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PubMed1982

Planning blocked mitosis experiments for efficient estimation of population-doubling time and cell-cycle time.

In this paper the standard errors of both classical and recently proposed estimators of mean population-doubling time and mean cell-cycle time are derived as functions of the number of cells counted and the counting times in a blocked mitosis experiment. Practical suggestions are made regarding the allocation of cell counts that will reduce the standard errors. It is shown that the proposal of Jagers (1977, Bulletin of the International Statistical Institute 47 (2), 418-422) for estimating cell-cycle time yields, quite generally, smaller standard error than do the classical estimators. Finally, a relationship between the mean and variance of cell-cycle time and the mean doubling time is derived; in some cases this relationship justifies the classical identification of mean doubling time and mean cycle time.

Cell Cycle↗
PubMed1995

[The influence of electrical time interval indices and aging on the left atrial systolic time intervals].

The influence of aging and heart rate on left ventricular systolic time intervals is well known, but the effects on left atrial systolic time intervals, a new index of left atrial function, remain unknown. The influence of aging and heart rate on left atrial systolic time intervals was investigated in 43 normal subjects (13-72 years of age) by Doppler echocardiography. Atrial pre-ejection period, atrial ejection time, and corrected atrial pre-ejection period were obtained by transmitral Doppler echocardiography. Simple regression analysis showed atrial pre-ejection period significantly correlated with P wave duration (PP; r = 0.78), and PR interval (PR; r = 0.60), but not with RR interval (RR). However, multiple regression analysis showed atrial pre-ejection period significantly correlated only with PP. Simple regression analysis found atrial ejection time significantly correlated with PP (r = 0.38), and PR (r = 0.39), but not with RR. However, multiple regression analysis found atrial ejection time did not correlate with any factor significantly. Aging was significantly correlated with corrected atrial pre-ejection period (r = -0.37), but not with corrected atrial ejection time and atrial pre-ejection period. Atrial ejection time significantly correlated with corrected atrial pre-ejection period (r = -0.37), but not with atrial pre-ejection period. Corrected atrial pre-ejection period is a clinically useful index of left atrial systolic function.

Adolescent↗
PubMed1997

Adolescent gender differences in time alone and time devoted to conversation.

On the basis of past theory and research, it is hypothesized that adolescent females will spend more time in conversation and less time alone than their male counterparts. The hypotheses are tested in data from 2,004 seventh and ninth grade students in a southeastern metropolitan area. With a number of potentially relevant variables taken into account, self-reports of average number of hours per week spent alone and spent in conversation are both substantially higher among girls than among boys contradicting the time alone hypothesis but supporting the conversation time hypothesis and the generalizability of an earlier finding of an adolescent gender difference in time spent in conversation. The findings are tentatively interpreted in terms of males' orientation toward sports, encouraging nonconversation time with others, and females' orientation toward close interpersonal relationships, encouraging talk with intimates. In additional nonhypothesized findings, black students report significantly more conversation time and time alone than do white students.

Adolescent↗
PubMed1980

Monitoring of heparin treatment. Comparison of thrombin time, activated partial thromboplastin time, and plasma heparin concentration, and analysis of the behavior of antithrombin III.

Three laboratory methods for monitoring heparin treatment have been compared using 63 plasma samples: the thrombin time, the activated partial thromboplastin time, and the measurement of the heparin concentration using a chromogenic substrate. A good correlation was found between the methods. However, the intensity of anticoagulation was identical in only 27 of the 63 samples (43%) when the thrombin time and the activated partial thromboplastin time were compared. Fully discordant results were recorded for four samples (6%). The thrombin time was found to be more closely related to the plasma heparin concentration than was the activated partial thromboplastin time. Both antithrombin-III activity and immunologic levels were lower in the group with strong heparinization. It is suggested that the thrombin time is a good and safe method for monitoring heparin treatment.

Antithrombin III↗
PubMed2004

Perceptions of work-time and leisure-time among managers and field staff in a UK primary health care trust.

