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Biomedical subjects

J C Boyd

Publications and source records attributed to J C Boyd.

At least 73 records · Page 4Linked to original sources
PubMed1984

Relationship of potassium and magnesium concentrations in serum to cardiac arrhythmias.

Low concentrations of potassium and magnesium in serum have been implicated in cardiac arrhythmias; the importance of mild hypokalemia or hypomagnesemia is uncertain. To investigate possible associations among use of diuretics, the concentration of these ions in serum, and the onset of clinically important arrhythmias, we reviewed records of 103 patients admitted to our Coronary Care Unit during three months and found mild to moderate hypokalemia and hypo- magnesemia in 18 and 24%, respectively. The significant correlation between the concentrations of magnesium and potassium in serum at admission (r = 0.27, p less than 0.007) remained constant in patients, whether they were receiving diuretics or not. Potassium concentrations were significantly lower (p less than 0.05) in patients receiving diuretics (3.93 mmol/L) than in those who were not (4.21 mmol/L), but the mean concentrations of magnesium did not differ significantly. Except for myocardial infarction, no single variable or combination of variables was highly predictive of cardiac arrhythmias in these patients. We conclude that there is no strong predictive relationship between mildly decreased concentrations of magnesium or potassium in serum and onset of cardiac arrhythmias.

Arrhythmias, Cardiac↗
PubMed1983

Frequency of hypomagnesemia in hypokalemic states.

Although both hypokalemia and hypomagnesemia have been linked with life-threatening cardiac arrhythmias, published studies disagree regarding the frequency of simultaneously low serum potassium and magnesium concentrations. To investigate the possible associations between the concentrations of these ions in serum, we carried out a retrospective study of all paired magnesium-potassium measurements reported from our laboratory during two separate two-week periods. Of 963 paired measurements in 421 patients, 12% of the samples were hypokalemic and 26% were hypomagnesemic. The frequency of hypomagnesemia was significantly greater in hypokalemic samples (38%) compared with nonhypokalemic samples (25%). The potential clinical importance of this relationship requires further investigation.

Autoanalysis↗
PubMed1983

Stage II glottic carcinoma: prognostic factors and management.

Three hundred thirty-six patients with squamous cell carcinoma of the glottic larynx treated at the University of Virginia Medical Center from 1960 through 1977 were reviewed. Seventy patients with T2N0M0 disease, grouped according to the criteria of the American Joint Committee on Cancer, 1978, form the basis of this report. The 5-year actuarial survivals, recurrences, salvages, and prognostic factors were examined. Treatment was radiation, surgery, or a combination of radiation and surgery. Impaired vocal cord mobility in Stage II glottic squamous cell carcinoma is the crucial significant prognostic factor in predicting response to therapy, survival, and response to salvage therapy for recurrences. The 90% 5-year recurrence-free rate with freely mobile cords is comparable to that achieved with Stage I lesions. Impaired mobility resulted in a 5-year recurrence-free rate of 73%, which is comparable to that of T3N0 lesions. We support the concept of reclassifying Stage II disease into Stage IIa (mobile cords) and Stage IIb (impaired mobility). Based on this review and those reported in the literature, we recommend radiation therapy for Stage IIa disease. Surgery results in fewer recurrences and in longer survival than irradiation when the vocal cords are not freely mobile (Stage IIb).

Carcinoma, Squamous Cell↗
PubMed1982

Staging of supraglottic cancer.

