医学文献检索教学的改革

探讨了优化教材内容,编制配套资料;改进教学方式和教学手段以及完善考试方法等文检课改革办法,提出编写"教材"和"讲义"两个版本;建立以网络检索为核心的教材体系;采用基于问题的教学法和启发式教学模式;开发网上资源模拟课件,现场上网教学模式和文检课计算机模拟考核等具体改革方案.     

Investigation of bone changes in microgravity during long and short duration space flight: comparison of techniques

BACKGROUND: Loss of bone mass is a continuing problem in long-term space flight. Although counter-measure programmes have been developed, effective assessment of these programmes is hampered by a lack of monitoring techniques that can be used in-flight. MATERIALS AND METHODS: Three techniques were used to evaluate changes in bone during two missions of 180 and 20 days to the MIR space station, involving three subjects. Dual energy X-ray absorptiometry (DXA) was used before and after flight to measure whole body and regional bone mineral density (BMD). Ultrasonic measurements of velocity (SOS) and broadband attenuation (BUA) of the calcaneus were measured during the 180 day mission and before and after the 20 day mission. Phase velocity of flexural waves in the tibia was also measured on the same days as the ultrasonic measurements of the calcaneus. RESULTS: DXA measurements demonstrated significant variation between different sites in the body for changes in BMD, with the greatest changes occurring in the lumbar spine and proximal femur. There was a trend for increasing phase velocity in the tibia during the 180 mission, but this was not significant. BUA and SOS measurements of the calcaneus showed consistent but divergent patterns of changes during the mission. CONCLUSION: Although in-flight measurements of bone using ultrasound or phase velocity may provide information on the kinetics of bone loss in space flight, the heterogeneity of response in the skeleton means that it is difficult to predict overall bone loss from measurements at one particular site.     

尾吊大鼠肺组织原癌基因C-fos的表达及川芎嗪对其影响

目的:研究模拟失重大鼠肺组织内原癌基因C-fos的表达变化及川芎嗪对其影响.方法:尾部-30(悬吊(TS)大鼠模拟失重生理效应.健康30只Wistar大鼠随机分为对照组(CON)、尾吊7 d组(TS7研d)和尾吊 川芎嗪7 d组(Treated).采用免疫组织化学法和原位杂交法观察大鼠肺组织内C-fos表达水平的变化.结果:尾吊7 d组肺组织、肺腺泡血管和微血管内血管内皮细胞、血管平滑肌细胞的细胞内原癌基因C-fos蛋白及其mRNA明显高于对照组(P<0.01),经川芎嗪干预(treated组)大鼠肺组织蛋白的平均光密度值和阳性面积百分比与尾吊7 d组比较均降低(P<0.01,P<0.05).结论:尾吊模拟失重引起大鼠肺组织C-fos蛋白及其mRNA表达水平增加,川芎嗪可下调肺组织C-fos蛋白及其mRNA表达水平.     

稳定性过氧乙酸杀菌效果试验观察

目的 了解过氧乙酸稳定性改善及影响杀菌效果.方法 对过氧乙酸含量的下降速率进行测定分析,同时采用实验室和模拟现场的试验手段观察其对枯草芽胞杆菌黑色变种芽胞杀灭效果;空气消毒效果以密闭房间中自然菌作为观察对象,采用微粒子气溶胶喷雾,观察其对空气自然菌的杀菌效果.结果 该一元型过氧乙酸稳定性好,于(25±1)℃的恒温箱内储存12个月,其过氧乙酸含量的下降率≤10%,经模拟现场试验,试验组以1000 mg/L过氧乙酸对污染在止血钳齿部的枯草芽胞杆菌黑色变种芽胞作用10 min,杀灭对数值＞3.00;1500 mg/L过氧乙酸作用30 min达到完全杀灭;以1000 mg/L过氧乙酸、按10 ml/m3用量进行气溶胶喷雾作用30 min,对室内空气中自然菌消亡率＞90.0%.结论 该过氧乙酸的稳定性得到了较大的改善,而不影响其杀菌效果.     

