Contrapositive logic suggests space radiation not having a strong impact on mortality of US astronauts and Soviet and Russian cosmonauts.

Space travelers are exposed to unique forms of ionizing radiation that pose potentially serious health hazards. Prior analyses have attempted to quantify excess mortality risk for astronauts exposed to space radiation, but low statistical power has frustrated inferences. If exposure to deep space radiation were causally linked to deaths due to two particular causes, e.g., cancer and cardiovascular disease, then those cause-specific deaths would not be statistically independent. In this case, a Kaplan-Meier survival curve for a specific cause that treats deaths due to competing causes as uninformative censored events would result in biased estimates of survival probabilities. Here we look for evidence of a deleterious effect of historical exposure to space radiation by assessing whether or not there is evidence for such bias in Kaplan-Meier estimates of survival probabilities for cardiovascular disease and cancer. Evidence of such bias may implicate space radiation as a common causal link to these two disease processes. An absence of such evidence would be evidence that no such common causal link to radiation exposure during space travel exists. We found that survival estimates from the Kaplan-Meier curves were largely congruent with those of competing risk methods, suggesting that if ionizing radiation is impacting the risk of death due to cancer and cardiovascular disease, the effect is not dramatic.

A Cohort Mortality Study Among Soviet and Russian Cosmonauts, 1961-2014.

INTRODUCTION: Over 500 people from different countries have been to space since the first manned spaceflight in 1961. Factors of space and spaceflights might cause functional and somatic disorders, leading to increased mortality. Our research goal was to assess cause-specific risk of death among Soviet and Russian cosmonauts who had at least one spaceflight. METHODS: The epidemiological cohort study included 115 male cosmonauts. The observation period was 54 yr (January 1, 1961-December 31, 2014) and 2707 person-years of follow-up were obtained. By the end of the period, 84 cosmonauts were still alive and 31 were deceased. The reference groups were the male population of Russia and of the Moscow Region, where Zvezdny City (Star City) is located. Mortality risk was assessed by standardized mortality ratio (SMR) with 95% confidence intervals (95% CI). RESULTS: Death risk in the cohort was significantly lower than that in both reference groups: for all causes (А00-Y98; SMR = 40), for diseases of the circulatory system (I00-I99; SMR = 37 and 35 compared to Russia and the Moscow Region, respectively), and for other causes, i.e., all causes except circulatory diseases, cancer, and accidents, (SMR = 8). Death risk for accidents (V01-Y98) in the cohort was 1.8-1.9 times lower than that in both reference groups: SMR = 52 (95% CI 19-139) and 56 (21-151), but was not statistically significant. SMR for cancer (C00-C97) was also below 100 (71 and 66), but insignificant. DISCUSSION: Our findings mainly characterize mortality among the first cosmonauts who have flown to space from 1961 through the 1970s, which indicates the necessity of continuing research.Ushakov IB, Voronkov YI, Bukhtiyarov IV, Tikhonova GI, Gorchakova TYu, Bryleva MS. A cohort mortality study among Soviet and Russian cosmonauts, 1961-2014. Aerosp Med Hum Perform. 2017; 88(12):1060-1065.

Comparative efficacy and the window of radioprotection for adrenergic and serotoninergic agents and aminothiols in experiments with small and large animals.

This review gives a comparative evaluation of the radioprotective properties and the therapeutic index (TI) of radioprotectors from various pharmacological group in experiments on both small and large animals. It presents a hypothesis explaining the decrease in the TI of cystamine and 5-methoxytryptamine (mexamine), and the retention of that of α1-adrenomimetic indralin, and also compares the effects on large and small animals. The considerable differences in the therapeutic indices of catecholamines, serotonin and cystamine are a consequence of specific features of their mechanisms of radioprotective action. Radioprotectors acting via receptor mediation tend to provide a more expanded window of protection. The reduction in the TI of cystamine in larger animals, such as dogs, may be caused by the greater increase in toxicity of aminothiols in relation to the decrease in their optimal doses for radioprotective effect in going from mice to dogs, which is a consequence of the slower metabolic processes in larger animals. The somatogenic phase of intoxication by cystamine is significantly longer than the duration of its radioprotective effect, and increases with irradiation. The decrease in the radioprotective effect and the TI of mexamine in experiments with dogs may be caused by their lower sensitivity to the acute hypoxia induced by the mexamine. This is because of lower gradient in oxygen tension between tissue cells and blood capillaries under acute hypoxia that is determined by lower initial oxygen consumption in a large animal as compared with a small animal. Indralin likely provides optimal radioprotective effects and a higher TI for large animals via the increased specificity of its adrenergic effect on tissue respiration, which supports the development of acute hypoxia in the radiosensitive tissues of large animals. The stimulatory effect of indralin on early post-irradiation haematopoietic recovery cannot provide a high level of radioprotective action for large animals, but it may promote recovery.

Protective effect and the therapeutic index of indralin in juvenile rhesus monkeys.

The radioprotective effect of indralin in rhesus monkeys was examined over 60 d following gamma irradiation. Male and female rhesus macaques (Macaca mulatta) 2-3-years-old and weighing 2.1-3.5 kg were used. Animals were exposed to total-body gamma irradiation from (60)Co at a dose of 6.8 Gy (lethal dose, 100% lethality over 30 days). Indralin (40-120 mg kg(-1)) was administered intramuscularly 5 min prior to radiation exposure. Indralin taken at a dose of 120 mg kg(-1) protected five out of six monkeys (compared with the radiation control group, in which all 10 animals died). The average effective dose of indralin in the monkeys exposed to gamma irradiation for 30 min was equal to 77.3 (63.3-94.3) mg kg(-1), and the maximum tolerated dose of indralin administered to monkeys was 800 mg kg(-1). Indralin reduced radiation-induced injuries in macaques, thus resulting in a less severe course of acute radiation syndrome. Delayed and less pronounced manifestation of the haemorrhagic syndrome of the disease, and milder forms of both leukopenia and anaemia were also noted. The therapeutic index for indralin, expressed as the ratio of the maximum tolerated dose to the average effective dose, was equal to 10. Therefore, indralin has a significant radioprotective effect against radiation and has a high therapeutic index in rhesus monkeys.

The mechanism [correction of mehanism] of spatial [correction of spetial] orientation in conditions of G-stress.

Six test subjects were subjected to lateral (+Gy) and longitudinal-lateral (+Gz/+Gy) accelerations in a centrifuge with a rotation radius of 6.55 m. During rotation, test subjects were instructed to indicate the position of subjective visual vertical. Results of this study demonstrated that during exposure to +Gy and +Gz/+Gy accelerations, the direction of the indicated subjective vertical approached the direction of the resultant acceleration vector when the lateral component increased. This observed effect decreases with an increase of the longitudinal component of the acceleration. It was suggested that exposure to (i.e. "pulling") high lateral acceleration (up to 2-3 Gy) in highly maneuverable aircraft can hinder spatial orientation of a pilot due to this persistent illusory spatial position as reported above. Our analysis showed that the process of spatial orientation under the conditions of G-load influence becomes more difficult and it is depending on the compromise between visual and vestibular-proprioceptive inputs. On account of this finding, it may be proposed that under conditions of G-load influence, pilots that rely primarily on visual perception may be exposed to higher risk of spatial disorientation.