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At least 739 records · Page 41Linked to original sources
PubMed2002

Weight change after myocardial infarction: statistical perspectives for future study.

OBJECTIVES: Survivors of acute myocardial infarction (MI) often experience weight changes and weight management is often appropriate. Estimates of the sample size required in intervention weight loss studies are essential to the success of future evaluations. The aims of this study were therefore two-fold: (1) to describe pilot data on the effectiveness of advice for weight loss; (2) to provide information on the sample size required for future research to assess weight management in similar patients. METHODS: Further analysis of data from a randomized controlled study carried out in 84 post-MI patients attending cardiac rehabilitation. Forty-three intervention patients received dietary advice in line with current UK guidelines. Additionally, overweight intervention subjects were given individualized weight management advice. Forty-two control patients were recruited and received usual care. Anthropometric measurements were made at baseline and followed up at 52 weeks post-rehabilitation. Power calculations were performed using these data to determine the required sample size to adequately power a study examining the effectiveness of weight management. RESULTS: Seventy patients completed the study. At 52 weeks anthropometric measurements were unchanged in the 25 overweight patients provided with weight management advice, and also for all those (n = 20) with body mass index <25 kg m-2. In contrast, anthropometric measurements increased significantly (body weight +2.4 kg, P = 0.02; waist circumference +2.6 cm, P = 0.008) in overweight control patients. A minimum sample size of 71 patients is required for a future study of weight change in overweight subjects, and 58 for a study of healthy weight subjects. CONCLUSIONS: Pilot data suggested that significant weight changes occur in patients not given nutritional or weight management advice after MI. Power calculations carried out on these data indicate that a sample size at least three times as large as the present study is required to accurately evaluate weight management in this group.

Adult↗
PubMed1999

Effects of sodium nitroprusside on hemodialysis-induced platelet activation.

BACKGROUND: Hemodialysis (HD) is associated with increased platelet activation as reflected by enhanced P-selectin expression on platelets and by increased formation of heterotypic platelet-leukocyte aggregates. Both may play a pathophysiologic role in HD-associated platelet dysfunction or the propagation of atherosclerosis. As nitric oxide (NO) is a potent inhibitor of platelet activation, we were interested in whether HD-induced platelet activation could be blunted by a NO donor. METHODS: After a pilot study in 12 patients to gain an estimate for the sample size, the main trial was conducted as a randomized, double-blind, placebo-controlled, two-way, cross-over study. Twelve patients received an infusion of sodium nitroprusside (1 microgram/kg/min for over 15 min) or placebo into the inlet port of the HD device. RESULTS: Platelet activation increased within five minutes after start of HD (P < 0.05). Infusion of sodium nitroprusside neither decreased platelet activation (P-selectin + platelets) nor affected the number of platelet-leukocyte aggregates (CD41+ neutrophils) as measured by flow cytometry. CONCLUSION: Although NO may have inhibitory effects on platelet activation in vivo, our results confirm recent findings showing that NO donors were ineffective in preventing platelet activation by extracorporeal circulation during cardiopulmonary bypass or plateletpheresis. Thus, NO donors do not appear to be ideal candidate drugs to inhibit HD-associated platelet activation.

Adult↗
PubMed2001

[Clinical research methods].

The methodology of clinical research will be commented upon according to the components of the research design: a precise question, hypotheses derived from that which can be examined empirically, the biometrical estimation of the sample size and its practicability, the selection of control groups, measures for assessing psychopathological phenomena, analysing the data and preparing the findings for publication, further the time structure of the research project, and some aspects of the framework of clinical research: patient access, financing of the needed resources and ethical implications.

Humans↗
PubMed2000

Nonoperative treatments for sciatica: a pilot study for a randomized clinical trial.

