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Biomedical subjects

J G Whitwam

Publications and source records attributed to J G Whitwam.

At least 73 records · Page 4Linked to original sources
PubMed1990

Aortic compression by the uterus: identification with the Finapres digital arterial pressure instrument.

Aortic compression by the uterus at term was diagnosed when reversible reductions in toe pulse pressure, measured using a Finapres digital blood pressure instrument, were found in the absence of systemic hypotension, monitored by a second instrument with the cuff on a finger. Aortic compression was found in the left or right pelvic tilt positions in 14 of 32 women, sometimes with up to 34 degrees of tilt, and was relieved by increasing the amount of tilt, except in a twin pregnancy where compression became more severe as left pelvic tilt was increased from 13 degrees to 28 degrees. Compression was also found in two women in the semi-recumbent position. Factors associated with an increased likelihood of aortic compression were non-engagement of the fetal head, occipito-posterior position of the fetal head, and cervical dilatation less than 5 cm.

Adult↗
PubMed1989

Circulatory depression with high peep in the surfactant-deficient rabbit.

Surfactant depletion was induced by lung lavage in 10 rabbits. Ascending aortic blood flow was measured at normocapnia at 0, 5 and 10 cm H2O PEEP before and after lavage. Aortic blood flow was reduced by PEEP, by a maximum of 24% before lavage and 60% after lavage. It was concluded that, although adequate arterial oxygenation can be maintained with 10 cm H2O PEEP in surfactant-depleted rabbit's lungs, the circulatory impairment may result in inadequate oxygen delivery.

Animals↗
PubMed1989

Crystalloid versus colloid for circulatory preload for epidural caesarean section.

Sixty mothers were randomly allocated to receive either 2 litres of crystalloid or 1 litre of colloid solution (hydroxyethyl starch) in order to preload the circulation prior to elective Caesarean section under epidural anaesthesia. There were no differences in the incidence of hypotension, degree of haemodilution, umbilical cord blood gas tensions or umbilical blood osmolalities between the two groups.

Adult↗
PubMed1989

Effect of sternotomy and cardiopulmonary bypass on airway pressures and respiratory mechanics during high frequency ventilation.

The airway pressures at ventilatory frequencies of 15, 60, 100, 120 and 150 breaths per minute were measured in eight adult patients undergoing coronary artery bypass grafting. Measurements were made perioperatively at four stages: precardiopulmonary bypass with the chest closed, precardiopulmonary bypass with the chest open, postcardiopulmonary bypass with the chest open and postcardiopulmonary bypass with the chest closed. In five patients thoracic compliance and airways resistance were also measured at these times. Neither sternotomy nor cardiopulmonary bypass made any significant difference to the airway pressures during normal and high frequency ventilation, nor were lung mechanics affected.

Airway Resistance↗
PubMed1988

Selective depression by alfentanil of group III and IV somatosympathetic reflexes in the dog.

The effect of alfentanil on sympathetic reflexes evoked by supramaximal electrical stimulation of the radial nerve has been observed in five dogs anaesthetized with alpha-chloralose, paralysed with suxamethonium and artificially ventilated. In five dogs during the infusion of alfentanil at a rate of 20 micrograms kg-1 min-1 the late long latency sympathetic response evoked by unmyelinated fibres (group IV, C) was abolished at a mean dose of 68.8 (SE 2.85) micrograms kg-1. The infusion rate was then increased to 200 micrograms kg-1 min-1 and the early, short latency response evoked by small myelinated fibres (group III, A delta) was eliminated at mean total dose of 809 (SE 72) micrograms kg-1. When the infusion was stopped the group III reflex returned within 1-5 min and recovery to approximately 50% of control for both reflexes occurred within 15-60 min in different preparations. Mean arterial pressure and mean heart rate decreased from 140 (6) mm Hg and 132 (11) beat min-1 to 100 (7) mm Hg and 70 (6) beat min-1, respectively, by the time the group IV response was eliminated; that is, after a mean infusion time of 3.4 min. Thereafter, there was no further cardiovascular depression. Within 3 min of the administration of naloxone 2 mg i.v., the sympathetic reflexes, arterial pressure and heart rate returned to within control values.

Action Potentials↗
PubMed1988

A new infant ventilator for normal and high-frequency ventilation: influence of tracheal tube on distal airway pressure during high-frequency ventilation.

A new infant ventilator for both normal and high-frequency ventilation is described. High pressure gas delivered via a jet in the breathing limb of a T-piece, in which there are no valves, drives respiratory fresh gas (RFG), supplied to the tracheal tube from any low pressure source, into the lungs. Observations on anesthetized rabbits showed that after setting up for a PaCO2 of 36 torr at 30 cycle/min, it remained around 36 torr when the ventilation frequency was progressively increased to 200 cycle/min. The mean peak proximal airway and tracheal pressures were 13 and 12, 11 and 7, and 13 cm H2O (PEEP 2.1 cm H2O) and 7.4 cm H2O (PEEP 3.1 cm H2O) at 30, 100 and 200 cycle/min, respectively. In this open valveless breathing system, desynchronized spontaneous and artificial ventilation occurred quietly without any marked variation in the airway pressures. This preliminary study on a new pneumatic system shows its potential for simplifying and improving infant ventilation.

