Medical prevention of space motion sickness--animal model of therapeutic effect of a new medicine on motion sickness.

Space motion sickness (MS) is one of the most important problems in the field of space medicine. In order to prevent space MS, a new medicine, PMPA, has been prepared by means of synthesizing in our laboratory. The purposes of this study were to set up animal models of PMPA against MS, and to observe its effects on anti-MS, and to prove its function of antagonism to choline. Eight cats, forty rabbits and two hundred and ten rats were selected as animal subjects. The parallel swing stimulus, a method causing the reversal syndromes and tests of anti-choline function were used in our experiments. The results are as follows: (1) The score of MS symptoms in cats with PMPA or scopolamine (SCOP) is significantly lower than that in cats with placebo (p<0.01), while the incidences of efficiency and prevention of PMPA (87.5%, 75%) are higher than those of SCOP (75.0%, 50%) in cats. (2) PMPA of 1.6 mg/kg or 0.8 mg/kg could antagonize the reversal syndromes and repress reversal rotation significantly in rabbits like SCOP in comparison with placebo (p<0.01). (3) PMPA could inhibit tremor evoked by oxotremorine or by nicotine-procaine in rats like SCOP, and play an important role in the antagonism to central M-choline and N-choline receptors. The animal experiments demonstrate that PMPA is an effective medicine against MS with antagonism function to choline.

[Relationship between EGG and the dynamic process of motion sickness induced by optokinetic vection].

OBJECTIVE: To investigate the correlation between Electrogastrography (EGG) and the occurrence of nausea or/and vomit as well as the development of motion sickness (MS) induced by optokinetic stimulation (OPS) and to provide a clue and method for prediction and prevention of MS. METHOD: Twenty male subjects, aged from 18 to 25 years, performed the test only once with the optokinetic drum rotated around a vertical axis at the speed of 60 degrees/s for 15 min. Nausea and EGG signals were observed and recorded. RESULT: (1)Both the increment of tachygastric percentage and the decrement of primary wave percentage of EGG in eleven subjects with nausea were significantly larger than those in nine subjects with no nausea (both P < 0.001). (2)The circular vection preceded the changes of EGG in eleven subjects with nausea while the MS scores in eleven subjects with nausea were higher than those in nine subjects with no nausea (P < 0.001). (3)During the rotation of drum, the decrement of primary wave percentage or the increment of tachygastria percentage also preceded the occurrence of nausea in eleven subjects with nausea (both P < 0.01). CONCLUSION: (l)The changes of EGG in subjects with nausea were significantly greater than those of EGG in subjects with no nausea. (2)There was a close relationship between circular vection or illusory self-rotation and EGG changes as well as the occurring of nausea induced by OPS. (3)Changes of EGG preceded the nausea of MS induced by OPS.

[Weightlessness and heat stress on astronauts].

Thermal emergency situations have more than once been encountered since the beginning of manned space flights in 1961. This article contemplates human thermal tolerance in weightlessness as complicated with headward [correction of headword] fluid shifts, plasma volume loss, cardiovascular deconditioning, reduced exercise capacity and energy metabolism changes, etc. With these considerations, it is necessary to further investigate the thermoregulation in spaceflight for the health and safety of astronauts.

Thermal physiological consideration of precooling procedures in manned space craft.

OBJECTIVE: To explore a space craft precooling temperature at which excessive thermal stress on the crew member could be prevented or reduced in an overheated launch or reentry module. METHOD: Five young male volunteers wearing a space suit participated in 25 tests at sea level. The space suit was either ventilated in a volume air flow rate of 100 L/min (STPD) with ambient air at temperatures (Ta) of 15 degrees C, 10 degrees C, and 5 degrees C, respectively, or not ventilated. Rectal (Tr), mean skin (Tsk) and mean body (Tb) temperatures were measured. RESULT: At Ta 15 degrees C, Tr decreased without significance (from 37.0 +/- 0.2C to 36.7 +/- 0.3 degrees C) in 120-min tests, whereas mean Tsk and mean Tb decreased significantly, and subjects had local cold strain whether the space suit was ventilated or not; while at Ta 10 degrees C, Tr decreased from 37.0 +/- 0.3 degrees C to 36.3 +/- 0.3 degrees C (P < 0.05), subjects had a whole body cold strain, and both mean Tsk and Tb dropped continuously and significantly. CONCLUSION: Ambient temperature 15 degrees C, at which the thermal comfort states of crew was not significantly degraded, was acceptable after precooling in a space craft.

[Ground-based studies on thermoregulation at simulated microgravity by head-down tilt bed rest].

