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Biomedical subjects

W W Mapleson

Publications and source records attributed to W W Mapleson.

At least 55 records · Page 3Linked to original sources
PubMed1992

A model lung with direct representation of respiratory muscle activity.

We describe the theory, construction and testing of an active model lung. This is designed so that when it is connected to a ventilator, the interaction between spontaneous ventilatory activity in the patient and the pressures and flows generated by the ventilator are reproduced faithfully. A waveform of negative pressure, pmus, equivalent to the action of the respiratory muscles, is applied indirectly to the compliance unit of a conventional model lung. It is shown that, when the compliance and resistance of a subject have been measured, the waveform of pmus can be determined. This was undertaken in three volunteers breathing under various conditions, including connection to a ventilator operating in different modes. When these conditions were reproduced with the lung model replacing, but matched to, each subject, the original waveforms of flow and pressure at the mouth were reproduced.

Adult↗
PubMed1991

Comparison of arterial and arterialized venous concentrations of propofol during infusion of propofol.

Seven patients received a series of low-dose propofol infusions designed to produce three successive pseudo-steady states of arterial blood concentration: 0.06, 0.17 and 0.43 micrograms ml-1. Arterial and arterialized venous blood samples were obtained simultaneously at the end of each infusion. The results indicate that 95% of the arterialized venous concentrations may be expected to lie within 1 +/- 43% of the corresponding arterial concentration, or -5 +/- 35% if one set of measurements with poor agreement between duplicate aliquots is omitted.

Arteries↗
PubMed1991

Effect of sub-anaesthetic infusions of propofol on peak velocity of saccadic eye movements.

Peak velocity of saccadic eye movements was studied in six healthy volunteers who received either 0.9% sodium chloride (as a control) or a stepwise rising propofol infusion regime of 0.24, 0.6 and 1.5 mg kg-1 h-1, which produced arterialized venous concentrations equivalent to 1%, 6% and 13% of the estimated EC50 for propofol. The infusion lasted for 75 min (25 min at each infusion rate) and was followed by a 2-h post-infusion recovery period. Peak saccadic velocity was highly significantly depressed during the 15-25-min period after the start of the second and third propofol infusions compared with saline. The relationship between arterialized venous blood concentration and peak saccadic velocity was similar during recovery when concentrations were falling to that during increasing blood propofol concentrations. Peak saccadic velocity decreased linearly with increasing log10 propofol concentration in the range of 25-800 ng ml-1 (14% of control per decade). Measured arterialized venous-blood propofol concentrations were variable, and systematically greater than computer predictions at the two higher infusion rates. In only half the subjects were the subjective assessments significantly correlated with log10 propofol concentrations or with percentage reduction in peak saccadic velocity.

Adult↗
PubMed1988

A comparison of oxygen therapy devices used in the postoperative recovery period.

Seventy-one patients scheduled to undergo upper or lower abdominal surgical procedures were allocated at random to one of seven treatment groups: in the recovery room they were to receive oxygen via a 40% Ventimask with 10 litres/minute oxygen flow, or via either a Hudson mask or a nasal cannula with 3, 6 or 9 litres/minute oxygen flow. The 40% Ventimask gave the most consistent, satisfactory postoperative values of PaO2 but the much cheaper nasal cannula at 6 or 9 litres/minute was generally adequate in conscious patients. The performance of the intermediately priced Hudson mask was similar to that of the nasal cannula at these flows. The unconscious state was associated with a 45% lower PaO2 than the rousable or awake states. Differences between the treatments with regard to postoperative PaCO2 were small and non-significant. The nasal cannula with 6 litres/minute humidified oxygen flow is recommended for routine treatment, and the Ventimask for unconscious patients.

Abdomen↗
PubMed1987

Computation of the effect of Donnan equilibrium on pH in equilibrium dialysis.

In equilibrium dialysis, with a nondiffusible, charged protein on one side of the membrane, Donnan equilibrium leads to a pH difference across the membrane. Therefore, with an ionizable drug, the concentration dissolved in water will be different on the two sides of the membrane to an extent dependent on the pH difference and the pKa of the drug. This must be allowed for in calculating the concentration bound to protein. This paper develops, with certain restrictions, a method of calculating the pH difference when the solutions contain electrolytes, acids, including CO2, and proteins. The method is applicable to pH differences across passive cell membranes.

Blood Proteins↗
PubMed1987

Minimum volume of discard for valid blood sampling from indwelling arterial cannulae.

The volume of discard for valid blood sampling from indwelling femoral (leader cath) and radial (Venflon) arterial cannulae (with internal volume of cannula plus connecting tubing of approximately 2 ml) was investigated by analysing sequential 2-ml aliquots of 10-ml samples. The aliquots were analysed for pH, carbon dioxide tension, oxygen tension, standard bicarbonate, haemoglobin concentration, haemoglobin oxygen saturation and potassium concentration. Analysis of variance showed that, for these variables and these catheters, a valid blood sample was obtained after discarding 4 ml, but not after only 2 ml. The haemoglobin concentration, as measured by a Corning oximeter, provided good warning of inadequate discard.

Analysis of Variance↗
PubMed1987

Comparison of temazepam elixir and trimeprazine syrup as oral premedication in children undergoing tonsillectomy and associated procedures.

