The exercise and environmental physiology of extravehicular activity

Extravehicular activity (EVA), i.e., exercise performed under unique environmental conditions, is indispensable for supporting daily living in weightlessness and for further space exploration. From 1965-1996 an average of 20 h x yr(-1) were spent performing EVA. International Space Station (ISS) assembly will require 135 h x yr(-1) of EVA, and 138 h x yr(-1) is planned for post-construction maintenance. The extravehicular mobility unit (EMU), used to protect astronauts during EVA, has a decreased pressure of 4.3 psi that could increase astronauts' risk of decompression sickness (DCS). Exercise in and repeated exposure to this hypobaria may increase the incidence of DCS, although weightlessness may attenuate this risk. Exercise thermoregulation within the EMU is poorly understood; the liquid cooling garment (LCG), worn next to the skin and designed to handle thermal stress, is manually controlled. Astronauts may become dehydrated (by up to 2.6% of body weight) during a 5-h EVA, further exacerbating the thermoregulatory challenge. The EVA is performed mainly with upper body muscles; but astronauts usually exercise at only 26-32% of their upper body maximal oxygen uptake (VO2max). For a given ground-based work task in air (as opposed to water), the submaximal VO2 is greater while VO2max and metabolic efficiency are lower during ground-based arm exercise as compared with leg exercise, and cardiovascular responses to exercise and training are also different for arms and legs. Preflight testing and training, whether conducted in air or water, must account for these differences if ground-based data are extrapolated for flight requirements. Astronauts experience deconditioning during microgravity resulting in a 10-20% loss in arm strength, a 20-30% loss in thigh strength, and decreased lower-body aerobic exercise capacity. Data from ground-based simulations of weightlessness such as bed rest induce a 6-8% decrease in upper-body strength, a 10-16% loss in thigh extensor strength, and a 15-20% decrease in lower-body aerobic exercise capacity. Changes in EVA support systems and training based on a greater understanding of the physiological aspects of exercise in the EVA environment will help to insure the health, safety, and efficiency of working astronauts.     

Incidence of Epstein-Barr virus in astronaut saliva during spaceflight

BACKGROUND: Astronauts experience psychological and physical stresses that may result in reactivation of latent viruses during space-flight, potentially increasing the risk of disease among crewmembers. HYPOTHESIS: The shedding of Epstein-Barr virus (EBV) in the saliva of astronauts will increase during spaceflight. METHODS: A total of 534 saliva specimens were collected from 11 EBV-seropositive astronauts before, during, and after four space shuttle missions. The presence of EBV DNA in saliva, assessed by polymerase chain reaction (PCR), was used to determine shedding patterns before, during, and after space-flight. RESULTS: EBV DNA was detected more frequently before flight than during (p < 0.001) or after (p < 0.01) flight. No significant difference between the inflight and postflight periods was detected in the frequency of occurrence of EBV DNA. CONCLUSIONS: The increased frequency of shedding of EBV before flight suggests that stress levels may be greater before launch than during or after spaceflight.     

Urine volume and its effects on renal stone risk in astronauts

BACKGROUND: Urine composition in astronauts during and immediately after spaceflight changes in ways that increase the renal stone-forming potential for calcium oxalate, calcium phosphate, and uric acid saturation. We examined the effect of urine volume on the risk of renal stone formation in 356 astronauts. METHODS: Renal stone-forming risk was evaluated from 24-h urine samples collected from astronauts before and after 4- to 17-d Space Shuttle flights. Urinary chemistries were performed and the relative supersaturations of calcium oxalate, brushite, sodium urate, struvite, and uric acid saturation were calculated from the biochemical results. RESULTS: Urinary supersaturation levels of stone-forming salts were inversely related to urinary output both before and after spaceflight. Urine volume > 2 L x d(-1) reduced the risk of renal-stone development without affecting urinary citrate concentrations as compared with the increased risk observed in those astronauts who excreted urine volumes < L x d(-1). CONCLUSION: Results from this study indicate that increasing daily urinary output alone is an effective countermeasure to reduce the renal stone-forming risk immediately after spaceflight. However, increasing urinary output during flight may not be entirely effective in minimizing the potential risk of renal stone formation due to the changes in the urine chemistry in astronauts exposed to microgravity. Keywords: urine volume, spaceflight, renal calculi.     

