A new method for measuring total coronary blood flow using the lithium dilution method

BACKGROUND: The aim in this study is to evaluate a new method of measuring total coronary blood flow (TCBF) in (1) an in vitro model and in (2) an animal model by the lithium dilution method. METHODS: (1) Ringer's solution was circulated in a closed circuit with the main flow as a systemic circulation, and the side flow as a coronary circulation by a roller pump. Two peaks originating from the main and side flow were recorded by the lithium dilution method. The flow was calculated using the Fick principle based on the ratio of the areas under the curve. The validity of this method was evaluated by Bland Altman analysis. (2) Four beagles were anesthetized and subjected to insertion of two pulmonary artery catheters. The position of the catheters was confirmed as being in the pulmonary artery and in the right atrium. Lithium chloride solution was injected into the pulmonary artery and the change in lithium concentration at the right atrium was recorded. TCBF was estimated by the method used in the in vitro study. RESULTS: (1) The calculated flow correlated well with the actual flow (r2 = 0.86). (2) The estimated TCBF at baseline, with low-dose nitroglycerin, and with high-dose nitroglycerin was 206 +/- 43.0 mL/min, 304 +/- 50.3 mL/min, and 348 +/- 50.1 mL/min, respectively (mean +/- SE). TCBF was significantly increased by nitroglycerin infusion. CONCLUSION: A new method of measuring TCBF using the lithium dilution method was reliable and useful both in vitro and in an animal model. This may be clinically useful method for measuring TCBF.     

Testing the agreement of medical instruments: Overestimation of bias in the Bland–Altman analysis

ObjectivesThe Bland–Altman method is the most popular method used to assess the agreement of medical instruments. The main concern about this method is the presence of proportional bias. The slope of the regression line fitted to the Bland–Altman plot should be tested to exclude proportional bias. The aim of this study was to determine whether the overestimation of bias in the Bland–Altman analysis is still present even when the proportional bias has been excluded.MethodsData were collected from participants attending a workplace health screening program in a public university in Malaysia between 2009 and 2010. Variables collected were blood glucose level, body weight and systolic blood pressure (n = 300 per variable). Readings from the original clinical dataset were compared with twenty randomly generated datasets for each variable. The Bland–Altman limits of agreement was used to determine the agreement. The presence of proportional bias was excluded for all datasets using the recommended method.ResultsThe range of predicted bias was higher than the simulated bias for all datasets. The overestimation of bias increased as the range of actual bias increased.ConclusionTesting the slope of regression line of the Bland–Altman plot does not remove the artifactual bias in the prediction.     

Best reproducibility of the ankle-arm index was calculated using Doppler and dividing highest ankle pressure by highest arm pressure

BACKGROUND AND OBJECTIVE: To investigate which method of ankle-arm index (AAI) measurement in terms of selected arteries and blood pressure devices yields the highest reproducibility. STUDY DESIGN AND SETTING: In this cross-sectional study, duplicate AAI measurements were obtained at the right and left side in 320 postmenopausal women. Analyses were done as proposed by Bland and Altman and intraclass correlation coefficients were calculated. RESULTS: The mean and standard deviation (SD) of the first and second systolic blood pressure (SBP) measurement separately did not differ from the mean and SD of the duplicate SBP measurements averaged. Coefficients of repeatability and intraclass correlation coefficients were comparable when the ankle SBP was measured in the posterior tibial artery or dorsalis pedis artery. Coefficients of repeatability as well as the intraclass correlation were better when the SBP in the brachial artery was measured with Doppler than with Dinamap. CONCLUSIONS: To achieve the best reproducibility and smallest systematic difference in the AAI, single SBP measurements should be obtained by Doppler in the brachial artery, posterior tibial artery and dorsalis pedis artery. The AAI should be calculated for each foot separately by dividing the highest ankle SBP by the highest arm SBP.     