OBJECTIVES: To assess the feasibility of patient recruitment, the ability of patients and clinicians to comply with study protocols, and the use of data collection instruments to collect cost-effectiveness data, and to obtain variability estimates for sample-size calculations for a full-scale trial. STUDY DESIGN: Prospective, observer-blinded, pilot randomized clinical trial. SETTING: Primary contact chiropractic and medical clinics. PATIENTS: Ages 20 to 65 years, with low back-related radiating leg pain (sciatica). OUTCOME MEASURES: Self-report questionnaires were administered at baseline and 3 and 12 weeks after randomization. The measures included leg and back pain severity, frequency and bothersomeness of symptoms, leg/back disability, medication use, global improvement, satisfaction, and health care utilization. INTERVENTIONS: Medical care, chiropractic care, and epidural steroid injections. RESULTS: A total of 706 persons were screened by phone to determine initial eligibility. Of these, over 90% of those persons contacted did not meet the entrance criteria. The most common reason for disqualification was that the duration of the complaint was longer than 3 months. Twenty patients were randomized into the study. All 3 groups showed substantial improvements in the main patient-rated outcomes at the end of the 12-week intervention phase. For leg pain, back pain, frequency and bothersomeness of leg symptoms, and Roland-Morris disability score, the percent improvement varied from 50% to 84%, and the corresponding effect sizes ranged from 0.8 to 2.2. Bothersomeness of leg symptoms was the most responsive outcome associated with the largest magnitude of effect size. All within-group changes from baseline were statistically significant (P <.01). No between-group comparisons were planned or performed because of the insufficient sample size and high risk of committing type I and type II errors. CONCLUSIONS: Pilot studies such as these are important for the determination of the feasibility of conducting costly, larger scale trials. Recruitment for a full-scale study of sciatica of 2 to 12 weeks duration is not feasible, given the methods used in this pilot study. Our results do indicate, however, that there are substantial numbers of patients with sciatica more chronic in nature who would be interested in participating in a similar study. In addition, collaboration with a local health maintenance organization would likely facilitate clinician referrals and optimize the recruitment process. Patient and provider compliance was high in the pilot study, which indicates that most study protocols are feasible. Additionally, we were able to collect complete outcomes data, including those regarding health care use. A suggested modification by investigators and outside consultants has resulted in the replacement of the medication group with a minimal intervention control group (ie, self-care advice). As a result, a second pilot study of patients with sciatica of more than 4 weeks duration has been planned before a full-scale trial is attempted.

Adult↗
PubMed2000

Reproducibility of the maximum accumulated oxygen deficit and run time to exhaustion during short-distance running.

The aim of this study was to determine the reproducibility of the maximal accumulated oxygen deficit and the associated exercise time to exhaustion during short-distance running. Fifteen well-trained males (mean +/- s: VO2max = 58.0+/-4.6 ml x kg(-1) x min(-1)) performed the maximum accumulated oxygen deficit test at an exercise intensity equivalent to 125% VO2max. The test was repeated at the same time of day on three occasions within 3 weeks. There was no significant systematic bias between trials for either maximum accumulated oxygen deficit (man +/- s: trial 1 = 69.0+/-13.1; trial 2 = 71.4+/-12.5; trial 3 = 70.4+/-15.0 ml O2 Eq x kg(-1); ANOVA, F = 0.70, PP= 0.51) or exercise time to exhaustion (trial 1 = 194 + 31.1; trial 2 = 198 + 33.2; trial 3 = 201 + 36.8 s; F= 1.49, P = 0.24). In addition, other traditional measures of reliability were also favourable. These included intraclass correlation coefficients of 0.91 and 0.87, and sample coefficients of variation of 6.8% and 5.0%, for maximum accumulated oxygen deficit and exercise time to exhaustion respectively. However, the '95% limits of agreement' were 0+/-15.1 ml O2 Eq (1.01 multiply/divide 1.26 as a ratio) and 0+/-33.5 s (1.0 multiply/divide 1.18 as a ratio) for maximum accumulated oxygen deficit and exercise time to exhaustion respectively. We estimate that the sample sizes required to detect a 10% change in exercise time to exhaustion and maximum accumulated oxygen deficit after a repeated measures experiment are 10 and 20 respectively. Unlike the results of previous maximum accumulated oxygen deficit studies, we conclude that it is not a reliable measure.