Cardiovascular deconditioning during space flight and the use of saline as a countermeasure to orthostatic intolerance

Alterations in the physiology of the cardiovascular system have been noted during all exposures to the microgravity experienced in space flight. Of most importance to the operational function of Space Shuttle crewmembers is orthostatic intolerance. Although complex changes occur as a result of adaptation to weightlessness, the redistribution and loss of body fluid apparently plays a substantial role. Utilizing ground-based bed rest data as an analog to the absence of gravitational force encountered in orbital flight, a saline loading countermeasure was developed. In this study, 17 crewmembers consumed various amounts of salt and fluid prior to the reentry phase of Space Shuttle flights; 9 other astronauts served as control subjects. The countermeasure reduced the heart rate response to orthostatic stress 29% and reversed the fall in mean blood pressure. A Cardiovascular Index of Deconditioning (defined as CID = delta HR - delta SBP + delta DBP) equalled 21 in those who utilized the countermeasure, a significant improvement toward baseline (p less than 0.003) when compared to the control group CID = 49. The encouraging results of these investigations have led to the adoption of the countermeasure as an operational procedure by Shuttle crewmembers.     

International Space Station medical standards and certification for space flight participants

INTRODUCTION: The medical community of the International Space Station (ISS) has developed joint medical standards and evaluation requirements for Space Flight Participants ("space tourists") which are used by the ISS medical certification board to determine medical eligibility of individuals other than professional astronauts (cosmonauts) for short-duration space flight to the ISS. These individuals are generally fare-paying passengers without operational responsibilities. MATERIAL AND CONTEXT: By means of this publication, the medical standards and evaluation requirements for the ISS Space Flight Participants are offered to the aerospace medicine and commercial spaceflight communities for reference purposes. It is emphasized that the criteria applied to the ISS spaceflight participant candidates are substantially less stringent than those for professional astronauts and/or crewmembers of visiting and long-duration missions to the ISS. CONCLUSIONS: These medical standards are released by the government space agencies to facilitate the development of robust medical screening and medical risk assessment approaches in the context of the evolving commercial human spaceflight industry.     

Hearing and performance during a 70-h exposure to noise simulating the space station environment

INTRODUCTION: Elevated hearing thresholds have been documented in some astronauts after long-term spaceflights although noise levels were lower than those normally associated with noise-induced hearing loss in ground-based operations. The present study was conducted to determine whether prolonged exposure (70 h) to levels (72 dBA) recorded on the International Space Station (ISS) service module would impact diverse measures of auditory function, as well as cognition and memory, motivation, and cardiovascular function. METHOD: Five mixed gender subgroups of five normal-hearing subjects, aged 20-50 yr, were sequestered for 70 h in an environment that modeled conditions on the ISS. They were assigned to one of three background conditions: quiet (n = 5), continuous noise from the ISS service module (n = 10), or continuous noise during the day only (n = 10). Subjects were tested repeatedly within and across days as individuals or pair mates. RESULTS: There were no negative effects of the noise on any of the outcome measures. Introduction of a delay or noise in a communication channel used in the assessment of speech communicability significantly affected the time taken for joint problem solving by partners. DISCUSSION: The results of this study were not consistent with the observation of hearing loss measured after spaceflights. Nor were changes evident in cognition, motivation, or cardiovascular function. Factors which might account for the discrepancy are discussed.     

