Cardiovascular System Under Simulated Weightlessness: Head-Down Bed Rest vs. Dry Immersion

Abstract

Background: The most applicable human models of weightlessness are −6 • headdown bed rest (HDBR) and head-out dry immersion (DI). A detailed experimental comparison of cardiovascular responses in both models has not yet been carried out, in spite of numerous studies having been performed in each of the models separately. Objectives: We compared changes in central hemodynamics, autonomic regulation, plasma volume, and water balance induced by −6 • HDBR and DI. Methods: Eleven subjects participated in a 21-day HDBR and 12 subjects in a 3-day DI. During exposure, measurements of the water balance, blood pressure, and heart rate were performed daily. Plasma volume evolution was assessed by the Dill-Costill method. In order to assess orthostatic tolerance time (OTT), central hemodynamic responses to orthostatic stimuli, and autonomous regulation, the 80 • lower body negative pressure-tilt test was conducted before and right after both exposures. Results: For most of the studied parameters, the changes were co-directional, although they differed in their extent. The changes in systolic blood pressure and total peripheral resistance after HDBR were more pronounced than those after DI. The OTT was decreased in both groups: to 14.2 ± 3.1 min (vs. 27.9 ± 2.5 min before exposure) in the group of 21-day HDBR and to 8.7 ± 2.1 min (vs. 27.7 ± 1.2 min before exposure) in the group of 3-day DI. Conclusions: In general, cardiovascular changes during the 21-day HDBR and 3day DI were co-directional. In some cases, changes in the parameters after 3-day DI exceeded changes after the 21-day HDBR, while in other cases the opposite was true. Significantly stronger effects of DI on cardiovascular function may be due to hypovolemia and support unloading (supportlessness).

The First Female Dry Immersion (NAIAD-2020): Design and Specifics of a 3-Day Study

“…In general, an increase in DBP is recorded for male immersions in the first week of immersion, in contrast to our study (Shul'zhenko et al, 1980;Borovik et al, 2020). Comparison of blood pressure and heart rate values (de Abreu et al, 2017;Amirova et al, 2020b) in DI of the same duration between men and women volunteers using two-way ANOVA showed a significant difference between the sexes in heart rate [F(1,80) = 94.57; P < 0.0001] throughout the entire observation period and in SBP [F(1,80) = 38.28; P < 0.0001] -only during immersion. The heart rate in women was, on average, 15 beats per minute higher, while SBP was lower by 14.8 mm Hg.…”

“…This condition is similar to weightlessness, with water hydrostatic pressure distributed equally over the body surface ( Grigor’ev et al, 2004 ; Navasiolava et al, 2011 ). Dry immersion promotes rapid gravitational deconditioning for somatosensor, cardiovascular and other systems ( Navasiolava et al, 2011 ; Tomilovskaya et al, 2019 ; Amirova et al, 2020b ). Dry immersion, as well as HDBR, is accompanied by central hypervolemia, however, there is also evidence that DI has a more powerful effect on the cardiovascular system than −8° HDBR does ( Krupina et al, 1982 ).…”

Autonomic Function in Parkinson's Disease Subjects Across Repeated Short-Term Dry Immersion: Evidence From Linear and Non-linear HRV Parameters

“…Similarly, the modest decrease of BP and heart rate (HR), as well as the increased variability of HR, which evidenced on compensatory mechanisms, was detected during 45-min DI sessions in healthy young subjects (Gerasimova- Meigal and Meigal, 2019;Meigal et al, 2020). These data are in line with the dynamics of BP and HR in healthy young subjects during short-term DI (3-5 days; Tomilovskaya et al, 2019;Amirova et al, 2020). Nonetheless, many humoral factors, which are important for systemic vascular resistance and microcirculation, for example, markers of endothelial state and inflammation, are perceived unchanged by 7 days of DI (Tomilovskaya et al, 2019;Amirova et al, 2020).…”

“…Earlier we have shown that ground-based microgravity modeled with a short-term session of DI diminished tremor and muscle rigidity in Parkinson's disease (PD; Meigal et al, 2018Meigal et al, , 2021aMiroshnichenko et al, 2018), which can be attributed to the well-established atonia-inducing effect of DI on the skeletal muscle of healthy subjects (Navasiolava et al, 2011;Amirova et al, 2020). Additionally, the performance of the visual-motor reaction time tasks with higher cognition demand has improved after a program of DI sessions (Meigal et al, 2021b).…”

“…Under modeled microgravity, the body of the subject experiences the main effects of space flight, such as redistribution of the extracellular fluid of the body, hypokinesia, and lack of support (Tomilovskaya et al, 2019;Pandiarajan and Hargens, 2020). Compared with other methods, "dry" immersion (DI) is considered the most sparing method of modeling microgravity in Earth conditions, since the redistribution of blood to the upper body and head that occurs during DI session is not so pronounced as with other methods, e.g., antiorthostatic hypokinesia (Watenpaugh, 2016;Tomilovskaya et al, 2019;Amirova et al, 2020).…”