Decrease of asymmetric dimethylarginine predicts acute mountain sickness.

INTRODUCTION: Each year, 40 million tourists worldwide are at risk of getting acute mountain sickness (AMS), because they travel to altitudes of over 2500 m. As asymmetric dimethylarginine (ADMA) is a nitric oxide synthase (NOS) inhibitor, it should increase pulmonary artery pressure (PAP) and raise the risk of acute mountain sickness and high-altitude pulmonary edema (HAPE). With this in mind, we investigated whether changes in ADMA levels (Δ-ADMA) at an altitude of 4000 m can predict an individual's susceptibility to AMS or HAPE. METHODS: Twelve subjects spent two nights in a hypobaric chamber, the first night without exposure to altitude conditions and the second night at a simulated altitude of 4000 m. At identical time points during both nights (after 2, 5, and 11 hours), we determined ADMA serum levels, PAP by Doppler echocardiography and estimated hypoxia related symptoms by Lake Louise Score (LLS). RESULTS: Contrary to our initial hypothesis, subjects with a marked increase in ADMA at 4000 m showed PAP levels below the critical threshold for HAPE and were not affected by AMS. By contrast, subjects with a decrease in ADMA suffered from AMS and had PAP levels above 40 mmHg. After 2 hours of hypoxia we found a significant relationship between Δ-PAP t(2) (Spearmans ρ = 0.30, p ≤ 0.05) respectively Δ-ADMA t(2) (ρ = -0.92, p ≤ 0.05) and LLS. CONCLUSION: After 2 hours of hypoxia, the Δ-ADMA (positive or negative) can predict an LLS of >5 with a sensitivity of 80% and a specificity of 100% and can help assess the risk of an increase in PAP to more than 40 mmHg and thus the risk of HAPE (ϕ coefficient: 0.69; p ≤ 0.05).

Changes of pressure and humidity affect olfactory function.

The present study aimed at investigating the question whether olfactory function changes in relation to barometric pressure and humidity. Using climate chambers, odor threshold and discrimination for butanol were tested in 75 healthy volunteers under hypobaric and hyperbaric, and different humidity conditions. Among other effects, olfactory sensitivity at threshold level, but not suprathreshold odor discrimination, was impaired in a hypobaric compared to a hyperbaric milieu, and thresholds were lower in humid, compared to relatively dry conditions. In conclusion, environmental conditions modulate the sense of smell, and may, consecutively, influence results from olfactory tests.

Change of voice characteristics during +3 Gz acceleration.

BACKGROUND: This study was performed to test the feasibility of an experimental approach for assessing voice changes during exposure to increased +Gz acceleration. Such changes are probably due to mechanical alterations of the structures involved in voice production. This may be relevant to automatic speech analysis for flight control. Because voice control by means of auditory feedback may compensate for acceleration effects, the investigations included conditions with masked auditory feedback. METHOD: Four male subjects read standard speech test material while seated in a human centrifuge both during sustained +3 Gz acceleration and in a reference condition. Both test runs were repeated with masking of the auditory feedback by a white noise presented via headphones. Microphone and acceleration signals were recorded on a PC-based dynamic signal acquisition board. Long-time average spectra (LTAS), fundamental frequency (F0), and the frequency of the first, second, and third formant (F1, F2, F3) of the vowels /a/, /o/, and /i/ were extracted from the microphone signal for the different conditions. RESULTS: LTAS clearly differed between the masking conditions, but not between reference and +3 Gz conditions. F0 clearly rose with auditory masking and showed a small increase under +3 Gz acceleration. Several effects of +3 Gz acceleration on formant frequencies were found, all of rather small magnitude. Increased acceleration lowered F2 for the vowel /i/. A decrease of F3 was observed for vowels /i/ and /o/. CONCLUSION: This pilot study has shown the feasibility of an experimental approach to assessing voice changes during exposure to increased +Gz acceleration. Exposure to +3 Gz showed small effects on FO and several formant frequencies. A definitive forthcoming study should assess the significance of these effects by investigating a greater number of subjects during exposure to acceleration higher than +3 Gz.

Hypergravity and dehydration-induced shifts of interstitial fluid in the skin monitored by ultrasound.

INTRODUCTION: Spaceflight is associated with a shift of interstitial fluid toward the skin of the head and a fluid loss that can decrease superficial tissue thickness (TT). To collect the physiological data needed to develop techniques for monitoring the hydration status of astronauts during spaceflight, we investigated the changes in TT induced by a 12-h nil-by-mouth period and a 30-min period of +2 Gz hypergravity measured at forehead and tibia. METHODS: There were 16 male volunteers who were twice subjected to 30 min of +2 Gz acceleration in a human centrifuge, once following an oral fluid load of 250 ml x h(-1) (procedure A), and once following a nil-by-mouth period of 12 h (procedure B). The TT at the forehead (TT-f) and tibia (TT-t) was measured before (t0), after 10 min (t10), and after 30 min (t30) of hypergravity using a miniature 10 MHz A-mode ultrasound device. The bodyweight, hematocrit (HCT), and plasma viscosity (PVS) were measured at tO and t0. RESULTS: The nil-by-mouth period induced a significant weight loss and increase in HCT and PVS. A significant increase was noted in TT-t, but not in TT-f (p < 0.05). Following both procedures, exposure to hypergravity produced declines in TT-f at t10 and t30 compared with baseline (p < 0.05), whereas TT-t was not influenced. CONCLUSIONS: Changes in interstitial fluid load of superficial tissues can be tracked by A-mode ultrasonography. Fluid loss-induced changes are best detected at the tibia, hypergravity-induced changes at the forehead.