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Biomedical subjects

J R Laycock

Publications and source records attributed to J R Laycock.

13 recordsLinked to original sources
PubMed1988

Potency of atracurium and vecuronium at the diaphragm and the adductor pollicis muscle.

Train-of-four stimulation was applied to the ulnar and phrenic nerves in 18 adult patients anaesthetized with nitrous oxide and halothane in oxygen. The response of the adductor pollicis and the diaphragm were measured. Incremental doses of atracurium and vecuronium were given, with an infusion to replace drug lost by elimination or distribution. The mean (SEM) doses of atracurium associated with 50% and 90% depression of response to the first stimulation in the train-of-four (ED50 and ED90) were 90 (9) and 133 (10) micrograms kg-1 at the adductor pollicis, and 130 (9) and 245 (17) micrograms kg-1 at the diaphragm, respectively. The mean (SEM) ED50 and ED90 of vecuronium were 25 (2) and 38 (4) micrograms kg-1 at the adductor pollicis and 34 (3) and 58 (5) micrograms kg-1 at the diaphragm, respectively. The mean (SEM) ED50 ratios were 1.56 (0.16) for atracurium and 1.47 (0.16) for vecuronium. ED90 ratios were 1.93 (0.29) and 1.55 (0.17) for atracurium and vecuronium, respectively. It is concluded that both atracurium and vecuronium exhibit a similar degree of sparing of the diaphragm.

Adult↗
PubMed1988

The potency of pancuronium at the adductor pollicis and diaphragm in infants and children.

To measure the potency of pancuronium at the diaphragm and adductor pollicis in infants and children, train-of-four stimulation was applied to the ulnar and phrenic nerves under N2O-halothane anesthesia. The force of contraction of the adductor pollicis was measured and compared with the diaphragmatic electromyogram (EMG). Cumulative dose response curves were determined for pancuronium in 18 patients divided equally into three age groups: 0-1 yr, 1-3 yr, and 3-10 yr. The potency of pancuronium at both muscles decreased with increasing age (P less than 0.05), while the adductor pollicis:diaphragm potency ratio remained constant. The mean doses (+/- SEM) required to depress adductor pollicis first twitch responses by 90% (ED90) were 42 +/- 3.3 micrograms/kg in the 0-1-yr group, 47 +/- 4.2 micrograms/kg in the 1-3-yr group, and 62 +/- 4.1 micrograms/kg in the 3-10-yr group. Corresponding figures for the diaphragm were 70 +/- 4.3 micrograms/kg, 81 +/- 5.1 micrograms/kg, and 101 +/- 4.4 micrograms/kg, respectively. The ED90 ratios (diaphragm ED90/adductor pollicis ED90) in the three age groups were 1.69 +/- .07, 1.75 +/- .14, and 1.64 +/- .09, respectively. These results are consistent with similar rates of maturation of the diaphragm and the adductor pollicis muscles in infancy and childhood. Thus, train-of-four monitoring of the adductor pollicis is likely to overestimate the degree of neuromuscular blockade of the diaphragm in pediatric patients.

Aging↗
PubMed1986

Changes in brain surface oxygen tension during profound hypotension induced with sodium nitroprusside or adenosine in the sheep.

Brain surface oxygen tensions were measured, in sheep (n = 8), with a seven-barrelled mini-electrode polarized by sweep potentials. Mean arterial pressure was reduced to 30 mm Hg with either sodium nitroprusside or adenosine. At this value of mean arterial pressure, oxygen supply to cerebral tissue was impaired. There was no significant difference between the two agents in the degree to which the oxygen supply was reduced.

Adenosine↗
PubMed1986

Suxamethonium-induced hyperkalaemia following cold injury.

Within the space of 9 days, a 4-month-old baby requiring cardiac surgery was exposed to two periods of hypothermic circulatory arrest for surgery, and prolonged surface cooling postoperatively. At the end of this period, the administration of suxamethonium was associated with a marked rise in serum potassium.

Heart Defects, Congenital↗
PubMed1986

Psychomotor testing of on-call anaesthetists.

The critical flicker fusion frequency and choice reaction times of 16 on-call anaesthetists were measured between 1400 and 1600, at 2300 and at 0200 hours. Critical flicker fusion decreased between the afternoon and 2300; there was no further change between 2300 and 0200. No significant differences in choice reaction times were found on any of these different occasions.

Anesthesiology↗
PubMed1985

Hypovolaemia and healing in colonic anastomoses.

Colonic anastomotic leakage is more common following emergency resections than after elective operations. Transient hypovolaemia, which is more likely to occur during emergency surgery, has been shown to impair collagen metabolism in abdominal and skin wounds but its effect on colonic anastomotic healing has not been previously examined. Acute intra-operative loss of 10 per cent circulating blood volume in rats significantly impaired collagen concentration in both ileocolic (P less than 0.02) and colocolic (P less than 0.05) anastomoses measured on the third postoperative day. This degree of blood loss did not significantly affect early anastomotic strength. Hypovolaemia leads to tissue hypoxia, and this in turn may lead to impaired anastomotic healing. Measurement of tissue oxygen tension may predict poor healing by identifying inadequate intestinal perfusion. Colonic pTO2 measured in rabbits was significantly lower than in small bowel (37 +/- 18 mmHg versus 42 +/- 18 mmHg; P less than 0.001), and fell significantly in colon following 10 per cent blood loss (P less than 0.001). We conclude that adequate intra-operative fluid replacement during colonic resection and anastomosis is a prerequisite for successful healing.

Animals↗
PubMedDate not supplied

Sweep potential polarography and multiwire surface tissue electrodes.

A multitipped seven barrelled platinum electrode for brain surface oxygen measurements during neurosurgery is described. Its performance has been examined when employed under conditions of sweep potential polarography. Although there is no plateau within the oxygen polarogram, the electrode displays linear performance within the physiological range, gives reproducible results in practice, has an acceptable temperature coefficient and a fast response time.

Cerebral Cortex↗
PubMedDate not supplied

Effect of hypotension induced by ATP and adenosine on brain surface oxygen tensions in the sheep.

A multitipped oxygen electrode has been used to measure cortical surface oxygen tensions in the sheep. A histogram of the pattern of supply of oxygen to cortical tissue within the microcirculation during normal conditions is presented. Systemic arterial pressure was reduced to a mean of 30 mmHg with either Adenosine or ATP, and further oxygen tension measurements undertaken. The oxygen histogram was shifted to the left in these circumstances, and there was an increase in the frequency of occurrence of very low tissue oxygen tensions. This suggests that the use of these agents to induce profound hypotension may be associated with significant ischaemia within the microcirculation.

Adenosine↗
PubMedDate not supplied

Effect of carotid artery ligation and infusion of fluosol FC-43 emulsion on brain surface oxygen tensions.

In eight rabbits, the common carotid artery was ligated and multiple estimations of brain surface oxygen tension performed using a seven barrelled mini-electrode. In five rabbits ligation of the carotid artery resulted in impairment of cortical oxygenation. The remaining three rabbits showed no impairment in the supply of oxygen to the cerebral cortex after carotid occlusion. In the five rabbits who displayed a reduction in oxygen supply after carotid ligation, ventilation with 33% oxygen after the infusion of 15 ml/kg of Fluosol FC-43 produced an improvement in cortical oxygenation in only three of the five rabbits. When these animals were ventilated with 100% oxygen after carotid ligation and Fluosol infusion, oxygen supply in all five was commensurate with or greater than that during control conditions.

Animals↗