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Biomedical subjects

W M Gray

Publications and source records attributed to W M Gray.

At least 37 records · Page 2Linked to original sources
PubMed1989

Automatic control of neuromuscular block with atracurium.

We have developed and tested a system for providing automatic control of neuromuscular block with atracurium. The degree of neuromuscular block was monitored in the small muscles of the hand using a Datex Relaxograph, and the signal was used as the controlled variable for a proportional plus integral controller. A preloaded integral was used to shorten the period of stabilization. The system was tested in 36 patients undergoing surgery and found to produce stable block. For a target T1 of 20% of control value, the mean block was 18.7 (SD 1.3) % of baseline T1 and the mean consumption of atracurium was 5.39 (SD 1.23) micrograms kg-1 min-1. The block was sufficiently stable to act as a background for studies of pharmacological and physiological interactions with atracurium.

Adult↗
PubMed1989

Occupational exposure to nitrous oxide in four hospitals.

Diffusive samplers were used to measure the exposure of the anaesthetist, anaesthetic assistant and circulating nurse to nitrous oxide in every operating theatre of four Glasgow hospitals. Each theatre was surveyed over 1 or 2 weeks; samples were taken during every operating session. The exposures were in general surprisingly high. The anaesthetist's exposure was greater than ppm on about half the occasions. The study underlines the need for theatre ventilation systems and scavenging equipment to be properly maintained and for scavenging facilities to be used effectively. It is concluded that regular monitoring of staff exposures is required to check the effectiveness of antipollution measures.

Environmental Exposure↗
PubMed1988

Measurement of arterial pressure using catheter-transducer systems. Improvement using the Accudynamic.

The dynamic performance of arterial manometers depends upon the values of the natural frequency fo and the damping factor beta. Satisfactory reproduction of all arterial waveforms requires that fo should be greater than about 13 Hz; for an fo of 13 Hz, beta should have a value of 0.5, but, as fo increases, an increasing range of beta values is permissible. We measured fo and beta for two pressure transducers (Gould P23 Statham and Gould Disposable) in combination with Portex or Gould catheter tubing of lengths varying from 100 cm to 300 cm. All combinations were considerably underdamped, with the best having an fo of 30 Hz and a beta of 0.1. We also investigated the performance of a commercial device, the Accudynamic, designed to allow beta to be increased without affecting fo. We found that the Accudynamic worked well, allowing acceptable performance to be obtained from the Gould Disposable transducer with catheters up to 200 cm in length.

Blood Pressure Determination↗
PubMed1988

Long-term performance of Tec vaporizers. Basis for a rational maintenance policy.

We reviewed the maintenance records of Tec vaporizers which had been in clinical use for up to 4 years. Tec 4s and Enfluratec 3s were found to be extremely reliable, but Fluotec 3s suffered progressively from mechanical and calibration problems. Their most recurrent fault was sticking valves caused probably by thymol crystallizing on the valve faces. This fault did not occur with Fluotec 4s, which are designed to prevent liquid agent reaching the valve surfaces. We found, in a study of the effects of thymol accumulation, that only occasional draining of a Fluotec vaporizer is required to keep thymol concentration below the level at which its output is reduced. We conclude that, if regular field calibration checks are carried out as a safety measure, the service interval for Tec vaporizers could be extended beyond Ohmeda's present recommendation of one year.

Anesthesia, Inhalation↗
PubMed1988

Dependence of the output of a halothane vaporizer on thymol concentration.

The effect of thymol accumulation inside a Fluotec 3 vaporizer on the concentration of halothane delivered by the vaporizer was investigated. The vaporizer output was reduced progressively as the thymol concentration increased, but the reduction was less than that predicted by Raoult's Law. A reduction of 5% in output required an increase in thymol concentration of a factor of 650 compared to the concentration in fresh halothane, while a reduction of 10% required a 1100-fold increase in thymol concentration. The equilibration of the thymol from the wicks throughout the vaporizing chamber was very slow after the vaporizer was drained and filled with fresh halothane; the half-time was 2.7 days.

Anesthesia, Inhalation↗
PubMed1986

Exposure of midwives to nitrous oxide in four hospitals.

The exposure of midwives to nitrous oxide in four hospitals was measured with personal samplers. In three of the four hospitals the average exposure was not significantly less than 100 parts per million (ppm). In one hospital the average exposure was 360 ppm; this was reduced by a factor of about 2.5 when a trial scavenging system was used. Differences in working practices and in the layout, size, and ventilation of the labour suites contributed to the observed differences in average exposure. Midwives and other staff working in the labour room are potentially at risk from excessive occupational exposure to nitrous oxide.

Anesthesia, Obstetrical↗
PubMed1986

A static calibration method for the gas chromatographic determination of per cent concentrations of volatile anaesthetic agents.

A method is described for preparing static standards of per cent concentrations of volatile anaesthetic agents, that is designed to minimize adsorptive losses in the container used for the standards. The extent to which this aim has been realized was investigated for atmospheres of halothane, enflurane and isoflurane, both by monitoring the relative concentration within the container over a period of 30 min after the standard was prepared, and by measuring the absolute concentration of the volatile agents. Gas chromatography was used for both sets of measurements, with liquid standards being used for the absolute measurements. No discernible loss of volatile agent occurred over the 30-min period, and the measured concentrations agreed closely with the predicted values. The standard mixtures prepared by the method were suitable for calibrating a gas chromatograph, and allowed accurate determinations of volatile anaesthetics to be made. The relative standard error of the predicted concentration for a single standard mixture was less than 0.5%, and the calibration accuracy could be further improved by taking the mean chromatograph response to several standard mixtures prepared in succession.

