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Altman Plots (altman + plot)
Selected AbstractsAssessment of different techniques for subcutaneous glucose monitoring in Type 1 diabetic patients during ,real-life' glucose excursionsDIABETIC MEDICINE, Issue 3 2010J. K. Mader Diabet. Med. 27, 332,338 (2010) Abstract Aims, To compare the accuracy of two marketed subcutaneous glucose monitoring devices (Guardian RT, GRT; GlucoDay S, GDS) and standard microdialysis (CMA60; MD) in Type 1 diabetic patients. Methods, Seven male Type diabetic patients were investigated over a period of 26 h simulating real-life meal glucose excursions. Catheters of the three systems were inserted into subcutaneous adipose tissue of the abdominal region. For MD, interstitial fluid was sampled at 30- to 60-min intervals for offline glucose determination. Reference samples were taken at 15- to 60-min intervals. All three systems were prospectively calibrated to reference. Median differences, median absolute relative differences (MARD), median absolute differences (MAD), Bland,Altman plot and Clark Error Grid were used to determine accuracy. Results, Bland,Altman analysis indicated a mean glucose difference (2 standard deviations) between reference and interstitial glucose of ,10.5 (41.8) % for GRT, 20.2 (55.9) % for GDS and 6.5 (35.2) % for MD, respectively. Overall MAD (interquartile range) was 1.07 (0.39; 2.04) mmol/l for GRT, 1.59 (0.54; 3.08) mmol/l for GDS and 0.76 (0.26; 1.58) mmol/l for MD. Overall MARD was 15.0 (5.6; 23.4) % (GRT), 19.7 (6.1; 37.6) % (GDS) and 8.7 (4.1; 18.3) % (MD), respectively. Total sensor failure occurred in two subjects using GRT and one subject using GDS. Conclusions, The three investigated technologies had comparable performance. Whereas GRT underestimated actual blood glucose, GDS and MD overestimated blood glucose. Considerable deviations during daily life meal glucose excursions from reference glucose were observed for all three investigated technologies. Present technologies may require further improvement until individual data can lead to direct and automated generation of therapeutic advice in diabetes management. [source] Overestimation of Left Ventricular Mass and Misclassification of Ventricular Geometry in Heart Failure Patients by Two-Dimensional Echocardiography in Comparison with Three-Dimensional EchocardiographyECHOCARDIOGRAPHY, Issue 3 2010Dmitry Abramov M.D. Background: Accurate assessment of left ventricular hypertrophy (LVH) and ventricular geometry is important, especially in patients with heart failure (HF). The aim of this study was to compare the assessment of ventricular size and geometry by 2D and 3D echocardiography in normotensive controls and among HF patients with a normal and a reduced ejection fraction. Methods: One hundred eleven patients, including 42 normotensive patients without cardiac disease, 41 hypertensive patients with HF and a normal ejection fraction (HFNEF), and 28 patients with HF and a low ejection fraction (HFLEF), underwent 2DE and freehand 3DE. The differences between 2DE and 3DE derived LVM were evaluated by use of a Bland,Altman plot. Differences in classification of geometric types among the cohort between 2DE and 3DE were determined. Results: Two-dimensional echocardiography overestimated ventricular mass compared to 3D echocardiography (3DE) among normal (166 ± 36 vs. 145 ± 20 gm, P = 0.002), HFNEF (258 ± 108 vs. 175 ± 47gm, P < 0.001), and HFLEF (444 ± 136 vs. 259 ± 77 gm, P < 0.001) patients. The overestimation of mass by 2DE increased in patients with larger ventricular size. The use of 3DE to assess ventricular geometry resulted in reclassification of ventricular geometric patterns in 76% of patients with HFNEF and in 21% of patients with HFLEF. Conclusion: 2DE overestimates ventricular mass when compared to 3DE among patients with heart failure with both normal and low ejection fractions and leads to significant misclassification of ventricular geometry in many heart failure patients. (Echocardiography 2010;27:223-229) [source] New method of predicting dry weight using bioelectrical impedance analysis in haemodialysis patientsNEPHROLOGY, Issue 8 2009SEOUNG WOO LEE SUMMARY: Aim: There were significant differences in the slopes of the ultrafiltration (UF) amount removed during haemodialysis (HD) sessions versus the percentage change in the extracellular fluid/total body water ratio for the right lower extremity (ECF/TBWright leg) plot in normohydrated (NH) and overhydrated states. The purpose of this study was to develop and validate a method for predicting dry weight (DW) using these results. Methods: It was hypothesized that for patients to become NH, the slope of