优化原理与小动脉血流量─管径关系

作者假设血液为符合幂定律的非牛顿流体，对小动脉血管系统进行了详细的优化分析。导出了血流量与管径立方成正比的结论以及壁面切变率与管径无关的推论。此结果既包含了前人对于牛顿血流的研究成果，又能克服后者的不足，而与近期的生理测定一致。     

Shear Rate Dependence of Ultrasound Backscattering from Blood Samples Characterized by Different Levels of Erythrocyte Aggregation

The objectives were (1) to determine the effect of the erythrocyte aggregation level (wide range of aggregation) and shear rate (which also affects aggregation) on the ultrasound backscattered power, and (2) to evaluate the reproducibility of the ultrasound method. Experiments were performed under steady flow (100–1250 ml/min) in a 12.7 mm diameter vertical tube. Doppler ultrasound at 10 MHz was used to measure simultaneously the velocity and the backscattered power across the tube. For each radial position, the shear rate was computed from the derivative of the velocity profile. The backscattered power decayed exponentially as a function of the shear rate, and for a given shear rate, the power increased monotonically with the level of aggregation measured by laser reflectometry. Using blood samples simulating hypo-, normal, and hyperaggregating erythrocytes, the power of the ultrasound signal varied respectively by –7.8, –13.2, and –16.1 dB as a function of the shear rate (from 0.4 to 50 s^–1). The reproducibility of the backscattered power was 5.5 dB, which is less than the variations observed as a function of the shear rate. In conclusion, ultrasound backscattering is sensitive to the level of erythrocyte aggregation. At a first glance, ultrasound seems less accurate when compared to laser reflectometry but it is suggested that this is because ultrasound backscattering may be sensitive to structural aggregate changes that are not detected by the laser method. © 2000 Biomedical Engineering Society. PAC00: 8718-h, 8719Tt, 8750Kk     

Power spectral analysis of the electroencephalographic and hemodynamic correlates of propofol anesthesia in the rat: Intravenous infusion

Based on the tail-flick response to noxious thermal stimuli, we determined in the present study that effective antinociception could be achieved in adult male Sprague-Dawley rats 15 min after intravenous infusion of propofol at 60 mg/kg/h. Simultaneous power spectral analysis of the electroencephalographic (EEG) and systemic arterial pressure signals further revealed a concomitant depression of the activity of all EEG frequency bands (δ, θ, , β), alongside hypotension, negative inotropic and chronotropic actions, and attenuated baroreceptor reflex and vasomotor activity. These effects were congruent with a plasma concentration of propofol in the arterial blood of 1.70 ± 0.13 μg/ml, as determined by high-performance liquid chromatography.     

Potential impact of hormonal male contraception: cross-cultural implications for development of novel preparations

The prospect of a hormonal male contraceptive is no longer distant. Data on the potential impact of this improvement in contraceptive provision, however, is limited, particularly between different cultures. We have therefore carried out a multi-centre study to assess men's attitudes to proposed novel hormonal methods. Questionnaire-based structured interviews were administered to men in Edinburgh, Cape Town, Shanghai and Hong Kong. Approximately 450 men were interviewed in Edinburgh, Shanghai and Hong Kong, and a slightly larger group (n = 493) in Cape Town to give samples (n > 150) of black, coloured and white men. Knowledge of existing male and female methods of contraception was high in all centres and groups. The majority of men welcomed a new hormonal method of contraception, 44-83% stating that they would use a male contraceptive pill. Overall, a pill was more acceptable than an injectable form (most popularly given at 3-6 month intervals); long-acting implants were least so except in Shanghai. Familiarity with comparable female methods appeared to influence acceptability, for both oral and injectable methods. Hong Kong was the only centre where a male method (condom) was currently the most commonly used; men there appeared to rate the convenience of condoms highly while being least likely to think that they provided effective protection against pregnancy compared to other centres, and were least enthusiastic about novel male methods. The acceptability of potential male hormonal methods of contraception was high in some groups but showed wide variability, determining factors including cultural background and current contraceptive usage. These results suggest that the emerging emphasis that men should have greater involvement in family planning will be substantiated when appropriate contraceptive methods become available.     

The use of ratings of perceived exertion for regulating exercise levels in rowing ergometry

The purpose of this study was to examine the validity of the use of ratings of perceived exertion (RPE) to estimate and regulate exercise intensity during rowing ergometry. Nine competitive male rowers [mean age 28.6 years, (SD 6.3)] completed two rowing trials on an ergometer. The first trial (estimation) consisted of an incremental protocol designed to elicit a range of work outputs (WO) and heart rates (HR). The subjects indicated their perception of effort using a 15-point scale at each intensity level. In the second trial (production), 7–14 days later, the subjects were asked to produce exercise intensities corresponding to five levels of RPE: 15,11,17,13, and 19. Data analysis revealed high Pearson correlation coefficients between HR and RPE (r = 0.95,P < 0.01) and WO and RPE (r = 0.96,P < 0.01) during the estimation trial. In addition, significant correlations (P < 0.01) were obtained between the estimation and production trials for HR (r = 0.82) and WO (r = 0.84). Posthoc analysis of variance revealed that the observed differences in mean HR were not significant (P > 0.05) at three of the five intensity levels (RPE 15,17 and 19), but were at the two lowest RPE levels (11 and 13). Significant mean differences in WO were seen at all but RPE 17. These data support the validity of the RPE scale as a measure of physiological strain among competitive male rowers, and offer support for its use as a method of regulating the intensity of rowing ergometry, especially at higher levels.     

