Increasing the efficiency of Monte Carlo cohort simulations with variance reduction techniques.

The authors discuss techniques for Monte Carlo (MC) cohort simulations that reduce the number of simulation replications required to achieve a given degree of precision for various output measures. Known as variance reduction techniques, they are often used in industrial engineering and operations research models, but they are seldom used in medical models. However, most MC cohort simulations are well suited to the implementation of these techniques. The authors discuss the cost of implementation versus the benefit of reduced replications.     

Intensive care research coordinators: who are they and what do they do? Results of a binational survey.

Research coordinators in intensive care are a growing specialty about which little is known. This cross-sectional study surveyed the Australia and New Zealand Intensive Care Research Coordinators' Group (n = 49) regarding demographics, education, employment history, job structure, and role content. Most research coordinators were highly qualified and experienced nurses who undertake pharmaceutical trials, multicenter projects, departmental medical and nursing research, audits and data registries, and their own projects.     

Theoretical and practical considerations in the doubly-labelled water (2H2(18)O) method for the measurement of carbon dioxide production rate in man

In the doubly-labelled water (2H2(18)O) method for the measurement of carbon dioxide production rate in man, single exponential disappearance curves for 2H2O and H2(18)O in body water are used; the precision with which the slopes and intercepts of the curves are estimated determines the precision of the estimate of carbon dioxide production rate. In studies with infants, and in computer simulations, the effect of different experimental regimes on the overall precision of the carbon dioxide production estimate was investigated. When the number of data points used was progressively reduced by shortening the total observation period from 7 d (about 3 biological half-lives for the isotopes) to 1 d there was a deleterious effect on precision and in the infants there was an upward bias in the values for carbon dioxide production. When the number of data points was reduced by removing points from the middle of the exponential curves with the maintenance of the 7-d experimental period, precision was also reduced but by less than in the former procedure and there were no consistent trends in the average values for carbon dioxide production.     

Scholarly productivity: are nurse academics catching up?

The aim of this study was to document the amount of recent change in Australian nurse academics' scholarly productivity and to investigate the influence of demographic factors such as gender, academic rank, qualifications, increase in qualifications, state of residence, university and university size. Scholarly productivity was calculated from an audit of journal articles. The findings of this study indicate that, while there has been a slight increase in scholarly productivity in the last five years, nursing still lags behind other disciplines. Scholarly productivity was found to be positively associated with highest academic qualification, academic rank and promotion. The study indicates the continuing need for senior nurse academics to provide mentoring to colleagues and foster the development of skills associated with scholarly productivity.     

Protection of CGS 10078B against ouabain-induced arrhythmia in the cat

CGS 10078B (CGS; 1-[2,3-dihydro-1,4-(2S)-benzodioxin-2-yl]-5-[2,3-dihydro-1,4-(2R)- benzodioxin-2-yl]-3-(1R,5S)-aza-1,5-pentanediol methane sulfonate) is an agent with alpha- and beta-receptor and calcium channel blocking actions. To study its antiarrhythmic activity, cats were anesthetized with alpha-chloralose, ventilated, and given atropine and gallamine. CGS (10 or 20 mg/kg, i.v.) was infused 15 min prior to ouabain. Bolus injections of ouabain (25 micrograms/kg, i.v.) were given every 15 min until death (D). Some cats were pretreated with reserpine (R; 5 mg/kg, i.p.) 24 h prior to the experiment. In other cats 6-hydroxydopamine (6-OHDA; 20 mg/kg, i.v.) was administered 3 days prior to CGS 20 mg/kg and ouabain. Data were compared with those of Lathers [Eur. J. Pharmacol. 64: 95, 1980], i.e., with 12 cats who received only ouabain and with 11 pretreated with timolol (T; 5 mg/kg, i.v.) prior to ouabain. After CGS (10 or 20 mg/kg, i.v.), but just prior to the first dose of ouabain, the blood pressure (BP) was decreased (p less than 0.05) from control (165 +/- 6 vs. 96 +/- 7, and 136 +/- 5 vs. 90 +/- 10 mm Hg, respectively). Comparable heart rate (HR) values were also decreased (p less than 0.05) from 225 +/- 17 to 166 +/- 14 and from 193 +/- 8 to 152 +/- 6 beats/min. 11 min after T, BP and HR had decreased (p less than 0.05) from 133 +/- 6 to 103 +/- 7 mm Hg and from 134 +/- 4 to 104 +/- 6 beats/min, respectively. Ouabain did not influence these decreases in BP and HR. CGS (10 or 20 mg/kg, i.v.) increased (p less than 0.05) the time to ouabain-induced arrhythmia (AR) and D. The magnitude of the protection appeared to be similar to that afforded by T. R given prior to CGS (20 mg/kg, i.v.) also increased the time to ouabain-induced AR and D while 6-OHDA increased the time to AR. The CGS protection against ouabain-induced AR was still present in animals pretreated with R or 6-OHDA. This indicates that the antiarrhythmic affect is not dependent upon adrenergic neuronal blockade.     

