Open-loop accommodation in emmetropia and myopia

PURPOSE: To investigate the influence of method of measurement and refractive error on the open-loop accommodation response. METHODS: Open-loop accommodation was measured in darkness (dark accommodation, DA) and using a pinhole pupil (pinhole accommodation, PA) in emmetropic subjects (EMMs, n = 63), subjects with late-onset myopia (LOMs, n = 50) and subjects with early onset myopia (EOMs, n = 51). Further a control experiment examined the differences between DA and bright-field accommodation (BA) conditions in a subset of subjects. All measurements of open-loop accommodation were carried out monocularly using a Canon R1 infra-red optometer in static recording mode. All myopic subjects were fully corrected using soft contact lenses. RESULTS: A significant variation (p < 0.001) in open-loop accommodation was found between DA and PA, but no variation in open-loop level was observed between the three refractive groups. There was no interaction between these two factors. No significant difference was found between the BA level and DA level in any of the refractive groups. CONCLUSIONS: Open-loop accommodation response positions vary according to the experimental conditions employed during measurement. No refractive group differences in the open-loop response were apparent.     

Functional involvement of vasopressin in the maintenance of systemic arterial blood pressures after phenoxybenzamine or phentolamine administration: studies in Long-Evans and Brattleboro rats

The alpha adrenoceptor antagonists phenoxybenzamine and phentolamine are reported to have opposite effects on vasopressin release, the former inhibiting and the latter enhancing it. In this study we have assessed the functional involvement of vasopressin in the maintenance of blood pressure in conscious rats after administration of either phenoxybenzamine or phentolamine. In normal (Long-Evans) rats, phenoxybenzamine caused a small fall in arterial blood pressure, whereas phentolamine initially caused a profound hypotension which was followed by a fluctuating recovery back to normotensive levels. Similar effects were seen in rats deficient in hypothalamic vasopressin (Brattleboro strain). Administration of an antagonist of the cardiovascular actions of vasopressin [1-(beta-mercapto-beta, beta-cyclopentamethylenepropionic acid)-8-D-arginine vasopressin] in the presence of either alpha adrenoceptor antagonist alone was without effect in Long-Evans or Brattleboro rats, but, under these conditions, subsequent administration of captopril caused a profound and sustained hypotension in both strains. Administration of captopril in the presence of either alpha adrenoceptor antagonist alone caused a prompt fall in blood pressure which was sustained for the duration of the experiment in the Brattleboro rats. However, under these conditions, the blood pressure of the Long-Evans rats showed some recovery over the subsequent 45 min; this recovery was antagonized by [1-(beta-mercapto-beta, beta-cyclopentamethylenepropionic acid)-8-D-argine vasopressin]. It is concluded that after alpha adrenoceptor antagonism with either phenoxybenzamine or phentolamine, the renin-angiotensin system exerts a major pressor influence. However, after captopril administration in the presence of phenoxybenzamine or phentolamine, vasopressin contributes to the maintenance of arterial blood pressure in Long-Evans rats; the magnitude of this contribution is similar irrespective of the alpha adrenoceptor antagonist used.     

诱导化疗在局部晚期头颈癌中的作用

作为标准化的非手术治疗,诱导化疗(ICT)在治疗局部晚期头颈鳞癌已有几十年的历史,但是关于其作用尚存争议。同期放化疗(CRT)是目前标准化的非手术治疗,然而由于ICT能够使肿瘤体积缩小,提高放疗的可行性,改善患者对放疗的耐受力,增加放疗后器官功能保留的可能性及降低远处转移率。所以,对ICT的研究从未停止。该文对近期随机试验进行回顾分析,与手术或单独CRT比较,评估ICT中紫杉醇的价值。Meta分析比较ICT中紫杉醇和顺铂及5氟尿嘧啶的作用。之前的随机试验中,并没有ICT提高生存率的报道。但     

Demographic characteristics and prevalence of serologic markers among donors who use the confidential unit exclusion process: the Retrovirus Epidemiology Donor Study

