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PubMed1990

Electrophysiological effects of m-nisoldipine and nisoldipine on papillary muscles of guinea pig.

UNLABELLED: The effects of m-nisoldipine (m-Nis) and nisoldipine (Nis) on action potentials of papillary muscles in guinea pigs were studied using intracellular microelectrodes. THE RESULTS: (1) APD and Vmaxs in normal papillary muscles were reduced by m-Nis and Nis. However, the APA, Vmaxf and overshoot were not affected. (2) In the partially depolarized papillary muscles, the APA, overshoot, Vmax and APD were depressed in a dose-dependent manner. The inhibitory effects of Nis on APA, APD50 and PPD were greater than those of the m-Nis. (3) There was a good correlation between APD50 and PPD derived from a linear regression. By the linear equation, PPD was easily calculated from APD50.

Action Potentials↗
PubMed1990

[Reactive products of oxygen, antioxidative and lysosomal enzymes in the blood cells as markers of aging and indicators for the determination of functional age].

Reactive products of oxygen, lysosomal enzymes, and catalase in PMNL were studied in 174 men of different ages. In two age groups also superoxide dismutase was determined in erythrocytes. Of the given parameters of PMNL markers of aging were selectively established by using the method of correlation analysis and simple linear regression. Combinations of the parameters studied assessed by the method of multivariant linear regression provided equations for calculating the functional age are required due to underestimation or overestimation of the results in the extreme parts of the regression curve.

Adult↗
PubMed1989

[Dose-effect relationships between blood lead and free erythrocyte protoporphyrin or zinc protoporphyrin].

Studies on dose-effect relationships between blood lead (PbB) and free erythrocyte protoporphyrin (FEP) or zinc protoporphyrin (ZPP) in 583 workers (male 326, female 257) was conducted. Good dose-effect relationships and S-shaped curves between PbB and logFEP, logZPP or log (ZPP/Hb) were established. Sectioned linear regression showed that linear correlation was obtained while PbB between 0.48 (10 micrograms/dl) and 3.36 mumol/L (70 micrograms/dl) (male) or 0.48 (10 micrograms/dl) and 2.88 mumol/L (60 micrograms/dl) (female). However, while PbB below 0.48 mumol/L (10 micrograms/dl), there was no linear correlation. The increasing of FEP, ZPP slowed down remarkably as PbB were beyond 3.36 mumol/L (70 micrograms/dl) (male) or 2.88 mumol/L (60 micrograms/dl) (female). Therefore, the degree of lead poisoning can't be classified by the values of FEP, ZPP among plumbism.

Dose-Response Relationship, Drug↗
PubMed1989

Estimation of ligand binding parameters by simultaneous fitting of association and dissociation data: a Monte Carlo simulation study.

A new procedure for analysis of ligand binding kinetics was evaluated by Monte Carlo simulations. In this, all association and dissociation data were fitted simultaneously to a set of nonlinear equations. This should have several advantages over more conventional methods; data are better used in a single fitting procedure in which the degrees of freedom are maximized and the error term is spread over more observations; all relevant parameters (Bmax, k1, and k-1) are obtained directly; values obtained from measurements are not treated as errorless; and it yields a single residual term that can be used for statistical comparison among binding models and/or experiments. We have compared this approach with the common practice of analyzing the association and dissociation phases separately, either by nonlinear regression or by linear regression after suitable transformations. With respect to both the precision and accuracy of parameter estimates, the simultaneous procedure was superior to the other two methods. The properties of the simultaneous procedure were further investigated, concerning both parameter estimation and the probability of reliably detecting a second binding site. For the latter, the relative density of receptor subtypes and the dissociation rate constants were found to be of major importance, whereas association rate constants and ligand concentration were of minor importance in this respect. The probability of resolving two sites by kinetic or equilibrium data under similar conditions with the aid of a single labeled ligand was examined. When the selectivity of the ligand was low, the resolution was found to be more probable when based on kinetic, rather than equilibrium, data. This was true at higher selectivities as well, provided kinetic data were obtained at two different ligand concentrations.