the UF amount versus the percentage changes in ECF/TBWright leg plot should be same as that of NH patients and a method for predicting DW was developed. To validate the accuracy of this method, the ECF/TBWright leg was measured by eight-point tactile-electrode bioelectrical impedance analysis before and after HD in 17 newly enrolled NH patients. Using the current DW (cDW) of subjects as a reference, we compared the accuracies of pDW1 (our devised method) and pDW2 (the normovolaemia/hypervolaemia slope method). Results: The mean cDW, pDW1 and pDW2 values were 56.8 ± 7.9, 56.4 ± 7.7 and 56.3 ± 8.0 kg, respectively. No significant differences existed between cDW, pDW1 and pDW2. pDW1 had a lower root mean square error than pDW2 (1.12 vs 1.69). On the Bland,Altman plot, differences between pDW1 and cDW were closer to zero than between pDW2 and cDW. Conclusion: A new method was developed of predicting the DW using the relationship between the UF amount and the percentage change in the ECF/TBW ratio of the lower extremities after HD. The devised method appears to be as accurate as the normovolaemia/hypervolaemia slope method. [source] Comparison of gastric volumes in response to isocaloric liquid and mixed meals in humansNEUROGASTROENTEROLOGY & MOTILITY, Issue 5 2004H. De Schepper Abstract Aims:, To compare gastric volume responses to ingestion of isocaloric liquid or mixed (solid,liquid) meals and document the intra- and interindividual reproducibility of gastric volume measurement using single photon emission computed tomography (SPECT) imaging after i.v. 99mTc-pertechnetate. Methods:, Eight healthy volunteers performed two studies at least 9 months apart. Gastric volumes were measured after a 317 kcal liquid nutrient meal. Within 2 weeks of the second liquid meal study, participants performed a third study, ingesting an isocaloric mixed meal. The order of the mixed and second liquid meals was randomized; Bland,Altman plot displayed data on repeated studies with liquid meal and paired t -test compared gastric volumes after mixed or liquid isocaloric meals. Results:, Fasting and postprandial gastric volumes associated with the two liquid meals were not significantly different; inter- and intra-individual coefficients of variation were 13 and 13.8%. In response to the mixed meal, there was a lower absolute postprandial volume and lower change in gastric volume over fasting volume compared with the response to the liquid meal (P = 0.0001). Conclusion:, The SPECT measurement of gastric volumes in response to a nutrient liquid meal is reproducible. The magnitude of the volume response is greater after the liquid meal compared with the isocaloric mixed meal. [source] The rate of urinary cortisol excretion at work is persistently elevated in women at familial risk for breast cancerAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2008Gary D. James We recently reported that healthy women at familial risk for breast cancer (FH+) have higher urinary cortisol levels at work than women without familial risk (FH,). The purpose of this study was to evaluate whether this group difference persisted over a 1-month period. Subjects were healthy women (FH+, N = 42, age = 37.6 ± 9.3, FH,, N = 93, age 38.4 ± 9.0) employed primarily in clerical or technical positions at three medical centers in New York City who collected timed urine samples in three contrasting daily environments, at work (,11AM,3PM), home (,6PM,10PM) and during sleep (,10PM,6AM) on 2 mid-week workdays ,1 month apart. Two-way repeated measures ANOVA revealed that cortisol excretion differed across the environments (P < 0.001), and that there was also a significant interaction between daily environment and family history group (P < 0.049), such that FH+ women maintained higher cortisol excretion at work over the 2 days than FH, women. A Bland,Altman plot showed that both overall and by family history group, the rate of cortisol excretion at work was generally reproducible, although there was a heteroscadasticity in the relationship that likely reflected excessive stressfulness on one of the study days in a small minority of subjects. These results suggest that the presence of a potent background stressor (familial breast cancer risk) can influence more acute cortisol responses in daily life over time. Am. J. Hum. Biol., 2008. © 2008 Wiley-Liss, Inc. [source] The Time Course of New T-Wave ECG Descriptors Following Single- and Double-Dose Administration of Sotalol in Healthy SubjectsANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 1 2010Fabrice Extramiana M.D., Ph.D. Introduction: The aim of the study was to assess the time course effect of IKr blockade on ECG biomarkers of ventricular