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To identify strength and performance thresholds below which task performance is impaired. A new weighted suit system was used to manipulate strength-to-body-weight ratio during the performance of simulated space explorations tasks. Statistical models were used to evaluate various measures of muscle strength and performance on their ability to predict the probability that subjects could complete the tasks in an acceptable amount of time. Thresholds were defined as the point of greatest change in probability per change in the predictor variable. For each task, median time was used to define the boundary between “acceptable” and “unacceptable” completion times. Fitness thresholds for four space explorations tasks were identified using 23 physiological input variables. Area under receiver operator characteristic curves varied from a low of 0.68 to a high of 0.92. An experimental analog for altering strength-to-body weight combined with a probability-based statistical model for success was suitable for identifying thresholds for task performance below which tasks could either not be completed or time to completion was unacceptably high. These results provide data for strength recommendations for exploration mission ambulatory task performance. Furthermore, the approach can be used to identify thresholds for other areas where occupationally relevant tasks vary considerably.

Sex and gender differences have long been a research topic of interest, yet few studies have explored the specific differences in neurological responses between men and women during and after spaceflight. Knowledge in this field is limited due to the significant disproportion of sexes enrolled in the astronaut corps. Research indicates that general neurological and sensory differences exist between the sexes, such as those in laterality of amygdala activity, sensitivity and discrimination in vision processing, and neuronal cell death (apoptosis) pathways. In spaceflight, sex differences may include a higher incidence of entry and space motion sickness and of post-flight vestibular instability in female as opposed to male astronauts who flew on both short- and long-duration missions. Hearing and auditory function in crewmembers shows the expected hearing threshold differences between men and women, in which female astronauts exhibit better hearing thresholds. Longitudinal observations of hearing thresholds for crewmembers yield normal age-related decrements; however, no evidence of sex-related differences from spaceflight has been observed. The impact of sex and gender differences should be studied by making spaceflight accessible and flying more women into space. Only in this way will we know if increasingly longer-duration missions cause significantly different neurophysiological responses in men and women.

To better understand the effects of varying head movement frequencies on human balance control, 12 healthy adult humans were studied during static and dynamic (0.14, 0.33, 0.6 Hz) head tilts of +/- 30 degrees in the pitch and roll planes. Postural sway was measured during upright stance with eyes closed and altered somatosensory inputs provided by a computerized dynamic posturography (CDP) system. Subjects were able to maintain upright stance with static head tilts, although postural sway was increased during neck extension. Postural stability was decreased during dynamic head tilts, and the degree of destabilization varied directly with increasing frequency of head tilt. In the absence of vision and accurate foot support surface inputs, postural stability may be compromised during dynamic head tilts due to a decreased ability of the vestibular system to discern the orientation of gravity. This instability may compound the risk of falling following recovery from balance disorders or adaptation to altered gravity conditions such as space flight. Thus, dynamic head tilts may improve the diagnostic sensitivity of computerized dynamic posturography, particularly for healthy subjects recovering from temporary balance control deficits.

BACKGROUND: Compact and automated sensors are desired for assessing the health of cell cultures in biotechnology experiments. While several single-analyte sensors exist to measure culture health, a multi-analyte sensor would simplify the cell culture system. One such multi-analyte sensor, the Paratrend 7 manufactured by Diametrics Medical, consists of three optical fibers for measuring pH, dissolved carbon dioxide (pCO(2)), dissolved oxygen (pO(2)), and a thermocouple to measure temperature. The sensor bundle was designed for intra-vascular measurements in clinical settings, and can be used in bioreactors operated both on the ground and in NASA's Space Shuttle and International Space Station (ISS) experiments. METHODS: A Paratrend 7 sensor was placed at the outlet of a bioreactor inoculated with BHK-21 (baby hamster kidney) cells. The pH, pCO(2), pO(2), and temperature data were transferred continuously to an external computer. Cell culture medium, manually extracted from the bioreactor through a sampling port, was also assayed using a bench top blood gas analyzer (BGA). RESULTS: Two Paratrend 7 sensors were used over a single cell culture experiment (64 days). When compared to the manually obtained BGA samples, the sensor had good agreement for pH, pCO(2), and pO(2) with bias (and precision) 0.005(0.024), 8.0 mmHg (4.4 mmHg), and 11 mmHg (17 mmHg), respectively for the first two sensors. A third Paratrend sensor (operated for 141 days) had similar agreement (0.02+/-0.15 for pH, -4+/-8 mm Hg for pCO(2), and 24+/-18 mmHg for pO(2)). CONCLUSION: The resulting biases and precisions are com- parable to Paratrend sensor clinical results. Although the pO(2) differences may be acceptable for clinically relevant measurement ranges, the O(2) sensor in this bundle may not be reliable enough for the ranges of pO(2) in these cell culture studies without periodic calibration.

