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Biomedical subjects

J C Clark

Publications and source records attributed to J C Clark.

At least 109 records · Page 6Linked to original sources
PubMed1982

Rate of uptake of carbon monoxide at different inspired concentrations in humans.

The rate of uptake of carbon monoxide (CO) in the lungs of normal subjects were measured at inspired concentrations of less than 1, 300, and 3,000 ppm (less than 0.0001-0.3%) using radioactive CO (11CO). In nine subjects the rate of uptake was monitored at the mouth during rebreathing. At inspired CO concentrations of approximately 1, 300, and 3,000 ppm and a mean alveolar O2 fraction of 0.15, the mean lung diffusing capacity was 25.8, 26.4, and 25.3 ml . min-1. Torr-1, respectively. In seven subjects the measurements were repeated after a period of O2 breathing, giving a mean alveolar O2 fraction of 0.78. The calculated membrane diffusing capacity was 31.9, 33.7, and 32.0 ml . min-1. Torr-1 at less than 1, 300, and 3,000 ppm inspired CO. We conclude that there is no difference in the rate of uptake of CO over the range of concentrations studied in these experiments. No evidence for the presence of a facilitated transport system for CO in the normal human lung was found.

Adult↗
PubMed1981

Measurements of regional ventilation using nitrogen-13 and krypton-81m in mechanically ventilated dogs.

13N2 and 81Krm were used to measure changes in upper/lower (U/L) ratios of regional ventilation in supine anaesthetised dogs mechanically ventilated at different tidal volumes and the results compared. Analysis of the slopes of the 13N2 washout curves indicated that U/L specific ventilation was less than unity at low tidal volumes and decreased as tidal volume increased. U/L total ventilation, measured using the specific ventilation results and estimations of relative lung using 13N2, also decreased with increase in tidal volume. Preferential distribution of ventilation to dependent lung regions thus increased with tidal volume despite the opposing hydrostatic forces from the abdomen. Regional count density distributions in 81Krm images of the lungs were analysed. At high specific ventilation rates, correction of 81Krm count density is required in order to obtain correct regional ventilation information. The specific ventilation rates in this series were such that the uncorrected U/L count ratios of 81Krm increased as tidal volume increased in contrast to the decrease in U/L total ventilation recorded by the 13N2 method. When corrections using the 13N2 specific ventilation results were applied, the changes in U/L 81Krm count ratios with tidal volume showed a similar trend to the changes in total ventilation measured with 13N2. Sources of error in the two techniques are briefly discussed.

Animals↗
PubMed1981

Mucosal cell proliferation in duodenal ulcer and duodenitis.

Mucosal cell proliferation in the first part of the duodenum was studied in 24 patients using a tissue culture technique in which endoscopic biopsies were subjected to autoradiography after exposure to tritiated thymidine. Eight patients had a normal duodenum, eight had duodenal ulcer, and eight had symptomatic chronic non-specific duodenitis. The mean crypt labelling index (LI) in normal duodenum was 8.8 0.4% (SEM). Increased labelling indices of 15.6 +/- 1.7% were found near the edge of duodenal ulcers and 17.8 1.8% in duodenitis. Treatment with cimetidine reduced both the severity of duodenitis and the mean crypt LI. The LI of histologically normal duodenal mucosa distal to ulcer of duodenitis was similar to that of the control subjects' mucosa. The increased mucosal cell proliferation seen in severe duodenitis, either alone or associated with duodenal ulceration, suggested that erosions and ulcers arose when the crypts passed into 'high output failure' and were unable to compensate for further epithelial cell loss. There was no evidence in out study for a generalised failure of mucosal cell proliferation in duodenal ulcer or duodenitis.

Adult↗
PubMed1980

Conditions for measuring DNA synthesis in PHA stimulated human lymphocytes in 20 microliters hanging drops with various cell concentrations and periods of culture.

