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Biomedical subjects

C L Merlet

Publications and source records attributed to C L Merlet.

4 recordsLinked to original sources
PubMed1971

Maternal hyperventilation and foetal hypocapnia in sheep.

1. In anaesthetized foetal lambs near term, hypocapnia induced by maternal hyperventilation abolished the rise of arterial pressure and femoral vasoconstriction caused by hypoxaemia. This is consistent with interaction of P(CO2) and P(O2) on the foetal aortic bodies.2. In immature lambs (0.6-0.77 of term) maternal hyperventilation caused a fall in foetal carotid P(CO2) commensurate with that in the maternal blood. In mature lambs (at 0.9 or more of term) the fall in foetal carotid P(CO2) was less than that in maternal blood, whether the foetus was exteriorized or in utero.3. The mean transplacental gradient for P(CO2) (maternal arterial-umbilical vascular), when the foetus was replaced with a mechanical pump recirculating foetal blood, was 6.3 mm Hg. This is attributed to placental CO(2) production, and is nearly half the mean P(CO2) gradient (maternal artery-foetal carotid) of about 14 mm Hg during normal maternal ventilation.4. The mean maternal-umbilical transcotyledonary venous gradients (avoiding vascular shunts through the myometrium and intercotyledonary chorion) were for P(CO2) 1.7 mm Hg and for P(O2) 13.4 mm Hg.5. Maternal hyperventilation (P(a, CO2) approximately 20 mm Hg) caused a small fall in mean foetal carotid P(O2) (5 mm Hg), which was readily reversible with no evidence of progressive acidaemia.

Animals↗
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↗