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Biomedical subjects

M K Sykes

Publications and source records attributed to M K Sykes.

At least 19 recordsLinked to original sources
PubMed1992

Effect of ventilation with positive end-expiratory pressure on the development of lung damage in experimental acid aspiration pneumonia in the rabbit.

Sixteen anaesthetized rabbits were subjected to tracheostomy and lung damage produced by the instillation of 4.5 ml/kg hydrochloric acid (pH 1.5) into the trachea. Half of the animals were ventilated with a positive end-expiratory pressure (PEEP) of 3 cmH2O and half with a PEEP of 10 cmH2O for 5 h, the mean airway pressure being kept at 12 cmH2O by adjustment of the end-inspiratory pause time. Pressure-volume curves were recorded every hour. Although the arterial PO2 values and compliance above the inflection point on the pressure-volume curve were greater in the group submitted to 10 cmH2O PEEP, there were no significant differences between the groups in terms of survival and histological findings.

Animals↗
PubMed1992

In vitro performance test system for pulse oximeters.

An in vitro system was developed capable of testing the accuracy and reproducibility of pulse oximeter readings. The pulse oximeter probe receives signals through a pulsating blood cuvette. The development of the design of the cuvette is described. Using the final design (or 'model finger'), a comparison is made between readings from a Datex Satlite pulse oximeter (SpO2) and saturation values obtained by use of a multi-wavelength bench oximeter (SaO2). Linear regression analysis of the data gives SpO2 = 0.88 SaO2 + 11.2 (r = 0.979, p < 0.001).

Fingers↗
PubMed1992

Response of 10 pulse oximeters to an in vitro test system.

Pulse oximeters are often used in situations in which severe hypoxaemia may occur. We have developed an in vitro system to test the accuracy of pulse oximeter calibration. The probe of 10 different oximeters was attached to a model finger in an in vitro blood circuit, and pulse oximeter readings (SpO2) were compared with multi-wavelength in vitro oximeter readings (SO2) over a range of SO2 values from 50 to 100%. The oximeters tested varied widely in their accuracy and linearity. We conclude that the system can test the accuracy, reproducibility and linearity of response of pulse oximeter readings at low oxyhaemoglobin saturations.

Calibration↗
PubMed1992

An evaluation of the Brüel and Kjaer monitor 1304.

A laboratory evaluation was performed on the Brüel and Kjaer multigas monitor 1304, incorporating a pulse oximeter. The instrument was tested for accuracy, stability, response and delay times, frequency response and the effects of water vapour, alcohol, cyclopropane and sevoflurane. The instrument's performance was found to be within or very close to the manufacturer's specifications for accuracy, stability and response and delay times. It was unaffected by water vapour and alcohol and the effect of cyclopropane on the vapour channel was lower than has been reported for other analysers. The response to sevoflurane was of the same order as that of the other vapours. A 90% response to square wave changes of gas composition was maintained up to 60 breaths.min-1 for CO2, O2, and N2O and up to 40 breaths.min-1 for the vapours when the nafion sampling tube was used.

Anesthesia, Inhalation↗
PubMed1991

Tracheal tube resistance and airway and alveolar pressures during mechanical ventilation in the neonate.

The relationship between peak airway pressure, alveolar pressure and respiratory frequency was calculated for the range of compliances and airway resistances which might be encountered during mechanical ventilation of a 3-kg neonate. The pressure/flow relationships of 2.5, 3.0, 3.5 and 4-mm tracheal tubes were determined at a series of flows from 0.5 to 4 litres/minute. Peak airway and alveolar pressures were then measured at various frequencies and inspiratory:expiratory ratios with the tubes incorporated in a model lung. Large differences between peak airway and alveolar pressures developed when frequency was increased or inspiratory time decreased; the differences were greatest with the smaller tubes. Shortening expiratory time by increasing the frequency or altering the inspiratory:expiratory ratio resulted in increased end-expiratory pressure because of incomplete emptying of the lung.

Airway Resistance↗
PubMed1990

Delayed detection of hypoxic events by pulse oximeters: computer simulations.

There is a variable delay between a reduction in alveolar PO2 and the decrease in arterial oxygen saturation recorded on a pulse oximeter. The decrease in arterial oxygen saturation in response to disconnexion of a paralysed patient from the breathing system, oxygen supply failure with continued mechanical ventilation and disconnexion of the fresh gas supply to Mapleson D and circle absorption breathing systems were studied by simulations on the MacPuf computer model of the cardiorespiratory system. The simulations revealed that there were marked differences between the rate of arterial desaturation which resulted from each of the three types of oxygen supply failure and that arterial oxygen saturation may reach dangerous levels before a pulse oximeter alarm is activated.

Computer Simulation↗
PubMed1989

A randomized comparison of total extracorporeal CO2 removal with conventional mechanical ventilation in experimental hyaline membrane disease.

Apnoeic oxygenation (AO) combined with extracorporeal CO2 removal (ECCO2R), using venovenous perfusion across a membrane area of 0.1 m2 has been shown to be feasible in six healthy anaesthetized rabbits. In a further twelve rabbits, ECCO2R has been randomly compared with conventional mechanical ventilation (CMV) following saline lavage to induce respiratory failure. Blood gases were maintained for up to 6 h within the same range (PaO2 = 8-20 kPa, PaCO2 = 4-6 kPa) in two groups of six by varying airway pressures and the oxygen fraction delivered either to the membrane lung (ECCO2R group) or to the ventilator (CMV group). The influence of single hourly sustained inflations (SI) on oxygenation was studied. ECCO2R subjects remained stable and survived. CMV subjects deteriorated and had 80% mortality. Hyaline membranes were absent from ECCO2R subjects and present in all CMV subjects. The response to SI suggests that a lung volume recruitment is maintained during AO for up to 1 h but is ineffective during CMV.

Animals↗
PubMed1989

A new microprocessor-controlled anaesthetic machine.

This paper describes the development of a microprocessor controlled anaesthetic machine comprising an integrated anaesthetic apparatus and monitoring system. Following prolonged reliability trials in the laboratory, changes have been made to major components which were described in earlier publications.

Anesthesiology↗