In 1977, The American Joint Committee for Cancer Staging and End-Results Reporting (AJC) revised its 1972 staging system for supraglottic cancer of the larynx. These changes included the following: (1) reclassifying T1b carcinomas as T2 carcinomas, (2) reclassifying extension onto the medial wall of the piriform sinus or postcricoid mucosa as T3 carcinomas rather than T4 carcinomas, (3) restructuring of the N classification, and (4) changing the classification of T4 NO carcinomas from stage III to stage IV. To correlate these changes with prognosis, the cases of 178 patients with supraglottic laryngeal cancer who were treated at the University of Virginia Medical Center, Charlottesville, from 1955 to 1976 were reviewed. Each case was classified using both the 1972 and 1977 AJC TNM system. Using the 1972 staging system, the following determinations were made regarding our patient population: stage I, 43 patients; stage II, 15 patients; stage III, 116 patients; and stage IV, four patients. Using the 1977 cancer staging system, the following determinations were made: stage I, 19 patients; stage II, 37 patients; stage III, 37 patients. six specific changes in the TNM classification system seem to be justified. However, the upstaging of T4 NO supraglottic cancers from stage III to stage IV seems to be unjustified; T4 NO cancers should be returned to the state III grouping.

Actuarial Analysis↗
PubMed1982

A comparison of log P and molecular connectivity in the structure-activity analysis of some antimicrobial agents.

Several congeneric series of antimicrobial agents previously studied by Hansch analysis have been investigated using molecular connectivity as the descriptor of molecular structure. In all cases connectivity gave comparable or improved correlations compared with log P, particularly where the pattern of molecular substitution was more complex. It was concluded that the use of computer-generated connectivity terms had advantages over calculated log P values in its ease of application and should be considered at least for initial screening of structure-activity data.

Anti-Bacterial Agents↗
PubMed1982

The relationship between molecular connectivity and partition coefficients.

Kier & Hall (1976) demonstrated that a relationship existed between molecular connectivity and Log P (the Log of the octanol/water partition coefficient) for several classes of compounds and also for the combined classes. This work utilized a number of Log P values calculated using Pi values. We have reinvestigated this relationship using experimentally determined Log P values. The results confirm Kier & Hall's findings although different connectivity indices are brought into the equations.

Alcohols↗
PubMed1982

The multivariate reference range: an alternative interpretation of multi-test profiles.

To test the utility of multivariate interpretation of laboratory data, we developed a multivariate reference range based of the Mahalonobis distance (D2) measure. Results for 20 commonly measured clinical chemistry analytes were collated for two sophomore medical-school classes (118 and 143 individuals in 1979 and 1980, respectively). The data for each test were examined for fit to a gaussian (normal) distribution by using a Kolmogorov--Smirnov test. Those results discovered to have a non-normal distribution were "normalized" by used the of a two-stage log-exponential transform. After this transformation, the D2 distance for each student group followed the expected chi-square distribution with 20 degrees of freedom. For each student's D2 distance an associated chi-square percentile was derived, and a cutoff percentile (95%) was selected to differentiate multivariately the "normal" from "abnormal" test results. Whereas more than two-thirds of the students had univariate test abnormalities, fewer than 7% had abnormal multivariate D2 scores. Analysis showed that the multivariate reference range could sensitively detect minor variations of multiple analytes but could also be quite insensitive to highly abnormal results for a single analtye. The multivariate approach has promise as a tool to avoid unnecessary followup of falsely abnormal test results, but further study and validation in a clinical setting are required.

Adult↗
PubMed1982

A multi-stage Gaussian transformation algorithm for clinical laboratory data.

We have developed a multi-stage computer algorithm to transform non-normally distributed data to a normal distribution. This transformation is of value for calculation of laboratory reference intervals and for normalization of clinical laboratory variates before applying statistical procedures in which underlying data normality is assumed. The algorithm is able to normalize most laboratory data distributions with either negative or positive coefficients of skewness or kurtosis. Stepwise, a logarithmic transform removes asymmetry (skewness), then a Z-score transform and power function transform remove residual peakedness or flatness (kurtosis). Powerful statistical tests of data normality in the procedure help the user evaluate both the necessity for and the success of the data transformation. Erroneous assessments of data normality caused by rounded laboratory test values have been minimized by introducing computer-generated random noise into the data values. Reference interval endpoints that were estimated parametrically (mean +/- 2 SD) by using successfully transformed data were found to have a smaller root-mean-squared error than those estimated by the non-parametric percentile technique.