AIMS: The aims of the research were to explore the issues around the perception of District Nurses in an inner London Primary Health Care Trust of their use of work-time and leisure-time, and to reveal how the boundaries between these two aspects can become blurred and impinge on each other. BACKGROUND: Time use is helpful in considerations of wider issues such as satisfaction at work and work-life balance. METHODS: The data were collected by a questionnaire to seek the views of managers and field staff on issues such as the impact on the quality of patient care of the nurses' perception of work-time and leisure-time. RESULTS: The research identified the different perception of "work-time" that employees have in relation to their place within the hierarchical structure. CONCLUSIONS: The findings answered the question of whether time is perceived differently, dependent on one's occupation within the Trust.

Adaptation, Psychological↗
PubMed2002

Correlation between activated clotting time and activated partial thromboplastin times.

OBJECTIVE: To evaluate the correlation between clotting time tests and heparin concentration, the correlation between activated clotting time (ACT) and activated partial thromboplastin time (aPTT) results, and to compare the clinical decisions based on ACT results with those based on aPTT results. METHODS: Retrospective evaluation of a large database containing heparin concentrations, ACT results (1 device), and aPTT results (3 different instruments: 2 bedside, 1 laboratory-based). Correlations between heparin concentrations and clotting time tests and between ACT results and aPTT results were determined. Clinical decisions regarding heparin dosage adjustments based on ACT results were compared with those based on aPTT results. RESULTS: Correlations between clotting time tests and heparin concentrations were r = 0.72 for ACT and r = 0.74-0.86 for the aPTT instruments. The laboratory-based aPTT had the highest correlation to heparin concentrations. The correlation between ACT and aPTT results ranged from r = 0.64-0.67. Heparin dosage adjustment decisions based on ACT results agreed with decisions based on aPTT results 59-63% of the time. CONCLUSIONS: The laboratory-based aPTT has a stronger correlation to heparin concentration than the bedside-based aPTT and ACT. The correlation between ACT and aPTT was similar among 3 different aPTT instruments. Decisions to adjust heparin therapy based on ACT results differed from decisions based on aPTT results more than one-third of the time.

Anticoagulants↗
PubMed1988

Quantification of reaction time and time perception during Space Shuttle operations.

A microprocessor-based test battery containing simple reaction time, choice reaction time, and time perception tasks was flown aboard a 1985 Space Shuttle flight. Data were obtained from four crewmembers. Individual subject means indicate a correlation between change in reaction time during the flight and the presence of space motion sickness symptoms. The time perception task results indicate that the shortest duration task time (2 s) is progressively overestimated as the mission proceeds and is statistically significant (p less than 0.01) when comparing preflight and postflight baselines. The tasks that required longer periods of time to estimate (8, 12, and 16 s) are less affected.

Analysis of Variance↗
PubMed1993

Decentralized testing for prothrombin time and activated partial thromboplastin time using a dry chemistry portable analyzer.

Previous work has established the precision and accuracy of a portable blood coagulation analysis system using paramagnetic particles contained in a dry reagent on a disposable test card. We examined the deployment of this technology in decentralized hospital settings and compared test results obtained in the surgical intensive care unit, coronary care unit, and outpatient cardiology clinic with those obtained in the central laboratory. Nursing personnel were instructed in the use of the system, and quality control testing was performed daily by the laboratory staff. In the intensive care units, patient subjects included those on whom tests of prothrombin time and activated partial thromboplastin time had been ordered. Immediate determinations were performed by the intensive care unit nursing staff on the same citrated, whole-blood samples that were subsequently sent to the central laboratory. In the outpatient cardiology clinic, fingerstick blood samples were obtained for prothrombin time determinations with the dry chemistry system. Paired prothrombin time samples obtained by venipuncture were run in the hospital laboratory. The study involved multiple users, multiple locations, two lots of activated partial thromboplastin time cards, and several different instruments, over an extended period. Correlation coefficients between the dry chemistry system and the hospital laboratory under these conditions were in an acceptable range in all sites studied. We concluded that, with appropriate training and quality assurance, the dry chemistry system provides an acceptable alternative to the hospital laboratory for prothrombin time and activated partial thromboplastin time determinations.