An ultrasound system has been developed to generate contrast microbubbles in vivo. Possible uses include diagnosis of reflux in the urinary tract. In vivo and in vitro experiments were designed to elucidate the microbubble generation process using 1.8 MHz acoustic bursts at 125 ms. In in vivo experiments on rabbits, the peak rarefactional pressure threshold for contrast generation, as visualized with a diagnostic ultrasound system, decreased with increasing pCO/sub 2/. For the in vitro aqueous studies the threshold decreased almost a factor of two for increasing particle concentration (0.2 /spl mu/m dia. polystyrene) from 10/sup 8/ to 10/sup 10/ particles/cc. The thresholds were at least twice as high for more saturated fluids, and CO/sub 2/ samples had considerably lower thresholds than respective under-saturations in air. At a fixed pressure amplitude, echogenicity tended to increase with both increasing particle and gas content; this was more pronounced for samples containing CO/sub 2/. Even in a restricted-nuclei environment such as the human urinary bladder, generation of vaporous cavitation should be possible; however subsequently, abundant gas is needed to grow vaporous bubbles to persistent and imageable sizes, to assist in the diagnosis of urinary reflux.

A surgical urinary reflux model has been developed in canines, to test a less invasive method for diagnosing urinary reflux (VUR) using ultrasound contrast microbubbles generated by transcutaneous application of high intensity focused ultrasound (HIFU) in the urinary bladder. This surgical reflux procedure was performed on two canines. After approximately six weeks of recovery, examinations performed tested for reflux over the next seven weeks.

An ultrasound system has been developed to generate microbubbles in vivo for use as ultrasound contrast agent. Possible application include diagnosis of reflux in the urinary tract. In experiments designed to elucidate the contrast microbubble generation process, acoustic bursts (at 1.8 MHz, 125 ms) were propagated through a latex rubber balloon, modeled after a rabbit urinary bladder, containing fluids of various air and carbon dioxide saturations and concentrations of cavitation nuclei (0.198-micron-diam polystyrene particles). The peak rarefactional pressure threshold for contrast microbubble generation, as visualized with a diagnostic ultrasound system, decreased approximately a factor of 2 for increasing particle concentration from 10(8) to 10(10) particles/cc, with the lowest threshold of 5.24 MPa. For samples with gas saturations below 50% and 10(10) particles/cc, the average thresholds were at least twice as high as those of more saturated fluids (with mean threshold for saturated fluids of 6.45 MPa), and samples containing CO2 had considerably lower thresholds than respective under-saturations in air. At a fixed pressure amplitude, echogenicity tended to increase with both increasing particle concentration and gas saturation; this was more favorable for samples containing CO2. Even in a restricted-nuclei environment such as the urinary bladder, generation of vaporous cavitation should be possible; however, subsequently, abundant gas is needed to grow vaporous bubbles to persistent and imageable sizes, to assist in the diagnosis of urinary reflux.

A surgical reflux procedure, performed on two canines, was used to test a less invasive method for diagnosing urinary reflux. After approximately 6 weeks of recovery, examinations tested for reflux over the next 7 weeks. The canines were positioned prone (slightly head down) on a tilted table with a hole exposing the depilated abdomen, where a 1.18 MHz high intensity focused ultrasound transducer could be coupled. The reflux condition was evaluated first using standard fluoroscopy and x‐ray contrast instilled in the bladder by a gravity feed through a transurethral catheter. For high grade reflux, dilute contrast agent (Optison) was tested using harmonic color Doppler at 3 MHz on a Toshiba Powervision 8000 scanner imaging the kidney. Finally, aqueous solutions with elevated CO2 were placed in the bladder and microbubbles generated using a 10 s application of 1.18 MHz ultrasound (25 cycle bursts with 0.5% duty factor and 8.4 MPa). Bubbles were detected in the kidney on two occasions with strong color Doppler signal, near that from dilute Optison. Methods can naturally produce evelated CO2, and contrast bubbles should be producible transcutaneously for reflux diagnosis without ionizing radiation and catheterization. [Work supported in part by a USPHS grant 2 RO1DK42290.]