BACKGROUND: Most blood centers utilize a confidential unit exclusion (CUE) process, intended to reduce the risk of transfusion-associated infectious diseases by allowing high-risk donors confidentially to exclude their blood from use for transfusion. The effectiveness of this method remains controversial. STUDY DESIGN AND METHODS: Confirmatory or supplemental test results for antibodies to human immunodeficiency virus, human T-lymphotropic virus type I, and hepatitis C virus, as well as hepatitis B surface antigen and syphilis and screening test results for antibodies to hepatitis B core (antigen) and alanine aminotransferase levels were obtained for approximately 1.8 million units donated during 1991 and 1992 at five blood centers within the United States. The prevalences of these infectious disease markers in units that the donors confidentially excluded (CUE+) and units that the donors did not exclude (CUE-) were calculated and examined within demographic subgroups. RESULTS: Units that were CUE+ were 8 to 41 times more likely to be seropositive for antibodies to human immunodeficiency virus and hepatitis C virus, hepatitis B surface antigen, and syphilis and three to four times more likely to react for antibody to hepatitis B core (antigen) or to have elevated alanine aminotransferase levels than units that were CUE- (p < 0.001). The positive predictive value of CUE (the percentage of CUE+ units that were confirmed seropositive for any marker) was 3.5 percent, and the sensitivity of CUE (the percentage of confirmed-seropositive units that were CUE+) was 2.3 percent. CONCLUSION: The current CUE process has low sensitivity and apparently low positive predictive value, and in many cases, it appeared that donors misunderstood it. Yet, CUE was not a “random process,” as CUE+ units were more likely to be seropositive for any infectious disease marker than CUE- units. This suggests that efforts to improve the CUE system may be warranted. As risk factors for transfusion-transmitted infection become more difficult to identify by history-based screening, however, such efforts may have limited effect.     

A fat lot of good: balance and trends in fat intake in children with cystic fibrosis

BackgroundThe fundamental nutritional treatment of a high fat diet for cystic fibrosis (CF) is established and essentially unchanged in the last 25 years. However, recent concerns have emerged regarding the potential risks of such a diet. We investigated the diets of children with CF to determine the source of energy, energy imbalance, and changing trends of fat intake.MethodIn a prospective longitudinal study over 8 years at a single paediatric CF clinic three-day food diaries that included supplementary nutrition (SN) either as enteral feeds or oral nutritional supplements (ONS), were analysed annually. Influence of year on percent energy by type (fat, carbohydrate and protein) and on fat component: saturated (SFA); monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) was examined.Results136 food diaries were analysed in 27 children (age range 1–18 years). 51 (37%) food diaries included SN (enteral feeds n = 15 and ONS n = 36). Mean energy intake was 1726 Kcals (oral diet alone) and 2245 Kcals (including SN). Percent energy from macronutrients did not change significantly over time (protein p = 0.06; carbohydrate p = 0.44; fat p = 0.07) and remained within recommended levels. Mean caloric contribution from fat was 38.7% from oral diet alone and 37.8% including SN. Percent energy derived from SFA remained statistically unchanged (SFA p = 0.57) but fell from MUFA (p = 0.05) and PUFA (p = 0.004). Mean SFA consistently contributed > 134% (mean 158%) of reference nutrient intake and mean PUFA intake < 100% (92%).ConclusionMacronutrient intakes did not change significantly in our population of CF children, but there was a consistent imbalance of fat-sources with over-dependence on saturated fats which, in the context of increased survival in CF may potentially increase risk of cardiovascular disease. Further studies are needed to confirm our findings, investigate consequences of fat imbalance and guide clearer advice regarding appropriate proportions of sources of fat for CF patients.     