Thyroid function changes related to use of iodinated water in the U.S. Space Program

BACKGROUND: The National Aeronautics and Space Administration (NASA) has used iodination as a method of microbial disinfection of potable water systems in U.S. spacecraft and long-duration habitability modules. A review of thyroid function tests of NASA astronauts who had consumed iodinated water during spaceflight was conducted. METHODS: Thyroid function tests of all past and present astronauts were reviewed. Medical records of astronauts with a diagnosis of thyroid disease were reviewed. Iodine consumption by space crews from water and food was determined. Serum thyroid-stimulating hormone (TSH) and urinary iodine excretion from space crews were measured following modification of the Space Shuttle potable water system to remove most of the iodine. RESULTS: Mean TSH significantly increased in 134 astronauts who had consumed iodinated water during spaceflight. Serum TSH, and urine iodine levels of Space Shuttle crewmembers who flew following modification of the potable water supply system to remove iodine did not show a statistically significant change. There was no evidence supporting association between clinical thyroid disease and the number of spaceflights, amount of iodine consumed, or duration of iodine exposure. CONCLUSIONS: It is suggested that pharmacological doses of iodine consumed by astronauts transiently decrease thyroid function, as reflected by elevated serum TSH values. Although adverse effects of excess iodine consumption in susceptible individuals are well documented, exposure to high doses of iodine during spaceflight did not result in a statistically significant increase in long-term thyroid disease in the astronaut population.     

Plasma protein synthesis after spaceflight

INTRODUCTION: Astronauts land in a protein-depleted state. An anabolic phase takes place during the postflight period as muscle regains the lost protein. Yet where dietary intake has been measured after spaceflight, there does not appear to be any significant increase in dietary protein intake relative to preflight to provide additional amino acids to support muscles as they regain protein. We hypothesized that protein synthesis in other tissues is sub-optimal after spaceflight because of substrate competition for amino acids occurring between the muscles needing protein and other tissues. METHODS: We measured selected plasma protein synthesis rates before and after spaceflight on the Shuttle using the 15N glycine-hippuric acid method. The fractional protein synthesis rates (FSR) of four plasma proteins, fibrinogen, complement C-3, ceruloplasmin, and haptoglobin, were measured before and after a 16-d flight on the Space Shuttle. Data was obtained for four subjects. Preflight measurements of plasma protein synthesis rates were made 45 and 7 d before launch. Postflight measurements were done on the day of landing and 6 and 14 d later. RESULTS: Compared with preflight, plasma protein synthesis rates were reduced 6 d after landing. DISCUSSION: Plasma protein synthesis rates are depressed after spaceflight. The observations are consistent with amino acids being the limiting factor due to substrate competition between the muscles needing protein and other tissues.     

Hemodynamic effects of midodrine after spaceflight in astronauts without orthostatic hypotension

INTRODUCTION: Orthostatic hypotension and presyncope are common and potentially serious risks for astronauts returning from space. Susceptible subjects fail to generate an adequate adrenergic response to upright posture. The alpha-1 adrenergic agonist, midodrine, may be an effective countermeasure. We tested the hypothesis that midodrine would have no negative hemodynamic effect on healthy astronauts returning from space. METHODS: Five male astronauts participated in preflight and post-flight tilt testing on a control flight as well as on the test flights, where midodrine (10 mg, orally) was administered after landing approximately 1 h before testing. RESULTS: None of these astronauts exhibited orthostatic hypotension or presyncope before or after either flight. Midodrine did not cause any untoward reactions in these subjects before or after flight; in fact, a modest beneficial effect was seen on postflight tachycardia (p = 0.036). DISCUSSION: These data show that midodrine protected against post-spaceflight increases in heart rate without having any adverse hemodynamic effects on non-presyncopal, male astronauts. Among these subjects, midodrine was a safe cardiovascular countermeasure.     

100 years of observation on British radiologists: mortality from cancer and other causes 1897-1997.