Chemistry Techniques, Analytical↗
PubMedDate not supplied

Private versus social opportunity cost of time: valuing time in the demand for health care.

In this paper we examine whether the current method of valuing time within economic appraisals is appropriate. The cost to society of time taken to use health care may differ from the private opportunity cost of such time. However, demand for health care may be affected by the private opportunity time cost and not by the value of time to society. In this paper we show that the private opportunity cost of time is a better predictor of demand for a screening service than the societal approach. It is important, therefore, to use the private opportunity cost of time when assessing the demand for, and impact of, a health care intervention.

Bone Density↗
PubMed2000

Timing of surgery for enterovesical fistula in Crohn's disease: decision analysis using a time-dependent compartment model.

OBJECTIVES: Previous decision analyses of inflam matory bowel diseases (IBD) have used decision trees and Markov chains. Occasionally IBD patients present with medical problems that are difficult or even impossible to phrase in terms of such established decision tools. This article aims to introduce modeling by a time-dependent compartment mode and demonstrate its feasibility for decision analysis in IBD METHODS: A Crohn's disease patient presented with a pelvic abscess and an enterovesical fistula. Being hesitant to operate in an acutely inflamed area, the surgeon recommended that the patient continue antibiotic therapy until the abscess had re solved. The gastroenterologist argued that the patient had already been treated with antibiotics for a prolonged time period and expressed concern that the patient's overall diminished health status would deteriorate by further delay of surgery. The occurrence of fistula, abscess, urinary tract infection, antibiotic therapy, surgical operation, and health-related quality of life were modeled as separate compartments, with time-dependent relationships among them. The simulation was carried out on an Excel spreadsheet. RESULTS: In the model, the surgeon's predictions were associated with rapid resolution of the pelvic abscess under antibiotic therapy and improvement of the patient's health status. The gastroenterologist's predictions resulted in a smaller decline in abscess size and further deterioration of the patient's health while waiting for a definitive treatment. The disagreement between surgery and gastroenterology arose from predicting different time courses for the individual disease events, in essence, from assigning different time constants to the time-dependent influences of the disease model. CONCLUSIONS: The compartment model provides a simple and generally applicable method to assess time dependent-changes of a complex disease. The present analysis also serves to illustrate the usefulness of such models in simulating disease behavior.

Abdominal Abscess↗
PubMedDate not supplied

The effect of covariates on the induction time of AIDS using improved imputation of exact seroconversion times.

This paper explores the effects of covariates such as age, gender, chronological time of seroconversion, and mode of virus transmission on the interval between HIV seroconversion and the development of AIDS. For many cohorts which are available to provide information about such effects, both the time of seroconversion and the time of onset of AIDS may be right- or interval-censored. To analyse these doubly-censored data, we propose a method in which we first estimate the marginal distribution of the chronological time of seroconversion and use this distribution to impute the seroconversion time for each subject. Subsequently, we estimate the distribution of induction times conditional on the seroconversion distribution. We apply this technique to a cohort of HIV seropositive subjects recruited from various outpatient facilities throughout Italy and show that age at seroconversion has the greatest effect on induction time.

Acquired Immunodeficiency Syndrome↗
PubMed1995

The time course and relation of positive signal-averaged electrocardiograms by time-domain and spectral temporal mapping analyses after infarction.

We evaluated the time course of development of positive signal-averaged electrocardiograms (SA-ECGs) by time-domain and Spectral Temporal Mapping (STM) analyses after myocardial infarction in 88 patients without bundle branch block. The incidence of positive SA-ECGs by time-domain analysis peaked at 4 to 8 weeks postinfarction whereas the peak incidence by STM analysis varied from 4 days to 4 to 10 months postinfarction. Positive time-domain SA-ECGs demonstrated a significantly reduced factor of normality (NF) compared with negative time-domain SA-ECGs by X, Z, or vector STM analyses, but marked overlap was present for the standard deviations of positive and negative SA-ECGs in all STM leads. Chi square analysis demonstrated a significant correlation only between X-lead STM analysis and time-domain analysis; however, the two methods were markedly discordant. Although there is a statistically significant relation between time-domain and STM analyses of SA-ECGs, the two analyses are not clinically interchangeable.