Retrading,production, and asset market performance

Prior studies have shown that traders quickly converge to the price–quantity equilibrium in markets for goods that are immediately consumed, but they produce speculative price bubbles in resalable asset markets. We present a stock-flow model of durable assets in which the existing stock of assets is subject to depreciation and producers may produce additional units of the asset. In our laboratory experiments inexperienced consumers who can resell their units disregard the consumption value of the assets and compete vigorously with producers, depressing prices and production. Consumers who have first participated in experiments without resale learn to heed their consumption values and, when they are given the option to resell, trade at equilibrium prices. Reproducibility is therefore the most natural and most effective treatment for suppression of bubbles in asset market experiments.Contrary to rational theory the first asset market experiments with complete common information on fundamental value exhibited unexpectedly strong tendencies to yield price bubbles (1). The results, however, were soon extended (2, 3), independently replicated (4–8), and have quite important consequences for improved understanding of the sources of instability in the economy (9–11).In contrast with these robust asset market findings, earlier experiments had established that repeated trade across time periods in static supply and demand experiments yielded efficient rapid convergence to rational competitive equilibrium outcomes under strictly private decentralized information (12). In the supply and demand experiments, however, trades were for immediate consumption, as with hamburgers and haircuts; as noted in ref. 13, items could not be retraded and individuals knew in advance that they were specialized as buyers or sellers and could not switch roles depending on price as in asset markets. [These features also characterize nondurable goods and services in the US national accounts and represent approximately 75% of private product. Instability in the US national accounts arises from the remaining 25% (11)].Motivated by the glaring contrast in these two kinds of markets, Dickhaut et al. (13) reformulated the traditional supply and demand environment by explicitly modeling two goods: “cash” as a means of payment and a “commodity” that had a heterogeneous end-of-period “dividend” consumption yield value. This formulation exactly parallels the asset trading environment, except that cash and commodity endowments have only a one-period life and dividends are not common. Individual subjects received diverse endowments, but in each of 10 periods a subject was endowed with the same amounts of cash and commodity, thus inducing pure static supply and demand conditions across 10 periods. This reformulated framework allowed the study of convergence in a 2 × 2 design, (retrade, no retrade) × (low cash, high cash). Convergence was markedly slower in retrade vs. no retrade because traders who could retrade had difficulty learning from market prices their optimal role as buyers or sellers. High cash exacerbated this difficulty relative to low cash, in line with previous findings (14).Haruvy et al. (ref. 15, p. 7) observe that because durable goods can be retraded they carry an implicit option value for resale at a higher or lower price depending on individual expectations. [Harrison and Kreps (16) also demonstrated this possibility in a theoretical model.] A perishable good has only consumptive utility value, if purchased, whereas a durable good will yield consumptive value if retained, but a resale value if not. Thus, durable goods can involve a speculative motive whereas nondurables cannot. It is this speculative motive that has driven price bubbles in studies of asset markets.Previous studies have modeled a durable asset whose life extends over the entire horizon of the experiment; in those studies—unlike house or automobile markets, for example—no new units were produced and existing units did not depreciate during the course of the experiment. [However, Haruvy et al. (15) study a securities market subject to external interventions to repurchase existing shares that reduce the asset stock, or issue new shares that increase the stock.] In this paper we model producers who at private unit cost may elect to sell newly produced units that add to the existing stock; also, we introduce an elementary “replacement demand” for asset units: The existing units “depreciate” with a constant probability, independent of age and price. Hence, there is a net addition (or loss) of asset units in the market depending on whether production is greater than or less than the depreciation rate. We set the stage for experimental studies of asset market trading characterized by dynamic stock-flow trajectories over time with the stock determined endogenously. [Abstract general stock-flow models were introduced by Clower (17) for capital asset pricing and Smith (18) for the theory of the firm.] In our new experiments we find that resale inhibits price discovery, which in turn distorts production and retards efficiency. However, whereas resale has generated price bubbles in asset markets without production, in our asset markets resale suppresses prices well below equilibrium. This is because many consumers fail to specialize as buyers, and instead compete with producers as sellers. When we rerun the resale experiments with subjects who are experienced as specialized buyers and sellers in the no-resale treatment prices and production converge to equilibrium and efficiency improves. Reproducibility is therefore the most natural and most effective treatment for suppression of bubbles in asset market experiments. [Hong et al. (19) develop a theoretical model in which release of locked up shares can suppress a price bubble following an initial public offering.]