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Biomedical subjects

A B Baker

Publications and source records attributed to A B Baker.

At least 55 records · Page 3Linked to original sources
PubMed1994

Incidence of ventricular fibrillation after aortic cross-clamp release using lignocaine cardioplegia.

The occurrence of ventricular fibrillation after aortic de-clamping during cardiac surgery is common, and if prolonged may contribute to myocardial ischaemia. The use of lignocaine cardioplegia to minimize reperfusion ventricular fibrillation was studied in 141 patients undergoing first time coronary artery surgery in a double blind prospective randomized trial: 71 patients received lignocaine 100 mg/l in their cardioplegia, whereas a control group of 70 patients received cardioplegia without lignocaine. Lignocaine cardioplegia reduced significantly the incidence of reperfusion ventricular fibrillation from 63% to 42%. Of those patients developing reperfusion ventricular fibrillation, a higher proportion receiving lignocaine cardioplegia underwent spontaneous defibrillation (30% vs 11%) though this was not statistically significant. The incidence of atrio-ventricular (A-V) block necessitating ventricular pacing to separate from cardiopulmonary bypass was significantly higher in the lignocaine treated group (44%) than in the control group (20%): this may have been due to the additive effect of procaine in the cardioplegia solution. In the majority of cases this A-V block was transient and had resolved prior to the completion of surgery.

Adult↗
PubMed1993

Effect on lung volumes of oxygen concentration when breathing is restricted.

We have examined the effect of the fractional concentration of nitrogen (FIN2) on the decrease in lung volumes which occurs during restricted breathing with oxygen-nitrogen mixtures. Conscious human subjects breathed one of five gas mixtures of oxygen and nitrogen for 15 min on each of five occasions. For the final 5 min of each 15-min period, functional residual capacity (FRC) was reduced by one tidal volume, by external pressurization. After return to normal breathing, the subjects showed a statistically significant decrease in FRC and residual volume (RV), which became larger as FIO2 increased from 30% to 100%. This reduction in lung volumes was resistant to early reexpansion. The maximum decrease in both FRC and RV was found with 100% oxygen, and was 10% of the control lung volumes. The use of a mixture of 75% nitrogen and 25% oxygen prevented this decrease in lung volumes. Nitrogen 50% reduced the decrease in FRC, but did not affect the decrease in RV. The difference in effect on lung volumes between FIO2 25% and 30% was statistically significant, indicating a watershed area for FIN2 between 70% and 75%.

Adult↗
PubMed1993

Solubility characteristics of the ideal agent for measurement of cardiac output by soluble gas uptake methods.

Measurements of the rate of uptake of soluble gases such as nitrous oxide or acetylene has been used as the basis of a method of cardiac output estimation since 1912. Using theoretical models of single, multiple and rebreathing techniques of cardiac output measurement, we determined the effect of solubility in blood and lung tissue on the changes in the final expired concentration of the gas. Decreasing lung tissue solubility increased the sensitivity of all three models to cardiac output changes. When the lung tissue/blood partition coefficient was 1, the optimum blood/gas partition coefficients were 2.6 for the single-breath model, 4.1 for the three breath-model and 3.5 for the rebreathing model. A selection of gases, including volatile anaesthetic agents was studied using the same models. Under most conditions, enflurane approximated most closely to the requirements for an ideal agent for use in this technique of cardiac output measurement.

Anesthetics↗
PubMed1993

Analysis of uncertainty in theoretical methods of cardiac output measurement using the "Monte Carlo" technique.

We have developed three models which describe the relationship between cardiac output and the uptake of volatile anaesthetic agents, based on the Fick equation, and determined if these models could provide useful methods of cardiac output measurement. Because many variables are involved in the calculation of cardiac output using these methods, a "Monte Carlo" simulation was performed to investigate the combined effect of uncertainties in several variables on the resultant cardiac output estimate. We found that the single-breath model was most accurate when the inspired concentration was large, while the rebreathing model was better with smaller inspired concentrations. The three-breath model was the least accurate under all conditions studied. Volatile anaesthetics were generally more accurate than nitrous oxide, with both enflurane and halothane more accurate than isoflurane. The "Monte Carlo" technique provides a valuable tool for analysis of errors in measurement methods.

Anesthetics↗
PubMed1993

Gas uptake from an unventilated area of lung: computer model of absorption atelectasis.