repolarization and to evaluate the accuracy of a fully automatic approach for QT duration evaluation. Methods: Twelve-lead digital ECG Holter was recorded in 38 healthy subjects (27 males, mean age = 27.4 ± 8.0 years) on baseline conditions (day 0) and after administration of 160 mg (day 1) and 320 mg (day 2) of d-l sotalol. For each 24-hour period and each subject, ECGs were extracted every 10 minutes during the 4-hour period following drug dosage. Ventricular repolarization was characterized using three biomarker categories: conventional ECG time intervals, principal component analysis (PCA) analysis on the T wave, and fully automatic biomarkers computed from a mathematical model of the T wave. Results: QT interval was significantly prolonged starting 1 hour 20 minutes after drug dosing with 160 mg and 1 hour 10 minutes after drug dosing with 320 mg. PCA ventricular repolarization parameters sotalol-induced changes were delayed (>3 hours). After sotalol dosing, the early phase of the T wave changed earlier than the late phase prolongation. Globally, the modeled surrogate QT paralleled manual QT changes. The duration of manual QT and automatic surrogate QT were strongly correlated (R2= 0.92, P < 0.001). The Bland and Altman plot revealed a nonstationary systematic bias (bias = 26.5 ms ± 1.96*SD = 16 ms). Conclusions: Changes in different ECG biomarkers of ventricular repolarization display different kinetics after administration of a potent potassium channel blocker. These differences need to be taken into account when designing ventricular repolarization ECG studies. Ann Noninvasive Electrocardiol 2010;15(1):26,35 [source] SPE/RIA vs LC/MS for measurement of low levels of budesonide in plasmaBIOMEDICAL CHROMATOGRAPHY, Issue 1 2003H. Dimova Abstract A radioimmunoassay is described that measures budesonide in plasma after solid-phase extraction (SPE/RIA) of the analyte. The performance of the assay was compared with that of a selective LC/MS method. The limit of quantitation of budesonide determined for the LC/MS and SPE/RIA assay was 50,pg/mL and 120,pg/mL, respectively. Based on quality control samples, a higher variability was observed for the SPE/RIA (CV between 4.5 and 23.0%) than for the LC/MS method (CV between 7.5 and 12.5%). Plasma samples obtained from healthy volunteers after administration of budesonide rectal foam were assayed by both methods. In a subset of samples, these results were compared with those measured by direct RIA to evaluate the selectivity of two assays. About two times higher budesonide levels were measured with the direct RIA (lacking the extraction step), presumably because of cross-reactivity with budesonide metabolites, indicating that the extraction step in SPE/RIA is necessary for selectivity. Both SPE/RIA and LC/MS methods were found to be selective, sensitive and suitable for pharmacokinetic studies. Results obtained from the two methods were compared with a number of statistical methods. Ratios of results obtained for the clinical samples were close to 1 (ratio LC-MS/ SPE/RIA,=,0.98,±,0.27). Linear regression indicated a slope of 1.17,±,0.0378. The concordance correlation (r,=,0.91) indicated that the agreement between both methods was fair while the Bland,Altman plot indicated that the agreement was less pronounced at higher concentrations (1,3,ng/mL). In summary, the results confirm that the SPE/RIA is an alternative to HPLC/MS and that among the statistical methods tested the concordance correlation analysis was judged to be the most informative test to assess the comparability of two methods. Copyright © 2002 John Wiley & Sons, Ltd. [source] A comparison of fetal organ measurements by echo-planar magnetic resonance imaging and ultrasoundBJOG : AN INTERNATIONAL JOURNAL OF OBSTETRICS & GYNAECOLOGY, Issue 1 2005Keith R. Duncan Objectives To compare fetal organ size measured using echo-planar magnetic resonance imaging and 2D ultrasound. To determine the relative accuracy with which each technique can predict fetal growth restriction. Design A cross sectional, observational study comparing two different measurement techniques against a gold standard, in a normal clinical population and an abnormal population. Setting and Population Seventy-four pregnant women (33 who were ultimately found to be normal and 37 with fetal growth restricted fetuses) were recruited from the City Hospital Nottingham UK to be scanned once (at various gestations). Methods Each fetus had a standard ultrasound biometry assessment followed by magnetic resonance imaging measurement of organ volumes. Main outcome measures For each measurement for both techniques, the normal population was plotted with 90% confidence