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Results for “multiple linear regression”

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PubMed1975

Correlation of kinetic parameters and thermal behavior of segmented polyurethane elastomers with biological responses.

Kinetic studies of thermal degradation of 16 segmented polyether polyurethane samples, containing various amounts of 3,4-diaminotoluene and dibutyltin diacetate as additives, were carried out by thermogravimetry. From a single dynamic thermogravimetric experiment, the temperatures of initiation of degradation, 10, 25, and 50% (w/w) of degradation, as well as the activation energies for degradation, were determined. The activation energies were computed from the thermogravimetric curves using Broido's graphical approximation method, which applies to first-order decomposition kinetics. The results of stepwise multiple linear regression analysis indicate that the biological responses to elastomar samples, such as tissue culture, hemolysis, intramuscular implant, intradermal irritation, systemic toxicity, and histopathological rating, and the cumulative biological response index are highly correlated with thermal stability and kinetic measurements of the materials.

Animals↗

PubMed1978

Functional group contribution of bile salt molecules to partitioning of a quaternary ammonium N,N-dimethyl derivative of propranolol.

A quaternary ammonium N,N-dimethyl derivative of propranolol was extracted from pH 7.4 phosphate buffer into 1-octanol as ion-pairs with 12 different bile salts. The binding number, n, and the extraction constant, Ke, were determined. To obtain group contribution values of the bile salt molecule from the ion-pair extraction data, multiple linear regression analysis by the Free-Wilson technique was applied. The results showed that the fundamental premise of the functional group's contribution to the ion-pair extraction is valid. The functional groups of counterions contribute to the partitioning of the ammonium compound independently and additively in this system.

Bile Acids and Salts↗

PubMed1991

Role of hydrogen bonding in general anesthesia.

The importance of hydrogen bonding in determining the potency of a general anesthetic is controversial. In order to investigate the role of hydrogen bonding further, we have used a multiple linear regression approach to quantify the relative importance of various physical properties of an anesthetic molecule (i.e., its ability to donate or accept a hydrogen bond, its dipolarity and polarizability, and its size) in determining its anesthetic potency. For comparison, we have applied the same approach to partitioning between water and three simple, but contrasting solvents (n-octanol, n-hexadecane, and N,N-dimethylacetamide) and to inhibition of an enzyme (firefly luciferase) which mimics many of the properties of general anesthetic target sites in animals. We present equations which accurately predict potencies (over many orders of magnitude) for producing general anesthesia and inhibiting the firefly luciferase enzyme. We find that the aqueous potency (defined as the reciprocal of the aqueous EC50 concentration) of a molecule as a general anesthetic or an inhibitor of luciferase is determined overwhelmingly by its size (which increases potency) and its ability to accept a hydrogen bond (which decreases potency), but only marginally by its ability to donate a hydrogen bond or by its dipolarity and polarizability. We conclude that general anesthetic target sites in animals must have, in addition to their overall hydrophobicity, a polar component which is a relatively poor hydrogen bond donor, but which can accept a hydrogen bond about as well as water.

Adenosine Triphosphate↗

PubMed1992

Molecular connectivity model for determination of isoelectric point of amino acids.

A molecular connectivity model for the calculation of the isoelectric point of amino acids is presented. The model requires calculation of the molecular connectivity values of only the functional fragments of the amino acids. Multiple linear regression with two variables shows the best fit between experimental and calculated data.

Amino Acids↗

PubMed1991

Pilot study for the development of a monitoring device for ventilated children.

Airway pressure and air flow were measured at the endotracheal tube in 13 children on a variety of ventilators. These signals were stored for analysis on a computer. Further data sets were obtained after 24 hours or following major interventions. Air flow rate was integrated to give volume. Pulmonary resistance and elastance were obtained by multiple linear regression. Pressure-volume, pressure-flow and flow-volume loops were plotted. "Closed" pressure-volume and pressure-flow loops (by subtraction of the resistive or elastic pressure components, respectively) were also displayed, giving compliance and resistance loops. The loops from the initial data set were taken as the baseline, and loops from later data sets were superimposed to provide visual comparisons. Change in clinical status was reflected by the change in slope of compliance and resistance loops. A 30% change in compliance or resistance was easily observed. There was minimal interference with patient care. This pilot study demonstrates that changes in respiratory mechanics can be displayed safely and easily in ventilated patients using resistance and compliance loops. Further work is necessary to confirm the usefulness of real time of these displays.

