The Effects of Hind Limb Suspension and Cast Mediated Immobilization on Bone Strength Properties

Sanseverino, Matthew J.; Speacht, Toni L.; Donahue, Henry J.; Lau, Anthony G.

doi:10.1109/embc.2018.8512691

Cited by 3 publications

(1 citation statement)

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“…Due to the limited possibilities of in-flight research, ground-based analogs are used for reproducing and studying the effects of microgravity on the human body. For example, limb casting and limb suspension have been used to study bone density reduction and neuromuscular alterations due to inactivity and unloading ( Kitahara et al, 2003 ; De Boer et al, 2007 ; Sanseverino et al, 2018 ), while bed rest and dry immersion are the most widely used ground analogs for simulating the effects of prolonged weightlessness exposure on the different physiological systems. In particular, Head-Down (−6°) Tilt (HDT) bed rest elicits extensively reduced motor activity ( Sandler and Vernikos, 1986 ), as well as the elimination of the regular alternation between 1 and 0 Gz along the head-to-foot axis, and the characteristic fluids redistribution occurring during sustained exposure to microgravity ( Montgomery, 1993 ).…”

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confidence: 99%

Evaluation of Cardiac Circadian Rhythm Deconditioning Induced by 5-to-60 Days of Head-Down Bed Rest

et al. 2021

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Head-down tilt (HDT) bed rest elicits changes in cardiac circadian rhythms, generating possible adverse health outcomes such as increased arrhythmic risk. Our aim was to study the impact of HDT duration on the circadian rhythms of heart beat (RR) and ventricular repolarization (QTend) duration intervals from 24-h Holter ECG recordings acquired in 63 subjects during six different HDT bed rest campaigns of different duration (two 5-day, two 21-day, and two 60-day). Circadian rhythms of RR and QTend intervals series were evaluated by Cosinor analysis, resulting in a value of midline (MESOR), oscillation amplitude (OA) and acrophase (φ). In addition, the QTc (with Bazett correction) was computed, and day-time, night-time, maximum and minimum RR, QTend and QTc intervals were calculated. Statistical analysis was conducted, comparing: (1) the effects at 5 (HDT5), 21 (HDT21) and 58 (HDT58) days of HDT with baseline (PRE); (2) trends in recovery period at post-HDT epochs (R) in 5-day, 21-day, and 60-day HDT separately vs. PRE; (3) differences at R + 0 due to bed rest duration; (4) changes between the last HDT acquisition and the respective R + 0 in 5-day, 21-day, and 60-day HDT. During HDT, major changes were observed at HDT5, with increased RR and QTend intervals’ MESOR, mostly related to day-time lengthening and increased minima, while the QTc shortened. Afterward, a progressive trend toward baseline values was observed with HDT progression. Additionally, the φ anticipated, and the OA was reduced during HDT, decreasing system’s ability to react to incoming stimuli. Consequently, the restoration of the orthostatic position elicited the shortening of RR and QTend intervals together with QTc prolongation, notwithstanding the period spent in HDT. However, the magnitude of post-HDT changes, as well as the difference between the last HDT day and R + 0, showed a trend to increase with increasing HDT duration, and 5/7 days were not sufficient for recovering after 60-day HDT. Additionally, the φ postponed and the OA significantly increased at R + 0 compared to PRE after 5-day and 60-day HDT, possibly increasing the arrhythmic risk. These results provide evidence that continuous monitoring of astronauts’ circadian rhythms, and further investigations on possible measures for counteracting the observed modifications, will be key for future missions including long periods of weightlessness and gravity transitions, for preserving astronauts’ health and mission success.

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