intervals. Fetal growth restricted subjects were compared with the normal population using this plot; 2 × 2 tables were created for each measurement. This was used to calculate the relative sensitivities and positive predictive value of the different measurements. A Bland,Altman plot was used to compare the ultrasound and magnetic resonance imaging measurements of fetal weight. Results Brain sparing was seen in ultrasonic head circumference measurements, but an overall reduction in fetal growth restriction brain volume was apparent using magnetic resonance imaging at late gestations. Across the whole range of gestational ages, ultrasound assessment of fetal weight was the best predictor of fetal growth restriction. Conclusion Ultrasound fetal weight assessment appears to identify more fetuses with fetal growth restriction than abdominal circumference. The brain sparing apparent in ultrasonic head circumference measurements of fetuses with fetal growth restriction masks a reduction in brain volume observed with magnetic resonance imaging. [source] The Validity of Using Multiple Imputation for Missing Out-of-hospital Data in a State Trauma RegistryACADEMIC EMERGENCY MEDICINE, Issue 3 2006Craig D. Newgard MD Objectives: To assess 1) the agreement of multiply imputed out-of-hospital values previously missing in a state trauma registry compared with known ambulance values and 2) the potential impact of using multiple imputation versus a commonly used method for handling missing data (i.e., complete case analysis) in a typical multivariable injury analysis. Methods: This was a retrospective cohort analysis. Multiply imputed out-of-hospital data from 1998 to 2003 for four variables (intubation attempt, Glasgow Coma Scale score, systolic blood pressure, and respiratory rate) were compared with known values from probabilistically linked ambulance records using measures of agreement (,, weighted ,, and Bland,Altman plots). Ambulance values were assumed to represent the "true" values for all analyses. A hypothetical multivariable regression model was used to demonstrate the impact (i.e., bias and precision of model results) of handling missing out-of-hospital data with multiple imputation versus complete case analysis. Results: A total of 6,150 matched ambulance and trauma registry records were available for comparison. Multiply imputed values for the four out-of-hospital variables demonstrated fair to good agreement with known ambulance values. When included in typical multivariable analyses, multiple imputation increased precision and reduced bias compared with using complete case analysis for the same data set. Conclusions: Multiply imputed out-of-hospital values for intubation attempt, Glasgow Coma Scale score, systolic blood pressure, and respiratory rate have fair to good agreement with known ambulance values. Multiple imputation also increased precision and reduced bias compared with complete case analysis in a typical multivariable injury model, and it should be considered for studies using out-of-hospital data from a trauma registry, particularly when substantial portions of data are missing. [source] Venous stasis and routine hematologic testingINTERNATIONAL JOURNAL OF LABORATORY HEMATOLOGY, Issue 5 2006G. LIPPI Summary Prolonged venous stasis, as generated by a long tourniquet placement, produces spurious variations in several measurable analytes. To verify to what extent venous stasis influences routine hematologic testing, we assessed routine hematologic parameters, including hemoglobin, hematocrit, red blood cell count (RBC), main cell hemoglobin (MHC), main cell volume (MCV), platelet count (PLT), main platelet volume (MPV), white blood cell count (WBC) and WBC differential on the Advia 120 automated hematology analyzer in 30 healthy volunteers, either without venous stasis (no stasis) or after application of a 60 mmHg standardized external pressure by a sphygmomanometer, for 1 (1-min stasis) and 3 min (3-min stasis). Although the overall correlation between measures was globally acceptable, the mean values for paired samples were significantly different in all parameters tested, except MCV, MHC, PLT, MPV, eosinophils, basophils and large unstained cells after 1-min stasis and all parameters except MCV, MHC, MPV and basophils after 3-min venous stasis. As expected RBC, hemoglobin and hematocrit displayed a significant trend towards increase, whereas WBC and the WBC subpopulations were decreased. Difference between measurements by Bland and Altman plots exceeded the current analytical quality specifications for desirable bias for WBC, RBC, hemoglobin, hematocrit, lymphocytes and monocytes in samples collected after either 1- and 3-min