Child↗

PubMedDate not supplied

The contributions of cigarette yield, consumption, inhalation and puffing behaviour to the prediction of smoke exposure.

The overall predictability of smoke exposure indicators and the importance of different influencing factors were assessed in a cross-sectional study (n = 144), using multiple linear regression and bivariate correlation analyses. Respiratory CO, and plasma nicotine and cotinine concentrations were measured before and after smoking, for lip or holder smoking, and natural or standardized (30 puffs) puffing. The prediction of smoke exposure measures varied considerably across sampling times, smoking conditions, and dependent variables. The variance of plasma cotinine and nicotine were predictable to a considerable extent (30%; 19-41%) by cigarette yield, consumption and self-reported inhalation, whereas respiratory CO was less predictable (15-27%). Generally, consumption was the most important predictor, surpassed by nicotine yield for post-smoking plasma nicotine. Smoke exposure from a single smoking period could be predicted to a variable degree (CO, 11-42%; nicotine, 33-54%) by a subset of smoker's sex, cigarette yield, self-reported inhalation and puffing characteristics. The highest prediction was found under standardized smoking conditions (30 puffs through a holder), the lowest under natural smoking conditions. The best subset of predictors, especially with respect to puffing parameters, was found to vary considerably across smoking conditions and dependent variables.

Administration, Inhalation↗

PubMed1992

Effect of coronary reperfusion on technetium-99m methoxyisobutylisonitrile uptake by viable and necrotic myocardium in the dog.

Technetium-99m hexakis-2-methoxyisobutyl isonitrile (99mTc-MIBI) distribution is flow-dependent, permitting the imaging of coronary perfusion defects. However, the behaviour of this tracer in viable and necrotic tissues within the ischaemic area at risk is still being debated. In a clinically relevant canine model, dogs were submitted either to a 24-h permanent occlusion (group 1) of the left descending coronary artery (LAD) or to a 90-min LAD occlusion followed by 22.5 h reperfusion (group 2). 99mTc-MIBI and radiolabelled microspheres were injected 3 h before sacrifice. After delimiting the area at risk and the infarct by Evans blue perfusion and triphenyltetrazolium chloride staining, heart slices were imaged by scintigraphy and tissue radioactivity measured in a gamma-counter. In the necrotic area of both groups, the 99mTc-MIBI distribution was proportional to the myocardial blood flow, approximating a 1:1 ratio (identity line slope 1, intercept 0) with highly significant correlation coefficients (group 1 r = 0.87, group 2 r = 0.86), whereas in the viable-ischaemic area of both groups, the data points are widespread above and below the identity line, indicating both over- and underestimations of blood flow in these tissue areas. These results were more pronounced following reperfusion as compared with permanent occlusion. Multiple linear regression analysis confirms differences (P less than 0.001) in 99mTc-MIBI distributions between the viable-ischaemic and the necrotic zones. Delineation of the ischaemic area at risk was possible only with permanent occlusion. A hypoperfused area was observed after reperfusion but differs from the anatomical infarcted area.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Epithelial permeability in corneal grafts by fluorophotometry.

The epithelial permeability to fluorescein of 27 clear corneal grafts in 23 patients was determined by fluorophotometry at greater than 1 year after penetrating keratoplasty (PKP) so as to study the recovery of corneal epithelial function. The mean epithelial permeability of the corneal grafts did not differ significantly from that of normal corneas (0.042 +/- 0.016 and 0.038 +/- 0.017 nm/s, respectively; P greater than 0.3). Multiple linear regression analysis showed that permeability correlated with recipient age but not with donor age (permeability increase, 0.00054 nm/s per year; r = 0.6, P less than 0.005 and r = 0.1, P greater than 0.5, respectively). These results indicate that corneal grafts can regain a normal epithelial barrier function and that recovery of epithelial function is better in young than in old recipients.