Binding Sites↗
PubMed1989

[Description and assessment of a rapid new method for measuring erythrocyte sedimentation rate].

A new method for the rapid photometric determination of the erythrocyte sedimentation rate (ESR) is described and compared with the Westergren technique. The basis of this method is the development of a new physical equation valid for transport processes, in which sedimentation processes can be described by means of a linear regression analysis. After the mathematical transformation, the measured ESR data follow a linear function. The apparatus evaluated measures within a few minutes the velocity profile of the ESR over a distance of about 2 X 10(-4) meter by kinetic determination of the optical density of a short blood column filled in a small cuvette. A microprocessor calculates the linear regression and derives the one and two hour values by extrapolation. The correlation of this method with the standard Westergren technique, determined over 20 days is acceptable (R = 0.95; n = 368). The reproducibility of the same sample (n = 20) is better than that of the conventional procedure. The reproducibility determined with different instruments (n = 20) is comparable to the precision of the Westergren method. The practical value of this new time- and blood-saving, well standardized method for an efficient patient-care is discussed.

Blood Sedimentation↗
PubMed1987

Fitting curves to data using nonlinear regression: a practical and nonmathematical review.

Many types of data are best analyzed by fitting a curve using nonlinear regression, and computer programs that perform these calculations are readily available. Like every scientific technique, however, a nonlinear regression program can produce misleading results when used inappropriately. This article reviews the use of nonlinear regression in a practical and nonmathematical manner to answer the following questions: Why is nonlinear regression superior to linear regression of transformed data? How does nonlinear regression differ from polynomial regression and cubic spline? How do nonlinear regression programs work? What choices must an investigator make before performing nonlinear regression? What do the final results mean? How can two sets of data or two fits to one set of data be compared? What problems can cause the results to be wrong? This review is designed to demystify nonlinear regression so that both its power and its limitations will be appreciated.

Data Interpretation, Statistical↗
PubMedDate not supplied

Use of femur length as a means of assessing M-mode ventricular dimensions during second and third trimesters of pregnancy in normal fetus.

Eighty-two normal fetuses were scanned from 18 to 41 weeks of gestation. The following M-mode measurements were correlated with the femur length: end-diastolic right ventricular (r = 0.93), left ventricular (r = 0.92), biventricular outer (r = 0.94), and biventricular inner (r = 0.94) dimensions; tricuspid (r = 0.93) and mitral (r = 0.92) valve opening excursion; right (r = 0.76) and left (r = 0.70) ventricular wall thickness; and interventricular septal thickness (r = 0.75). Polynomial regression demonstrated that linear regression best described the data from which the mean and 5% and 95% confidence limits for predicted M-mode measurements were computed for the femur length.

Diastole↗
PubMed1978

[Comparison of procedures for determining Michaelis-Menten parameters together with their standard deviations using simulated measurement series].

The direct non-linear fit of Cleland and different methods applying linear regression analysis to linearized forms of the Michaelis-Menten equation have been compared. Comparison was made with respect to bias and standard deviation of the estimated values of Km, Vm, deltak and deltav. The Lineweaver-Burk method, weighted by approximately v3, turned out to produce estimates nearly as reliable as the direct fit of Cleland if one does not know whether the velocities are subject to constant absolute or relative errors. The comparison was based on ca. 10000 simulated series of velocity measurements. Runs with fewer simulated measurement series showed that for comparing different evaluation methods, at least 1000 measurement series should be simulated in order to get reliable results.

Enzymes↗
PubMed1995

[Non-significant in univariate but significant in multivariate analysis: a discussion with examples].