stasis. These results provide clear evidence that venous stasis during venipuncture might produce spurious and clinically meaningful biases in the measurement of several hematologic parameters, prompting further considerations on the usefulness of adopting appropriate preventive measures for minimizing such influences. [source] Analysis of the breath hydrogen test for carbohydrate malabsorption: Validation of a pocket-sized breath test analyserJOURNAL OF PAEDIATRICS AND CHILD HEALTH, Issue 4 2000Ws Lee Objective: To assess the validity and clinical application of a hand-held breath hydrogen (H2) analyzer (BreatH2, Europa Scientific, Crewe, UK). Methodology: Breath samples of patients referred to the Gastroenterology Unit, Women's and Children's Hospital, North Adelaide, South Australia, for confirmation of the diagnosis of carbohydrate malabsorption were analysed with the Quintron microlyzer (Quintron Instrument Co., Milwaukee, USA) and the BreatH2 analyser, using the Quintron microlyzer as the gold standard. Results: Twenty-nine breath H2 tests (BHT) were performed in 29 patients aged 2 months to 61 years. The sensitivity and specificity of the BreatH2 analyser in detecting a positive BHT using the Quintron microlyser as the gold standard were 0.90 and 0.95 with positive and negative predictive values of 0.90 and 0.95, respectively. There was one false positive and one false negative reading. Bland,Altman plots showed a high degree of agreement between the values obtained with two different methods. Conclusions: The diagnosis of carbohydrate malabsorption, using a portable breath H2 analyser (BreatH2), achieved an acceptable degree of sensitivity and specificity, enabling it to be used where no alternative is available. [source] Comparability of a hand-held nitric oxide analyser with online and offline chemiluminescence-based nitric oxide measurementPEDIATRIC ALLERGY AND IMMUNOLOGY, Issue 7 2009Barbara Schiller Practicability is crucial for successful implementation of fractional exhaled nitric oxide (FeNO) measurement into asthma management. The study aimed at comparing a conventional chemiluminescence NO analyser (EcoMedics®) with a hand-held device (NIOX MINO®) and offline FeNO measurement using a commercially available system in an unselected cohort of children aged 6,16 yr. A secondary objective was to confirm FeNO stability over time in 15 samples from adult volunteers obtained using the offline system. Sixty-six children (mean ± s.d. age 11.8 ± 3.0 yr) underwent single breath FeNO measurement in triplets with each device. Offline collected FeNO was measured after offline breath collection into a Mylar balloon and subsequent analysis using the chemiluminescence NO analyser. Variability and between-method agreement were assessed, and stability over time within the Mylar balloons was tested by repeated hourly measurements. FeNO levels ranged from 2 to 113 p.p.b. Intra-class correlation was excellent (r = 0.98, p < 0.001 for each pair). Bland,Altman plots and back-transformation of logarithmic mean differences revealed fair agreement between methods. Stability over time was confirmed over 10 h both at room temperature and when stored under cooling conditions. FeNO values obtained using the chemiluminescence NO analyser, the portable NIOX MINO® system and the offline collection technique show between-method agreement within clinically acceptable range. [source] Comparison of different near-infrared spectroscopic cerebral oxygenation indices with central venous and jugular venous oxygenation saturation in childrenPEDIATRIC ANESTHESIA, Issue 2 2008NICOLE NAGDYMAN Summary Background:, We compared two different near-infrared spectrophotometers: cerebral tissue oxygenation index (TOI) measured by NIRO 200 and regional cerebral oxygenation index (rSO2) measured by INVOS 5100 with venous oxygen saturation in the jugular bulb (SjO2) and central SvO2 from the superior caval vein (SVC) during elective cardiac catheterization in children. Methods:, A prospective observational clinical study in 31 children with congenital heart defects in a catheterization laboratory was undertaken. TOI was compared with SjO2 in the left jugular bulb and with SvO2. rSO2 was compared with SjO2 from the right jugular bulb and SvO2. Linear regression analysis and Pearson's correlation coefficient were calculated and Bland,Altman analyses were performed. Results:, Cerebral TOI and SjO2 were significantly correlated (r = 0.56, P < 0.0001), as well as TOI and SvO2 with r = 0.74 (P < 0.0001). Bland,Altman plots showed a mean bias of ,4.3% with limits of agreement of 15.7% and ,24.3% for TOI and SjO2 and a mean bias of ,4.9% with limits of agreement of 10.3% and ,20.1% for TOI and SvO2. Cerebral rSO2 and SjO2 showed a significant correlation (r = 0.83, P < 0.0001) and rSO2 and SvO2 showed excellent correlation with r = 0.93 (P < 0.0001). Bland,Altman plots showed a mean bias of ,5.2% with limits of agreement of between 8.4% and ,18.8% for rSO2 and SjO2 and a mean bias of 5.6% with limits of agreement of 13.4% and ,2.2% for rSO2 and SvO2. Conclusions:, Both near-infrared spectroscopy devices demonstrate a significant correlation with SjO2 and SvO2 values; nevertheless both devices demonstrate a substantial bias of the measurements to both SjO2 and SvO2. [source] The reproducibility of ethnic differences in the proportional awake,sleep blood pressure decline among womenAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 3 2010Helene M. Van Berge-Landry A growing body of evidence indicates that African Americans (AA), on average, have a smaller proportional decline in blood pressure (BP) from waking to sleep than European Americans (EA), but this difference is largely based on correlational data from a single assessment day. The persistence of this difference over repeated sampling is not well established. The purpose of this study was to evaluate whether ethnic differences in the awake,sleep BP decline between AA and EA persisted over three monthly assessments. The subjects were 47 AA (age = 39.7 ± 8.7) and 92 EA (age = 37.4 ± 9.2) normotensive women. Subjects had 24-h ambulatory BP monitoring done on midweek workdays at 1-month intervals for three consecutive months. The proportional decline in BP was calculated as follows: (average awake , average sleep)/average sleep. The persistence of ethnic differences was evaluated using repeated-measures ANCOVA and by examining Bland,Altman plots. The ANCOVA results revealed that overall, the proportional decline of AA women was less than that of EA women for both SBP (P < 0.038) and DBP (P < 0.083), consistent with previous research, and that there were also no significant ethnic differences by monthly assessment. Bland,Altman plots revealed that overall and by ethnicity, the proportional decline in BP among individual subjects over the 3 months was also reproducible. These results suggest that the ethnic difference in awake,sleep BP between AA and EA women persists over time and that the awake,sleep decline in BP among individuals, whether AA or EA, is also reproducible. Am. J. Hum. Biol., 2010. © 2009 Wiley-Liss, Inc. [source] TUNEL assay and SCSA determine different aspects of sperm DNA damageANDROLOGIA, Issue 5 2010R. Henkel Summary For the determination of sperm DNA damage, different assays are used. However, no further distinction is made and the literature generally speaks about DNA damage. Thus, this study aimed at comparing the sperm chromatin structure assay (SCSA) and the TUNEL assay. In 79 patients, sperm DNA damage was determined flow cytometrically using the SCSA and the TUNEL assay. Moreover, normal sperm morphology was evaluated according to strict criteria. A statistical comparison of the two methods was performed using standard correlations, Bland and Altman plots, Passing,Bablok regressions and concordance correlation. Results show a significant difference between P- and G-pattern morphology only for the mean channel fluorescence of the SCSA. Spearman's rank correlations between the different parameters of both assays, SCSA and TUNEL, revealed significant associations between the parameters of the assays. However, when applying Bland and Altman plots, Passing,Bablok regression and concordance correlation results showed that these methods are not comparable. These different techniques determine different aspects of sperm DNA damage, i.e. ,real' DNA damage for the TUNEL assay and ,potential' DNA damage in terms of susceptibility to DNA denaturation for the SCSA. Thus, one should clearly distinguish between the different assays, not only practically and methodologically but also linguistically. [source] Comparing Methods of Measurement for Detecting Drug-Induced Changes in the QT Interval: Implications for Thoroughly Conducted ECG StudiesANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2004Nkechi E. Azie M.D. Background:,The aim of this study was to compare the reproducibility and sensitivity of four commonly used methods for QT interval assessment when applied to ECG data obtained after infusion of ibutilide. Methods:,Four methods were compared: (1) 12-lead simultaneous ECG (12-SIM), (2) lead II ECG (LEAD II), both measured on a digitizing board, (3) 3-LEAD ECG using a manual tangential method, and (4) a computer-based, proprietary algorithm, 12SLÔ ECG Analysis software (AUT). QT intervals were measured in 10 healthy volunteers