Adult↗

PubMed1992

Factors contributing to deficiencies in cell-mediated immunity in esophageal cancer patients.

Based on the previous data which indicated a preoperative decrease in cell-mediated immunity (CMI) is associated with the occurrence of infectious complications following surgery on patients with esophageal cancer, we examined possible factors contributing to a decrease in CMI levels. A multiple linear regression analysis was made on data from 76 patients with esophageal cancer and 53 with gastric cancer as the control. In patients with esophageal cancer, both protein-calorie malnutrition (PCM) and age factor contributed to a decrease in CMI, although the contribution of the latter was weak while the stage of the cancer and the grade of dysphagia showed no such contribution. The PCM and stage of the cancer were contributing factors in patients with gastric cancer. Thus, these results indicate that PCM and old age, and not the presence of malignant tumors, play a significant role in deficiency in CMI in patients with esophageal cancer.

Age Factors↗

PubMed1992

Increases in immunoglobulin and complement in patients with esophageal or gastric cancer.

Based on data providing evidence that the enhancement of serum IgG and IgA is associated with the occurrence of infectious complications following surgery in patients with esophageal cancer, we examined the possible factors contributing to alterations in the serum IgG, IgA, IgM, C3, C4, and CH50 levels. A multiple linear regression analysis was made on data obtained from 71 patients with esophageal cancer and 57 with gastric cancer. In the patients with esophageal cancer, age and protein-calorie malnutrition (PCM) were related to the elevation of IgG levels while the stage of cancer was linked to that of IgA. The sex and IgM levels were also seen to be related. Age and the stage of cancer were associated with reductions in C3, C4, and CH50 levels, although in the patients with gastric cancer, the stage of cancer and elevations of these complement levels were related. Thus, age, PCM, and tumor malignancy are all factors related to the enhancement of IgG or IgA in patients with esophageal cancer.

Adenocarcinoma↗

PubMed1979

Relationship between dose and plasma level of digoxin and patient characteristics.

The correlation between the daily dose of digoxin, its plasma level and clinical characteristics of 213 patients receiving beta-acetyldigoxin treatment has been evaluated. After logarithmic transformation of lognormally distributed variables multiple linear regression analysis was performed. Eight predictor variables were chosen: sex, age, height, weight, glycoside dose, creatinine and potassium level in serum and dose of spironolactone. The resulting correlation coefficient was 0.46, i.e. only 100 x r2 = 21.4% of the variance of the steady state digoxin plasma level could be interpreted with the aid of these variables. For only 4 of the 8 variables (age, glycoside dose, serum level of creatinine, and spironolactone dose) were partial coefficients of regression and of correlation significantly different from zero. Almost 80% of the variance could not be accounted for. This finding is in accordance with conclusions in the literature.

Adult↗

PubMed1992

Evaluation of Bayesian estimation in comparison to NONMEM for population pharmacokinetic data analysis: application to pefloxacin in intensive care unit patients.

The pharmacokinetics of pefloxacin (PF) were investigated in a population of 74 intensive care unit patients receiving 400 mg bid as 1-hr infusion using (i) Bayesian estimation (BE) of individual patient parameters followed by multiple linear regression (MLR) analysis and (ii) NONMEM analysis. The data consisted of 3 to 9 PF plasma levels per patient measured over 1 to 3 dosage intervals (total 113) according to four different limited (suboptimal) sampling 3-point protocols. Twenty-nine covariates (including 15 comedications) were considered to explain the interpatient variability. Predicted PF CL for a patient with median covariates values was similar in both BE/MLR and NONMEM analysis (4.02 and 3.92 L/hr, respectively). Bilirubin level and age were identified as the major determinants of PF CL by both approaches with similar predicted magnitude of effects (about 40 and 30% decrease of median CL, respectively). Confounding effects were observed between creatinine clearance (26% decrease of PF CL in the BE/MLR model), simplified acute physiology score (a global score based on 14 biological and clinical variables) (18% decrease of median CL in the NONMEM model) and age (entered in both models) which were highly correlated in our data base. However, both models predicted similar PF CL for actual subpopulations by using actual covariate values. Finally, the NONMEM analysis allowed identification of an effect of weight on CL (decrease of CL for weight < 65 kg) whereas the BE/MLR analysis predicted an increase of CL in patients treated with phenobarbital. In conclusion, both approaches allowed identification of the major risk factors of PF pharmacokinetics in ICU patients. Their potential use at different stages of drug development is discussed.

