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Biomedical subjects

J B Owen-Thomas

Publications and source records attributed to J B Owen-Thomas.

At least 19 recordsLinked to original sources
PubMed1975

The estimation of carbon dioxide concentration in the presence of nitrous oxide, using a Lloyd-Haldane apparatus.

A method of gas analysis is described for estimating carbon dioxide in the presence of nitrous oxide, using a modified Lloyd-Haldane apparatus. Some of the sample, after scrubbing with soda-lime, bubbles through the potash and this eliminates the solubility effect of nitrous oxide by equilibrating the standard potash solution with nitrous oxide at the tension of the sample analysed and eliminating absorption of nitrous oxide from the burette. The results show close agreement with another apparatus and method based on different principles. The method is absolute, requiring neither empirical nor theoretical correction.

Carbon Dioxide↗
PubMed1975

A paramagnetic method for measuring the carbon dioxide concentration of a gas.

A paramagnetic method of carbon dioxide analysis enables the simultaneous analysis of carbon dioxide and oxygen to be made at 2-min intervals. The method depends upon observing the change of oxygen concentration in a gas mixture before and after absorbing the carbon dioxide component. The carrier-gas in the experiments reported was nitrogen. The output of the paramagnetic meter was measured both by a digital voltmeter and by a chart recorded and the carbon dioxide concentrations calculated from these observations (Y1% and Y2% respectively) were compared with those obtained by Lloyd-Haldane (x%) gas analysis, for carbon dioxide concentration of 2-20% in a range of oxygen concentrations of about 9-90%. The agreement between paramagnetic and Lloyd-Haldane carbon dioxide analysis is shown in the following linear regression equations: Y1=0.996x-0.001 (r=0.9999+/-0.04 SEM of estimate; P less than 0.001); Y2=0.997x-0.006 (r=0.9999+/-0.06 SEM of estimate; P less than 0.001). Carbon dioxide in nitrogen was measured by the prior addition of an arbitrary concentration of oxygen, to a gas sample. The method is applicable to the measurement of carbon dioxide and oxygen, when the carrier-gas may have characteristics which preclude the use of katharometer, infra-red or Haldane analysis.

Absorption↗
PubMed1969

Hypoxaemia and aortic chemoreceptor function in foetal lambs.

1. In foetal lambs the effect of raising and lowering arterial P(O2) (by varying the O(2) content of the maternal inspired gas mixture) was studied in order to determine whether the systemic arterial chemoreceptors regulated the circulation.2. From 0.7 of term relative hypoxaemia (e.g. reducing carotid P(O2) from 40 to 20 mm Hg) caused a rise of arterial pressure and femoral vaso-constriction. These changes were unaffected or even increased by bilateral section of the nerves from the carotid sinus and body. They were abolished by section of the vagi or aortic nerves.3. It is concluded that in foetal lambs during the last third of gestation the circulation is under reflex control by the aortic chemoreceptors.

Animals↗
PubMed1969

Cyanide stimulation of the systemic arterial chemoreceptors in foetal lambs.

1. In foetal lambs, delivered by Caesarean section under light chloralose anaesthesia, injection of sodium cyanide into the left atrium or ascending aorta caused a rise of arterial pressure and femoral vasoconstriction. The response to 0.77 mg/kg was barely present at 0.6 of term; by 0.8 of term there was a large response to one third of this dose.2. The cardiovascular response to cyanide injection into the left atrium or ascending aorta was diminished either by section of the vagi or by carotid denervation, and was abolished by cutting both sets of nerves.3. Injection of sodium cyanide into both common carotids simultaneously caused a substantial cardiovascular response and often a respiratory effort, abolished by carotid denervation, whereas injection into a single carotid rarely caused an effect.4. It is concluded that the carotid chemoreceptors in mature foetal lambs can be excited by a stimulus of sufficient intensity, even though they do not respond to moderate hypoxaemia.

Animals↗
PubMed1969

Hypoxia and pulmonary arterial pressure in the rabbit.

1. The effect of hypoxia on pulmonary arterial pressure was studied in young and adult rabbits.2. In isolated perfused lungs, hypoxia caused no rise in pulmonary arterial pressure in rabbits on the day of birth. The size of the hypoxic response increased progressively until 9-11 days of age, when the adult response of a 20% rise of pulmonary arterial pressure at constant flow was attained.3. The intact adult rabbit responded to hypoxia with a 14-30% rise in pulmonary arterial pressure, attributed to vasoconstriction and independent of frequency or tidal volume during positive pressure ventilation.

Age Factors↗