at multiple time points during 24 hours at baseline and after single intravenous doses of ibutilide 0.25 and 0.5 mg. Changes in QT interval from baseline were calculated and compared across ECG methods, using Bland,Altman plots. Variability was studied using a mixed linear model. Results:,Baseline QT values differed between methods (range 376,395 ms), mainly based on the number of leads incorporated into the measurement, with LEAD II and 3-LEAD providing the shortest intervals. The 3-LEAD generated the largest QT change from baseline, whereas LEAD II and 12-SIM generated essentially identical result within narrow limits of agreement (0.4 ms mean difference, 95% confidence interval ± 20.5 ms). Variability with AUT (standard deviation 15.8 ms for within-subject values) was clearly larger than with 3-LEAD, LEAD II, and 12-SIM (9.6, 10.0, and 11.3 ms). Conclusion:,This study demonstrated significant differences among four commonly used methods for QT interval measurement after pharmacological prolongation of cardiac repolarization. Observed large differences in variability of measurements will have a substantial impact on the sample size required to detect QT prolongation in the range that is currently advised in regulatory guidance. [source] Comparison of two partial coherence interferometers for corneal pachymetry in high myopia and after LASIKACTA OPHTHALMOLOGICA, Issue 4 2009Anders Ivarsen Abstract. Purpose:, We aimed to compare the Haag-Streit optical low-coherence reflectometry (OLCR) pachymeter and the Zeiss Anterior Chamber Master (ACMaster) for measuring central corneal thickness (CCT) in high myopes and after laser in situ keratomileusis (LASIK) for myopia. Methods:, Central corneal thickness was measured in 55 eyes of 30 myopic subjects (spherical equivalent refraction of , 5.25 D to , 10.75 D, maximal astigmatism of , 2 D), and in 37 eyes of 21 patients 3 months after LASIK for myopia (preoperative spherical equivalent refraction of , 6.0 D to , 10.75 D, maximal astigmatism of , 2 D). All measurements were performed with the Haag-Streit OLCR pachymeter and the Zeiss ACMaster, using group refractive indices of 1.376 and 1.3851, respectively. Thickness measurements were compared using paired t -tests, Pearson's correlation, linear regression and Bland,Altman plots. Results:, In myopic subjects, CCT measured 531 ± 28 ,m and 533 ± 27 ,m with the OLCR pachymeter and the ACMaster, respectively (p < 0.01); all measurements correlated closely (r = 0.99, p < 0.01). In LASIK-treated eyes, CCT measured 472 ± 24 ,m using the OLCR pachymeter and 475 ± 23 ,m using the ACMaster (p < 0.01), again with close correlation between the two instruments (r = 0.99, p < 0.01). Conclusions:, Measurements of CCT in high myopes and after myopic LASIK were very similar with the Haag-Streit OLCR pachymeter and the Zeiss ACMaster. Using the current group refractive indices, the observed difference between the two instruments of < 3 ,m is of little clinical importance. Thus, it would seem safe to use the OLCR pachymeter and the ACMaster interchangeably for CCT measurements in myopia as well as after myopic LASIK. [source] Optical Coherence Tomography: A Noninvasive Method to Assess Wound ReepithelializationACADEMIC EMERGENCY MEDICINE, Issue 5 2007Adam J. Singer MD BackgroundAccurate assessment of wound healing may require invasive tissue biopsies, limiting its clinical usefulness in humans. Optical coherence tomography (OCT) is a novel, high-resolution method using light reflection to obtain noninvasive cross sectional imaging of biological tissues. ObjectivesTo evaluate the utility of OCT for assessing wound reepithelialization in a porcine model. MethodsThe authors conducted an animal study with two domestic pigs. Excisional cutaneous wounds were created over the ventral surface of the animals using an electric dermatome set at a depth of 600 ,m. The wounds were excised two or three days later and precisely marked to guide initial OCT and subsequent tissue slicing and microscopy. Comparing hematoxylin and eosin,stained histologic sections and the corresponding OCT images from each tissue sample permitted identification of the correlative micromorphology. Scatter and Bland,Altman plots were used to present the data. The primary measure of agreement was the standard deviation of the pairwise differences in percent reepithelialization between OCT and histology together with a 95% confidence interval. ResultsIn normal skin, the epidermis was characterized by a thin, bright layer indicating a high degree of light scattering on OCT. The dermis below was characterized by a thicker, darker area indicating less scattering of light. All fresh excisional wounds