Radiologists and radiotherapists were one of the earliest occupational groups to be exposed to ionizing radiation. Their patterns of mortality provide information on the long-term effects of fractionated external radiation exposure. British radiologists who registered with a radiological society between 1897 and 1979 have now been followed-up until 1 January 1997, and the mortality experience examined among those who registered with a society after 1920, when the first radiological protection recommendations were published. The observed number of cancer deaths in those who registered after 1920 was similar to that expected from death rates for all medical practitioners combined (SMR=1.04; 95% CI 0.89-1.21). However, there was evidence of an increasing trend in risk of cancer mortality with time since first registration with a radiological society (p=0.002), such that in those registered for more than 40 years there was a 41% excess risk of cancer mortality (SMR=1.41; 95% CI 1.03-1.90). This is probably a long-term effect of radiation exposure in those who first registered during 1921-1935 and 1936-1954. There was no evidence of an increase in cancer mortality among radiologists who first registered after 1954, in whom radiation exposures are likely to have been lower. Non-cancer causes of death were also examined in more detail than has been reported previously. There was no evidence of an effect of radiation on diseases other than cancer even in the earliest radiologists, despite the fact that doses of the size received by them have been associated with more than a doubling in the death rate among the survivors of the Japanese atomic bombings.     

Mortality in primary malignant brain tumors in the population of Belgrade

BACKGROUND: The aim of this investigation was the analysis of primary malignant brain tumors (PMBT)-related mortality in the Belgrade population during the period 1983-2000. METHODS: Mortality data (based on death records) for the period observed, as well as population data, were obtained from the unpublished material of the Municipal Institute of Statistics, Belgrade. The data analysis was adjusted to specific and standardized mortality rates and linear trend, using the world population as a standard. Regression coefficient was determined by Fisher's test. RESULTS: During the period 1983-2000, in the Belgrade population standardized mortality rates from PMBT were 6.29/100,000 (95% CI-confidence interval 5.33-7.24) for males, 4.50/100,000 (95% CI 3.84-5.17) for females, and 5.91/100,000 (95% CI 5.20-6.63) for total population. The age-specific mortality rates increased with age up to the age group 65-74, with the highest value of 21.21/100,000 (95% CI 16.03-26.39), and decreased in persons of 75 and more years of age. CONCLUSION: Mortality rates from PMBT in Belgrade had slightly increasing tendency in male (5.725 + 0.0592x, p = 0.545), and decreasing tendency in female population (y = 4.703-0.0213x, p = 0.756), while statistically significant increasing mortality rate was registered only in the age group 65-74 (y = 435 + 1.7707x, p = 0.0001).     

Postservice mortality of Air Force veterans occupationally exposed to herbicides during the Vietnam War: 20-year follow-up results

Since 1982, the Air Force Health Study has continued to assess the mortality for veterans of Operation Ranch Hand, the unit responsible for aerially spraying herbicides in Vietnam. The mortality for 1,262 Ranch Hand veterans to December 31, 1999 was contrasted with that for 19,078 comparison veterans. The relative risk (RR) for all-cause death was borderline significantly increased (RR, 1.15; 95% confidence interval, 1.0-1.3; p = 0.06). The risk of death caused by cancer was not increased (RR = 1.0), but the risk of death caused by circulatory system diseases was significantly increased among enlisted ground crew workers (RR = 1.7; 95% confidence interval, 1.2-2.4; p = 0.001). Results for Ranch Hand all-cause death differed from previous reports, with the RR now exceeding 1.0. The risk of death attributable to circulatory system diseases continues to be increased, especially for enlisted ground crew, a subgroup with relatively high skin exposure to herbicides.     

Heart rate reserve as a predictor of cardiovascular and all-cause mortality in men

This study examined the relationship of heart rate reserve (HRR: maximal heart rate - resting heart rate) and cardiovascular disease mortality (CVD) or all-cause mortality among healthy men. METHODS: Subjects were 27,459 healthy men, age 20-59 yr, who completed a maximal treadmill exercise test and answered a health questionnaire at the baseline examination. We followed study participants from the baseline visit to the date of death or December 31, 1996, for survivors. RESULTS: Over an average follow-up of 13.0 +/- 6.2 yr, there were 724 deaths, 205 (28.3%) from CVD. For analyses, the men were stratified into two age groups: younger (20-39 yr) and older (40-59 yr). Cox regression analysis was used to adjust for age, resting heart rate, cardiorespiratory fitness (CRF), resting systolic blood pressure (SBP), SBP difference, cholesterol, triglycerides, body mass index (BMI), smoking, and alcohol consumption. Among younger men, HRR was the only factor associated with CVD mortality (instantaneous relative risk (RR) and 95% confidence interval for HRR = 0.6, 0.5-0.9 for CVD mortality by 10 beats.min(-1) increment), whereas only CRF and BMI were associated with all-cause mortality. Among older men, HRR was inversely associated with CVD and all-cause mortality, as were several other known risk factors, including CRF (RR(per 2 METs), and 95% CI for HRR = 0.7, 0.5-0.9 for CVD mortality and 0.8, 0.7-0.9 for all-cause mortality). CONCLUSIONS HRR, independent from CRF, was inversely associated with CVD mortality among men in this study. HRR may be an important exercise test parameter to predict CVD mortality in younger men, whereas CRF and other established risk factors are better predictors of CVD and all-cause mortality in older men.     