Corrosion behavior of Cu and the Cu-Zn-Al shape memory alloy in simulated uterine fluid

Chemical immersion tests, electrochemical methods and atomic absorption spectrometry were employed to investigate the corrosion behavior of Cu and the Cu-Zn-Al shape memory alloy (SMA) in simulated uterine fluid. The effect of pH on corrosion rate and corrosion potential was also investigated. The results indicated that in the static state in simulated uterine fluid, dealuminumification of the Cu-Zn-Al alloy occurred with Cl- combining with aluminum ions to form hydroxyl aluminum chloride. The hydroxyl aluminum chloride hydrolyzed readily and facilitated further dealuminumification corrosion. The corrosion process of Cu and Cu-Zn-Al SMA in simulated uterine fluid was controlled by cathodic reduction of oxygen. Because the tendency for surface ionization is greater for aluminum than for zinc, a compact protective aluminum layer was formed, which inhibited the cathodic reduction of oxygen. Hence, the corrosion rate of Cu-Zn-Al SMA was smaller than that of Cu in simulated uterine fluid. With increasing pH, the corrosion rate of Cu and Cu-Zn-Al SMA in simulated uterine fluid decreased and the open-circuit potential moved in a positive direction.     

The structure and response properties of Golgi tendon organs in control and hypodynamia-hypokinesia rats

The Golgi tendon organs (GTOs) are encapsulated mechano-receptors that, in normal conditions, monitor via Ib afferent fibers the contractile force. A 14-day period of hypodynamia, absence of weight bearing and hypokinesia, and reduction of motor activity (HH) is known to induce changes in postural muscles such as the soleus. At present, there is no data available regarding the Ib afferent feedback in normal rats (CONT group) and in rats after a hypodynamia-hypokinesia (HH group) period. Consequently, the aim of our study was to determine the HH effects on the morphological (histochemistry on gross morphology) and electrophysiological properties of the GTOs in rat soleus muscle. In the histological study, nine CONT and nineteen HH GTOs of the soleus muscle were identified. The results demonstrated that HH GTOs were morphologically similar to the CONT GTOs. Regarding the electrophysiological study, a L2-L6 laminectomy was performed under deep anesthesia (sodium pentobarbital, 60 mg kg(-1)). Responses in single Ib fibers from the L5 dorsal root to the isometric twitch and tetanic fused contractions of "in-series" motor units (MUs) were recorded. Twenty-three and twenty-eight GTO/MU pairs were studied in the CONT and HH groups, respectively. In the HH group, the Ib afferent response exhibited a decrease in dynamic peak for the high stimulation frequencies and an increase in static sensitivity for all stimulation frequencies. Our results suggest that after an HH period, the GTOs continue to fulfil their mechano-sensory function to signal the contractile force but with a higher static sensitivity.     

Neuromuscular adaptations to spaceflight are specific to postural muscles

The effects of microgravity were determined in muscles of differing function and myofiber-type composition. Rats were assigned either to a 10-day spaceflight mission or to ground-based control conditions. Following the experimental period, hindlimb muscles were obtained from both groups. Cytofluorescent techniques were used to examine neuromuscular junctions (NMJs) from both slow- and fast-twitch fibers. Histochemical procedures were employed to assess myofiber profiles (size and type). Results indicate that microgravity did not alter NMJ structure or myofiber profile in the tibialis anterior, a predominantly fast-twitch, nonpostural muscle. Similarly, the NMJs and myofibers of deep regions of the gastrocnemius, a locomotor muscle possessing a mixed fiber population, were unaffected by spaceflight. In contrast, both myofibers and NMJs of the soleus-a postural muscle-demonstrated significant (P < 0.05) plasticity following exposure to spaceflight. Moreover, NMJs of both fast- and slow-twitch myofibers displayed similar remodeling in that muscle. Our findings suggest that the deleterious effects of microgravity are most apparent among postural muscles, and are manifested both in myofibers and their synapses.     