We have studied conditions for measuring the uptake of [3H]thymidine ([3H]Tdr) by human lymphocytes in inverted microcultures, varying cell concentrations and periods in culture. Analysis of variance of the log values for [3H]Tdr uptake may be used to separate effects of variables and their interactions. A pulse time of 2 h, a total thymidine concentration of about 1 microgram/ml and a specific activity of [3H]Tdr of 2 Ci/mmole were optimal. Variables such as cell concentration, period of culture, type of serum and dose of PHA were shown to interact, suggesting that these variables should be examined together especially when comparing different samples of lymphocytes. Conditions for doing this simply in small volumes are now available for culturing, thymidine pulsing, harvesting and analysis of data.

Cell Division↗
PubMed1978

Study of regional cerebral metabolism and blood flow relationships in man using the method of continuously inhaling oxygen-15 and oxygen-15 labelled carbon dioxide.

A new technique for assessing regional oxygen use and blood flow has been applied to a wide range of neurological patients. The method couples the brain's high metabolic demand for oxygen with a shortlived radioactive form of this metabolite, namely oxygen-15 (half life: 2.1 min). This combination produces during the continuous inhalation of either molecular oxygen-15 or labelled carbon dioxide, steady state functional images of the brain which are relatively free of contribution from extracerebral tissues. These are complementary images in that they relate to regional oxygen uptake and blood flow and hence offer a direct insight to the regional demand-to-supply relationships within the brain in physiological and pathological conditions. In the clinical groups studied, metabolic and circulatory defects were observed and instances of cerebrovascular insufficiency and relative luxury perfusion were defined which hitherto have been deduced from indirect methods. The clinical acceptability of this non-invasive approach allowed us to study those categories of patients which normally do not warrant invasive examination.

Adult↗
PubMed1978

The electrocardiogram of Macaca fascicularis.

Electrocardiograms from 16 male cynomolgus monkeys (Macaca fascicularis) were studied. Standard and augmented limb leads (I, II, III, aVR, aVL, aVF) were obtained with the animals restrained in a sitting position. Normal electrocardiographic parameters were determined, including PR and QT intervals; P, QRS, and T wave axes; P and QRS wave widths. Voltages in all standard and augmented limb leads were lower than previously reported for similar size monkeys.

Animals↗
PubMed1976

Enterovirus infections in neonates.

Twenty-seven ill neonates with enterovirus infections were studied to learn if enterovirus infection can be distinguished from neonatal sepsis. Enterovirus infection was associated with the summer-fall season (93%), recent maternal illness (59%), absence of other perinatal problems (81%), and findings of fever (93%), viral meningitis (62%), diarrhea (81%), and rash (41%). Four children developed thrombocytopenia and three necrotizing enterocolitis. Three children died, all with Coxsackie B virus infections that likely were acquired in utero. Although no single feature is pathognomonic, this constellation of epidemiologic and clinical findings, coupled with negative bacterial cultures, should suggest the possibility of neonatal enterovirus infection.

Bacterial Infections↗
PubMed1976

Colposcopic management of abnormal cervical cytology during pregnancy.

A total of 104 pregnant patients with abnormal cervical cells were referred to the Dysplasia Clinic for evaluation and management by colposcopy. Seventy-one pregnant patients presenting with basal cell atypia on cytologic examination had colposcopically directed biopsy revealing 8.45% severe dysplasia and 1.41% carcinoma in situ. Cytologic study in 31 pregnant patients with basal cell dysplasia revealed severe dysplasia in 29% and carcinoma in situ in 12.9% of the colposcopic biopsies. Cervical cytology revealed carcinoma in situ in two patients. Directed biopsy in both cases revealed carcinoma in situ with one case of questionable microinvasion. Colposcopically observed normal and abnormal physiologic findings and the pregnant cervix, complications after conization during pregnancy, and the impact of colposcopy in the management of the cytologically abnormal cervix during pregnancy are discussed.

Adult↗