Cardiovascular effects of anti-G suit and cooling garment during space shuttle re-entry and landing

BACKGROUND: Many cardiovascular changes associated with spaceflight reduce the ability of the cardiovascular system to oppose gravity on return to Earth, leaving astronauts susceptible to orthostatic hypotension during re-entry and landing. Consequently, an anti-G suit was developed to protect arterial pressure during re-entry. A liquid cooling garment (LCG) was then needed to alleviate the thermal stress resulting from use of the launch and entry suit. METHODS: We studied 34 astronauts on 22 flights (4-16 d). Subjects were studied 10 d before launch and on landing day. Preflight, crewmembers were suited with their anti-G suits set to the intended inflation for re-entry. Three consecutive measurements of heart rate and arterial pressure were obtained while seated and then again while standing. Three subjects who inflated the anti-G suits also donned the LCG for landing. Arterial pressure and heart rate were measured every 5 min during the de-orbit maneuver, through maximum G-loading (max-G) and touch down (TD). After TD, crew-members again initiated three seated measurements followed by three standing measurements. RESULTS: Astronauts with inflated anti-G suits had higher arterial pressure than those who did not have inflated anti-G suits during re-entry and landing (133.1 +/- 2.5/76.1 +/- 2.1 vs. 128.3 +/- 4.2/79.3 +/- 2.9, de-orbit; 157.3 +/- 4.5/102.1 +/- 3.6 vs. 145.2 +/- 10.5/95.7 + 5.5, max-G; 159.6 +/- 3.9/103.7 +/- 3.3 vs. 134.1 +/- 5.1/85.7 +/- 3.1, TD). In the group with inflated anti-G suits, those who also wore the LCG exhibited significantly lower heart rates than those who did not (75.7 +/- 11.5 vs. 86.5 +/- 6.2, de-orbit; 79.5 +/- 24.8 vs. 112.1 +/- 8.7, max-G; 84.7 +/- 8.0 vs. 110.5 +/- 7.9, TD). CONCLUSIONS: The anti-G suit is effective in supporting arterial pressure. The addition of the LCG lowers heart rate during re-entry.     

Decision analysis in aerospace medicine: costs and benefits of a hyperbaric facility in space

INTRODUCTION: Assembly and maintenance of the International Space Station (ISS) requires an unprecedented number of spacewalks, which expose astronauts to the risk of decompression sickness (DCS). We illustrate the use of decision analysis to compare a hyperbaric oxygen (HBO) chamber to currently available therapy for DCS treatment on the ISS. METHODS: A decision-analytic model that simulates events over the lifespan of the ISS was constructed. Inputs to the model for probabilities, costs, and measures of morbidity and mortality were derived from a variety of sources, including a systematic literature review and an iterative consultation process with personnel at the Canadian Space Agency and the National Aeronautics and Space Administration (NASA). The decision model was analyzed using the methods of Monte-Carlo simulation and expected value calculation. Main outcome measures included the present value of costs and quality adjusted life years (QALYs), and the cumulative probability of mission-related events over the life cycle of the ISS. Sensitivity analysis was performed. RESULTS: The HBO chamber strategy is associated with a mean cost of -12.5 million dollarsw (a net cost saving of 12.5 million dollars) with a 95% CI (-112.8 million dollars, 51.3 million dollars). An HBO chamber reduces the likelihood of a premature shuttle return and a premature Soyuz return by 8% and 3%, respectively. The result is sensitive to the lifespan of the ISS. CONCLUSIONS: At a 50 million dollars cost, an HBO chamber is likely, though not certain, to result in cost savings. Decision analysis is a useful tool for use in priority setting in aerospace medicine.     