Perhaps as a result of higher research standard and advancement in computer technology, the amount and level of statistical analysis required by medical journals become more and more demanding. It is now realized by researchers that univariate analysis alone may not be sufficient, especially for complex data sets. Additional, and sometimes even contradictory, results may be found using multivariate analysis. During the course of data analysis, a common practice is to include in multivariate analysis only those variables that are statistically significant in univariate analysis. Such a habit is risky as some variables not significant in univariate analysis may become significant in multivariate analysis. In this study, we identify, with examples, four possible scenarios in which the above situation could occur: (1) the effect of unbalanced sample size; (2) the influence of missing data; (3) an extremely large within group variation, relative to between group variation; and (4) the presence of interaction. In addition to detailed analysis steps, raw data sets are also available for readers to verify all the results presented. Although we only used the log-rank test and Cox regression for illustration purposes, the underlying concepts can be applied to other multivariate procedures such as the logistic regression and multiple linear regression.

Analysis of Variance↗
PubMed2002

Evaluation of a dual hemoglobin A(2)/A(1c) quantitation kit on the bio-rad variant II automated hemoglobin analyzer.

CONTEXT: Quantitation of hemoglobin (Hb) A(1c) and investigation of hemoglobinopathy on the Bio-Rad Variant analyzers require a switch between 2 separate kits that is time consuming and causes errors. OBJECTIVE: Evaluation of a new Variant II HbA(2)/HbA(1c) Dual kit capable of both Hb A(1c) quantitation and hemoglobinopathy investigation on a single kit. DESIGN: We evaluated Hb A(1c), Hb A(2), and Hb F quantitation for precision, linearity, and correlation with current methodology. We also evaluated detection of Hb variants and correlation of Hb Barts quantitation. SETTING: Hamilton Regional Laboratory Medicine Program, Provincial Hemoglobinopathy Laboratory, St Joseph's Healthcare Site, Hamilton, Ontario. PATIENTS: Patient blood samples submitted for Hb A(1c) quantitation or hemoglobinopathy investigation. MAIN OUTCOME MEASURES: Precision, linearity, linear regression, and reference interval validation. RESULTS: We provide tables and figures illustrating precision, linearity, linear regression, and quantitation of Hb variants. We validated reference intervals for Hb A(1c), Hb A(2), and Hb F. CONCLUSIONS: The dual kit provides precise Hb A(1c), Hb A(2), and Hb F quantitation. The results show good linearity and correlate well with the results of current methods. We detected all clinically important Hb variants and a wide variety of rare variants. The dual kit has several advantages: it eliminates the need for extensive kit switch over; improves utility for newborn screening because of its quantification of Hb Barts; permits quantification of Hb A(1c) using the beta-Thal method; and eliminates the need for separate Hb A(2) reference intervals for patients with Hb S because of its accurate quantitation of Hb A(2) in the presence of Hb S.

Fetal Hemoglobin↗
PubMed1982

Calculation of the left ventricular ejection fraction by gated radionuclide angiography without direct background correction.

The mathematical characteristics of the cardiac background were studied in 50 patients who underwent both gated radionuclide angiography and cardiac catheterization. The background-corrected ejection fraction (BCEF) was calculated in the standard manner using an operator-defined periventricular background region. The "uncorrected" ejection fraction (UEF) was calculated from the uncorrected left ventricular time-activity curve and compared to both the BCEF and the angiographic ejection fraction (AEF), UEF exhibited remarkable linear correlation with both BCEF and AEF. The empirically determined linear regression equation, AEF = 2.18 (UEF) + 0.13, allowed calculation of a radionuclide ejection fraction corresponding to angiographic methods without direct background correction. When measurement of the left ventricular ejection fraction using this linear regression method was tested prospectively in 25 catheterized patients, the radionuclide regression ejection fraction showed excellent linear correlation with AEF (r = 0.85) and minimal inter-observer variability.

Adult↗
PubMed1993

Prediction equations for single-breath carbon monoxide diffusing capacity from a Chinese population.

