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Biomedical subjects

G T Lewis

Publications and source records attributed to G T Lewis.

13 recordsLinked to original sources
PubMed1993

The contribution of respiratory function tests to clinical diagnosis.

The purpose of this study was to investigate the amount of diagnostic information contained in a set of routine lung function studies and to attempt to determine which tests could be omitted without significant loss of discrimination. Cluster analysis was performed on a set of physiological and questionnaire data, collected prospectively in 1,542 male patients, referred consecutively for measurement of forced expired volumes, static lung volumes and measurements of the transfer factor for carbon monoxide. A respiratory questionnaire was completed for each patient. A physician assigned the patients to a rigorously defined diagnostic category, based on supporting clinical information, as well as pulmonary function, apart from 241 patients with unusual diagnoses and those in whom the criteria did not apply satisfactorily. This diagnosis was never included as a classification variable. Basing the classification on three independent measurements, total lung capacity, the ratio of forced expiratory volume in one second (FEV1) to vital capacity, and the transfer factor for carbon monoxide, the computer generated six groups: one normal, one showing an isolated gas exchange defect, and four with varying degrees of restriction and obstruction. This classification performed well in separating the patients with the clinical diagnoses of chronic airflow obstruction, bronchial asthma and interstitial lung disease from those with ischaemic and valvular heart disease and other miscellaneous disorders. Omitting total lung capacity resulted in some loss of specificity, but valid information was still obtained. The inclusion of all the static and dynamic lung volumes and of carbon monoxide transfer coefficient made little difference.(ABSTRACT TRUNCATED AT 250 WORDS)

Cluster Analysis↗
PubMed1990

Study of the possible interaction between fentanyl and propofol using a computer-controlled infusion of propofol.

A computer-controlled infusion of propofol designed to achieve a target blood concentration of propofol 3 microgram ml-1 was used to investigate the possibility of an interaction between propofol and fentanyl in 32 patients undergoing body surface surgery. In 16 patients who were not receiving a neuromuscular blocker during maintenance anaesthesia with 67% nitrous oxide, there were no significant differences in blood concentrations of propofol between eight patients who received fentanyl 5 micrograms kg-1 before induction of anaesthesia, and eight patients who did not. In a further 16 patients who received vecuronium during maintenance anaesthesia with 67% nitrous oxide, there were no significant differences in blood propofol concentrations between eight patients who received fentanyl 5 micrograms kg-1 before induction of anaesthesia, and eight patients who did not. Fentanyl administered i.v. immediately before a computer-controlled infusion of propofol resulted in more satisfactory anaesthetic conditions than when fentanyl was not used, but did not significantly prolong the recovery time.

Adult↗
PubMed1989

Computer controlled infusion of propofol.

A computer controlled infusion pump was used to deliver propofol to two groups of eight patients undergoing body surface surgery. The patients were premedicated with morphine sulphate i.m. and anaesthesia was supplemented with 66% nitrous oxide in oxygen. Patients in group 1 breathed spontaneously, whereas patients in group 2 underwent artificial ventilation to a normal PaCO2. The computer program was designed to achieve and maintain a blood concentration of propofol 3 micrograms ml-1 as rapidly as possible, basing calculations on a three-compartment pharmacokinetic model. Mean blood propofol concentrations were found to be close to the predicted target from 10 to 120 min in group 1, but were 5-20% higher from 20 min in group 2.

Adult↗
PubMed1989

Resistance to airflow in anaesthetic breathing systems.

We have examined, under reproducible conditions, the resistance to airflow of complete anaesthetic breathing systems (Magill, Coaxial Lack, Parallel Lack and Bain systems) and components of these systems. All systems had resistances within the recommended ranges at all flows likely to be experienced in normal clinical practice. The Magill system had the lowest resistance under all conditions. It is concluded that comparisons should be made only between complete breathing systems.

Airway Resistance↗
PubMed1989

The skull base and nasopharynx in Down's syndrome in relation to hearing impairment.

Children with Down's syndrome have a higher incidence of middle ear effusion than normal children. Twenty-eight patients with Down's syndrome and 33 age and sex-matched normal controls were studied. They were subdivided into 2 further matched groups on the basis of having normal or impaired hearing. Each underwent pneumatic otoscopy, audiometry and lateral head and neck radiography. This study examines radiological parameters to determine whether skeletal or soft tissue factors within the skull base or nasopharynx could be implicated as a cause or diagnostic feature of Eustachian tube dysfunction. The nasopharynx tended to be smaller in those with Down's syndrome and this resulted in a reduction in the airway size due to encroachment by the soft tissues. The angle between the base of skull and hard palate was significantly less acute in those with Down's syndrome and in those with hearing loss.

Child↗
PubMed1988

Sensory discrimination and dynamic activity in the anorectum: evidence using a new ambulatory technique.

The anal canal in health is extremely sensitive to thermal stimuli, If temperature sensation plays a part in sensory discrimination two conditions must be fulfilled: there must be a temperature gradient along the anorectum and rectal contents must be able to come into contact with the sensitive anal mucosa. In a study of 53 normal subjects we demonstrated this temperature gradient with a median temperature difference between the rectum and lower, mid and upper anal canal of 0.4, 0.2 and 0.1 degrees C respectively. The second condition was examined in 15 normal ambulatory subjects by measuring mid-anal sphincter (SP) and rectal pressures (RP) with a microtransducer catheter. The signals were digitalized and recorded in a portable electronic memory for later computer display, and analysis. Marked spontaneous sphincter relaxation resulting in equalization of RP and SP occurred 7 times per hour (1-4). The conscious sensation of the presence of flatus was associated with an SP reduction of 30 mmHg (20-50 mmHg) and an RP increase of 7 mmHg (0-15 mmHg), such that RP greater than or equal to SP in 80 per cent of 144 recorded events. Using this new technique we have demonstrated the highly dynamic nature of the anal sphincter. Several times an hour the sphincter relaxes with subsequent equalization of rectal and anal pressures, allowing entry of rectal contents into the anal canal so that its presence and nature can be determined.