Evidence for dual modulation of pepsinogen secretion using isoproterenol, carbachol, CCK-8, forskolin, 8 bromo-cAMP, and A23187 probes

The cellular mechanisms by which pepsinogen (PNG) secretion is controlled are not understood. The aim of this study was to explore whether modulation of PNG secretion is mediated by cAMP or calcium-calmodulin (C-C). PNG secretion in isolated rabbit gastric fundic glands (IGG) was tested, using agents believed to act via cAMP or C-C. IGG were stimulated for 30 minutes with histamine (H) 10(-5) M, isoproterenol (I) 10(-5) M, carbachol (C) 10(-5) M, cholecystokinin-octapeptide (CCK-8) 10(-7) M, forskolin (F) 10(-5) M, 8 bromo-cAMP (8B) 10(-3) M, and A23187 (A) 10(-6) M. PNG levels were determined by spectrophotometric assay of hemoglobin digestion products. PNG amounts secreted were (mean per cent above basal levels of total IGG PNG units +/- SEM): H, -0.02 +/- 0.30%; I, 3.5 +/- 0.9%; C, 5.1 +/- 2.2%; CCK-8, 5.3 +/- 1.5%; F, 10.6 +/- 3.8%; 8B, 13.8 +/- 4.5%; A, 2.1 +/- 1.1%. All secretagogues except H stimulated PNG release significantly above basal levels (p less than 0.05). A primary histaminergic mechanism for pepsinogen secretion is unlikely. Since two other adenylate cyclase activators, isoproterenol and forskolin and the 3':5'-cyclic adenosine monophosphate analog 8-bromo cAMP stimulated pepsinogen secretion, cAMP-dependence is probable. Since carbachol, CCK-8, and A23187, which are believed to act via calcium-calmodulin, also stimulated pepsinogen secretion, this system, too, presumably plays a substantial role. Thus the data support a dual 3':5'-cyclic adenosine monophosphate/calcium-calmodulin modulation of pepsinogen secretion.     

The effects of hyponatraemia and subarachnoid haemorrhage on the cerebral vasomotor responses of the rabbit

Impairment of cerebral autoregulation and development of hyponatraemia are both implicated in the pathogenesis of delayed cerebral ischaemia and infarction following subarachnoid haemorrhage (SAH) but the pathophysiology and interactions involved are not fully understood. We have studied the effects of hyponatraemia and SAH on the cerebral vasomotor responses of the rabbit. Cerebrovascular reactivity to hypercapnia and cerebral autoregulation to trimetaphan-induced hypotension were determined in normal and hyponatraemic rabbits before and 6 days after experimental SAH produced by two intracisternal injections of autologous blood. Hyponatraemia (mean plasma sodium of 119 mM) was induced gradually over 48 h by administration of Desmopressin and intraperitoneal 5% dextrose. Sham animals received normal saline. The cerebrovascular reactivity (% change +/- SD in cortical CBF/mm Hg PaCO2, measured by hydrogen clearance) of hyponatraemic (4.8 +/- 3.0%) and SAH (1.3 +/- 2.0%) animals was significantly less (p less than 0.05) than control (11.6 +/- 4.0%) and sham (8 +/- 2.0%) animals, whereas the reactivity of hyponatraemic-SAH animals was preserved (9.8 +/- 6.0%). Hyponatraemia and SAH alone each significantly impaired CBF autoregulation but their combined effects were not additive. Systemic hyponatraemia impairs normal cerebral vasomotor responses but does not augment the effects of experimental SAH in the rabbit.