Most available prediction equations for the single breath carbon monoxide diffusing capacity, or DLCO, are based on white populations and do not account for racial differences. We performed this test on 436 Chinese adults. The method of measurement essentially followed the American Thoracic Society recommendations. Data on 306 subjects who had two technically acceptable test results provided prediction equations and upper and lower 95% confidence limits for healthy nonsmokers. Simple linear equations using age, height, and body weight as independent variables were generated and compared with nonlinear models. The use of nonlinear models did not add to the predictability of standard linear regressions. The distribution of residuals (predicted-measured values) was Gaussian with simple linear regressions. A comparison of predicted values for DLCO, calculated from different equations in an independent group of healthy subjects, revealed that the present set of equations had the smallest residual mean and standard deviation rankings compared with other equations for white subjects. These are the first DLCO equations proposed for Chinese men and women aged 20 to 70 yr. The predicted values from this study for DLCO and alveolar volume (VA), were significantly lower than those of most equations for white subjects, but were not for DLCO/VA. Although a portion of the differences may be explained by the additive effects of technical factors, the discrepancies can also be attributed to the smaller body size in this ethnic group, and consequently to the smaller lung volumes. Equations derived from whites, with inclusion of smokers, provided predicted values comparable to, or even lower than, those from this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2003

Increased expression of p16(INK4a) and p27(Kip1) cyclin-dependent kinase inhibitor genes in aging human kidney and chronic allograft nephropathy.

BACKGROUND: The goal of the current study was to examine the potential value of p16(INK4a) and p27(Kip1) cyclin-dependent kinase inhibitor (CDKI) genes in the process of human kidney aging in vivo, and in the development of chronic allograft nephropathy (CAN). METHODS: Expression of p16(INK4a) and p27(Kip1) CDKI genes was evaluated and compared in 20 normal human kidney tissues of different ages (range, 21 to 80 years) and in 9 chronically rejected kidney grafts. Age dependency of marker expression was analyzed by the Pearson correlation and linear regression. RESULTS: Expression of p16 in cortical tubular (CTS) and interstitial (CIS) cells of normal kidney was age dependent (correlation coefficients: 0.608 and 0.726, 95% confidence interval [CI]: 0.227 to 0.828 and 0.417 to 0.884, respectively). Cortical tubular expression of p27 was also correlated with increasing age (0.672, 95% CI: 0.327 to 0.859). Linear regression analyses confirmed the linearity of marker relationship with age (coefficient of determination R(2):0.370, 0.452, and 0.527 for CIS p16, CTS p27, and CTS p16, respectively). The mean chronological and predicted graft ages (53 +/- 21 and 76 +/- 8.9 years, respectively) were significantly different (P = 0.0126). The glomeruli, tubules, and interstitial cells of rejected grafts expressed significantly higher levels of p16 and p27 than normal kidneys. Expression of p16 in glomerular and cortical interstitial cells was higher in grade 3 of CAN than in grade 2 (P = 0.013 and 0.004, respectively). CONCLUSION: The results of the current study show that expression of p16(INK4a) and p27(Kip1) CDKI genes is increased in cortical cells of the aging human kidney and in chronic allograft rejection, supporting the senescence theory of CAN.

Adolescent↗
PubMed1996

Quantitative CT predicts the severity of physiologic dysfunction in patients with lymphangioleiomyomatosis.

