Abstract
PurposeIncreasing the level of gravity passively on a centrifuge, should be equal to or even more beneficial not only to astronauts living in a microgravity environment but also to patients confined to bed. Gravity therapy (GT) may have beneficial effects on numerous conditions, such as immobility due to neuromuscular disorders, balance disorders, stroke, sports injuries. However, the appropriate configuration for administering the Gz load remains to be determined.MethodsTo address these issues, we studied graded G-loads from 0.5 to 2.0g in 24 young healthy, male and female participants, trained on a short arm human centrifuge (SAHC) combined with mild activity exercise within 40–59% MHR, provided by an onboard bicycle ergometer. Hemodynamic parameters, as cardiac output (CO), stroke volume (SV), mean arterial pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were analyzed, as well as blood gas analysis. A one-way repeated measures ANOVA and pairwise comparisons were conducted with a level of significance p < 0.05.ResultsSignificant changes in heart rate variability (HRV) and its spectral components (Class, Fmax, and VHF) were found in all g loads when compared to standing (p < 0.001), except in 1.7 and 2.0g. There were significant changes in CO, cardiac index (CI), and cardiac power (CP) (p < 0.001), and in MAP (p = 0.003) at different artificial gravity (AG) levels. Dose-response curves were determined based on statistically significant changes in cardiovascular parameters, as well as in identifying the optimal G level for training, as well as the optimal G level for training. There were statistically significant gender differences in Cardiac Output/CO (p = 0.002) and Cardiac Power/CP (p = 0.016) during the AG training as compared to standing. More specifically, these cardiovascular parameters were significantly higher for male than female participants. Also, there was a statistically significant (p = 0.022) gender by experimental condition interaction, since the high-frequency parameter of the heart rate variability was attenuated during AG training as compared to standing but only for the female participants (p = 0.004).ConclusionThe comprehensive cardiovascular evaluation of the response to a range of graded AG loads, as compared to standing, in male and female subjects provides the dose-response framework that enables us to explore and validate the usefulness of the centrifuge as a medical device. It further allows its use in precisely selecting personalized gravity therapy (GT) as needed for treatment or rehabilitation of individuals confined to bed.
Highlights
Life evolved and adapted within the gravitational field of Earth and gravity is critical to our existence, since we have to rely on Earth’s gravity, as a fundamental reference, in structuring musculoskeletal support and in the organizing of bodily fluids
From the correlation matrix (Figure 8) of the hemodynamic parameters of cardiac output (CO) and mean arterial pressure (MAP) standing significantly correlated with 1.7 and 2.0g. This enhances the significance of those parameters to construct dose response curves and determine
Based on the study of Migeotte et al (2009), who underlined the need for further investigation on the changes in graded g load and the gravity gradient in order to find the appropriate g load for short-arm human centrifuge (SAHC) countermeasure, we aimed to examine whether the SAHC training could induce cardiac responses analogous to the standing position
Summary
Life evolved and adapted within the gravitational field of Earth and gravity is critical to our existence, since we have to rely on Earth’s gravity, as a fundamental reference, in structuring musculoskeletal support and in the organizing of bodily fluids. We evolved specialized motion-sensing receptors in our inner ears acting like biological guidance systems. Years of space research in weightlessness and analog environments led to the conclusion that physiological health and performance on Earth is significantly dependent on gravity (Vernikos et al, 1996; Vernikos, 1996, 1997, 2008, 2017; Blaber et al, 2013b; Tanaka et al, 2016). When gravity is not used efficiently (due to lifestyle, inactivity or bedrest) to maintain the level of health that is appropriate to living in Earth’s 1G environment, it leads to negative consequences in all human physiological systems (Sandler and Vernikos, 1986; Rittweger and Frings-Meuthen, 2013; McDonnell et al, 2019). Orthostatic intolerance (OI), an inability to regulate blood pressure (BP) on assuming an upright stance (Robertson, 1999; Lambert and Lambert, 2014), is commonly experienced by astronauts upon their return to Earth after both short and long duration spaceflight (Buckey et al, 1996; Vernikos, 1996; Lee et al, 2015), as well as in people who resume posture after being confined to bed for experimental, clinical or pathological reasons (Goswami, 2017; Goswami et al, 2017)
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