The post-mission period is difficult to consider in advance, for crews as well as for organizations. As longer, farther, and more dangerous space missions are planned, in-flight counter-measures and post-flight readaptation should become physically and psychologically more taxing. Studies on the long term effects of such missions will be required.

While no simulation or spaceflight analogue can produce the exact psychological environment of a real long duration space mission, comparisons may be drawned from similar settings such as polar stations.

Post-mission psychological studies conducted in such settings will be presented, and related to future Moon/Mars expeditions.

Introduction: Central and peripheral neural processes and subsequently motor performance has been reported to be impaired during hypergravity (+Gz). Current research has mostly focused on physiological explanations (e.g., vestibular activity) and neglected psycho-physiological effects (e.g., arousal). To evaluate the interaction between psycho-physiological effects and motor performance in +Gz, the present study combines physiological (EEG), endocrinological (blood hormone concentration) and psychological measurements (perceived physical and mental state) with a motor performance and motor learning task conducted in +Gz.

Methods: Motor performance was investigated in human subjects manually tracking a sinusoidal moving target either in normal gravity (1Gz) or in three times terrestrial gravity (3Gz). To evaluate motor learning, the cursor feedback was then left-right inversed, and subjects had to adapt their performance to this disturbance while remaining in 3Gz. Brain cortical activity was measured by EEG before, during and after exposure to 3Gz. Data was then subdivided into q, a, b and g frequencies. Stress hormone concentration (e.g. cortisol) and perceived physical and mental state were recorded before and after 3Gz.

Results: Motor performance was decreased in 3Gz, whereas motor learning was not negatively impaired. An increase in the q frequency range and in the higher EEG frequency ranges (>12Hz) was found during acceleration to 3Gz, particulary pronounced in the frontal and occipital leads, probably reflecting enhanced perceptive, motivational/emotional and/or attentional processes. All tested stress hormones were dramatically increased, whereas perceived physical and mental state seemed to be decreased.

Discussion: Our data confirm, that motor performance is decreased in sustained +Gz. Furthermore, we can show that the acceleration is accompanied by a high level of arousal, reflected by the shift in EEG frequencies, by an increase in stress hormone concentration and by a decrease of the subjective physical and mental state. Therefore, our findings demonstrate that psycho-physiological changes have to be regarded as a relevant factor for changes in central and peripheral neural processes during phases of hypergravity.

Rationale and Objectives: The biologically active molecule nitric oxide (NO) was first discovered as a "signaling molecule in the cardiovascular system". Later NO was found in expired gas in part per billion (ppb) amounts. Increased levels of expired NO are found in asthma and other inflammatory airway diseases. Increased NO levels are also found after occupational exposures to dust. The expired NO is believed to be formed in the alveoli and in the conductive airways. However, the partitioning between alveolar and conductive-airway sources remains controversial; possibly a large amount of the NO formed in the distal lung parts is taken up by the blood and can not reach the expired gas. This makes it difficult to accurately estimate the total amount of NO that is formed in the lungs. We tested the hypothesis that part of the NO formed in the conductive airways is eliminated by axial back diffusion into the pulmonary capillary blood. This was achieved by studying conditions with differing rates of NO uptake to the blood. We varied the blood uptake of NO by exposing healthy humans to conditions with differing lung-to-blood diffusing capacities for gases such as NO. This was achieved by means of micro- and hypergravity. Due to the more homogenous distribution of alveolar volume vs. lung blood volume in microgravity, lung diffusing capacity is markedly increased in sustained microgravity. In contrast, the lungs are distorted and the lung blood redistributed in hypergravity causing a marked reduction in lung diffusing capacity.

Methods: Three subjects were studied before and during their first week of microgravity (μG) on the International Space Station. Their exhaled NO concentration was measured using a standard expiration flow of 50 ml s^-1. In addition, ten other subjects were studied in a human centrifuge under the conditions of normal (1G) and two (2G) and three times (3G) increased gravity. Their exhaled NO concentration was measured during flows of 50, 100, 200 and 500 ml s^-1. In all gravity conditions, a counterpressure of + 1.5 kPa was used during the exhalations to close the soft palate and hence avoid contamination with nasal NO.

Measurements and Main Results: At normal gravity exhaled NO concentrations were 13.9 (± 6.4, n=3) (mean (± SD), n=x) and 16.0 (± 4.3, n=10). In microgravity exhaled NO values were reduced by 35 % (P = 0.04, n=3) and in hypergravity increased by 16 - 22 % (P = 0.001 for a flow of 50 ml s^-1, n=10). In the hypergravity trials, linear relationships were found between 1/flow and exhaled NO, with 1/flow zero intercepts (flow → ∞, "alveolar NO") ranging between 1 - 4 ppb at normal gravity, which confirmed previous findings of a steady-state, low alveolar concentration. "Alveolar" NO was 2.3 (± 1.1) ppb at 1G and increased significantly to 3.9 (± 1.4) and 3.8 (± 0.8) ppb at 2G and 3G (P < 0.001).

Conclusions: The direct relationship between gravity in the head to feet direction and exhaled NO and "alveolar" NO in the range μG – 2G, support the notion of a significant back-diffusion of NO from the conductive airways to the alveoli, and that uptake of NO in the blood markedly influences exhaled NO. Generally our results show that effects of gravity on the lungs must be considered when interpreting expired NO as a diagnostic tool in clinical medicine.

Exposure to spaceflight conditions, including microgravity, has been shown to alter immune function in both humans and animals. Such alterations include changes in cytokine production, lymphocyte proliferation and natural killer cell function. The present study tested the possibility that the neurovestibular system may contribute to alterations in immune function that occur secondary to exposure to altered gravity. To test this prediction, this study used the head tilt mouse model (abbr. het). The het mouse lacks macular otoconia and therefore cannot detect changes in linear accelerations, which includes gravitational accelerations. Both female and male het mice and age-matched heterozygote (het/+) and homozygote (+/+) wildtype littermates (n=6/group) were exposed to 2 1/2 weeks of hypergravity (2G) via chronic centrifugation.

Control cohorts were maintained at normal Earth’s gravity (1G). All animals were housed on a 12:12 light-dark (LD12:12) cycle with ad libitum food and water. At the end of the hypergravity exposure, spleens were immediately harvested from all mice. Splenocytes were stimulated with the T-cell mitogen concanavalin A (ConA) and production levels of the cytokine IL-2, as a measurement of immune competence, were quantified using the Bio-Plex cytokine assay (Bio-Rad Laboratories, Hercules, CA). Wildtype female and male mice exposed to hypergravity demonstrated a significant reduction in the production of IL-2 (p = 0.012 and p = 0.030 respectively). In contrast, IL-2 production levels were not significantly reduced as compared to parallel het 1G controls in both female and male het mice (p = 0.208 and 0.355 respectively). These results are consistent with previous microgravity studies indicating that exposure to altered gravity can reduce an organism's ability to mount a cellular-mediated immune response. These results further demonstrate a probable role for the macular gravity receptors in this gravity-associated immunomodulation. As in prior studies, gender differences in immunoregulatory responses are also identified, as significantly higher IL-2 production responses were consistently seen in females compared to males.