PURPOSE: To assess quantitative high-resolution CT (quantitative CT) as a diagnostic and prognostic tool in pulmonary lymphangioleiomyomatosis. METHODS: Spirometry, lung volumes, diffusing capacity, exercise physiology, and expiratory high-resolution CT (HRCT) examinations were performed on a cohort of ten patients with the diagnosis of lymphangioleiomyomatosis (LAM) referred to a tertiary care center. HRCT examinations were also done on ten normal control subjects. A thresholding technique was used to quantitatively assess the amount of abnormal cystic parenchyma present on each of the two images obtained for each subject with LAM and for each normal control subject. This numeric index of cystic parenchyma, the quantitative CT index, was then examined (1) as a diagnostic measure to distinguish the subjects with LAM from the normal control subjects and (2) as a prognostic measure to assess disease severity in the subjects with LAM. Linear regression of the quantitative CT index against physiologic indexes of pulmonary function and exercise performance was analyzed to determine the relationship between this radiologic assessment of disease severity and functional impairment. RESULTS: The quantitative CT index was significantly greater for the LAM patients, 37.2 +/- 6.9 (SEM), compared with the control group, 0.8 +/- 0.2 (p = 0.0001). Linear regression analysis demonstrated significant linear correlation between the quantitative CT index and measures of airflow (FEV1, r = -0.90, p = 0.0005), air trapping (residual volume, r = 0.70, p = 0.02), diffusing capacity (diffusing capacity for carbon monoxide, r = -0.76, p = 0.01), gas exchange (alveolar to arterial oxygen gradient) at rest, r = 0.69, p = 0.007, and at maximum exercise, r = 0.79, p = 0.007) and exercise performance (maximum workload, r = -0.84, p = 0.002), and oxygen utilization (oxygen utilization at maximum exercise, r = -0.76, p = 0.01). CONCLUSION: Quantitative CT techniques can distinguish subjects with LAM from normal controls. Further, the quantitative CT index correlates well with physiologic measurements of airflow, lung volumes, diffusing capacity, and exercise performance and, thus, may provide a useful measure of disease severity.

Adult↗
PubMed2000

Dietary patterns in a high-risk population for glucose intolerance. Japanese-Brazilian Diabetes Study Group.

We evaluated dietary habits as risk factor for glucose intolerance in a high risk population of Japanese-Brazilians enrolled in a study on the prevalence of diabetes (DM). Based on oral glucose tolerance test and WHO criteria, 331 had normal tolerance (NGT), 88 impaired tolerance (IGT) and 83 had type 2 DM (51 self-reported, 32 newly diagnosed diabetics). Clinical, laboratory and dietary data, assessed by food frequency questionnaire (FFQ), were compared between the NGT group and another composed of IGT and newly diagnosed DM (disturbed glucose tolerance or DGT group). Associations of total energy intake and nutrient intakes with glucose intolerance were analyzed by logistic regression. Also, subjects with NGT and DGT entered into separate models of multiple linear regression including BMI as the dependent variable, and total energy intake or each nutrient as independent variables. DGT group showed higher waist-to-hip ratio, blood pressure, plasma glucose and insulin levels and worse lipid profile. Total energy intake, macronutrients, fibers, alcohol and saturated fat intakes did not differ between groups; DGT was not associated with any nutrient intake in multivariate analyses. BMI of the subjects with DGT but not with NGT was associated with protein and cholesterol intakes in linear regression analysis. Our findings did not support an association between nutritional factors and glucose intolerance even in subjects who are unaware of their DGT, using FFQ to reflect current habits. However, we suggest that protein and cholesterol intakes may be markers of increased BMI. Despite assuming that obesity and insulin resistance precedes DM, FFQ may not be useful in the assessment of unfavorable dietary patterns among subjects at risk for glucose intolerance, such as Japanese-Brazilians with elevated BMI.

Adult↗
PubMed1994

Movement-related phasic muscle activation. III. The duration of phasic agonist activity initiating movement.

To test the hypothesis that phasic muscle activation is related to the acceleration-deceleration characteristics of the resulting movement, we examined the relation between the duration of the acceleratory phase of a variety of movement types and the duration of the phasic muscle activity producing the acceleration (the initial agonist burst, AG1). Movements of five types were studied: (1) step-tracking movements of different amplitudes (10-90 deg) and durations (200-800 ms), (2) movements of the same amplitude (40 deg) and duration (600 ms) varying only in their symmetry ratio (SR, ratio of acceleration to deceleration durations), (3) movements in which acceleration duration was changed while acceleration magnitude was held constant, (4) oscillatory movements of different frequencies and peak amplitudes, (5) step-tracking movements against different inertial loads. Subjects made movements about the elbow joint in the horizontal plane. Surface electromyographic (EMG) activity was recorded from the biceps and the lateral head of the triceps muscles. Under all movement conditions tested and with acceleration duration ranging from 100 to 500 ms, acceleration duration varied linearly with the duration of AG1. Correlation coefficients for the linear regression lines ranged from 0.8 to 0.99. The slope of the best fit linear regression lines ranged from 0.5 to 1.6 and tended to be higher for extensions than flexions. The variations in slope may arise from differing mechanical properties of the biceps and triceps muscles, as well as from active forces produced in the antagonist. AG1 duration was unchanged by inertial loading when subjects kept acceleration duration constant. If subjects responded to an increase in inertial load with an increase in acceleration duration, there was a corresponding increase in AG1 duration. The data demonstrate a general relation between one characteristic of muscle activation (AG1 duration) and the resulting movement. The linear form of the relation is invariant across movement amplitude (range 10-90 deg), speed, duration (range 200-800 ms) and temporal profile (SR range 0.3-2.7), and is also independent of movement type (step, oscillatory). Such a general and simple relation between EMG and movement suggests that, at least to a first approximation, the nervous system can rather simply determine the muscle activation patterns needed to produce movements with desired characteristics.