Comparisons of headward fluid shifts, plasma volume losses, altered vasodilator and vasoconstrictor responses, reduced exercise capacities, etc. between microgravity and head-down tilt (HDT) bedrest suggested that HDT model was suitable for simulating thermoregulation under microgravity. Both microgravity and simulated microgravity by HDT exposures degraded human thermoregulation ability in some aspects. The features of the responses to heat stress on men after HDT exposures were higher increase rate in rectal temperature, attenuated increase rates of skin temperature and body heat conductance, less heat dissipation from core to skin and higher sensitivity of sweating etc.

[Effects of simulated weightlessness on vasoreactivity of hindlimb arterial bed in rats].

OBJECTIVE: To investigate the alterations in vasoreactivity of hindlimb arterial bed after simulated weightlessness. METHOD: The tail-suspended rat model was used to simulate weightlessness, and the alterations in vasoreactivity of arterial bed were examined in vitro using isolated, constant flow perfused hindlimb of 2-wk suspended rats and control rats. RESULT: Perfusion flow-pressure relationship of hindlimb arterial bed showed no significant differences between suspended rats and control rats; but vascular responses to KCl (20-100 mM) and PE(10(-8)-10(-4) M) were decreased in hindlimb arterial bed of suspended rats as compared with that of control rats. CONCLUSION: Contractile ability of resistance vessels was diminished in simulated weightlessness rats, and a compromised ability of resistance vessels to increase peripheral resistance may play an important role in occurrence of orthostatic intolerance.

Biomedical study on combined effects of simulated weightlessness and emergent depressurization of spacecraft.

Cabin emergent depressurization (CED) may occur in spacecraft during manned space flight. The purpose of this paper was to study the combined effects of simulated weightlessness (SW) and CED factors on humans and animals. It was found that the amplitude of T wave of human electrocardiograms (ECG) significantly decreased in bed rest and hypoxia compared with the control condition (P<0.05), and that suspension with pure O2 induced severer edema in the lungs of rats than that in only a pure O2 environment. SW and pure O2 caused middle ear congestion and decreased the barofunction during pressure changes. These results indicate that human response to CED factors become more serious under SW because of the blood redistribution.

[Thermal physiological analysis of man in an Intravehicular Activity space suit].

OBJECTIVE: To analyze the thermal physiological changes of man in a Intravehicular Activity (IVA) space suit. METHOD: Combined second design was used to arrange 24 tests in 6 young male subjects wearing an IVA space suit at sea level. RESULT: The relationship between common thermal physiological measurements and air ventilating parameters (air temperature, flow rate and its relative humidity) together with metabolic state (rest or work) of man were established in mathematical models. Possible applications of these models were illustrated. Metabolic heat production which influences the relations was also discussed. CONCLUSION: Thermal physiological changes of man in the space suit were properly expressed by the mathematical models in this paper.

[Alterations of arterial vasoconstrictor responsiveness in rats during and after tail-suspension].

Objective. To characterize the time course of alterations in vasoconstrictor properties of arteries during simulated weightlessness, and to examine whether these alterations are reversible. Method. The tail-suspended rat model was used to simulate weightlessness, and the alterations in vasoconstrictor response were examined in vitro using isolated arterial rings. Result. Compared with that of controls, contractile tension evoked by KCl and phenylephrine (PE) were lower in abdominal aortic, mesenteric and femoral arterial rings from 2 wk tail-suspended rats (P<0.05); after 4 wk tail-suspension, the responses of mesenteric and femoral arterial rings to KCl or PE were further decreased (P<0.05); but contraction responses of arterial rings from 8 wk tail-suspended rats were similar to that of 4 wk simulated microgravity rats. The reversibility of altered arterial vasoreactivity after 4 wk tail-suspension was observed for 5 wk. Vasoreactivity of abdominal aortic rings was recovered after first week of recovery, but it took five weeks that altered vasoreactivity of mesenteric and femoral artery got back to normal. Conclusion. The alterations in constrictor properties of arteries are dependent on both the duration of tail-suspension and the position of artery, the diminished vasoconstrictor properties appear to reach a new steady state after 4 wk tail-suspension, and the changes are reversible.

Motion sickness severity under interaction of vection and head movements.

Vection alone, or combined with head movements, has been shown to invoke motion sickness (MS). This study's purpose was to observe how different combinations of vection and head movements influenced the severity of MS. We tested 26 subjects in a rotating sphere at a speed of 45 degrees/s, resulting in vertical yaw, horizontal roll or pitch vection. Coincidently, subjects pitched, rolled, or yawed their heads (0.5 Hz, 20 degrees). We found that yaw vection combined with pitch or roll head movements significantly increased MS, while pitch vection with any type of head movement, or head and scene rotation about the same axis significantly reduced MS. When the head was kept stationary, pitch vection was most stressful for MS, followed by roll vection, then yaw vection, although yaw vection was the strongest sensation of self-rotation.