Adult↗
PubMed2001

Designs for clinical trials to test the efficacy of therapeutics in progressive multifocal leukoencephalopathy.

The design of a comparative treatment trial to evaluate the efficacy of therapeutics for progressive multifocal leukoencephalopathy (PML) is outlined. We propose a large simple randomized trial with patient survival as its primary endpoint, completed in a short period of time and involving a cohort with as few enrollment restrictions as possible. We use stratification as the counterweight to the lack of exclusion criteria and suggest that proper stratification will attenuate differences inherent in a heterogeneous subject cohort. Estimation of power, sample size, and study duration, implementation of interim analyses, toxicity management, and validation of secondary clinical measures are also addressed.

Antiviral Agents↗
PubMed2003

Detection of fetal growth restriction in patients with chronic hypertension: is it feasible?

OBJECTIVE: To determine the utility of sonographic estimated fetal weight (EFW) in diagnosing intrauterine growth restriction (IUGR, birth weight < 10% for gestational age) in patients with chronic hypertension. METHODS: All pregnant patients with hypertension delivered during a 5-year period at three centers were identified retrospectively. Patients with gestational hypertension, pre-eclampsia, diabetes mellitus, fetal anomalies and absence of a sonographic examination within 3 weeks of delivery were excluded. Likelihood ratio (LR) and guidelines established by the Evidence-Based Medicine Working Group were used to determine whether sonographic EFW is a reliable diagnostic test to detect IUGR. RESULTS: At the three centers, there were 264 patients with chronic hypertension (122, 77 and 65 at centers I, II and III, respectively). The incidence of IUGR ranged from 13% to 27% but was similar at the three locations (p = 0.064). The LR (with 95% confidence interval (CI)) of detecting IUGR was 4.4 (95% CI 2.5, 7.7), 2.3 (95% CI 1.4, 3.7) and 6.1 (95% CI 2.7, 13.7) at centers I, II and III, respectively. Based on the proportions of abnormal growth, we required 253 and 71 newborns with fetal growth restriction at centers I and II, respectively, to have narrow confidence intervals around the clinically important LR of 10. The extremely low incidence of IUGR at center III (13%) precluded the estimation of required sample size. CONCLUSION: Use of Evidence-Based Medicine Working Group guidelines indicates that sonographic EFW is slightly to moderately useful in detecting fetal growth restriction in patients with chronic hypertension.

Chronic Disease↗
PubMed1999

Determination of failure of treatment of plasmodium falciparum infection by using polymerase chain reaction single-strand conformational polymorphism fingerprinting.

The inability to distinguish failures of treatment of Plasmodium falciparum infection from new infections is an important impediment to the evaluation of antimalarial drugs. On the basis of a pilot study utilizing polymerase chain reaction (PCR) single-strand conformational polymorphism (SSCP) analysis to genotype P. falciparum isolates, we sought to confirm that PCR SSCP analysis could reliably distinguish infections for which treatment failed from unrelated infections with a sample size adequate to estimate the accuracy of this technique. PCR SSCP analysis of the MSP-1, MSP-2, and GLURP genes was performed on 72 paired isolates recovered from 36 individuals for whom treatment failed in Thailand. In every case (100% [95% confidence interval (CI), 90%-100%]), the PCR SSCP pattern of the recrudescent isolates matched that of the primary isolate. We determined whether PCR SSCP analysis could separate unrelated infections by comparing each recrudescent isolate with each of the unrelated primary isolates. Of 1,260 comparisons, 1,258 (99.8% [95% CI, 99.4%-100%]) were unique. The results indicate that PCR SSCP analysis can be used to differentiate infections for which treatment failed from reinfections.