Comparison of echocardiographic changes after short- and long-duration spaceflight

BACKGROUND: Previous echocardiographic studies of astronauts before and after short-duration (4-17 d) missions have demonstrated a decrease in resting left ventricular stroke volume, but maintained ejection fraction (EF) and cardiac output. Similar studies before and after long-duration (129-144 d) spaceflight have been rare and their overall results equivocal. METHODS: Echocardiographic measurements (M-mode, 2-D, and Doppler) were obtained from short-duration (n = 13) and long-duration (n = 4) crewmembers to evaluate cardiac chamber sizes and function. RESULTS: Compared with short-duration astronauts, long-duration crewmembers had decreases in EF (+6+/-0.02 vs. -10.5+/-0.03%, p = 0.005) and percent fractional shortening (+7+/-0.03 vs. -11+/-0.07%, p = 0.015), and an increase in left ventricular end systolic volume (-12+/-0.06 vs. +39+/-0.24%, p = 0.011). CONCLUSIONS: These data suggest a reduction in cardiac function that relates to mission duration. As the changes in BP and circulating blood volume are reported to be similar after short- and long-duration flights, the smaller EF after longer spaceflights may be due to a decrease in cardiac function rather than altered blood volume.     

The medical implications of space tourism

Commercial space travel may soon be a reality. If so, microgravity, high acceleration, and radiation exposure, all known hazards, will be accessible to the general public. Therefore, space tourism has medical implications. Even though the first flights will feature space exposure times of only a few minutes, the potential may someday exist for exposure times long enough to warrant careful consideration of the potential hazards to the space-faring public. The effects of acceleration and microgravity exposure are well known on the corps of astronauts and cosmonauts. The effects of space radiation are partially known on astronauts, but much remains to be discovered. However, there are problems using astronaut data to make inferences about the general public. Astronauts are not necessarily representative of the general public, since they are highly fit, highly screened individuals. Astronaut data can tell us very little about the potential hazards of microgravity in pediatric, obstetric and geriatric populations, all of whom are potential space tourists. Key issues in standard setting will be determining acceptable limits of pre-existing disease and inferring medical standards from mission profiles. It will not be a trivial task drafting minimal medical standards for commercial space travel. It will require the collaboration of space medicine physicians, making the best guesses possible, based on limited amounts of data, with limited applicability. A helpful departure point may be the USAF Class 3 medical standard, applicable to NASA payload specialists. It is time to begin preliminary discussions toward defining those standards. Keywords: acceleration, aerospace medicine, medical standards, microgravity, radiation, space, space tourism, environmental hazards, environmental medicine.     

Autopsy and postmortem examination case study on genetic risk factors for cardiac death: polymorphisms of endothelial nitric oxide synthase gene Glu298Asp variant and T-786C mutation, human paraoxonase 1 (PON1) gene and alpha2beta-adrenergic receptor gene

BACKGROUND/AIM: The Glu298Asp variant in exon 7 and T-786C mutation in the 5'-flanking region of the endothelial nitric oxide synthase (eNOS) gene, paraoxonase I gene (PON1), and alpha2beta-adrenergic receptor gene (alpha2beta-AR) have been reported to be genetic risk factors for coronary heart disease (CHD). The aim of this study was to investige the effects of these four genetic polymorphisms on the probability of death due to CHD, using data obtained from medico-legal autopsies. METHODS: Blood samples from three groups: healthy controls, dead cases with CHD and without CHD (the latter as a control for dead cases) were used. After DNA extraction, genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) test. RESULTS: The frequency of the T allele in Glu298Asp variant in the dead cases with CHD was significantly higher than that in the healthy control (p < 0.001, OR = 4.47) and that in the dead cases without CHD (p < 0.001, OR = 7.62). The gene frequency of PON1 was significandy different (p = 0.007) between dead cases with and without CHD, and was also significantly different (p = 0.025) between the healthy control and dead cases without CHD. The gene frequency of PON1 was not significantly different (p = 0.401) between the healthy controls and dead cases with CHD. Hence this gene was not associated with death due to CHD. The other polymorphisms (T-786C mutation, alpha2beta-AR) also showed no effect on death due to CHD. CONCLUSION: The polymorphism of Glu298Asp eNOS gene in dead cases may be useful for determining the cause of death in CHD cases in the Japanese population.     