Animals↗
PubMed1988

Intermittent high frequency ventilation: a new mode to measure changes in lung volume and alveolar gas concentration, enhance CO2 elimination and reduce intrapulmonary pressures.

A new method of artificial ventilation, intermittent high frequency ventilation (IHFV), is described in which high frequency ventilation (HFV) is intermittently interrupted so that short periods of ventilation and pauses in ventilation occur in sequence several times a minute. During the pauses in ventilation the increase in lung volume, which occurs during the short periods of HFV, is either exhaled completely or to a predetermined level which prevents sustained hyperinflation of the lungs but allows the maintenance of PEEP if required. The volume of gas expired during the ventilation pauses, i.e. gas retained during the periods of HFV, is measured. When this trapped gas is exhaled completely, the mean airway and compliance pressures are reduced by up to 50% compared to continuous HFV at the same frequency, inspiration:expiration (I:E) ratio and low tidal volume (VT). The alveolar CO2 concentration was measured in gas expired towards the end of the pauses in ventilation. CO2 elimination was improved, especially at high frequencies of ventilation, which allowed a further reduction in inflation pressures while maintaining a constant PaCO2.

Animals↗
PubMed1988

Assessment of a new valveless infant ventilator.

A new valveless ventilator, which uses an air jet to provide the driving force for positive pressure ventilation, was used on 13 newborn babies (10 of very low birthweight) who had severe respiratory disease. The ventilator differs from 'true' jet ventilators in that its driving gas does not take part in gas exchange. Functionally it is a pressure pre-set, time-cycled ventilator, whose performance is characterised by the rapid and precise maintenance of both inspiratory and expiratory airway opening pressure. All the babies had progressively worsening respiratory failure (mean values of arterial pCO2 were 9.46 kPa, with a pH of 7.14, and an inspired oxygen concentration of 92.5%) on conventional mechanical ventilation. On the new ventilator, with the same settings, there was a dramatic and highly significant improvement within 20 to 30 minutes (mean values of arterial pCO2 were 6.45 kPa, pH 7.26, and inspired oxygen concentration 85.7%). This improvement was maintained. The new ventilator represents an important advance in the management of babies with severe respiratory failure.

Carbon Dioxide↗
PubMed1987

Paroxysmal nocturnal haemoglobinuria. Peri-operative management of a patient with Budd-Chiari syndrome.

The peri-operative management of a patient with paroxysmal nocturnal haemoglobinuria and associated hypoplastic anaemia, who underwent successful elective surgery for the complication of Budd-Chiari syndrome, is described. Anaesthesia in patients with paroxysmal nocturnal haemoglobinuria should be based on drugs and materials least likely to cause complement activation. The reasons for use of a technique based on benzodiazepines, opioids, isoflurane and the avoidance of nitrous oxide are discussed.

Adult↗
PubMed1987

A new ventilator for closed breathing systems.

A new electronic ventilator for application during closed breathing system anaesthesia is described (OAV7700, Ohmeda). It is easy to use and can be mounted on any conventional anaesthetic machine. It has several desirable features, such as a simple control and display panel, appropriate alarms and a patient breathing system that can be autoclaved. Observations were made on seven patients undergoing major surgery. Anaesthetic gases were introduced at 1, 2 and 4 litres/minute at three points in the breathing system, one conventionally in the closed system, one at the ventilator and one in the tracheal tube. Carbon dioxide homeostasis was maintained during this procedure. The application of fresh gas flows of 2 and 4 litres/minute in the tracheal tube allowed a small but significant reduction in the mean tidal volume. However, it was concluded that a fresh gas flow of 1 litre/minute applied conventionally either into the closed system or at the ventilator, provided optimal conditions.

Aged↗
PubMed1987

High frequency ventilation and afferent vagal activity.

Recordings were made from pulmonary afferent fibres in the vagus nerves of anaesthetised dogs during conventional and high frequency ventilation. In single and multiple fibre preparations, the mean spike counts per minute at 14 breaths/minute were in the ranges 36.9-155.3 and 755-1921, respectively. These counts decreased by up to 61 and 44% respectively at 100 breaths/minute, and by 27-89% and 22-51% at 200 breaths/minute. At this frequency there was a further decrease of between 19 and 65% when the positive end expiratory pressure was removed. The findings of this study are intuitively acceptable, since pulmonary stretch receptor activity is proportional to tidal volume, and are in keeping with the clinical impression that high frequency ventilation per se does not eliminate respiratory drive.

Animals↗
PubMed1987

Benzodiazepines.

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Benzodiazepines↗
PubMed1987

Measurement of serum C-reactive protein concentration after renal transplantation.

A prospective study of serial serum C-reactive protein (CRP) concentrations was made on 21 patients who had received renal allografts. CRP was raised during 27 of 32 rejection episodes and in all of five episodes of rejection associated with infection. CRP values were persistently elevated in three irreversible rejection episodes. Significantly raised CRP concentrations were documented in 14 of 20 episodes of infection. In some cases CRP was a predictive indicator of rejection or infection. In all cases of infection or rejection associated with a rise in CRP, CRP values fell following successful treatment with appropriate agents. Serial CRP measurement used in conjunction with other clinical and biochemical parameters appears to be valuable clinically following renal transplantation.

Adult↗