A computer model of gas uptake from an area of nonventilated lung, such as a pulmonary lobe with an occluded bronchus or an alveolus with an occluded airway, is presented. Previous analyses have assumed that when an inert gas is present, equilibration of O2 and CO2 with mixed venous blood is sufficiently rapid to be treated as instantaneous. This is valid for insoluble gases such as N2 or He when the fractional concentration of inspired O2 (FIO2) is < or = 0.6 but is invalid for a relatively soluble gas such as N2O. When a mixture of O2 and an inert gas is breathed, the time for an area of unventilated lung to collapse depends on the solubility of the inert gas and FIO2. When the solubility is low (N2 or He), collapse takes longer than when 100% O2 is breathed, and the lower the FIO2 the longer the time to collapse. When the gas is more soluble (N2O) and FIO2 is > 0.3, collapse is more rapid than when 100% O2 is breathed.

Absorption↗
PubMed1990

Childhood cancer survivors: attained adult heights. Compared with sibling controls.

As part of a large collaborative study, the authors administered a pretested questionnaire to 62 childhood and adolescent cancer survivors and 62 same-sex sibling controls. The authors requested information regarding attained adult height on the questionnaire. Mean adult height of survivors (172.2 cm) was less than that of controls (174.1 cm), at a borderline significant difference of p = 0.0757. Multivariate analysis examined four potential, independent variables as possible predictors of this difference. The presence of brain tumor (vs. nonbrain tumor) (p less than .0001) and diagnosis at an early age (less than or equal to 8 years vs. 9-15 years) (p = .05) were factors significantly related to the differential; sex of patient and type of therapy were not. Our findings thus identify malignancy site and age at diagnosis as important predictors of adult height in childhood and adolescent cancer survivors.

Adolescent↗
PubMed1987

Dental damage during anaesthesia and surgery.

A review of the Accident Compensation Corporation (ACC) files on dental damage following anaesthesia or surgery was undertaken along with a survey of New Zealand anaesthetists asking about their practice with respect to protection of teeth during anaesthesia. These results confirm that damage is relatively common and that the majority of damaged teeth (62%) were known to have been previously restored, or weakened through periodontal disease prior to the damage occurring. The anaesthetists surveyed thought that dental damage was even more common than shown from the ACC records, and yet the vast majority of them did not routinely use specific protective guards and 45% of them did not ever use protective guards of any type.

Adolescent↗
PubMed1986

Computerised EEG monitoring for carotid endarterectomy.

A prospective study was undertaken in twenty patients undergoing carotid endarterectomy using computerised EEG monitoring in the form of a density-modulated spectral array, spectral edge frequency and integrated EEG power for monitoring cerebral ischaemia. This form of monitoring proved to be easy to use and understand. Because ischaemic EEG events longer than one minute were not necessarily followed by postoperative deficits, the definition of significant events that would cause ischaemia may need to be modified.

Brain Ischemia↗
PubMed1984

Measurement of lung volume by multiple indicator dilution. Testing a modelled hypothesis with on-line computation.

Respiratory mass spectrometry and on-line computation were used to estimate lung volume in normal subjects by a rebreathing technique, using oxygen, nitrogen and argon as indicators. The computation had previously been tested in a numerical model. In real normal lungs, it performed well enough for practical purposes, despite recognizable oversimplifications in the modelling assumptions. The differences in estimate to be expected from different composition changes between control and rebreathing were less than 100 ml, and those from different indicators within a composition change were less than 50 ml. The use of two indicators in lung volume measurement allows a correction for volume changes attributable to carbon dioxide and nitrous oxide, and a third indicator provides a degree of quality control.

Humans↗
PubMed1983

Changes in residual volume following oxygen breathing.

Nineteen volunteers breathed 100% oxygen for 10 min and then for a further 5 min at a restricted lung volume. Residual volume (RV) was shown to be significantly decreased by 120 ml when compared with control values breathing air. Functional residual capacity (FRC) also was decreased significantly by this manoeuvre. Other measurements indicated that the volume of FRC minus the closing capacity (CC) (FRC-CC) was not of importance in the development of the reduction in RV. It is postulated that such decreases in alveolar volume may contribute to postoperative hypoxia and morbidity.

Adolescent↗
PubMed1983

Oesophageal multipurpose monitoring probe.

An oesophageal probe which incorporates facilities for pressure, temperature, electrocardiographic and stethoscopic monitoring is described. Actual and potential uses are outlined.

Body Temperature↗