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Biomedical subjects

B V Lewis

Publications and source records attributed to B V Lewis.

At least 55 records · Page 3Linked to original sources
PubMed1969

Prolonged labour.

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Anesthesia, Obstetrical↗
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

Maternal placental and myometrial blood flow in the pregnant rabbit.

1. In anaesthetized rabbits 27-29 days pregnant (term is 31 days) uterine blood flow was measured in an extracorporeal loop between a carotid and the central end of an external iliac artery, the descending aorta and its other branches being tied. Mean flow was 45 +/- 2 ml. min(-1), or 105 +/- 4 ml. min(-1) per kg uterus and contents in thirty-four litters.2. The partition of uterine blood flow to placentas ( approximately 60%), myometrium ( approximately 27%) and vagina ( approximately 13%) as estimated by injection of isotopelabelled microspheres of 35 or 50 mu diameter, was similar in intact rabbits and in those with an extracorporeal loop.3. Maternal blood flow was greater to the placentas of larger foetuses both absolutely and per unit placental weight. Flow to the placentas of dead foetuses was much less than to those of live foetuses, but flow to the adjacent myometrium was not decreased.4. Maternal hypoxaemia (P(a, O2) approximately 40 mm Hg) caused vasoconstriction in the uterine vascular bed after 3-4 min. The distribution of blood flow within the uterus was altered, the placental fraction falling to 32%. This was unaffected by carotid denervation.5. These observations suggest that there are large differences in the physiological control of maternal blood flow to the placenta, myometrium and vagina.

Animals↗
PubMed1968

Vasomotor responses in the hind limbs of foetal and new-born lambs to asphyxia and aortic chemoreceptor stimulation.

1. Hind limb blood flow was measured in lambs of from 91 days gestation (delivered by Caesarean section) to 1 month after birth (term is about 147 days), under chloralose anaesthesia. Vascular resistance/100 g wet wt. increased progressively with age. There was reflex femoral vascular tone from the earliest age studied, as shown by vasodilatation on cutting the sciatic nerve.2. On asphyxia by cord occlusion reflex femoral vasoconstriction began earlier and was somewhat greater in older foetal lambs. At all ages, and after denervation of the hind limb, there was vasodilatation after local ischaemia, and a vasoconstriction of delayed onset during asphyxia attributed to release of noradrenaline into the circulation. The vasoconstrictor effect of noradrenaline in immature lambs was at least as great as at term or in the new-born.3. Injections of minimal effective doses of cyanide were used to localize possible chemoreceptor sites in foetal lambs. Injection into the left atrium caused a rise of arterial pressure, femoral vasoconstriction and a complex change in heart rate (usually bradycardia) but rarely any respiratory movement. After atropine, cyanide caused a large tachycardia. All responses were much reduced or abolished by cervical vagotomy.4. Injection of the same doses of cyanide into a jugular vein, the right ventricle, pulmonary or common carotid arteries of foetal lambs caused negligible cardiovascular or respiratory effects, whereas injection into the carotids of new-born lambs caused a profound hyperpnoea.5. It is concluded that the aortic chemoreceptors are active in the foetus, are supplied from the left heart, and that they probably represent the primary defence in blood gas homeostasis by their effects on the circulation.

Acetylcholine↗
PubMedDate not supplied

Treatment of menorrhagia by radiofrequency heating.

A new technique is described for the treatment of menorrhagia by heating the whole of the endometrial cavity of the uterus. A capacitively coupled probe at 27.12 MHz is inserted into the uterine cavity, which causes the basilis layer to be raised to approximately 50-55 degrees C whilst the rest of the pelvic contents remain at approximately normal (body) temperature. A major advantage of the method is that no special hysteroscopic skills are required, unlike the two other techniques currently used for endometrial ablation: the Nd-Yag laser or the hysteroresectoscopic loop. Also no toxic flushing/distension fluids are necessary, as are required for all hysteroscopic surgery. The method, however, does require the application of a large amount of RF power to the probe and so care must be taken to position the probe correctly in order to prevent any serious complications. Of 32 patients given a single treatment at a power level of 550 W for 20 min, the 'success rate' was 84% with 31% becoming amenhorrhoiec and 53% showing significant reduction in menstrual bleeding. However, retreatment is possible and by this means, combined with improved treatment techniques, an even higher success rate could be achieved. In two of the earlier patients treated at 550 W a fistula was produced at the anterior vaginal wall which had to be surgically repaired. The probe was subsequently modified, since when this problem has not recurred. This new treatment approach offers an alternative to hysterectomy in the treatment of menorrhagia and may offer a number of significant advantages over methods currently used for endometrial ablation.

Adult↗