Adult↗
PubMed1991

Swing time changes contribute to stride time adjustment in the walking rat.

Locomotor analysis is a useful tool for assessing normal and disturbed brain function. Previous studies have indicated that, during locomotion at walking velocities, the rat adjusts its velocity by changes to stride time and length. The present work has shown that, in the Sheffield strain rat, changes in stride time are achieved by a differential deployment of its two components, stance time and swing times. During slow walking, swing time changes provide minimal contribution to stride time reductions. At above average stride frequencies, however, swing time changes become significant, providing for more than half the reduction over parts of the range.

Animals↗
PubMed2004

Real-time B-mode ultrasound in the ED saves time in the diagnosis of deep vein thrombosis (DVT).

We hypothesize that EPs can decrease the time to disposition when performing examinations for deep venous thrombosis (DVT) compared with disposition times using imaging specialists (IS). We performed a prospective, single-blind observational study at an academic ED over the course of 1 year. Patients were enrolled based on study physician availability. EPs ordered the corroborative ultrasound, then performed their own examination. EPs recorded patient triage time, ED results, and disposition times for both EP and IS departments. One hundred fifty-six patients were enrolled. Thirty-four (22%) were diagnosed with a DVT. Mean time from triage to EP disposition was 95 minutes and mean time from triage to radiology disposition was 220 minutes. The difference of 125 minutes was statistically significant (P <.0001). EPs and ISs had excellent agreement (kappa = 0.9). Compression ultrasound performed by EPs resulted in a significant decreased time to disposition. Agreement with ISs was excellent.

Bias↗
PubMed2006

Effectiveness of prehospital wireless transmission of electrocardiograms to a cardiologist via hand-held device for patients with acute myocardial infarction (from the Timely Intervention in Myocardial Emergency, NorthEast Experience [TIME-NE]).

Percutaneous coronary intervention for patients with ST-segment elevation myocardial infarction (STEMI) decreases morbidity and mortality if performed within the first 2 hours of symptom onset. However, the American College of Cardiology/American Heart Association guideline for percutaneous coronary intervention door-to-balloon time (<90 minutes) in patients with STEMI is a infrequently accomplished goal. This study enrolled 277 patients with STEMI who were self-transported or transported by emergency medical services to NorthEast Medical Center for primary percutaneous coronary intervention. This study tested the hypothesis that prehospital wireless transmission of an electrocardiogram to a cardiologist's hand-held device results in shorter emergency department door-to-reperfusion time. A comparison was made between patients whose electrocardiogram was successfully transmitted during the intervention phase with (1) patients transported by the emergency medical services in the preintervention, (2) patients self-transported in the intervention phase, and (3) patients whose wireless transmission failed in the intervention phase. During the preintervention phase (2001 to 2003), 48 patients were enrolled. During the intervention phase (2003 to 2005), the following patients were enrolled: 101 self-transported patients, 24 patients with successful electrocardiographic transmission, and 19 patients for whom transmission failed. The median door-to-reperfusion time for patients with successful electrocardiographic transmission was 50 minutes, which was significantly shorter than a preintervention time of 101 minutes (p <0.0001), an intervention phase self-transport time of 96 minutes (p <0.0001), and a failed transmission time of 78 minutes (p <0.0001). In conclusion, prehospital wireless electrocardiographic transmission to a cardiologist's hand-held device significantly decreased emergency department door-to-reperfusion time, thus achieving the American College of Cardiology/American Heart Association guideline for patients with STEMI.