Adult↗
PubMed1988

Induction and maintenance of propofol anaesthesia. A manual infusion scheme.

A simple, manually controlled infusion scheme for continuous administration of propofol was derived by simulation of a computer algorithm designed to achieve a predetermined blood concentration of propofol within 2 minutes and to maintain a constant blood level for the duration of surgery. The manual infusion scheme for a target blood propofol concentration of 3 micrograms/ml, consisted of a loading dose of 1 mg/kg followed immediately by an infusion of 10 mg/kg/hour for 10 minutes, 8 mg/kg/hour for the next 10 minutes and 6 mg/kg/hour thereafter. An overall mean blood propofol concentration of 3.67 micrograms/ml was achieved within 2 minutes and maintained stable for the subsequent 80-90 minutes of surgery. The decrease of systolic and diastolic arterial pressures at induction was much less than that previously described after larger induction doses of propofol and there was a negligible haemodynamic response to laryngoscopy and intubation or to the subsequent surgery. The quality of induction and maintenance of anaesthesia was satisfactory in every patient.

Adult↗
PubMed1986

Are cardiovascular reflexes more commonly impaired in patients with bronchial carcinoma?

Non-invasive tests of cardiovascular autonomic function were performed in 69 patients with histologically proved bronchial carcinoma and the results compared with those obtained in a group of age and sex matched controls. Only two patients were under 50 years of age, and with the exception of the heart rate response to deep breathing the tests performed have no accepted normal ranges in patients of this age. None of the patients had features of florid, disabling autonomic neuropathy. All the tests of autonomic function showed declining performance with age but in addition there were significant differences in the results when the two groups were compared. In the group with carcinoma the resting heart rate was higher (p less than 0.05), the resting supine blood pressure lower (p less than 0.01), and the postural fall in blood pressure greater (p less than 0.01). Test results were not related to tumour histology, the presence of finger clubbing, drug history, or symptoms suggestive of autonomic dysfunction. Abnormal responses in tests of cardiovascular autonomic function are commonly found in elderly patients but bronchial carcinoma appears to have an additional effect. The precise mechanism of this effect remains a matter for speculation.

Adult↗
PubMed1986

Influence of knowledge of peak flow on self assessment of asthma: studies with a coded peak flow meter.

A portable peak flow meter based on a turbine transducer that can display results in code has been developed. Its performance compares well with the Wright peak flow meter. Records of subjective self assessment of asthma on a visual analogue scale and of peak flow (PEF) were compared in 12 subjects with asthma. PEF measurements were made with a coded meter for two weeks and an uncoded meter for two weeks in random order. The correlation between visual analogue scale score and PEF was invariably stronger when PEF was known. Changes in perception of asthma were measured by comparing the slopes and relative positions of the regressions of visual analogue on PEF. When PEF was uncoded awareness of asthma was significantly increased in five patients, predominantly those whose perception was poorest while they were using the coded meter, and decreased in only one patient. In two patients the results were unsuitable for this type of analysis. Knowledge of PEF therefore may influence subjective self assessment in patients with bronchial asthma. For objective studies of symptoms of asthma, PEF readings should be unknown to the patient. Perception of asthma may, however, be improved in patients with poor ability to detect changes in bronchial calibre by uncoded measurement of peak flow at home.

Adult↗
PubMed1984

An electronic peak flow meter with optional coded display.

A portable electronic spirometer giving peak expiratory flow rate has been developed and used successfully in studies of asthma. A turbine flow transducer produces a pulsed output whose frequency is proportional to flow. The output was coded to keep the results 'blind' to the patient. The code is suitable for use on other electronic instruments employing a similar display. It has been successfully used to investigate patients' perception of their asthma.

Asthma↗
PubMed1983

Almitrine bismesylate in congenital central hypoventilation.

We have carried out sequential studies of respiration and sleep state, from two weeks to two years of age in a girl with congenital central hypoventilation. When awake her minute ventilation (VE) and blood gases are normal, and when asleep she shows hypoventilation, with progressive hypoxia, hypercarbia and respiratory acidosis, most marked in NREM sleep. There has been no consistent change in VE (expressed as ml/kg/min) with age, awake or asleep, and she remains ventilator dependent when asleep. Growth and development are normal. We report a trial of almitrine bismesylate at the age of 21 months. A dose of 1.5 mg/kg/day orally for eight days produced minimal changes in VE, but when given 2.6 mg/kg/day for a further seven days there was a significant increase in VE in both NREM (27% increase) and in REM sleep (30% increase). These changes were accompanied by substantial improvements in blood gases, with PaCO2 less than 50 mmHg and PaO2 greater than 60 mmHg throughout a four hour study period asleep, off the ventilator, in air. After stopping almitrine bismesylate VE and blood gas values returned to pretreatment values. Almitrine bismesylate may be of value as an alternative to artificial ventilation in this condition.

Almitrine↗