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Biomedical subjects

R Shannon

Publications and source records attributed to R Shannon.

At least 91 records · Page 5Linked to original sources
PubMed1975

Respiratory frequency control during external elastic loading and chest compression.

Experiments were conducted to determine if extravagal (i.e. chest wall) respiratory mechanoreceptors are involved in the control of respiratory frequency during steady-state external elastic loading (EEL) and chest compression (CC) in the anesthetized (Dial), vagotomized cat and dog. Frequency versus PaCo2 curves obtained by breathing CO2 mixtures were compared with curves obtained during elastic loading and chest compression. There was no significant difference between the CO2 and EEL curves in cats or dogs indicating there is no extravagal mechanoreceptor information contributing to the control of respiratory frequency during EEL. Comparison of curves obtained with chest compression and CO2 breathing show that dogs respond to chest compression with an extravagal (i.e. involving chest wall mechanoreceptors) neural reflex increase in frequency.

Animals↗
PubMed1975

Distribution of levels of penicillin resistance among freshly isolated strains of N. gonorrhoeae. Application of a novel sensitivity assay.

A novel diffusion zone method of quantitative assay of the antibiotic sensitivity of bacterial strains was tested on freshly isolated gonococci. Smoothly variable estimates of the minimum inhibitory concentration of penicillin for these strains was obtained with sufficient accuracy and precision (coefficient of variation c. 10 per cent.) by means of a simple graphical analysis and without replication. Such estimates were free from the chief sources of error associated with the commonly applied 'incorporation' and 'diffusion' methods. The method revealed that 816 isolates of gonococci obtained in the Bristol area during a 6-month period fell into a large 'sensitive' group (MIC c. 0.02 unit per ml.) and three smaller more resistant groups, and that this pattern occurred in three widely spaced centres within the area. It is suggested that the method is capable of revealing details of distribution that may be masked by the usual techniques and that it is of wide applicability.

England↗
PubMed1973

Reversibility of the specific adsorption of colicin E2-P9 to cells of colicin-sensitive strains of Escherichia coli.

The adsorption of colicin E2-P9 to its specific receptors on cells of sensitive strains of Escherichia coli is reversible under normal experimental conditions. At temperatures above 20 C, colicin may desorb from one cell and be readsorbed by a second with potentially lethal consequences. However, desorption of colicin seems unable to rescue a cell once it has received a lethal dose. These findings have implications both for the nature and types of specific receptors, and for the assay of colicin by the survivor count (lethal unit) methods.

Adsorption↗
PubMed1967

Kinetics of lethal adsorption of colicin E-2 by Escherichia coli.

The kinetics of lethal adsorption of colicin E2 by Escherichia coli C6 were studied by means of survivor plots. These were determined by a method which allowed rapid sampling of the reaction mixture and estimation of approximate confidence limits for the plotted data. The results were consistent with the predictions of a hypothetical model that assumed a single-hit mechanism of colicin action upon a bacterial population whose cells varied in their number of specific (lethal) receptors for colicin. The possibility of nonlethal adsorption is discussed.

Adsorption↗
PubMed1966

Daily penicillin serum concentrations following injection of 2.4 mega-units of "all purpose" penicillin.

In order to investigate the reliability with which a given dose of benzathine penicillin will result in predictable ranges of penicillinaemia on any particular day during the week after injection, ambulant adult males were injected with 2 400 000 IU of "all-purpose" penicillin (600 000 IU potassium penicillin G, 600 000 IU procaine penicillin G and 1 200 000 IU of benzathine penicillin). Penicillin serum assays were performed, 24 each day, from the third to the seventh day after injection (120 assays in all).Statistical evaluation of the results showed that the means of the groups of 24 assays fell within narrow ranges, indicating that the long-acting component (benzathine penicillin) gives reliable daily ranges in a high proportion of cases. The results of a previous trial, using half the present dosage (1.2 mega-units of "all-purpose" penicillin) were compared statistically with those of the present trial. A very satisfactory degree of correlation between dosage and resulting daily serum concentration was observed-in general double the dose yielded double the daily concentration. The many factors which affect absorption rate are discussed and it is suggested that preparations which depend on an oily gel to delay absorption add an avoidable factor to the list of variables which may play an important part in producing the significant differences in serum levels commonly reported after the use of PAM preparations. The narrow ranges of penicillinaemia observed after 1.2 mega-units and 2.4 mega-units of benzathine penicillin and the degree of correlation observed in general between dose and resulting serum levels suggest that a large-scale controlled series of parallel trials should be undertaken to compare the relative long-acting qualities of PAM and benzathine penicillin.

Adult↗