Adult↗
PubMed1981

A multivariate approach to prognostication in experimental bacterial meningitis.

Known concentrations of type III pneumococci were inoculated into eighty-one rabbits by cisternal puncture. Antibiotic therapy was started the following day. Aliquots of cerebrospinal fluid (CSF) and plasma were sampled on day one immediately before therapy was started and at regular intervals thereafter for up to eight days. Samples were analyzed for glucose, lactate, lactic dehydrogenase, and creatine kinase in various combinations. Leukocyte counts were performed on all CSF specimens. The timing of the specimens proved critical to the prognostic utility of the analyses performed. Day two plasma glucose was the most important single measurement for prognostication. Day one values for CSF glucose, lactate, and leukocyte count were also important. Substantial gains in prognostic accuracy were achieved when clinical laboratory measurements were used in combination by discriminant function analysis.

Animals↗
PubMed1981

Parathyrin measured concurrently with free or total calcium in the differential diagnosis of hypercalcemia.

We assessed the diagnostic utility of measuring C-terminal immunoreactive parathyrin (i-PTH) concurrently with free (CaF) or total (CaT) calcium in four groups of patients: (1) 91 patients with histologically proven primary hyperparathyroidism; (2) seven patients without histological evidence of hyperparathyroidism; (3) 70 patients with non-parathyroid malignancies with hypercalcemia; and (4) 28 similar patients without hypercalcemia. In patients in Group 1, the use of either calcium measurement along with i-PTH increased diagnostic accuracy from 95 to 99%. In Group 2, values consistent with primary hyperparathyroidism were obtained for 21% of samples with i-PTH assay alone, 29% with i-PTH and CaT, and 12% with i-PTH and CaF. Surprisingly, 36% of samples from both malignancy groups (3 and 4) had above-normal i-PTH values. In patients with malignancy and hypercalcemia (Group 3) the following percentages were classified as possibly being hyperparathyroid: 26% with i-PTH assay alone; 31% with i-PTH and CaT, and 24% with i-PTH and CaF. Our data indicate that (a) about a fourth of patients with nonparathyroid malignancies also have evidence of hyperparathyroidism as judged by this (and probably all other) i-PTH methods based on C-terminal antibody specificity and that (b) measuring CaF and i-PTH rather than CaT and i-PTH gives a small increase in diagnostic accuracy.

Calcium↗
PubMed1979

Theoretic and experimental analysis of the ability of a commercially prepared system to detect mixtures of bacteria.

The validity of the biochemical identification of bacteria presumes that the inoculum consists of a pure growth of bacteria. The detection of mixtures of bacteria with the Analytab Enteric (API 20E) system was tested. Using a computer to predict the response of the API 20E system to mixed cultures, the presence of a mixture was not detected in 15% of all pairwise combinations of 324 common organisms of the Enterobacteriaceae family and in 19% of all pairwise combinations of Enterobacteriaceae with four gram-positive cocci. These theoretic predictions were confirmed experimentally for selected mixtures in which the bacteria were combined in equal concentrations. These results indicate that a purity subculture plate must be used to insure the detection of mixtures of bacteria, because the API 20E system fails to detect a large number of mixtures and may erroneously identify the organisms in such mixtures.

Bacteriological Techniques↗
PubMed1979

Relationship of free and total calcium in hypercalcemic conditions.