Anesthetics↗
PubMed1986

An evaluation of the Datex Normac anaesthetic agent monitor.

A new monitor for volatile anaesthetics, the Datex Normac, was assessed in the laboratory and operating theatre. The instrument had a warm up time of 90 minutes from cold, but only 5 minutes from standby. Zero drift was less than 0.01% over 7 hours, and repeated measurements of gain showed a coefficient of variation of less than 1%. However, gain drift of 6% occurred when the instrument was switched off between periods of use. Signal noise was less than 0.02 vol% on a new instrument, but was about six times greater on an instrument that had been in use for a year. The response time of 550 ms is short enough to allow breath by breath monitoring. When the instrument was calibrated on the enflurane setting, measurements made on the enflurane, halothane and isoflurane settings were accurate to within 6% of the reading. This is satisfactory for clinical purposes, but not for more demanding applications. Calibration canisters are available, and two that we tested were accurate to better than 0.1 vol%. Nitrous oxide, carbon dioxide and water vapour have very small effects on the monitor. The instrument provided trouble-free monitoring in theatre.

Anesthesia, Inhalation↗
PubMed1986

A critical appraisal of a rapid radiographic method of determining total lung capacity.

We have demonstrated that the total lung capacities of normal caucasian adults, can be satisfactorily estimated by means of a regression equation derived from a single set of three measurements taken from a specially exposed plain X-ray film of the chest. However, these equations differ from those found by workers who have studied patients with lung disease. It is concluded from this that different regression equations are to be expected for normal and diseased lungs, and that, the appropriate equation will depend not only on the presence of disease, but also on its type and severity. It is also concluded that the rapid radiographic method of estimating total lung capacity can make little contribution to the diagnostic assessment of lung disease. However, the regression equations appropriate to particular ethnic groups could be used to measure TLC in normal subjects rapidly and inexpensively in places where specialised respiratory equipment and trained personnel are lacking.

Adult↗
PubMed1986

Formal operations, the imaginary audience and the personal fable.

One hundred twenty-nine 6th, 8th, 10th/11th, and 12th graders were administered Enright, Lapsley, and Shukla's Adolescent Egocentrism Scale (AES) and How Is Your Logic?, a Piagetian-based, group-administered, written test of cognitive development. A series of ANOVAs on four scales of the AES (imaginary audience, personal fable, self-in-general, nonsocial) provided partial support for Inhelder and Piaget's, and Elkind's views that adolescent egocentrism is a function of beginning formal operations. Discussion focused on the difficulty of assessing the true thoughts/feelings of persons who are worried how they will appear to others.

Adolescent↗
PubMed1985

Nitrous oxide and wound healing.

Following a paravertebral surgical incision, mature, female rats under ether anaesthesia were exposed to either 3% nitrous oxide, continuously for 48 h, or 50% nitrous oxide, 4 h each day for 7 days. For each exposure group, a similar number of rats was exposed to atmospheres containing no nitrous oxide. Wound healing was assessed by measurement of the breaking strengths of wound samples. No statistically significant influence on breaking strength could be attributed to nitrous oxide following either exposure sequence.

Animals↗
PubMed1985

The evacuated canister method of personal sampling. An assessment of its suitability for routine monitoring of operating theatre pollution.

Although there is a recognised need for routine monitoring of the exposure of operating theatre staff to waste anaesthetic gases, there is as yet no standard method for carrying out such measurements. We have assessed a commercial version of one proposed sampling system--the evacuated canister--by testing it in the laboratory and also using it to carry out pilot surveys in operating theatres. We encountered many difficulties in using the system; some of these were caused by design faults in the commercial equipment, but others are inherent in the concept of using an evacuated canister for personal sampling.

Air Pollutants, Occupational↗
PubMed1984

Calibration atmosphere generator for operating theatre pollution studies. A system for the controlled production of trace concentrations of inhalation anaesthetics.

The design and performance of an apparatus for producing accurately known trace concentrations of anaesthetic agents in air is described. The generator was constructed to facilitate the testing and calibration of equipment used in measuring the personal exposure of operating theatre staff to waste anaesthetic gases, and operates on the principle of the controlled injection of the pure anaesthetic agent into a diluting air stream. It is compact, simple to construct and easy to operate. Furthermore, it has a short stabilization time and can provide a wide range of predetermined concentrations with very good repeatability. It appears to be considerably more flexible than systems which have been described previously and should be of interest to groups involved in monitoring pollution in the operating theatre.

Air Pollutants, Occupational↗
PubMed1984

Medishield AGS system and servo 900 ventilators. Investigation and remedy of hazard caused by defeat of 'low expired minute volume' alarm.

The use of the new Medishield anaesthetic gas scavenging system with ventilators in the Siemens-Elema Servo 900 series was investigated. It was discovered that this combination of equipment creates the hazard that a disconnexion in the patient breathing system may not be detected by the ventilator alarm. This happens because the suction generated by the scavenging system draws a considerable flow of room air through the expiratory system of the ventilator when a disconnexion occurs. Possible solutions to the problem were investigated, and it was discovered that the problem can be overcome by applying a small amount of positive end-expiratory pressure to counteract the suction from the scavenging system.

Air Pollution↗