Acceleration↗
PubMed1998

A comparison of linear and orthogonal regression analysis for local INR determination in ECAA coagulometer studies. European Concerted Action on Anticoagulation.

International sensitivity index calibrations based on the W.H.O. recommended method depend on orthogonal regression analysis. As this is not readily available in statistical packages, comparison has been made with simple linear regression analysis in a study of coagulometer effects on the International Normalized Ratio (INR) at 155 European centres. Sets of seven lyophilized normal and 20 lyophilized artificially depleted abnormal plasmas were provided with five coumarin test plasmas and two European Concerted Action on Anticoagulation reference thromboplastins (low International Sensitivity Index (ISI) human and high ISI rabbit). Local ISI based on the artificially depleted lyophilized plasmas using conventional orthogonal regression gave good correction for local coagulometer effects on the human reagent and minimal correction with the rabbit reagent INR. Results were considerably worse after attempts at correction using calibration based on linear regression analysis with both reagents. The results indicate that calibration of coagulometer prothrombin time systems using simple linear regression is not appropriate.

Animals↗
PubMed2004

Postoperative troponin-T predicts prolonged intensive care unit length of stay following cardiac surgery.

OBJECTIVE: To evaluate the use of postoperative cardiac troponin T (cTnT) for the prediction of prolonged intensive care unit length of stay following cardiac surgery. DESIGN: Prospective, single-center, observational cohort study of patients following cardiac surgical procedures. The enrollment period was from October through December 2000. Patients were enrolled on admission to the intensive care unit and followed until hospital discharge. SETTING: The cardiac surgical intensive care unit of the Massachusetts General Hospital. PATIENTS: A total of 222 consecutive patients were enrolled. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Perioperative clinical factors and serum concentrations of cTnT measured every 8 hrs after surgery were recorded. These clinical factors and the results of serum cTnT measurement were correlated with the need for prolonged intensive care unit length of stay (defined as >24 hrs). Univariable analysis identified factors predictive of prolonged intensive care unit length of stay. Stepwise logistic regression identified independent predictors of prolonged intensive care unit length of stay. Multiple linear regression was used to explore the direct relationship between cTnT concentrations at several postoperative time points and intensive care unit length of stay. At each time point assessed, cTnT concentrations from patients requiring a prolonged intensive care unit length of stay were significantly higher (all p <.001) than in those individuals with normal length of stay. In contrast, creatine kinase isoenzymes were not significantly different between patients with normal or prolonged intensive care unit length of stay. Multivariable analysis demonstrated that an immediate postoperative cTnT concentration > or =1.58 ng/mL was the strongest predictor of a prolonged intensive care unit length of stay (odds ratio, 5.6; 95% confidence interval, 2.9-10.8). Multiple linear regression analysis revealed that intensive care unit length of stay increased by 0.32 days with each incremental 1.0 ng/mL increase in cTnT measured at 18-24 hrs postprocedure. CONCLUSIONS: Elevated postoperative cTnT concentrations can prospectively identify patients requiring prolonged intensive care unit length of stay after cardiac surgery.

Aged↗