Animals↗
PubMed1987

The allelic correlation structure of Gainj- and Kalam-speaking people. II. The genetic distance between population subdivisions.

The patterning of allele frequency variability among 18 local groups of Gainj and Kalam speakers of highland Papua New Guinea is investigated using new genetic distance methods. The genetic distances proposed here are obtained by decomposing Sewall Wright's coefficient FST into a set of coefficients corresponding to all pairs of population subdivisions. Two statistical methods are given to estimate these quantities. One method provides estimates weighted by sample sizes, while the other method does not use sample size weighting. Both methods correct for the within-individual and between-individual-within-groups sums of squares. Genetic distances among the Gainj and Kalam subdivisions are analyzed with respect to demographic, geographic, and linguistic variables. We find that a demographic feature, group size, has the greatest demonstrable association with the patterning of genetic distances. The pattern of geographic distances among groups displays a weak congruence with the pattern of genetic distances, and the association of genetic and linguistic diversity is very low. An effect of differences in group size on genetic distances is not surprising, from basic theoretical considerations, but genetic distances have not often been analyzed with respect to these variables in the past. The lack of correspondence between genetic distances and linguistic and geographic differences is an unusual feature that distinguishes the Gainj and Kalam from most other tribal populations.

Alleles↗
PubMed1998

A meta-evaluation of smoking cessation intervention research among pregnant women: improving the science and art.

In 1986 Windsor and Orleans described guidelines and standards to evaluate the quality of smoking cessation intervention research among pregnant women. This paper presents a meta-evaluation (ME) of the evaluation research in this area from 1986 to 1998. ME is defined as a systematic review of experimental and quasi-experimental evaluation research using a standardized set of methodological criteria to rate the internal validity--efficacy or effectiveness--of intervention results. Five criteria were used to rate 23 smoking cessation intervention studies among pregnant smokers in prenatal care: (1) evaluation research design, (2) sample representativeness, sample size and power estimation, (3) population characteristics, (4) measurement quality, and (5) replicability of interventions. Eleven studies had sufficient methodological quality to produce results of high internal validity. Poor measurement of smoking status, patient selection biases and incorrect calculation of quit rates were the major methodological weakness. Recommendations for future evaluation research are made.

Female↗
PubMed1998

Methodological issues in biomonitoring of low level exposure to benzene.

Data from a pilot study on unmetabolized benzene and trans,trans muconic acid (t,t-MA) excretion in filling station attendants and unexposed controls were used to afford methodological issues in the biomonitoring of low benzene exposures (around 0.1 ppm). Urinary concentrations of benzene and t,t-MA were measured by dynamic head-space capillary GC/FID and HPLC, respectively. The accuracy of the HPLC determination of t,t-MA was assessed in terms of inter- and intra-method reliability. The adequacy of urinary t,t-MA and benzene as biological markers of low benzene exposure was evaluated by analysing the relationship between personal exposure to benzene and biomarker excretion. Filling station attendants excreted significantly higher amounts of benzene, but not of t,t-MA, than controls. Adjusting for occupational benzene exposure, smokers excreted significantly higher amounts of t,t-MA, but not of unmetabolized benzene, than nonsmokers. A comparative analysis of the present and previously published biomonitoring surveys showed a good inter-study agreement regarding the amount of t,t-MA and unmetabolized benzene excreted (about 0.1-0.2 mg/l and 1-2 micrograms/l, respectively) per unit of exposure (0.1 ppm). For each biomarker, based on the distribution of parameters observed in the pilot study, we calculated the minimum sample size required to estimate the population mean with given confidence and precision.

Adult↗
PubMed1981

Methods for determining the frequency of sexual intercourse and activities of daily living in young women.