Aged↗
PubMed2006

Validity and reliability of assessments of time. Comparisons of direct observations and estimates of time by the use of the resource utilization in dementia (RUD)-instrument.

When the costs of dementia are analyzed, interviews regarding caregiver time (both informal or formal) and other kinds of resource use are frequently used. However, it is unclear how valid such data are. The aims were to investigate the validity and reliability of interview-based estimated resource use, particularly caregiver time. Twenty institutionalized demented persons were studied during 3 months. A special team recorded the amount of time the caregivers spent on personal activities of daily living (PADL), instrumental activities of daily living (IADL), and supervision. After each session, the caregivers estimated the amount of time they had spent on care. Observed time was regarded as the golden standard. Intra-rater reliability was tested with proxy informants on 25 elderly living at home. In total, 110 observations and 108 estimations of caregiver time were made. The correlation coefficient between observed and estimated PADL-time was 0.81 (p < 0.001), in IADL 0.29 (p = 0.03), and in supervision 0.51 (p < 0.001). The intra-rater reliability was high for almost all items (Cronbach's alpha and intraclass correlation coefficient >0.9). There was a high correlation between interview-based data and register data regarding hospital care, family physician, and district nurse visits. In conclusion, interviews may serve as a valid and reliable substitute for observations.

Activities of Daily Living↗
PubMed2006

Time-sharing in pigeons: Independent effects of gap duration, position and discriminability from the timed signal.

Previous data suggest that in a peak-interval procedure with gaps, memory for the pre-gap interval varies with the discriminability of the gap from the to-be-timed signal. Here we extend this finding by manipulating the pre-gap and gap intervals as well as the visual contrast between the gap and the to-be-timed signal. The delay in response function after the gap was found to vary with the duration and position of the gap. However, for each gap duration and position, the delay in response increased with the gap-signal contrast: at 60% gap-signal contrast pigeons continued to accumulate time during the gap, at 80% gap-signal contrast pigeons stopped timing during the gap, and at 100% gap-signal contrast pigeons reset their timing after the gap. Data are accounted for by a time-sharing model assuming two concurrent processes during the gap--time accumulation and memory decay controlled by the salience of the gap--whose interplay results in a continuum of responses in the gap procedure.

Algorithms↗
PubMed2006

Effects of time, dose, and inversion time for acute myocardial infarct size measurements based on magnetic resonance imaging-delayed contrast enhancement.

OBJECTIVES: This study sought to investigate the influence of time, dose, and inversion time (TI) and their interactions on myocardial infarct size measurements to establish the foundation for a standardized protocol for multicenter trials. BACKGROUND: There is growing interest in using magnetic resonance imaging (MRI) infarct size measurements as an end point in clinical trials. However, no standardized protocol exists, and there are limited data concerning the effects of time, contrast agent dose, and TI. METHODS: First, we determined the influence of postcontrast imaging time (5 to 40 min), contrast agent dose (0.1 vs. 0.2 mmol/kg), TI, and their interactions in an animal model (n = 14). Second, we tested whether the findings of the animal study apply to patients and are generalizable. Therefore, we retested the diagnostic window in a multicenter study. A total of 48 patients with first acute myocardial infarction (AMI) from three centers were imaged twice (5 and 30 min) after injection of 0.15 mmol/kg gadolinium diethylenetriamine-pentaacetate using an adjusted TI. RESULTS: The animal study showed that the infarct size is independent of time and dose (p = 0.9 and p = 0.16, respectively) using an adjusted TI. Using a fixed TI, however, infarct size is a function of time and dose (p = 0.0001 and p = 0.01, respectively). The multicenter study showed that MRI 1 (16.9 +/- 12% of left ventricle) was not statistically different from MRI 2 (16.4 +/- 12% of left ventricle, p = NS) with no difference between sites (p = NS). CONCLUSIONS: The AMI size can be measured with MRI using a contrast dose between 0.1 and 0.2 mmol/kg and a time window of 5 to 30 min after contrast administration, provided that the TI is adjusted.

Adult↗