Simulated shuttle egress: role of helmet visor position during approach and landing.

BACKGROUND: We previously reported that carbon dioxide (CO2) rapidly accumulates in the helmet of the NASA Launch and Entry Suit (LES) during a simulated egress from the Space Shuttle following 6 min of visor-closed seated rest to simulate approach and landing. The purpose of this study was to determine if CO2 accumulation and walking time in the LES would be improved by helmet visor-open rather than visor-closed seated rest prior to the performance of the simulated egress. METHODS: Wearing the LES, 12 male subjects performed 4 laboratory egress simulations consisting of 6-min seated rest, 2-min stand, and 5-min walk at 1.56 m x s(-1) (3.5 mph). During seated rest, subjects sat either with the visor open, breathing room air until the visor was closed on standing, or with the visor closed for the duration of the simulation. For all visor-closed operations 100%, O2 was supplied. The G-suit was either deflated (0.0 psi) or inflated to 1.5 psi. Inspired CO2 and walking time were measured. Data were analyzed at the end of seated rest, standing, and after 5 min of walking at 0.0 psi or after 2 min of walking at 1.5 psi (>90% of data available). RESULTS: Walk time was not different following visor-open (0.0 psi: 5.0 +/- 0.0; 1.5 psi: 3.4 +/- 0.3 min) or visor-closed (0.0 psi: 4.8 +/- 0.2; 1.5 psi: 3.5 +/- 0.4 min) seated rest at either G-suit pressure. Inspired CO2 levels were not different between the two conditions during walking at 5 min at 0.0 psi (p = 0.50; Open: 4.39 +/- 0.14; Closed: 4.48 +/- 0.18%) or at 2 min at 1.5 psi (p = 0.53; Open: 3.59 +/- 0.12; Closed: 3.65 + 0.21%). CONCLUSIONS: Visor position during seated rest immediately preceding the egress walk had no effect on inspired CO2 or walking time.

Acute effects of thirty minutes of light-intensity, intermittent exercise on patients with chronic fatigue syndrome.

BACKGROUND AND PURPOSE: Currently, there is no consensus on exercise prescription for patients with chronic fatigue syndrome (CFS). This investigation examined whether light-intensity, intermittent physical activity exacerbated symptoms in patients with CFS immediately following exercise to 7 days following exercise. Subjects. Subjects were 9 women (mean age=44.2 years, SD=8.4, range=29-56; mean weight=74.2 kg, SD=18.8, range=56.36-110.91; and mean height=1.63 m, SD=0.8, range=1.55-1.78) and 1 man (age=48 years, weight=97.1 kg, and height= 1.98 m) who met the Centels for Disease Control and Prevention's criteria fi)r (FS. METHODS: Subjects performed 10 discontinuous 3-minute exercise bouts (separated by 3 minutes of recovery) at a self-selected, comfortable walking pace on a treadmill. Oxygen consumption, minute ventilation, respiratory exchange ratio, and heart rate were measured every minute during the exercise session. To assess degree of disability, general health status, activity level, symptoms, and mood, subjects completed various questionnaires before and after exercise. RESULTS: Results indicated that degree of disability, general health status, symptoms, and mood did not change immediately and up to 7 days following exercise. CONCLUSION AND DISCUSSION: Thirty minutes of intermittent walking did not exacerbate symptoms in subjects with CFS. The physiological data did not show any abnormal response to exercise. Although this study did not determine whether 30 minutes of continuous versus intermittent exercise would exacerbate symptoms, all 10 subjects felt that they could not exercise continuously for 30 minutes without experiencing symptom exacerbation. Despite this limitation, the results indicate that some individuals with CFS may be able to use low-level, intermittent exercise without exacerbating their symptoms.

Carbon dioxide accumulation, walking performance, and metabolic cost in the NASA launch and entry suit.

