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Biomedical subjects

R Mitchell

Publications and source records attributed to R Mitchell.

At least 379 records · Page 21Linked to original sources
PubMed1982

Statistical analysis of the direct count method for enumerating bacteria.

The direct count method for enumerating bacteria in natural environments is widely used. This paper analyzes the sources of variation contributed by the various levels of the method: subsamples, filters, and microscope fields. Based on a nested analysis of variance, we show that most of the variance (less than 80%) is caused by the fields and that the filters contributed nearly all of the remaining variance. The replication at each of the levels determines the total cost and error of a measurement. We compared several sampling schemes, including an optimal strategy which gives the lowest possible variance for a given cost. We recommend that preparing one filter from one subsample is adequate only if the samples are closely spaced in time or distance; otherwise, one filter should be prepared from two or preferably three subsamples. This sampling scheme emphasizes the importance of the highest level of replication. Our analysis shows that the accuracy of the direct count method can be substantially improved (by 20 to 50%) without a large increase in cost when the proper degree of replication at each level is performed.

Analysis of Variance↗
PubMed1982

Estimates of bacterial growth from changes in uptake rates and biomass.

Rates of nucleic acid synthesis have been used to examine microbiol growth in natural waters. These rates are calculated from the incorporation of [3H]adenine and [3H]thymidine for RNA and DNA syntheses, respectively. Several additional biochemical parameters must be measured or taken from the literature to estimate growth rates from the incorporation of the tritiated compounds. We propose a simple method of estimating a conversion factor which obviates measuring these biochemical parameters. The change in bacterial abundance and incorporation rates of [3H]thymidine was measured in samples from three environments. The incorporation of exogenous [3H]thymidine was closely coupled with growth and cell division as estimated from the increase in bacterial biomass. Analysis of the changes in incorporation rates and initial bacterial abundance yielded a conversion factor for calculating bacterial production rates from incorporation rates. Furthermore, the growth rate of only those bacteria incorporating the compound can be estimated. The data analysis and experimental design can be used to estimate the proportion of nondividing cells and to examine changes in cell volumes.

Bacteria↗
PubMed1981

Differential psychotherapy outcome among depressed and impulsive patients as a function of analytic and experiential treatment procedures.

Assessment of five psychotherapy procedures, broadly representing experiential and analytical orientations, was undertaken with two groups of clinic outpatients. The patient groups were similar in the length of treatment received, degree of psychological disturbance present, and the frequency with which they were exposed to each of the treatment procedures. Both therapist and external raters assessed the patients' improvement on target symptoms and global change measures at the conclusion of treatment. The results suggest a clear superiority of experiential treatment procedures across patient groups. However, analytic treatments achieved their greatest effect among depressive anxious patients and their least effect among impulsive externalizing patients.

Adult↗
PubMed1981

Solar radiation induces sublethal injury in Escherichia coli in seawater.

Sublethal injury was noted in Escherichia coli after cells were exposed to solar radiation. Injury was detected by differential plate counts between complete and minimal media that were observed with sunlight-exposed cells but not with cells kept in the dark. Since addition of catalase or pyruvate to minimal medium overcame or repaired this injury, the catalase system appeared to be the site of injury.

Catalase↗
PubMed1981

External microflora of a marine wood-boring isopod.

Bacteria associated with the marine wood-boring isopod Limnoria lignorum were enumerated by acridine orange epifluorescence microscopy and by plate counts on several media; the plate-viable bacteria were isolated and identified. Similar procedures were followed to enumerate and identify bacteria associated with the wood substrate from which the isopods were collected and with the surrounding water from the isopod habitat. Approximately 1.4 x 10 bacterial cells were associated with each individual L. lignorum. Aeromonas hydrophila, Pseudomonas, and Vibrio were the most common genera in the isopod microflora. Wood from L. lignorum burrows had an associated bacterial flora of 1.6 x 10 cells per mg (damp weight). A. hydrophila also predominated in the wood microflora. The water from which the isopod population was collected contained 2.3 x 10 bacteria per ml. Pseudomonas and Vibrio species were very common in the water microflora, but A. hydrophila was not detected. Interactions between the isopod, its associated microorganisms, and the microorganisms within the wood substrate are discussed in the light of the known absence of a resident digestive tract microflora in these animals.

Journal Article↗
PubMed1981

Blood lactate concentration following maximum exercise in trained subjects.

The time when blood lactate reaches peak concentration following maximum exercise is unclear. The post exercise venous blood lactate concentration was determined serially for 30 minutes in 13 trained men following maximum exercise on a motor driven treadmill. Lactates were determined enzymatically in duplicate. The VO2 max and percent body fat was 65.1 +/- 4.8 ml.kg-1.min-1 and 11.4 +/- 1.4, respectively. The venous lactate reached a peak concentration at the 6th minute (14.2 mmol.L-1) of an inactive recovery, and declined linearly thereafter to reach a concentration of 7.43 +/- 0.60 mmol.L-1 at the 30th minute. The net rate of lactate removal was .30 mmol.L-1.min-1. Statistical analysis found no significant difference in lactate concentration during the 4th, 5th and 6th minute post exercise, indicating that these post exercise times may be appropriate to sample venous blood for peak lactate concentration.

Adult↗
PubMed1981

Production of freeze-dried human antihaemophilic cryoprecipitate.

Concentration of factor VIII from fresh plasma by cryoprecipitation remains the basis for preparation of products used to treat haemophilia A. This paper describes the preparation of a factor VIII concentrate from small plasma pools in transfusion centres with drying facilities. The dried concentrate from one litre of plasma dissolves very well in 50 or 100 ml of distilled water and contains around 500 IU per bottle. The specific activity per mg protein is 0.19 IU and the fibrinogen concentration is half that in frozen cryoprecipitate. This method of drying causes no appreciable loss in the factor VIIIC activity and little denaturation as shown by the factor-VIII-related antigen/factor VIIIC ratio of 1.7.

Chemical Precipitation↗
PubMed1981

Left ventricular ejection fraction calculated from volumes and areas: underestimation by area method.

The ejection fraction is one of the most widely used measurements of left ventricular systolic function. Angiographic measurement of ejection fraction is based on determination of roentgenographic magnification and calculation of end-diastolic and end-systolic volumes, assuming a prolated ellipse. Because it is simple and radiographic magnification may not have been determined, some laboratories have obtained an "ejection fraction" by comparison of end-diastolic and end-systolic areas. A comparison of the two methods was made using ventriculograms of 538 patients from three cardiac catheterization laboratories. The area method of ejection fraction calculation consistently underestimates ejection fraction from left ventricular volumes. A regression equation was derived that allows adjustment of the ejection fraction obtained from areas to that from volumes.

Blood Volume Determination↗