This investigation assessed the effects of weightlessness on the central nervous system and specifically the sensorimotor system by inducing cortical reorganization through altered cortical excitability. The measures of cortical excitability will be evaluated for correlation with measures of lower limb functional recovery.

Transcranial magnetic stimulation (TMS) was used to evaluate motor cortex plasticity through the acquisition of recruitment curves. The location for application of the magnetic stimulation was determined by functional and structural brain magnetic resonance imaging (MRI). Data collected from these control subjects included resting motor threshold, paired pulse sequences, and cortical silent periods. The compound motor action potential and Hoffman reflex (H-reflex) response were collected as measures of peripheral stimulation.

Retention of Skeletal, Musculature and Postural Status with a Non-Invasive, Extremely Low-Level Mechanical Signal: A Ground-Based Evaluation of Efficacy.
PI: Clinton T. Rubin, PhD, Department of Biomedical Engineering, State University of New York, Stony Brook, New York 11794-2580

This study was designed to investigate the use of the human bed rest model of microgravity-induced osteopenia to evaluate the efficacy of a biomechanically based countermeasure, low magnitude mechanical stimuli (LMMS), to inhibit the bone loss that arises with disuse and its effect on loss of muscle strength and postural stability of the lower limb. During this campaign, data were collected from control subjects.

Changes in bone density were measured by dual-energy x- ray absorptiometry (DEXA), and quantitative computed tomography (QCT). Bone quantity (bone density) and bone quality were assessed by qualitative ultrasound and estimation of the bone's true mechanical properties. Lumbar spine MRIs were performed to investigate morphologic and biochemical changes in intervertebral discs. Disc volumes were measured for the lumbar discs L1/L2, L2/L3, L3/L4, and L4/L5. Functional assessment of posture was also performed during this campaign. Lower extremity somatosensory tests for light touch, proprioception, and vibration also were conducted to assess potential changes in postural stability.

Effect of Ultrasonic Bone Conductance on Orthostatic Tolerance during Bed Rest.
PI: Chester A. Ray, PhD, Professor of Medicine and Cellular and Molecular Physiology, Department of Medicine, Division of Cardiology, The Pennsylvania State College of Medicine, Hershey, Pennsylvania

This investigation was designed to assess muscle sympathetic nerve activity and its role in orthostatic intolerance (OI) through measurements of the vestibulosympathetic reflex. Microgravity has been shown to elicit marked changes in the vestibular system. A number of countermeasures have been developed to prevent or alleviate post-spaceflight OI. However, as yet, no single countermeasure has effectively prevented post-spaceflight OI.

Data from this campaign were used to determine if the vestibulosympathetic reflex is altered during and after bed rest and if ultrasonic bone stimulation (UBS) of the mastoid improved orthostatic tolerance and thus could serve as an effective and simple countermeasure for post-spaceflight OI.

The microneurographic method was used for measurement of sympathetic nerve activity. Cardiac parameters measured included arterial pressure, heart rate, blood flow, mean blood velocity measured by Doppler ultrasound, arterial diameter, and vascular resistance and conductance. Respiration pattern data also were collected in these subjects. Pitch head rotation was used to stimulate the vestibular system.

The head-up tilt protocol was used to stimulate orthostatic intolerance. UBS of the mastoid bone was used to determine if orthostatic tolerance was improved.

Campaign 3A represented the control group of subjects for these investigations and also evaluated whether ultrasonic bone stimulation of the mastoid improved orthostatic tolerance. Another investigator researched the mechanisms of the effects of bed rest on the cardiovascular system and explored potential gender differences in the response of the cardiovascular system. The Standard Measures protocols were performed together with these investigator studies during this campaign.

A post Campaign 3A data debrief meeting was held in the summer of 2005. All investigators and Standard Measures laboratories participated in this meeting to present their preliminary science results. Preliminary data demonstrated that the current model of 6-degree head-down tilt bed rest provided results similar to those observed during and following spaceflight. Additional data were presented that compared 60-day and 90-day bed rest studies and results for male and female subjects.

Results from Campaign 3A will be combined with the results from the previously completed Campaign 1 and the future bed rest campaigns. Data from these bed rest campaigns will serve as control data for the assessment and evaluation of the countermeasures, proposed by the investigators.

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