Usefulness of daily +2Gz load as a countermeasure against physiological problems during weightlessness.

UNLABELLED: Adaptation to head-down-tilt bed rest as a simulated microgravity leads to an abnormality of reflex control of circulation, hypovolemia and reduction of exercise capacity. We hypothesized that this cardiovascular deconditioning and reduction of exercise capacity could be prevented by a daily 1 hr centrifugation at +2Gz. To test this hypothesis, twenty healthy male subjects underwent 4 day of 6 degrees head-down-tilt bed rest. Ten of them were exposed to a +2Gz load for up to 30 min twice per day (the Gz group). The remaining 10 were not exposed to a Gz load (the no-Gz group). We estimated autonomic cardiovascular control by power spectral analysis of blood pressure and R-R interval variability, and baroreflex regulation by the transfer function analysis and the sequence method, before and after bed rest. Further, we measured hematocrit as an index of changes in plasma volume and maximal oxygen consumption as an index of exercise capacity, before and after bed rest. RESULT: In the no-Gz group, heart rate increased after bed rest. The high frequency power of R-R interval variability as an index of cardiac parasympathetic nervous activity, baroreflex gains estimated by transfer function analysis and the sequence method as index of the integrated arterial-cardiac baroreflex function decreased significantly. Associated with these changes, the ratio of low to high frequency power of R-R as an indicator of cardiac sympathovagal balance tended to increase after bed rest in the no-Gz group. However, those showed no significant changes after bed rest in the Gz group. Hematocrit increased after bed rest in the no-Gz group. It also tended to increase in the Gz group, however it did not achieve statistical significance. Maximal oxygen consumption decreased significantly to similar extent in both the groups. CONCLUSION: This result suggested that 1) a daily 1hr +2Gz load produced by a centrifuge might eliminate the changes in autonomic cardiovascular control during simulated weightlessness; 2) furthermore, it might partly reverse hypovolemia induced by bed rest; 3) however, it could not prevent the decreases in exercise capacity.

Effect of head-down-tilt bed rest and hypovolemia on dynamic regulation of heart rate and blood pressure.

Adaptation to head-down-tilt bed rest leads to an apparent abnormality of baroreflex regulation of cardiac period. We hypothesized that this "deconditioning response" could primarily be a result of hypovolemia, rather than a unique adaptation of the autonomic nervous system to bed rest. To test this hypothesis, nine healthy subjects underwent 2 wk of -6 degrees head-down bed rest. One year later, five of these same subjects underwent acute hypovolemia with furosemide to produce the same reductions in plasma volume observed after bed rest. We took advantage of power spectral and transfer function analysis to examine the dynamic relationship between blood pressure (BP) and R-R interval. We found that 1) there were no significant differences between these two interventions with respect to changes in numerous cardiovascular indices, including cardiac filling pressures, arterial pressure, cardiac output, or stroke volume; 2) normalized high-frequency (0.15-0.25 Hz) power of R-R interval variability decreased significantly after both conditions, consistent with similar degrees of vagal withdrawal; 3) transfer function gain (BP to R-R interval), used as an index of arterial-cardiac baroreflex sensitivity, decreased significantly to a similar extent after both conditions in the high-frequency range; the gain also decreased similarly when expressed as BP to heart rate x stroke volume, which provides an index of the ability of the baroreflex to alter BP by modifying systemic flow; and 4) however, the low-frequency (0.05-0.15 Hz) power of systolic BP variability decreased after bed rest (-22%) compared with an increase (+155%) after acute hypovolemia, suggesting a differential response for the regulation of vascular resistance (interaction, P < 0.05). The similarity of changes in the reflex control of the circulation under both conditions is consistent with the hypothesis that reductions in plasma volume may be largely responsible for the observed changes in cardiac baroreflex control after bed rest. However, changes in vasomotor function associated with these two conditions may be different and may suggest a cardiovascular remodeling after bed rest.

Purification of pectate oligosaccharides showing root-growth-promoting activity in lettuce using ultrafiltration and nanofiltration membranes.

Pectate oligosaccharides were separated from enzymatically hydrolyzed pectate by using ultrafiltration (UF) and nanofiltration (NF) membranes. The UF treatment was performed at a transmembrane pressure of 0.15 MPa and flow velocity of 0.6 m.s(-1), and nonhydrolyzed pectate was removed almost completely. The NF treatment was carried out at a transmembrane pressure of 0.5 MPa and flow velocity of 0.6 m.s(-1), and large amounts of monogalacturonic acid and sucrose, the contaminants included in the UF permeate were separated. Pectate oligosaccharides obtained by the diafiltration treatment of the NF concentrate were mainly composed of di- to pentasaccharides and exhibited root-growth-promoting activity in lettuce (approximately 1.8-fold) compared with the control. In particular, penta-, tetra-, and disaccharides were found to have strong activity.

Effects of daily 2-Gz load on human cardiovascular function during weightlessness simulation using 4-day head-down bed rest.

An onboard short arm human centrifuge has been proposed as a countermeasure against physiological problems during long exposure to weightlessness in space and during extra planetary exploration. However, there are few studies on the effects of intermittent application of a Gz load via centrifuge during weightlessness. The present study evaluated the effects of a daily 2-Gz load on cardiovascular function during simulated weightlessness using a 4-day head-down bed rest (HDBR) period. Twelve young male subjects were exposed a HDBR period. Eight of them were exposed to a Gz load for up to 30 min twice per day (the Gz group). The remaining 4 were not exposed to a Gz load; they served as controls (the no-Gz group). Compared with the pre-HDBR period, the no-Gz group showed percent changes in the RR interval, the standard deviation (SD) of the RR interval, parasympathetic nervous activity, and baroreflex sensitivity (BRS) that progressively decreased and reached significance at the end of the HDBR period (-5.96 +/- 2.60%, -33.82 +/- 9.60%, -46.3 +/- 12.7% and -30.9 +/- 7.2%, respectively). In the Gz group, however, the percent changes in the RR interval, the SD of the RR interval, parasympathetic nervous activity, and BRS showed no significant changes throughout the HDBR period. At the end of the HDBR period, these indexes were 2.22 +/- 2.21%, -2.31 +/- 12.28%, 5.08 +/- 14.82% and 10.6 +/- 12.5%, respectively, and significantly greater than those of the no-Gz group. Sympathovagal balance indicators showed no significant change in the Gz and no-Gz groups (5.17 +/- 12.85% and 18.5 +/- 10.7%, respectively). These results indicate that a daily load of 2-Gz eliminates reduction of the RR interval, the SD of the RR interval, parasympathetic nervous activity, and BRS, and that it can maintain autonomic cardiovascular function in short-term weightlessness.