How to regress and predict in a Bland–Altman plot? Review and contribution based on tolerance intervals and correlated‐errors‐in‐variables models

Two main methodologies for assessing equivalence in method‐comparison studies are presented separately in the literature. The first one is the well‐known and widely applied Bland–Altman approach with its agreement intervals, where two methods are considered interchangeable if their differences are not clinically significant. The second approach is based on errors‐in‐variables regression in a classical (X,Y) plot and focuses on confidence intervals, whereby two methods are considered equivalent when providing similar measures notwithstanding the random measurement errors. This paper reconciles these two methodologies and shows their similarities and differences using both real data and simulations. A new consistent correlated‐errors‐in‐variables regression is introduced as the errors are shown to be correlated in the Bland–Altman plot. Indeed, the coverage probabilities collapse and the biases soar when this correlation is ignored. Novel tolerance intervals are compared with agreement intervals with or without replicated data, and novel predictive intervals are introduced to predict a single measure in an (X,Y) plot or in a Bland–Atman plot with excellent coverage probabilities. We conclude that the (correlated)‐errors‐in‐variables regressions should not be avoided in method comparison studies, although the Bland–Altman approach is usually applied to avert their complexity. We argue that tolerance or predictive intervals are better alternatives than agreement intervals, and we provide guidelines for practitioners regarding method comparison studies. Copyright © 2016 John Wiley & Sons, Ltd.     

A framework for the meta‐analysis of Bland–Altman studies based on a limits of agreement approach

Bland–Altman method comparison studies are common in the medical sciences and are used to compare a new measure to a gold‐standard (often costlier or more invasive) measure. The distribution of these differences is summarized by two statistics, the ‘bias’ and standard deviation, and these measures are combined to provide estimates of the limits of agreement (LoA). When these LoA are within the bounds of clinically insignificant differences, the new non‐invasive measure is preferred. Very often, multiple Bland–Altman studies have been conducted comparing the same two measures, and random‐effects meta‐analysis provides a means to pool these estimates. We provide a framework for the meta‐analysis of Bland–Altman studies, including methods for estimating the LoA and measures of uncertainty (i.e., confidence intervals). Importantly, these LoA are likely to be wider than those typically reported in Bland–Altman meta‐analyses. Frequently, Bland–Altman studies report results based on repeated measures designs but do not properly adjust for this design in the analysis. Meta‐analyses of Bland–Altman studies frequently exclude these studies for this reason. We provide a meta‐analytic approach that allows inclusion of estimates from these studies. This includes adjustments to the estimate of the standard deviation and a method for pooling the estimates based upon robust variance estimation. An example is included based on a previously published meta‐analysis. Copyright © 2017 John Wiley & Sons, Ltd.     

A practical approach to Bland-Altman plots and variation coefficients for log transformed variables

OBJECTIVE: Indicators of reproducibility for log-transformed variables can often not be calculated straightforwardly and are subsequently incorrectly interpreted. METHODS AND RESULTS: We discuss meaningful Coefficients of Variation (CV) for log-transformed variables, which can be derived directly from the standard error of the log-transformed measurements. To provide easy interpretable Bland and Altman plots, we calculated limits of inter and intraobserver agreement (LA) for log-transformed variables and transform them back to the original scale. These LAs for agreement are subsequently plotted on the original scale in a conventional Bland and Altman plot. Both approaches were illustrated in a clinical example on the reproducibility of skinfold thickness measurements. CONCLUSION: In reproducibility, it is important to calculate meaningful CVs, LAs, and Bland-Altman plots for log-transformed variables. We provide a practical approach in which existing statistical methods are applied in the field of reproducibility, thus leading to parameters of reproducibility which can be interpreted on the original scale.     