Temazepam 0.5, 1.0 and 1.5 mg kg-1 in an elixir formulation (Euhypnos Elixir), was compared with trimeprazine tartrate 3 mg kg-1 in a syrup (Vallergan Forte Syrup), as premedication in 220 children (ASA grade I) undergoing tonsillectomy and associated procedures. Each patient was randomly allocated to one of the four treatments. The administration was blind to the observers in theatre, recovery room and postoperative ward, who assessed each patient according to a total of 14 criteria. A modelling technique allowed account to be taken of the effects of concomitant variables (e.g. age and duration of anaesthesia) where appropriate. No statistically significant difference was found between the efficacy of the treatments. The only statistically significant differences were that temazepam was associated with more ectopic beats under anaesthesia (P = 0.03 or 0.002, depending on the test applied), more postoperative vomiting (P = 0.04) and more postoperative restlessness (P less than 0.0001).

Adolescent↗
PubMed1987

Additional blood-gas variables for the rational control of oxygen therapy. With allowance for shifts of the oxygen dissociation curve.

When a sample of arterial blood is analysed for oxygen tension and, using a modern oximeter, for haemoglobin concentration and saturation, it is possible to calculate the position of the oxygen dissociation curve and two new variables: "P95" and "C(a-x)O2". P95 is the tension at which the haemoglobin would be 95% saturated and can, therefore, constitute a target tension for near-maximum arterial content of oxygen. C(a-x)O2 (the "conditional extraction" of oxygen) is the amount of oxygen, in ml/dl blood, which can be extracted from the arterial blood for a hypothetical mixed-venous oxygen tension PxO2. It is explained how it is possible to estimate the adequacy of tissue oxygenation by comparing any available estimate of the required extraction (normally about 5 ml dl-1) with conditional extractions calculated for three hypothetical values of PxO2 covering the clinical range. Methods of calculation are given. For accurate results at high arterial saturations, a peripheral venous sample may be required in addition to the arterial sample.

Cardiac Output↗
PubMed1986

Intracuff and "leak-past" pressures of red rubber, latex and p.v.c. tracheal tubes. A laboratory and clinical study.

Measurements were made in the laboratory of the changes with time of the intracuff pressure, the leak-past pressure (the airway pressure at which gas begins to leak past the cuff) and the cuff volume for 9.5-mm tracheal tubes: red rubber, latex (both Leyland Medical) and p.v.c. (Portex Blue Line). The cuffs were inflated with air and exposed to air or air with enflurane or halothane, usually for 90 min. Measurements of leak-past pressure with these tubes were also made for 75 min in patients whose lungs were ventilated with air and enflurane or air and halothane. The following conclusions can be drawn. Enflurane and halothane had little effect. The intracuff pressure always decreased, but the cuff material crept under the continuous stress, so that cuff volume changed little. The leak-past pressure actually increased over at least 75 min with the p.v.c. tubes, but decreased consistently with the red rubber and latex tubes.

Adult↗
PubMed1986

Respiratory function following nalbuphine and morphine in anaesthetized man.

In 40 patients anaesthetized with thiopentone, 66% nitrous oxide and 1% halothane, the effects of a single i.v. dose of nalbuphine 4.5, 8, 15, 25 or 50 mg/70 kg or morphine 3, 5, 10 or 17.5 mg/70 kg on total ventilation and end-tidal carbon dioxide concentration have been measured. Depression of respiration occurred with both drugs and with all doses. The lower doses of nalbuphine produced more depression than equianalgesic doses of morphine. Conventional equianalgesic doses produced similar degrees of depression. With the highest dose of morphine, respiratory impairment progressed to apnoea whereas, with nalbuphine, apnoea did not occur in any patient. With increasing dosage of nalbuphine there appeared to be a limit to the extent of respiratory depression. The highest dose of nalbuphine produced less depression than some lower doses, suggesting a reversal effect.

Adolescent↗
PubMed1986

Excessive work of breathing during intermittent mandatory ventilation.

Difficulties were experienced in weaning a patient from a ventilator by means of intermittent mandatory ventilation (IMV). The difficulty was overcome by installing an alternative IMV system (Hudson "disposable IMV valve") through which the patient drew her spontaneous breaths. Laboratory measurements showed that the resistance of the ventilator breathing system was much higher than that of the alternative system, mainly as a result of the resistance of the humidifier. It was calculated from measurements with a preset pattern of simulated breathing that the extra, external, work of breathing through the ventilator breathing system was approximately 1.5 times the normal internal mechanical work of breathing for a normal patient; with the alternative system, the extra work was only 0.5 times the normal. It is stressed that the breathing systems of IMV ventilators should be judged with the same rigour as other systems through which the patient is required to breathe spontaneously. It is recommended that manufacturers should provide the necessary information.

Aged↗
PubMed1985

Effect of premedication with controlled-release oral morphine on postoperative pain. A comparison with intramuscular morphine.

Thirty fit patients presenting for elective total hip replacement were randomly allocated to receive a premedication of 60 or 90 mg controlled-release oral morphine or 15 mg intramuscular morphine. Postoperative analgesia was assessed using on-demand intravenous pethidine supplementation requirements. In 15 patients free plasma morphine concentrations were measured. Both 60 and 90 mg controlled-release oral morphine led to a reduced pethidine requirement compared to the intramuscular group but the reduction was not statistically different.

Administration, Oral↗