To determine whether the frequency of sexual intercourse and other activities of daily living could be reliably measured in a population of women with or without prior urinary tract infections, a prospective pilot, case-control study was undertaken in a family practice clinic. Intensive self-recording of daily activities for one week was consistent with data collected for five more weeks spaced one month apart. Frequency of sexual activity was significantly higher on weekends. Control and bacteriuric subjects reported episodes of sexual intercourse about twice as frequently during the week of intensive recording than during the rest of the month when recording was only once a day. Although individual variation between weeks was minimal, considerable variation was observed among subjects. Voiding patterns were similar in both groups except for significantly higher rates prior to intercourse for controls. It is estimated that a sample size of at last 67-79 pairs will be required to ascertain whether there is a significant differences in frequency of sexual intercourse between cases and controls.

Activities of Daily Living↗
PubMed2002

Clinical evaluation of recombinant human bone morphogenetic protein-2.

Recombinant human bone morphogenetic protein-2 is an osteoinductive protein that plays a pivotal role in bone growth and regeneration. Several hundred studies were conducted in the past 7 years in numerous animal models to establish unequivocally the efficacy, safety, mechanism of action, pharmacokinetics, and surgical handling properties of recombinant human bone morphogenetic protein-2, building a solid foundation for clinical development programs. Pilot clinical trials have shown the feasibility and safety of recombinant human bone morphogenetic protein-2 treatment, and defined the effective dose for its use in open long bone fractures and for augmentation or preservation of the alveolar bone in the dental ridge. Prospective observational clinical studies helped define clinical efficacy end points, identify significant variables, and estimate appropriate population sample size for pivotal clinical trials. Pivotal clinical trials of recombinant human bone morphogenetic protein-2 are underway in patients with open tibial shaft fractures and in patients with a deficiency of the alveolar ridge.

Animals↗
PubMedDate not supplied

Use and satisfaction of the internet in obtaining information on brachial plexus birth palsies and its influence on decision-making.

The purpose of this study was to determine the influence of the Internet on parents regarding decisions for children with brachial plexus birth palsies (BPBP). A power analysis was performed to determine the appropriate sample size needed for estimating proportions in the general BPBP population. At least 100 surveys were needed for appropriate data analysis and 122 surveys were collected (100% response rate). Each participant filled out a 32-item survey on demographics, questions on Internet usage, and the influence of the Internet on care decisions. It is evident that parents commonly access the Internet. Of 122 participants, 108 (89%) searched the Internet for general BPBP information. Topics commonly researched include causes (76%), symptoms (70%), treatment/surgical options (84%), choice of physicians/surgeons (60%), and choice of hospitals/clinics (60%). Our study reveals that over half of the Internet users make clinical decisions based on their research and 98% report satisfaction with the outcome of their decisions. It is clear that parents of children with BPBP frequently use the Internet for information and available options regarding care for this rare condition.

Adult↗
PubMed1997

Serial measures of sinoatrial and atrioventricular nodal function in ambulatory patients.

We hypothesized that the outpatient assessment of SA and AV nodal (SAN, AVN) function could be a useful tool to determine the effectiveness of drugs and other treatments. We sought to examine the reproducibility, safety and ease of acquiring serial measurements of these parameters. Ten patients with permanent pacemakers underwent low current chest wall stimulation while their device was programmed to unipolar atrial triggered mode. Measurements at multiple conditioning drive train frequencies were obtained for: sinus nodal recovery time (SNRT); corrected sinus nodal recovery time (CSNRT); SA conduction time (SACT); AVN block cycle length (AVNBCL); and AVN effective refractory period (AVNERP). AVN function curves were also constructed. All studies were repeated after 2 weeks. Measures of sinus nodal and AVN function did not show significant differences between the two studies. The following co-efficients of correlation were obtained: SNRT800, r = 0.79; CSNRT800, r = 0.71; SNRT600, r = 0.71; CSNRT600, r = 0.44; SACT, r = 0.75; AVNBCL, r = 0.98; AVNERP800, r = 0.55; and AVNERP600, r = 0.99. AVN function curves did not significantly differ between week 1 versus week 2 at conditioning drive trains of either 800 ms or 600 ms. These data suggest that serial noninvasive electrophysiological measures of AVN and SAN function are reproducible over 2 weeks. Using data in this study, estimates of the sample size necessary for the evaluation of the effects of investigational drugs on the SAN and AVN in future studies are possible.