Adolescent↗

PubMed1992

Biometrical analysis of individual growth curves.

Longitudinal data for height (length) between birth and 2 years of age were examined for 690 Dutch Registry twin pairs. A two-stage analysis was performed, where individual growth curves were first fit to available data for each subject using a linear multiple regression procedure and estimated individual growth curve parameters were then subjected to multivariate biometrical analysis. Quadratic polynomial curves were found to adequately represent observed growth patterns for the majority of cases (median R2 = .98). A specific scalar model of sex limitation best characterized individual variation in growth curve parameters. That is, there was significantly greater genetic variation for boys than for girls in both the predicted length and rate of growth at 1 year of age and the amount of deceleration in individual growth curves across age.

Anthropometry↗

PubMed1976

Initial state, outcome, and autopsy findings in a series of 200 consecutive traumatic comas. A computerised analysis.

Based on 200 nonselected consecutive cases of primary traumatic coma a preliminary mathematical model--computed, multiple linear regression analysis--has been developed, which seems to be suitable for calculating the prognosis from some initial anamnestic and clinical data. It is to be expected that the analysis of greater material will help to establish an even better model, e.g. by a more detailed age subdivision and choice of more or other factors. It is the aim of this report to encourage further work in this field.

Adolescent↗

PubMed1978

[Plasma concentrations of digoxin in patients under intensive care conditions and in patients undergoing anesthesia and operation (author' transl)].

Pharmacokinetic behavior of digoxin or beta-acetyldigoxin was examined in 66 patients (27 patiets under intensive care conditions, partially with controlled breathing, 22 patients undergoing extirpation of the uterus and 17 patients treated with radium or chemotherapeutics; 19 males and 47 females) by determining plasma concentrations of digoxin (PDC). After intravenous and oral application with a maintenance dose of 0.20--0.50 mg/day blood was taken daily during a 2 to 3 week period, resulting in 510 determinations. 24 hours after the first application of 0.50 mg digoxin i.v. the mean values of PDC amounted to 0.62 +/- 0.08 ng/ml. After 0.40 or 0.25 mg digoxin per day i.v. therapeutical concentrations could be observed at the third vs fifth day. An equilibrium of PDC was reached on the 6th day after starting digitalization using maintenance doses. Intravenous application of 0.25, 0.40 or 0.50 mg digoxin per day resulted in a mean steady state of 0.68 +/- 0.37, 0.86 +/- 0.33 or 1.27 +/- 0.49 ng/ml PDC, respectively. The results were significantly different (p less than 0.01--0.001). Serial measurements indicated a great variation of PDC. In patients without renal failure the intraindividual variation of the plasma concentrations was maximal 37.4% referring to the mean steady state, interindividual 37.1% and the evaluation of the inter- and intraindividual differences amounted to 54.1%. After oral administration of digoxin (maintenance dose: 0.50 mg/day) or beta-acetyldigoxin (maintenance doses: 0.20--0.40 mg/day) differences in PDC of 38.3% and 29.7% were obtained. Body weight, age and serum creatinine concentration were partly responsible for the variance of PDC. Multiple linear regression between stead state PDC and dose, age, body weight and serum creatinine concentration revealed 62.1% of the variance of the PDC after intravenous administration of digoxin. After oral administration of beta-acetyldigoxin 39.9% were obtained. Thus, 40% of the variance were caused by differences in distribution and elimination of digoxin after i.v. application. After oral application additional 20% of the variance could be attributed to resorption and possible disturbances.

Cardiac Glycosides↗

PubMed1991

A noninvasive method of estimating mean pulmonary artery pressure in the pneumatic total artificial heart.