BACKGROUND: In the event of an emergency on landing, Space Shuttle crewmembers while wearing the Launch and Entry Suit (LES) must stand, move to the hatch, exit the spacecraft with the helmet visor closed breathing 100% O2, and walk or run unassisted to a distance of 380 m upwind from the vehicle. The purpose of this study was to characterize the inspired CO2 and metabolic requirements during a simulated unaided egress from the Space Shuttle in healthy subjects wearing the LES. METHODS: As a simulation of a Shuttle landing with an unaided egress, 12 male subjects completed a 6-min seated pre-breathe with 100% O2 followed by a 2-min stand and 5-min walking at 1.56 m x s(-1) (5.6 km x h(-1), 3.5 mph) with the helmet visor closed. During walks with four different G-suit pressures (0.0, 0.5, 1.0, 1.5 psi; 3.4, 6.9, 10.3 kPa), inspired CO2 and walking time were measured. After a 10-min seated recovery, subjects repeated the 5-min walk with the same G-suit pressure and the helmet visor open for the measurement of metabolic rate (VO2). RESULTS: When G-suit inflation levels were 1.0 or 1.5 psi, only one-third of our subjects were able to complete the 5-min visor-closed walk after a 6-min pre-breathe. Inspired CO2 levels measured at the mouth were routinely greater than 4% (30 mmHg) during walking. The metabolic cost at the 1.5 psi G-suit inflation was over 135% of the metabolic cost at 0.0 psi inflation. CONCLUSION: During unaided egress, G-suit inflation pressures of 1.0 and 1.5 psi resulted in elevated CO2 in the LES helmet and increased metabolic cost of walking, both of which may impact unaided egress performance. Neither the LES, the LES helmet, nor the G-suit were designed for ambulation. Data from this investigation suggests that adapting flight equipment for uses other than those for which it was originally designed can result in unforeseen problems.

The rotavirus nonstructural protein, NS35, possesses RNA-binding activity in vitro and in vivo.

Toward the goal of identifying and characterizing rotavirus RNA-binding proteins, we have used a gel retardation assay and protein-RNA cross-linking by ultraviolet (uv) light to examine cytoplasmic lysates prepared from SA11-infected cells for the presence of RNA-binding proteins. Analysis of band shifts produced in the gel retardation assay indicated that infected cells contained significant amounts of a viral protein which had affinity for both single-stranded and double-stranded RNA but lacked sequence specificity. Cross-linking of this protein to radiolabeled RNA in vitro followed by RNase treatment and immunoprecipitation with an anti-NS35 monoclonal antibody revealed that the RNA-binding activity was associated with NS35. Moreover, sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the protein-RNA complex isolated from native gels revealed that NS35 was the only viral protein component of the complex. Since NS35 expressed by translation in rabbit reticulocyte lysates exhibited affinity for poly(U)-Sepharose, NS35 must possess intrinsic RNA-binding activity that is able to function in the absence of other viral proteins. Immunoprecipitation of RNase-treated cross-links formed in intact cells following exposure to uv light confirmed that NS35 was intimately associated with ssRNA in the infected cell. On the basis of its ability to bind RNA and given that previous studies have shown that NS35 localizes to the viroplasm in infected cells, is essential for RNA replication, and is a component of replicase particles, we propose that NS35 functions to concentrate viral mRNAs in the viroplasm and that NS35-mRNA complexes serve as substrates for genome assortment and replication.

Rotavirus morphogenesis: domains in the major inner capsid protein essential for binding to single-shelled particles and for trimerization.

A cell-free system containing rotavirus subviral particles (SVPs), rabbit reticulocyte lysate, and [35S]methionine was programmed to synthesize viral protein by the addition of messenger RNA (mRNA). Electrophoretic analysis of single-shelled particles recovered from the system by CsCl centrifugation showed that newly made VP6 assembled into the particles in vitro. Electrophoretic analysis also showed that the newly made VP6 which bound to single-shelled particles in vitro was arranged in trimeric units. To identify the domain within VP6 essential for assembly into single-shelled particles, amino- and carboxyl-truncated species of VP6 were assayed for the ability to associate with single-shelled particles in the cell-free system. The truncated proteins were introduced into the system by adding VP6 mRNAs containing 5'- and 3'-terminal deletions. The terminally deleted mRNAs were prepared using SP6 RNA polymerase to transcribe portions of cDNAs of the rotavirus SA11 gene for VP6 (gene 6). Analysis of the ability of truncated VP6 to associate with single-shelled particles showed that a domain essential for assembly resides at the carboxyl-end of VP6 located between amino acid residues 251 and 397. To contrast the domain for assembly with that for trimerization, amino- and carboxyl-truncated species of VP6 were also examined by electrophoretic assay for the ability to trimerize in vitro. The results showed that the domain for trimerization resides near the center of VP6 located between amino acid residues 105 and 328. Comparison of the domains for assembly and trimerization showed that they are unique but may overlap. The fact that some truncated species of VP6, although able to bind to single-shelled particles were unable to form trimers in vitro, suggests that trimerization of VP6 is not prerequisite for the assembly of single-shelled particles.