Arrhythmia, Sinus↗
PubMed2006

Right ventricular versus biventricular antitachycardia pacing in the termination of ventricular tachyarrhythmia in patients receiving cardiac resynchronization therapy: the ADVANCE CRT-D trial.

BACKGROUND: The purpose of this investigation is to compare the efficacy of antitachycardia pacing (ATP) delivered via the right ventricular (RV) lead versus ATP delivered simultaneously via the right and left ventricular leads (biventricular [BiV]) in the termination of ventricular tachyarrhythmia (VT) in patients receiving cardiac resynchronization therapy (CRT) with ICD capabilities. METHODS AND RESULTS: The ADVANCE CRT is a prospective, multicenter, randomized, parallel trial evaluating RV versus BiV ATP in the termination of VT in CRT patients. The study will test the hypothesis that BiV ATP is superior to RV ATP in the termination of VT and fast VT. All patients with class I and IIa indications for an ICD implantation and CRT are included. The sample size has been estimated to 400 participants followed for 12 months to show a 10% benefit of BiV versus RV ATP. The efficacy of BiV ATP to terminate all VT presents the primary endpoint. The investigation is expected to be completed in 2007. CONCLUSIONS: The ADVANCE CRT trial is the first large randomized clinical investigation evaluating the efficacy of BiV ATP in patients under CRT and ICD therapy.

Adolescent↗
PubMed1994

Reliability of the continuous ECG after cardiopulmonary bypass and CABG surgery.

Because of ECG changes associated with phenomena such as myocardial stunning or reperfusion injury in patients undergoing coronary artery bypass graft (CABG) surgery, Holter recordings may not detect postoperative myocardial ischemia with the same sensitivity and accuracy achieved in patients undergoing noncardiac surgery. This study details the reasons for decreased sensitivity of Holter recordings under such circumstances and suggests guidelines for inclusion of patients undergoing CABG into future studies. Continuous ECG (Holter) recordings were obtained in 617 analyzable patients before, during, and for 24 to 48 hours after CABG surgery. Uninterpretable tracings occurred with greatest frequency in the immediate period after electrical defibrillation and decreased progressively thereafter; only 50% of recorded tracings were interpretable and the percent of interpretable recordings increased progressively for the next 9 hours and then remained constant. This study confirmed the great frequency with which ECG abnormalities occur in the early postoperative period following bypass or coronary artery revascularization; it supports the suitability of Holter monitoring in patients who undergo cardiopulmonary bypass and CABG only if rigorous criteria for ECG interpretability and patient exclusion are used. In addition, because precise data were available for analysis for two thirds of all recruited patients, these results should provide valuable guidelines for estimating the appropriate sample size in the design of future studies similar to this one.

Cardiopulmonary Bypass↗
PubMed1989

Optimal design of sampling schedules for studying glucose kinetics with tracers.

Minimum size sampling schedules for estimating glucose kinetic parameters from an impulsive (bolus) tracer injection in normal humans and rats are presented. Glucose kinetics are described by a two-compartment linear model, and reference values of the parameters are estimated from a data base with many samples. The optimal sampling schedule (OSS) is determined in each individual by using a D-optimal criterion and consists of four samples. A population optimal sampling schedule (POSS) applicable to all the individuals of a given population is then determined, and its reliability and efficiency in recovering kinetic parameters (e.g., rate constants, plasma clearance rate, and mean residence time) is assessed. The influence of model and measurement error on OSS is discussed. Moreover, the adoption of an enhanced POSS (EPOSS, 8 samples) is shown to improve accuracy and precision of parameter estimates in a predictable manner. Finally some suggestions are given for obtaining more information from turnover studies using a constant infusion of tracer, with or without a priming pulse of tracer.

Animals↗