Accurate hemodynamic monitoring is essential for the clinical management of the recipient of a total artificial heart (TAH). The high incidence of pulmonary congestive disorders in this population complicates this already formidable task. Lack of diagnostic pulmonary artery pressure (PAP) information is recognized as a fundamental source of these problems. Because conventional methods of obtaining hemodynamic information are difficult to implement in TAH recipients, improvement of TAH case management depends on the development of innovative monitoring strategies. Noninvasive monitoring techniques have been developed for three (right atrial pressure, left atrial pressure, and aortic pressure) of the four auxiliary circulatory pressures used to quantify hemodynamic performance. Development of the fourth, for PAP, was the subject of this work. We developed a noninvasive, in vitro method of estimating mean PAP in the Jarvik-7 TAH (Symbion, Inc, Salt Lake City, UT) recipient. This information was obtained by analyzing the relationship between the pneumatic right drive pressure (RDP) and PAP waveforms produced by a Jarvik-7 (70 ml) connected to a Donovan mock circulation and driven by a Utahdrive System IIIe Controller (Symbion, Inc, Salt Lake City, UT). Total artificial heart driver parameters (i.e., heart rate, percent systole, and vacuum) were manipulated to produce a range of ventricular filling volumes (FV), from 40 to 60 ml, for three distinct states of the pulmonary vasculature: hypotensive, normal, and hypertensive. A unique multiple-linear regression equation was derived for each FV from the RDP-PAP relationship exhibited under these conditions. Comparison of computed estimates of PAP with actual measurements showed overall average correlations of greater than 0.92, with a standard error of the estimate of less than 1.9 mm Hg. The mean difference between actual and computed PAP measurements was -0.03 +/- 2.0 Hg. Estimations were accurate within 8.5% of true PAP values. Additional experimentation revealed that while the RDP-PAP relationships are dependent on FV, they are independent of the manner in which FV was obtained. Estimates proved useful over the clinical operating range of the pneumatic heart driver, as well as over the normal physiologic range of PAP in the human. This method is readily applicable to a computer-based monitoring implementation, although its effectiveness needs to be demonstrated in vivo.

Aorta↗

PubMed1992

Sister chromatid exchanges in lymphocytes of normal and alcoholic subjects.

The effects of alcohol consumption, cigarette smoking and age on sister chromatid exchange (SCE) frequency in human lymphocytes were assessed by means of multiple linear regression. An increase in SCE rates was associated with alcohol consumption (p = 0.0001), smoking (p = 0.0231), and, to a small extent (p = 0.057), age. These three confounding factors explain 48% of the inter-personal variation in SCE rates among subjects studied.

Adult↗

PubMed1992

Quantitative measurement of two-component pH-sensitive colorimetric spectra using multilayer neural networks.

The purpose of this research was to develop a noise tolerant and faster processing approach for in vivo and in vitro spectrophotometric applications where distorted spectra are difficult to interpret quantitatively. A PC based multilayer neural network with a sigmoid activation function and a generalized delta learning rule was trained with a two component (protonated and unprotonated form) pH-dependent spectrum generated from microspectrophotometry of the vital dye neutral red (NR). The network makes use of the digitized absorption spectrum between 375 and 675 nm. The number of nodes in the input layer was determined by the required resolution. The number of output nodes determined the step size of the quantization value used to distinguish the input spectra (i.e. defined the number of distinct output steps). Mathematic analysis provided the conditions for which this network is guaranteed to converge. Simulation results showed that features of the input spectrum were successfully identified and stored in the weight matrix of the input and hidden layers. After convergent training with typical spectra, a calibration curve was constructed to interpret the output layer activity and therefore, predict interpolated pH values of unknown spectra. With its built-in redundant presentation, this approach needed no preprocessing procedures (baseline correction or intensive signal averaging) normally used in multicomponent analyses. The identification of unknown spectra with the activities of the output layer is a one step process using the convergent weight matrix. After learning from examples, real time applications can be accomplished without solving multiple linear equations as in the multiple linear regression method.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrogen-Ion Concentration↗