Quantification of muscle volume by echography: comparison with MRI data on subjects in long-term bed rest.

The objective of this study was to determine the accuracy of an echographic method for measuring the change in leg muscle volume against the gold standard, magnetic resonance imaging (MRI). Leg muscle volume was measured using an echographic scanner, which consisted of two metallic rails on which a probe holder moved via an electric engine. Ten to 20 transverse muscle views were collected along the area scanned, and the muscle cross-sectional area (CSA, cm2) was measured on each of them. The integration of all the CSAs along the scanned area provided the muscle volume (cm3). Echographic results were compared with MRI data on 24 subjects undergoing 60 d of bed rest (8 control "Con," 8 with exercise countermeasures "Ex" and 8 with nutrition countermeasures "Nut"). The vastus intermedius (VI) and the vastus medialis (VM) volumes decreased significantly and similarly in both Con and Nut (VI, -17%; VM, -21%; p < 0.02). In the Ex group, the VI and VM did not change significantly. The correlation coefficient between the muscle volume change measured with the echographic and MRI methods was 0.78. The present study confirms that the echographic scanner is sufficiently accurate for assessing muscle volume changes and detects the effect of exercise countermeasures on muscle volume during long-term bed rest.

WISE-2005: adrenergic responses of women following 56-days, 6 degrees head-down bed rest with or without exercise countermeasures.

We tested the hypotheses that women completing 56 days, 6 degrees head-down bed-rest (HDBR) would have changes in sensitivity of cardiovascular responses to adrenergic receptor stimulation and that frequent aerobic and resistive exercise would prevent these changes. Twenty-four women, eight controls, eight exercisers (lower body negative pressure treadmill and flywheel resistance exercise), and eight receiving nutritional supplement but no exercise were studied in baseline and during administration of the beta-agonist isoproterenol (ISO) and the alpha- and beta-agonist norepinephrine (NOR). In the control and nutrition groups, HDBR increased heart rate (HR) and reduced stroke volume (SV), and there was a significantly greater increase in HR with ISO after HDBR. In contrast, the HR and SV of the exercise group were unchanged from pre-HDBR. After HDBR, leg vascular resistance (LVR) was greater than pre-HDBR in the exercise group but reduced in control and nutrition. LVR was reduced with ISO and increased with NOR. Changes in total peripheral resistance were similar to those of LVR but of smaller magnitude, perhaps because changes in cerebrovascular resistance index were directionally opposite to those of LVR. There were no changes in sensitivity of the vascular resistance responses to adrenergic stimulation. The HR response might reflect a change in sensitivity or a necessary response to the reduction in SV after HDBR in control and nutrition groups. The reduced peripheral vascular resistance after HDBR might help to explain orthostatic intolerance in women. Exercise was an effective countermeasure to the HDBR effects.

Portal vein cross-sectional area and flow and orthostatic tolerance: a 90-day bed rest study.

The objective of this study was to evaluate the changes in the portal vein cross-sectional area (PV CSA) and flow during a stand test associated with orthostatic intolerance. Eighteen subjects underwent a 90-day head-down tilt (HDT) bed rest at 6 degrees: 9 controls (Con) and 9 with flywheel exercise countermeasures (CM). At post-HDT, nine subjects (5 CM, 4 Con) were tolerant, and nine were intolerant. The PV CSA was measured by echography. We found that at HDT day 85, the PV CSA at rest had increased less in the CM subjects than in the Con (+12 vs. +27% from pre-HDT supine; P < 0.05), whereas it increased similarly in tolerant and intolerant subjects (23 and 16%, respectively). Two days after the HDT, there was a decrease in the PV CSA supine compared with the pre-HDT PV CSA supine that was similar for all groups (Con: -11%, CM: -21%; tolerant: -10%, intolerant: -16%; P < 0.05). The PV CSA decreased significantly less from supine to standing in the Con than in the CM group (-2 vs. -10% compared with the pre-HDT stand test; P < 0.05). The PV CSA also decreased significantly from supine to standing compared with the pre-HDT stand test in the tolerant group but not in the intolerant group (-20 vs. +2%; P < 0.05). From these findings, we conclude the following. 1) Because the portal vein is the only output from the splanchnic vascular area, we suggest that the lower reduction in the PV CSA and flow associated with orthostatic intolerance was related to a lower splanchnic arterial vasoconstriction. 2) The flywheel exercise CM helped to reduce the distention of the splanchnic network at rest and to maintain partially the splanchnic vasoconstriction, but it did not reduce the orthostatic intolerance.