Reproducibility and agreement between three methods of intraocular pressure measurement

OBJECTIVE: The aim of the present study was to establish reproducibility between consecutive intraocular pressure measurements using the same method of tonometry as well as to assess agreement between 3 different methods of tonometry. MATERIALS AND METHODS: The study included 55 patients. Intraocular pressure of 94 eyes was measured, using Goldman applanation tonometry, Maklakoff applanation tonometry and indentation tonometry according to Schioetz method. The mean values and the differences in intraocular pressure measurements were calculated (using Bland and Altman method) in order to assess agreement between Goldman and Maklakoff applanation tonometry and Goldman and Schioetz tonometry. Reproducibility of the methods was assessed based on three consecutive intraocular pressure measurements on three groups of 20 eyes at 5-minute intervals. RESULTS: The mean intraocular pressure (Po) measured by Goldman method was 23.26 +/- 0.78 mmHg, the mean pressure estimates (Po) according to Maklakoff method were 19.4 +/- 0.64 mmHg and it (Po) was 21.18 +/- 0.74 mmHg using Schioetz tonometry. The correlation (Pearson) between Goldman Po and Maklakoff Po was 0.74 and between Goldman and Schioetz Po - 0.93. Mean differences were 4.12 +/- 0.53 and 2.08 +/- 0.3 mmHg respectively. Variation coefficients between consecutive measurements were: for Goldman tonometry - 2.00%, for Maklakoff - 7.90% and for Schioetz - 5.72%. CONCLUSIONS: According to Bland and Altman method there is low agreement between intraocular pressure estimates obtained by Goldman and Maklakoff tonometry, i.e. these methods are not interchangeable. This fact might be explained by the high variation coefficient of Maklakoff method. The low variation coefficient of Goldman tonometry makes it the most accurate of the three methods.     

基于示波法和柯氏音法的双踪电子血压测量系统

目的：为了深入研究示波法血压测量技术，获取基于个体特征的血压测量方法，我们设计了基于示波法和电子柯氏音法的血压测量平台，同步采集袖带放气过程中的振荡波和电子柯氏音。方法：使用固体振动传感器获取声音振动信号，使用压力传感器经过信号调理后获得袖带压力和振荡波信号，使用14bits数据采集卡USB6009同步采集上述信号。结果：对压力传感电路以及电子柯氏音电路经过定标后，开展了初步的预试验，试验结果表明该血压测量平台能够有效的获取袖带充放气过程的振动波以及电子柯氏音。     

The intra- and interobserver variability of ankle-arm blood pressure index according to its mode of calculation

To propose a standardization of calculus of the ankle-arm index as a diagnostic tool in the clinical setting and epidemiology of peripheral arterial disease, we aimed to study the reproducibility of its measurement through 15 different modes of calculation. The study was performed in a group of 194 vascular laboratory outpatients of a tertiary center. The intra- and interobserver variability was assessed by the intraclass correlation coefficient of agreement and the Bland & Altman method. Methods where the numerator was calculated by the average of posterior tibial and dorsalis pedis artery systolic pressures revealed to be the best reproducible. According to this study and former researches on this topic, we recommend the use of the average of posterior tibial and dorsalis pedis artery systolic pressures of the weakest limb for the numerator and the average of systolic pressures of humeral arteries for the denominator of the ankle-arm index.     

一种血压信号放大仪的研制

目的:研制一种血压信号放大装置,用于课堂教学或临床带教,也可用于临床诊断.方法:该仪器用压电薄膜传感器采集测量血压时肱动脉的振动信号,将其转换为弱电信号,然后利用音频放大电路将声音输出.结果:血压信号放大仪设计科学,测量血压时可以清晰地把肱动脉搏动音的变化用扬声器播放出来.结论:该血压信号放大装置使用方便,可应用于教学听诊和临床,也可用于其他脉搏信号的声音放大.     

