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Biomedical subjects

B Johnston

Publications and source records attributed to B Johnston.

At least 109 records · Page 6Linked to original sources
PubMed1981

Experimental cotton-fibre pulmonary embolism in the rat.

Cotton-wool fibres are not uncommonly introduced into systemic veins during medical procedures and are swept into the pulmonary circulation as emboli. To ascertain the histological changes which occur in the pulmonary vasculature, and the time scale of the various cellular reactions we induced experimental cotton-fibre pulmonary embolism in 51 rats. Within an hour the fibres became covered by platelets and plasma proteins and neutrophil polymorphs were attracted around them. By two hours macrophages congregated around the emboli and, with accumulation of epithelioid cells, granulomas were formed. By 16 hours these had increased in size with the appearance of foreign body giant cells, and reached their maximum size in three days. By 16 hours the granulomas were in the wall of the pulmonary artery with rupture of the elastic laminae. At the end of a week granulomas had passed through the wall to reach the alveolar spaces. By the sixth month all were extravascular, lying within the alveolar walls or in the peribronchiolar fibrous tissue. The continuity of the arterial media through which the granuloma had passed was restored without haemorrhage.

Animals↗
PubMed1980

Administration of drugs during cardiopulmonary bypass. An analysis of the fate of a bolus injected through different routes using radio-active technetium.

This study was conducted to determine the efficiency of delivery of drugs injected as boluses by the common routes available during cardiopulmonary bypass. Radioactive technetium (99mTc) was injected in a 50 microCi bolus into the central venous line or into the arterial or venous lines of the oxygenator and its passage monitored downstream by suitable radiation detectors. When injected into the central venous line, delivery was unpredictable and at times 50% or more of the dose may not appear for 5 min. When injected into the venous line of the oxygenator an average 5% of the total dose had not reached the detector during first passage, and had completely cleared at 2 min. No significant difference was found between the different oxygenators and it is concluded that the venous line of the oxygenator is the most efficient site for the achievement of rapid action of drugs.

Cardiopulmonary Bypass↗
PubMedDate not supplied

A multivariable analysis of factors governing the steady-state pharmacokinetics of valproic acid in 52 young epileptics.

A number of factors have been implicated in the interpatient variability of valproic acid (VPA) pharmacokinetics. These include patient age, concurrent anticonvulsant therapy, and dosage of VPA. In the clinical setting, it is important to determine which of these variables exert a major effect on the observed differences in VPA disposition. Accordingly, we analyzed the data from 52 young epileptic patients using multivariate statistical methods. Concurrent anticonvulsant therapy was the major determinant of VPA clearance in this patient population. The half-life of VPA was significantly related to age, but volume of distribution and clearance were not. The dosage of VPA affected the volume of distribution of VPA but not the half-life or clearance of this drug. These results provide a more rational understanding of VPA pharmacokinetics in the clinical setting and have implications for the monitoring and manipulation of VPA therapy in the epileptic population.

Adolescent↗
PubMedDate not supplied

Application of principal components analysis to 1H-NMR data obtained from propolis samples of different geographical origin.

Propolis is a widely used natural remedy and a range of biological activities have been attributed to it. The chemical composition of propolis is highly variable and its quality is often controlled on the basis of one or two marker compounds. In order to progress towards a method for the quality control of this complex material, HPLC and 1H-NMR approaches as methods of quality control have been compared. HPLC analyses of 43 samples of propolis were carried out and six marker compounds were quantified in each sample. The same samples were analysed using 1H-NMR and the spectra were then converted into their first derivative forms and digitised using the software application MestRe-C. The digitised data were subjected to principal component analysis using the software application Simca-P. It was found that the chemical composition of propolis mapped well according to the geographical origins of the samples studied when the first three principal components were used to display them. In addition, each sample was assessed for anti-oxidant activity, and the results were then overlaid onto the sample groupings according to 1H-NMR data. It was observed that anti-oxidant properties also mapped quite well according to geographical origin.

Geography↗
PubMedDate not supplied

Short- and long-term variability of echocardiographic stress-velocity indexes of cardiac function in a pediatric population.

This study determined the short- and long-term variability of stress-velocity relationships at end systole and peak systole. A prospective study during the short term (0 to 15 and 0 to 30 minutes) and long term (0 to 1 and 0 to 12 months) was performed calculating variability by the limits of agreement method. The study was performed in a tertiary-care pediatric echocardiographic laboratory. Twenty-five normal children underwent repeat testing as described. Standard blood pressure, carotid pulse tracing, and M-echocardiography of the left ventricle was performed at the intervals described. The rate-corrected mean velocity of fiber shortening (MVCFC), echocardiographic stress at end systole (SES), and echocardiographic stress at peak systole (SPS) were calculated for all recordings. The slopes of MVCFC-SES and MVCFC-SPS were determined by regression and plotted. With these slopes, the second and third stress values were normalized to the first stress value for the short and long term. The differences in normalized MVCFC and MVCFC (delta MVCFC) for 15 to 0 minutes, 30 to 0 months, 1 to 0 month, and 12 to 1 month were obtained for both SES and SPS, and 95% limits of agreement were estimated. The mean delta MVCFC for SES and SPS for the short and long term were not different from 0 or each other, indicating no bias. The 95% limits of agreement of delta MVCFCs (i.e., variability for SES at 15 to 0 minutes, 30 to 0 minutes, 1 to 0 month, and 12 to 0 month) were +/- 0.18, +/- 0.24, +/- 0.34, and +/- 0.27, respectively, and for SPS +/- 0.18, +/- 0.24, +/- 0.33, and +/- 0.28. Variability showed an increasing trend with time but was significant only from 15 to 0 minutes and 1 to 0 month (p = 0.006). This study has established short- and long-term variability in the stress-velocity relationship that is essential for monitoring acute and chronic changes in ventricular contractility in an individual patient.

Adolescent↗
PubMedDate not supplied

An autotransfusion apparatus.

An autotransfusion apparatus is described in detail and its use is illustrated with short case reports.

Adult↗
PubMedDate not supplied

Analysis of multivariables during porcine liver digestion to improve hepatocyte yield and viability for use in bioartificial liver support systems.

In order to achieve optimal BALSS function, preparation of porcine hepatocytes with high yield, viability, and P450 activity is known to be important. To date hepatocyte yields have varied from 0.58 x 10(10) to 3.45 x 10(10) and viabilities from 75% to 95% within and between laboratories, even when using the same digestion methods and procedures, indicating that hepatocyte isolation during porcine liver digestion is not fully optimized. The aim of this work was to identify the critical parameters affecting cell recovery during porcine liver harvesting by investigating 21 variables involved in the process, including pig body and liver weight, different digestion times of perfusates, pH, a range of concentrations of sodium and chloride in EDTA, and collagenase perfusates. Univariate and multivariate analysis of a retrospective study (n = 23) revealed that low perfusate pH during the process of digestion had a positive effect on hepatocyte yield (p < 0.05), while high (relative) concentrations of sodium and chloride in the perfusates had significant negative effects on hepatocyte viability (both p < 0.05). Sodium and chloride had narrow optimal ranges for achieving a >90% viability. These findings were then tested in a prospective study (n = 10) and further verified. High hepatocyte viabilities (91.8+/-1.6% p = 0.036) and yields (2.56+/-0.48 x 10(10)) were achieved consistently, and P450IA1 activity was increased after sodium and chloride concentrations and pH in the perfusates were controlled. The physiological mechanism by which sodium and chloride affects hepatocyte viability during porcine liver digestion is discussed.

Animals↗