mitigate spaceflight deconditioning. In this regard, short-arm human centrifuge (SAHC), capable of creating artificial hypergravity of different g-loads, provides an auspicious training tool. Here, we compare autonomic control of blood pressure during centrifugation creating 1-g and 2-g at feet with standing in natural gravity. Continuous blood pressure was acquired simultaneously from 13 healthy participants during supine baseline, standing, supine recovery, centrifugation of 1-g, and 2-g, from which heart rate (RR) and systolic blood pressure (SBP) were derived. The autonomic blood pressure regulation was assessed via spectral analysis of RR and SBP, spontaneous baroreflex sensitivity, and non-linear heart rate and blood pressure causality (RR↔SBP). While majority of these blood pressure regulatory indices were significantly different (p < 0.05) during standing and 2-g centrifugation compared to baseline, no change (p > 0.05) was observed in the same indices during 2-g centrifugation compared to standing. The findings of the study highlight the capability of artificial gravity (2-g at feet) created via SAHC toward evoking blood pressure regulatory controls analogous to standing, therefore, a potential utility toward mitigating deleterious effects of microgravity on cardiovascular performance and minimizing post-flight orthostatic intolerance in astronauts.

Short-Term Cardiovascular Response to Short-Radius Centrifugation With and Without Ergometer Exercise

“…As a result of these control actions, other cardiovascular variables such as blood pressure, PP, SV, and CO showed only small changes during this phase. This is consistent with previous short-radius centrifugation studies where subjects did not show differences in pressure numerics (MAP, SBP, DBP), between baseline in supine position, 1 G, or 2 G (measured at the feet) ( Goswami et al, 2015a ; Verma et al, 2018 ). With the exception of the gravity gradient, which is particularly pronounced during short-radius centrifugation, this follows the same overall cardiovascular mechanisms and responses that someone on Earth experiences when changing from supine to upright position.…”

“…Instead, subjects kept theirs immobile and aligned with their heart during the entire experiment. This technique has also been used in previous centrifugation studies ( Goswami et al, 2015a , b ; Verma et al, 2018 ). While the Nexfin and other similar systems such as Portapres, Finometer, and Finapres certainly have limitations, they currently are the only methods to measure continuous arterial blood pressure and estimate other CV variables continuously and non-invasively.…”

“…While the Nexfin and other similar systems such as Portapres, Finometer, and Finapres certainly have limitations, they currently are the only methods to measure continuous arterial blood pressure and estimate other CV variables continuously and non-invasively. These devices have been used extensively in the human life science space program and ground-based analog studies ( Fritsch-Yelle et al, 1994 ; Di Rienzo et al, 2008 ; Verheyden et al, 2009 ; Hughson et al, 2012 ; Stenger et al, 2013 ; Goswami et al, 2015a , b ; Lee et al, 2015 ; Linnarsson et al, 2015 ; Morita et al, 2016 ; Masatli et al, 2018 ; Verma et al, 2018 ), including in conditions where hydrostatic pressures are moderately altered such as Head-Up Tilt and LBNP ( Linnarsson et al, 2015 ; Goswami et al, 2015b ). Similarly, our study induced only moderate orthostatic stress, and we are using a device that facilitates comparison with other studies in the field, which is important.…”

“…Recent studies have investigated acute cardiovascular responses while being exposed to AG using a short-radius centrifuge. A study conducted at the Institute for Space Medicine and Physiology (MEDES), in Toulouse, France, investigated two gravity levels (1 G and 2 G, measured at the feet), and concluded that centrifugation at 2 G provides similar blood pressure regulatory indices ( Verma et al, 2018 ), and similar cardiovascular and cerebral responses ( Goswami et al, 2015a ) to standing. Another study conducted at the German Aerospace Institute (DLR) also investigated cardiovascular reactions to centrifugation at 1 and 2 G (measured at the feet) showing apparent gender-specific patterns in their cardiovascular responses ( Masatli et al, 2018 ).…”

Gravitational stress during parabolic flights reduces the number of circulating innate and adaptive leukocyte subsets in human blood

“…The short-arm human centrifuge (SAHC) can be applied to investigate the effects of hypergravity on humans, and is also used to countermeasure microgravity effects during long term space flight [ 13 , 14 ]. However, there are currently no studies available, which used SAHC to investigate hypergravity effects on the human immune system.…”