Functional alterations of mesenteric vascular bed, vas deferens and intestinal tracts in a rat hindlimb unloading model of microgravity

1. Prolonged bed rest or exposure to microgravity may cause several alterations in autonomic nervous system response (ANSR). 2. Hindlimb unloading (HU) rats were used as an animal model of simulated microgravity to investigate ANSR changes. The experiments were carried out to investigate the effects of simulated microgravity on the autonomic nervous response of the perfused mesenteric vascular bed (MVB), vas deferens and the colon and duodenum from 2-week HU rats. 3. In MVB preparations of HU rats, the frequency-dependent increases in perfusion pressure with perivascular nerve stimulation (PNS; 8-40 Hz) were inhibited, whereas the noradrenaline (NA) concentration-dependent (1-100 microM) perfusion pressure increases were potentiated. The latter most probably reflected up-regulation of alpha-adrenergic receptor function. Relaxant responses of NA-precontracted MVB to PNS (4-30 Hz) or isoprenaline were not different between control and HU preparations, while vasodilation induced by the endothelial agonist ACh was reduced. 4. Transmural stimulation (2-40 Hz) induced frequency-dependent twitches of the vas deferens which were reduced in vas deferens of HU rats, while the sensitivity to NA-induced contraction was significantly increased. 5. In the gastroenteric system of HU rat, direct contractile responses to carbachol or tachykinin as well as relaxant or contractile responses to nervous stimulation appeared unchanged both in the proximal colon rings and in duodenal longitudinal strips. 6. In conclusion, HU treatment affects peripheral tissues in which the main contractile mediators are the adrenergic ones such as resistance vessels and vas deferens, probably by reducing the release of neuromediator. This study validates NA signalling impairment as a widespread process in microgravity, which may most dramatically result in the clinical phenotype of orthostatic intolerance.     

Changes in bone turnover markers during 14-day 6° head-down bed rest

Osteoporosis caused by exposure to microgravity represents a serious clinical concern, but the mechanisms have yet to be fully elucidated. The present research aimed to elucidate the effects of microgravity environments on bone turnover, with a specific focus on changes in bone resorption markers such as type I collagen cross-linked N-telopeptides (NTx) and deoxypyridinoline (Dpyr), for which scant data are available regarding detailed time course. Methods using 6° head-down bed rest were utilized to simulate a microgravity environment. Eleven adult male volunteers underwent 6° head-down bed rest for 14 days; measurements were made of serum and urine Ca concentrations, in addition to osteocalcin (OC), bone alkaline phosphatase (ALP), NTx, and Dpyr as bone turnover markers. By the end of bed rest, concentrations of bone ALP had significantly increased, but OC displayed a tendency toward decrease. Concentrations of Dpyr significantly increased from day 6, remaining elevated until the end of bed rest. Concentrations of NTx significantly increased on day 13 and at the end of bed rest. Serum and urinary concentrations of Ca increased significantly at the end of bed rest. Bone ALP represents a relatively early marker of osteoblast differentiation at the matrix maturation phase and OC is a late marker in osteoblast differentiation at the calcification phase. The present results therefore suggest an absolute increase in bone resorption and normal or reduced bone formation, together causing prominent uncoupling and rapid bone loss after simulated microgravity. Moreover, the present results suggest that bone resorption is enhanced at an early stage of exposure to microgravity environments.     

The effects of limb elevation and increased intramuscular pressure on nerve and muscle function in the human leg

In this study we investigated the effects of increased intramuscular pressure (IMP) on nerve and muscle function in the leg and foot. In study A, muscle pressure was increased by inducing venous stasis in both legs, placed in plaster casts, of eight healthy subjects having a mean age of 29 years. The results from elevated and non-elevated limbs were compared. In study B, two different models for increasing IMP were studied in nine healthy subjects having a mean age of 32 years. The results of increased IMP and decreased blood perfusion pressure on local (=leg) and distal (=foot) function of muscle and nerve induced by venous stasis of a leg in a plaster cast and by external compression of the contralateral leg were compared. Contraction pressure of the tibialis anterior muscle in the leg was recorded. A biphasic compound muscle action potential was measured from the extensor hallucis brevis and the extensor digitorum muscles as an indication of foot muscle function. Muscle contraction pressure was 87 (SD 38) mmHg in the vein-obstructed leg and 133 (SD 42) mmHg in the externally compressed leg (P < 0.05). In both studies the skin sensibility of the feet was significantly lower in the vein-obstructed elevated leg after 30 min (P < 0.05). Vein stasis in an elevated human leg in a plaster cast defines a model for simulating imminent acute compartment syndrome with reversible neuromuscular dysfunction. Accepted: 17 April 2000