Modeling a Predictive Energy Equation Specific for Maintenance Hemodialysis

Background: Hypermetabolism is theorized in patients diagnosed with chronic kidney disease who are receiving maintenance hemodialysis (MHD). We aimed to distinguish key disease‐specific determinants of resting energy expenditure to create a predictive energy equation that more precisely establishes energy needs with the intent of preventing protein‐energy wasting. Materials and Methods: For this 3‐year multisite cross‐sectional study (N = 116), eligible participants were diagnosed with chronic kidney disease and were receiving MHD for at least 3 months. Predictors for the model included weight, sex, age, C‐reactive protein (CRP), glycosylated hemoglobin, and serum creatinine. The outcome variable was measured resting energy expenditure (mREE). Regression modeling was used to generate predictive formulas and Bland‐Altman analyses to evaluate accuracy. Results: The majority were male (60.3%), black (81.0%), and non‐Hispanic (76.7%), and 23% were ≥65 years old. After screening for multicollinearity, the best predictive model of mREE (R² = 0.67) included weight, age, sex, and CRP. Two alternative models with acceptable predictability (R² = 0.66) were derived with glycosylated hemoglobin or serum creatinine. Based on Bland‐Altman analyses, the maintenance hemodialysis equation that included CRP had the best precision, with the highest proportion of participants’ predicted energy expenditure classified as accurate (61.2%) and with the lowest number of individuals with underestimation or overestimation. Conclusions: This study confirms disease‐specific factors as key determinants of mREE in patients on MHD and provides a preliminary predictive energy equation. Further prospective research is necessary to test the reliability and validity of this equation across diverse populations of patients who are receiving MHD.     

The Stayhealthy bioelectrical impedance analyzer predicts body fat in children and adults

Bioelectrical impedance analysis (BIA) is a time-efficient and cost-effective method for estimating body composition. We hypothesized that there would be no significant difference between the Stayhealthy BC1 BIA and the selected reference methods when determining body composition. Thus, the purpose of the present study was to determine the validity of estimating percent body fat (%BF) using the Stayhealthy BIA with its most recently updated algorithms compared to the reference methods of dual-energy x-ray absorptiometry for adults and hydrostatic weighing for children. We measured %BF in 245 adults aged 18 to 80 years and 115 children aged 10 to 17 years. Body fat by BIA was determined using a single 50 kHz frequency handheld impedance device and proprietary software. Agreement between BIA and reference methods was assessed by Bland and Altman plots. Bland and Altman analysis for men, women, and children revealed good agreement between the reference methods and BIA. There was no significant difference by t tests between mean %BF by BIA for men, women, or children when compared to the respective reference method. Significant correlation values between BIA, and reference methods for all men, women, and children were 0.85, 0.88, and 0.79, respectively. Reliability (test-retest) was assessed by intraclass correlation coefficient and coefficient of variation. Intraclass correlation coefficient values were greater than 0.99 (P < .001) for men, women, and children with coefficient of variation values 3.3%, 1.8%, and 1.7%, respectively. The Stayhealthy BIA device demonstrated good agreement between reference methods using Bland and Altman analyses.     

Identification and reproducibility of dietary patterns in a Danish cohort: the Inter99 study

We aimed to identify dietary patterns in a Danish adult population and assess the reproducibility of the dietary patterns identified. Baseline data of 3,372 women and 3,191 men (30-60 years old) from the population-based survey Inter99 was used. Food intake, assessed by a FFQ, was aggregated into thirty-four separate food groups. Dietary patterns were identified by principal component analysis. Confirmatory factor analysis and Bland Altman plots were used to assess the reproducibility of the dietary patterns identified. The Bland Altman plots were used as an alternative and new method. Two factors were retained for both women and men, which accounted for 15.1-17.4 % of the total variation. The 'Traditional' pattern was characterised by high loadings ( > or = 0.40) on paté or high-fat meat for sandwiches, mayonnaise salads, red meat, potatoes, butter and lard, low-fat fish, low-fat meat for sandwiches, and sauces. The 'Modern' pattern was characterised by high loadings on vegetables, fruit, mixed vegetable dishes, vegetable oil and vinegar dressing, poultry, and pasta, rice and wheat kernels. Small differences were observed between patterns identified for women and men. The root mean square error approximation from the confirmatory factor analysis was 0.08. The variation observed from the Bland Altman plots of factors from explorative v. confirmative analyses and explorative analyses from two sub-samples was between 18.8 and 47.7 %. Pearson's correlation was >0.89 (P < 0.0001). The reproducibility was better for women than for men. We conclude that the 'Traditional' and 'Modern' dietary patterns identified were reproducible.     