EEG delta power during sleep in young and old rats

Delta EEG power density, which has been viewed as a measure of intensity of NREM sleep, declines across the lifetime in humans, cats, and hamsters, but data in rats have been unclear. It is also uncertain whether older rats differ from younger animals in the degree of change in delta power during recovery sleep following short-term sleep deprivation. We have examined delta power density in NREM sleep under baseline conditions and following 48 h of sleep deprivation in young (3 months), middle-aged (12 months), and older (24 months) rats. The presence or absence of age effects was highly dependent on the method of normalizing the data. When expressed as a fraction of total NREM EEG power, there was no age effect on baseline delta power density, or on the change from baseline to recovery conditions. When expressed as a multiple of delta power in REM under the same condition, the younger rats had higher delta power density than the middle-aged and older rats. For all the ages combined, there was an increase in delta power density in the recovery condition. When examined by age, the younger rats (which started from a higher level of delta power density than the other groups) did not have an increase in delta during recovery; the middle-aged rats tended to, and the older rats (which started from lower baseline levels) significantly increased delta power density in the recovery condition. This suggests that the lower delta power seen during baseline in older rats is not due to decreased ability to generate delta activity.     

The IHAT-GUT Iron Supplementation Trial in Rural Gambia: Barriers,Facilitators, and Benefits

Introduction: In most sub-Saharan African countries iron deficiency anaemia remains highly prevalent in children and this has not changed in the last 25 years. Supplementation with iron hydroxide adipate tartrate (IHAT) was being investigated in anaemic children in a phase two clinical trial (termed IHAT-GUT), conducted at the Medical Research Council Unit the Gambia at the London School of Hygiene and Tropical Medicine (LSHTM) (abbreviated as MRCG hereof). This qualitative study aimed to explore the personal perceptions of the trial staff in relation to conducting a clinical trial in such settings in order to highlight the health system specific needs and strengths in the rural, resource-poor setting of the Upper River Region in the Gambia. Methods: Individual interviews (n = 17) were conducted with local trial staff of the IHAT-GUT trial. Data were analysed using inductive thematic analysis. Results: Potential barriers and facilitators to conducting this clinical trial were identified at the patient, staff, and trial management levels. Several challenges, such as the rural location and cultural context, were identified but noted as not being long-term inhibitors. Participants believed the facilitators and benefits outnumbered the barriers, and included the impact on education and healthcare, the ambitious and knowledgeable locally recruited staff, and the local partnership. Conclusions: While facilitators and barriers were identified to conducting this clinical trial in a rural, resource-poor setting, the overall impact was perceived as beneficial, and this study is a useful example of community involvement and partnership for further health improvement programs. To effectively implement a nutrition intervention, the local health systems and context must be carefully considered through qualitative research beforehand.     

显著性概率地形图的一些基础问题探讨——少年组谱参量的正态分布转换问题

本文对41例年龄7—12岁右利健康儿童,头部选取5对(10个)样点,对各样点的功率和相对功率Ⅰ,Ⅱ的四个经典频带(δ,θ,α,β)进行几种数学转换,用正态性D检验法观察各参量转换前后的分布状态。结果,转换前,功率分布状态较差;而相对功率的参量原值近正态分布的情况较好,其中相对功率Ⅰ较相对功率Ⅱ更佳。而相对功率Ⅰ的X、log(X)和log(X/1—X)转换为最佳。就功率而言,log(x)转换最好,但仍不能完全满足各频带统计学的要求。     

肺音信号的自回归谱谱阵分析

本文应用自回归模型方法研究了各种肺音信号的ＡＲ谱谱阵，并与傅里叶功率谱谱阵作了对比，探讨了两种谱阵的特点与差异，实验结果表明：肺泡呼吸音ＡＲ模型阶次为６阶，气管音ＡＲ模型阶次为１４阶，哮鸣音与喘鸣音的ＡＲ模型阶次分别为１２阶与６阶，正常呼吸音（肺泡呼吸音与气管音）功率谱为连续谱，异常连续性肺音（哮鸣音与喘鸣音）功率谱为离散线状谱，音肺信号谱阵方法可显示出肺音的时变特性，有利于对肺音作动态分析。