阳江天然放射性高本底地区居民1987～1995年非肿瘤死亡再分析

目的　进一步分析阳江天然放射性高本底地区居民非肿瘤性疾病危险及其影响因素。方法　采用定群队列研究方法对居住在高本底地区和对照地区居民进行调查 ,现场调查分为队列成员追踪随访和死因确认。按外照射年剂量水平 ,将居住在高本底地区的人群分为高、中、低剂量 3个组 ,进行内比较。高本底地区 3个剂量组与对照组之间的比较采用相对危险 (RR) ,并计算了个人终生累计剂量与超额相对危险 (ERR/Sv)。结果　高本底地区居民非肿瘤死亡比对照地区增加 9% ,死亡危险明显高于对照地区 ,RR =1 0 9,P =0 0 1;危险显著增加的非肿瘤疾病主要是消化系统疾病 ,RR =1 4 6 ,P =0 0 0 4 ,其中慢性肝炎与肝硬化为RR =1.98,P =0 0 0 4 ;危险显著降低的主要是传染和寄生虫疾病 (RR =0 81,P =0 0 4 ) ,其中肺结核死亡为RR =0 .5 8,P <0 0 0 1。对各种死因及肝硬化危险在不同剂量组间的齐性检验结果表明 ,消化系疾病 (P =0 0 1)及肝硬化 (P =0 0 4 )组间差异有显著性 ,其ERR(95 %CI) /Sv也分别为 2 18(0 2 2 ,7 6 4 )和 10 94 (1 34,NA)。结论　高本底地区居民消化系疾病中的慢性肝炎和肝硬化死亡率高于对照地区且有统计学意义 ,不同于癌症死亡的结果 ;肺结核死亡则显著低于对照地区。但由于目前资料的局限性 ,     

Physical activity and mortality across cardiovascular disease risk groups

PURPOSE: Several cohort studies suggest that sedentary individuals have an increased risk of death compared with individuals who are physically active. Most of these studies have been conducted in highly selected patient populations who tend to be healthier and are from higher socioeconomic status (SES) groups. We examined the impact of a sedentary lifestyle on mortality by cardiovascular disease (CVD) risk group in a national sample of U.S. adults who represent a wide range of activity levels, health conditions, and SES groups. METHODS: Using data from the HRS, a nationally representative, observational study of 9824 U.S. adults aged 51-61 yr in 1992, we estimated the relative risk of death comparing sedentary individuals with those who are physically active by CVD risk group in a multivariate logistic regression model. RESULTS: Even after adjusting for confounders, regular moderate to vigorous physical activity was associated with substantially lower overall mortality (odds ratio (OR) = 0.62 (95% CI 0.44-0.86)) compared with sedentary individuals. High CVD risk individuals (21% of the population) accounted for 64% of deaths attributable to a sedentary lifestyle. Those with high CVD risk had the most significant benefit from being active (regular moderate to vigorous exercisers OR = 0.55 (95% CI 0.31-0.97) and occasional or light exercisers OR 0.55 (95% CI 0.41-0.74)) compared with high CVD risk individuals who were sedentary. CONCLUSION: A sedentary lifestyle is associated with a higher risk of death in preretirement-aged U.S. adults. Individuals with high CVD risk appear to get the largest benefit from being physically active. Physical activity interventions targeting high CVD risk individuals should be a medical and public health priority.