Pulsoximetric sensor for diagnosis of intrauterine foetus state during parturition

Detrimental changes in the degree of blood hemoglobin saturation with oxygen are important evidence of hypoxic states and can be regarded as objective indication to surgical delivery. A new method of fetal pulsoximetry was developed. This method is based on the use of a non-disposable atraumatic pulsoximetric sensor of reflectory type for diagnosis of intrauterine foetus state during parturition. The clinical trial of the system was carried out in 44 women in childbirth and revealed clear differentiation between hypoxic states.     

Validation of an improved area-based method of calculating general practice–level deprivation

ObjectiveTo compare the methods of calculating practice deprivation scores in the absence of patient-level data.Study Design and SettingThree methods of deriving general practice deprivation scores without patient-level data were compared against “gold standard” patient-level scores in 226 English practices. The three methods were lower super output area (LSOA), middle super output area (MSOA), and a geographical information systems (GIS) method. Working, if necessary, on the log scale, agreement between scores was assessed using Bland and Altman's method, Kappa statistics, and Pitman's test.ResultsBased on the antilog 95% limits of agreement from Bland–Altman plots, GIS methods showed least variation compared with gold standard (0.66–1.47), followed by MSOA (0.61–1.70) and LSOA (0.38–2.29) methods. The differences in variances between both GIS and MSOA, and LSOA and MSOA comparisons, were greater than would be expected by chance (Pitman's P < 0.001). High levels of agreement (kappa: 0.93, 0.86, and 0.80) were observed between GIS, MSOA, and LSOA methods compared with the “gold standard.”ConclusionIn situations where patient postcodes are unavailable, the GIS method is superior to area-based methods. However, where the GIS method cannot readily be applied, the MSOA method should be used in preference to the LSOA method.     

Comparison of the Cosmed K4 b(2) and the Deltatrac II metabolic cart in measuring resting energy expenditure in adults

BACKGROUND AND AIMS: The objective of the study was to compare data obtained from the Cosmed K4 b(2) and the Deltatrac II metabolic cart for the purpose of determining the validity of the Cosmed K4 b(2) in measuring resting energy expenditure. METHODS: Nine adult subjects (four male, five female) were measured. Resting energy expenditure was measured in consecutive sessions using the Cosmed K4 b(2), the Deltatrac II metabolic cart separately and the Cosmed K4 b(2) and Deltatrac II metabolic cart simultaneously, performed in random order. Resting energy expenditure (REE) data from both devices were then compared with values obtained from predictive equations. RESULTS: Bland and Altman analysis revealed a mean bias for the four variables, REE, respiratory quotient (RQ), V CO(2), V O(2) between data obtained from Cosmed K4 b(2) and Deltatrac II metabolic cart of 268+/-702 kcal/day, -0.0+/-0.2, 26.4+/-118.2 and 51.6+/-126.5 ml/min, respectively. Corresponding limits of agreement for the same four variables were all large. Also, Bland and Altman analysis revealed a larger mean bias between predicted REE and measured REE using Cosmed K4 b(2) data (-194+/-603 kcal/day) than using Deltatrac metabolic cart data (73+/-197 kcal/day). CONCLUSIONS: Variability between the two devices was very high and a degree of measurement error was detected. Data from the Cosmed K4 b(2) provided variable results on comparison with predicted values, thus, would seem an invalid device for measuring adults.     