An assessment of free and total calcium measurements was made in 691 patients with suspected hypercalcemia or disorders often associated with hypercalcemia. In 18.9% of the 1049 specimens analyzed from nine different patient groups, a different impression of hypercalcemia was obtained depending on whether the free or total calcium was considered. Analysis of the ratio of free to total calcium indicated that there are two main factors which influence the distribution of calcium in the serum of hypercalcemic patients: the concentrations of albumin and parathyroid hormone. A lowered albumin concentration accounted for the altered distribution of calcium in patients with malignancies and partially accounted for the altered distribution in patients postrenal transplantation. In patients with confirmed primary hyperparathyroidism a higher ratio of free to total calcium was found, which could not be explained by alterations in protein, albumin, pH, or CO2 content but was related to parathyroid hormone concentration. Free calcium appears to be a slightly better indicator of elevated calcium states than total calcium. Measurements of free calcium should be particularly useful in patients with altered albumin concentration, with multiple myeloma in whom a calcium-binding protein could be present, after renal transplantation, and with suspected hyperparathyroidism and normal or slightly elevated total calcium values.

Calcium↗
PubMed1978

Effect of atypical antibiotic resistance on microorganism identification by pattern recognition.

We classified microorganisms from the clinical laboratory by using information provided by the Gram stain and antibiotic sensitivity profiles obtained with the Bauer-Kirby technique. Approximately 4,000 microorganisms, routinely identified and tested for antibiotic sensitivities in a large hospital microbiology laboratory, were used as a data set for several pattern recognition classification methods: K--nearest-neighbor analysis, statistical isolinear multicomponent analysis, Bayesian inference, and linear discriminant analysis. K--nearest-neighbor analysis yielded the highest prospective classification accuracy for gram-negative organisms, 90%. When those organisms displaying an atypical antibiotic resistance pattern were excluded from the data, the gram-negative classification accuracy improved to 95%. These results are inferior to currently accepted biochemical identification methods. Microorganisms with atypical antibiotic resistance patterns are likely to be misidentified and are common enough (17% of our isolates) to limit the feasibility of routine identification of microorganisms from their antibiotic sensitivities.

Anti-Bacterial Agents↗
PubMed1978

Failure of total calcium corrected for protein, albumin, and pH to correctly assess free calcium status.

The clinical effectiveness of published algorithms in correcting serum total calcium (CaT) for the effects of protein, albumin, and pH was tested. Corrected calcium (CaC) values obtained by 13 of these methods were compared with values of measured free calcium (CaF) in 55 samples from normal controls and 404 samples from patients with various disorders of calcium metabolism. Three criteria were used to compare either CaC or CaT with measured CaF: 1) the correlation coefficient, 2) the average absolute deviation from measured CaF of the values of CaF predicted by the linear regression of CaF on each CaC, and 3) the number of samples in which CaC or CaT gave a different impression of normality than measured CaF. Application of the 13 published algorithms produced varied results, but none produced substantially better agreement between CaC and CaF than was found between CaT and CaF. The application of additional algorithms derived by multiple linear regression using our data base gave slightly better results than any of the published algorithms, but many values of CaC remained which were disparate from the measured value of CaF. Correction of measured total calcium by using other concurrently obtained chemistry values does not seem to adequately predict calcium status as measured by free calcium.

Autoanalysis↗
PubMed1975

Decreasing reliability of acid-fast smear techniques for detection of tuberculosis.

The ability of any screening test to correctly identify diseased patients is directly related to the prevalence of the disease in question. The continuing use of smears for the detection of acid-fast bacilli when the prevalence of tuberculosis is declining will produce increasing numbers of false-positive results. To determine the usefulness of smear techniques, we carried out a retrospective study of approximately 10 000 consecutive smears and cultures. Positive smears were classified as true- or false-positive on the basis of whether the corresponding cultures grew mycobacteria. The overall incidence of false-positive smears was 0.7%; however, the ratio of the number of false-positive to total positive smear was about 0.5. Thus, for each true-positive result, one false-positive result was obtained. Patients in the true-positive group had clinical and radiological evidence to support the diagnosis of tuberculosis, while those in the false-positive group had new findings of the disease. These data suggest that the smear is a poor screening technique in a population where the prevalence of tuberculosis is low.

Bacteriological Techniques↗