lacked an outer bright layer of epidermis immediately after injury. At days 2 and 3, the wounds were partially reepithelialized. A new bright layer with intense light scattering was present on OCT corresponding to the neoepidermis on hematoxylin and eosin,stained sections. The correlation between percent reepithelialization measured with OCT and histology was 0.66 (p < 0.001), and the standard deviation of the differences was 11.0% (95% confidence interval = 8.4% to 16.1%). ConclusionsOCT accurately detects the presence or absence of the epidermal layer of skin, allowing noninvasive tracking of wound reepithelialization. [source] Repeatability of corneal and ocular aberration measurements and changes in aberrations over one weekCLINICAL AND EXPERIMENTAL OPTOMETRY, Issue 3 2009Marco A Miranda MSc Background:, Both Shack-Hartmann aberrometry (IRX3, Imagine Eyes, Orsay, France) and Scheimpflug photography (Oculus Pentacam, Oculus Inc Wetzlar, Germany) are known to provide repeatable measurements. The variability in measurements of corneal and ocular aberrations obtained with these instruments over one week had not been assessed. The aim was to study the variability in corneal and ocular aberrations in the human eye over one week and to determine the impact of age on corneal and crystalline lens aberrations and on the variability of these measurements. Methods:, Monochromatic ocular aberrations were measured with the IRX3 and monochromatic corneal aberrations were measured using Scheimpflug photography on one eye of 23 normal subjects at periods of a few seconds, one hour and one week after the initial measurement. Results:, No significant differences were found between the initial aberrations and aberrations measured at 59 ± 24 seconds, 1.10 ± 0.24 hours and 7.11± 0.31 days later. Analysis with Bland and Altman plots showed that measurements with both instruments were highly repeatable over the times studied. There was no relationship between age and the variance of corneal and ocular aberrations (higher order, spherical and coma aberrations). Corneal spherical aberration did not show a significant correlation with age, whereas the lens aberrations changed from being negative in the younger age groups to positive in the older age group, however, these differences failed to reach statistical significance (p > 0.05). Conclusion:, The variability found in all the measurements was small and not clinically significant and could be attributable to instrument noise, changes in the tear film and to small fixational eye movements. [source] ANALYSIS OF SHORT-TERM REPRODUCIBILITY OF ARTERIAL VASOREACTIVITY BY PULSE-WAVE ANALYSIS AFTER PHARMACOLOGICAL CHALLENGECLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 1 2009Biju Paul SUMMARY 1Pulse-wave analysis (PWA) is an established method to assess arterial wave reflections and arterial vasoreactivity in humans. A high short-term reproducibility of baseline augmentation index (AIx) has been reported. However, the short-term reproducibility of AIx changes following pharmacological challenge with either inhaled salbutamol (endothelium-dependent vasodilatation) or sublingual glyceryl trinitrate (GTN; endothelium-independent vasodilatation), using appropriate statistical methods, is largely unknown. 2Baseline AIx and GTN- and salbutamol-mediated changes in AIx (all corrected for a heart rate of 75 b.p.m.) were measured on two separate occasions, 1 h apart, in 22 healthy controls (mean (±SD) age 52.0 ± 13.4 years) and 11 elderly patients with chronic heart failure (CHF; 73.1 ± 8.7 years). Reproducibility was assessed by measuring intraclass correlation coefficients (ICC), coefficients of variation (CV) and Bland,Altman plots. 3Baseline AIx showed good short-term reproducibility with high ICC in both the control and CHF groups (0.90 and 0.87, respectively). In contrast, in the control and CHF groups, the ICC of GTN- (0.58 and 0.17, respectively) and salbutamol-mediated (0.18 and 0.04, respectively) changes in AIx were substantially low. The CV was relatively low for baseline AIx in control and CHF groups (25.0 and 22.5%, respectively), but not for GTN- (22.3 and 59.8%, respectively) or salbutamol-mediated (45.1 and 184.0%, respectively) changes in AIx. Bland,Altman analysis revealed poor reproducibility, with limits of agreement beyond either +15% or ,15% for changes in AIx after GTN and salbutamol for both control and CHF groups. The changes in blood pressure and heart rate following pharmacological challenge were similar between the two measurements. 4The poor reproducibility of changes in AIx following pharmacological challenge questions the use of this method in acute studies. [source] | ||||||||||