To tolerate or to agree: A tutorial on tolerance intervals in method comparison studies with BivRegBLS R Package

The well-known agreement interval by Bland and Altman is extensively applied in method comparison studies. Two clinical measurement methods are considered interchangeable if their differences are not clinically significant. The agreement interval is commonly applied to assess the spread of the differences. However, this interval is approximate (too narrow) and several authors propose calculating a confidence interval around each bound. This article demonstrates that this approach is misleading, awkward, and confusing. On the other hand, tolerance intervals are exact and can include a confidence level if needed. Tolerance intervals are also easier to calculate and to interpret. Real data sets are used to illustrate the tolerance intervals with the R package BivRegBLS under normal or log-normal assumptions. Furthermore, it is also explained how to assess the coverage probabilities of the tolerance intervals with simulations.     

Oxygen transport in membrane oxygenators

Mass transfer properties of the Soviet membrane oxygenator, MOCT, are tested. The liquid chambers of the oxygenator are made of disk membranes separating the moving blood from gas chambers. Processes of transportation and saturation of the blood film with oxygen are described by the simultaneous solution of the hydrodynamic and diffusion problem that is complicated by the chemical reaction. To derive approximate analytical solution the concept of a spreading front separating the area of the saturated blood layer from the venous area is applied. The expression for the thickness of the saturated layer and the oxygen flow to the blood is deduced as a function of the following parameters: membrane permeability, blood output, hemoglobin concentration, etc. The analytical solution is found to be satisfactory in describing experimental data obtained in the course of laboratory, clinical and biomedical tests.     

Measurement of Body Composition in Burned Children: Is There a Gold Standard?

Background: Maintaining lean body mass (LBM) after a severe burn is an essential goal of modern burn treatment. An accurate determination of LBM is necessary for short‐ and long‐term therapeutic decisions. The aim of this study was to compare 2 measurement methods for body composition, whole‐body potassium counting (K count) and dual x‐ray absorptiometry (DEXA), in a large prospective clinical trial in severely burned pediatric patients. Methods: Two‐hundred seventy‐nine patients admitted with burns covering 40% of total body surface area (TBSA) were enrolled in the study. Patients enrolled were controls or received long‐term treatment with recombinant human growth hormone (rhGH). Near‐simultaneous measurements of LBM with DEXA and fat‐free mass (FFM) with K count were performed at hospital discharge and at 6, 9, 12, 18, and 24 months post injury. Results were correlated using Pearson's regression analysis. Agreement between the 2 methods was analyzed with the Bland‐Altman method. Results: Age, gender distribution, weight, burn size, and admission time from injury were not significantly different between control and treatment groups. rhGH and control patients at all time points postburn showed a good correlation between LBM and FFM measurements (R ² between 0.9 and 0.95). Bland‐Altman revealed that the mean bias and 95% limits of agreement depended only on patient weight and not on treatment or time postburn. The 95% limits ranged from 0.1 ± 2.9 kg for LBM or FFM in 7‐ to 18‐kg patients to 16.3± 17.8 kg for LBM or FFM in patients >60 kg. Conclusions: DEXA can provide a sufficiently accurate determination of LBM and changes in body composition, but a correction factor must be included for older children and adolescents with more LBM. DEXA scans are easier, cheaper, and less stressful for the patient, and this method should be used rather than the K count.     

Reliability and relative validity of a quantitative food-frequency questionnaire for use among adults in Italian population

Our objective was to assess the reliability and relative validity of a food frequency questionnaire (FFQ) among adult people. In a cross-sectional study carried out in northern Italy, 112 adults were recruited. A total of 189 food and drink items were selected according to those typically consumed by Italians. FFQ reliability was assessed by two repeated administrations at 6 weeks. The FFQ was validated using four 24-h recalls repeated in the same period of time. For the validation study, classification into quartiles from the two methods and Bland–Altman plot were also performed. The reliability study showed a good correlation between the two methods. Bland–Altman plots showed that the two methods are very likely to agree for individual energy and macronutrient intakes. The reliability and relative validity of this FFQ was good, supporting its use in assessing dietary intakes of Italians in nutritional surveillance programs and in epidemiological dietary surveys.