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Biomedical subjects

J Moxham

Publications and source records attributed to J Moxham.

At least 181 records · Page 10Linked to original sources
PubMed1988

Comparison of two different mouthpieces for the measurement of Pimax and Pemax in normal and weak subjects.

We investigated the effect of mouthpiece design on maximum static expiratory (PEmax) and inspiratory (PImax) mouth pressures. We measured PEmax from total lung capacity (TLC) and PImax from residual volume (RV) in 21 healthy volunteers, and in 40 patients referred for respiratory muscle testing. We compared two different mouthpieces, a semi-rigid plastic flanged type fitting inside the lips, and a 4 cm diameter rubber tube held against the lips. The tube mouthpiece gave significantly higher values for PEmax (p less than 0.02) in all subjects. PImax was also significantly higher (p less than 0.005) with the tube mouthpiece in subjects who recorded normal pressures. We conclude that maximum pressures are obtained in all normal subjects with the rubber tube mouthpiece, and that differences in quoted normal ranges of maximum static respiratory pressures reflect in part the design of the mouthpiece and the way in which it was used.

Equipment Design↗
PubMed1988

Aminophylline and the respiratory muscles: an alternative view.

The respiratory muscles constitute a pump as vital to life as the heart. In patients with severe lung disease, the work of breathing is increased greatly, whereas the capacity of the respiratory muscles to generate tension and ventilation is impaired. In these circumstances, respiratory muscle fatigue may occur. When the cardiac pump fails, it often is possible to improve its performance by drug therapy with inotropic agents. In recent years, attention has been focused on the possibility of enhancing respiratory muscle function with drugs. The agents most studied have been the methylxanthines, theophylline and aminophylline. In vitro studies have demonstrated an inotropic effect of theophyllines on all skeletal muscles tested, including the diaphragm. The effect of theophyllines on skeletal muscle is dose related and animal studies show that any effect in humans, where dosage is limited by toxicity, is likely to be small. Early studies in humans showed a substantial positive inotropic effect on the diaphragm, but subsequently, a large number of studies have yielded mixed results. Up to the present time, most studies have failed to demonstrate a positive action of theophyllines. Although is it possible that these drugs may have a very small beneficial effect on contractility, not easily detected by the methods of some investigators, such as small effect of potentially toxic drugs is likely to be of limited clinical value.

Aminophylline↗
PubMed1987

The relative accuracy of three transcutaneous dual electrodes at 45 degrees C in adults.

Measurements made by transcutaneous electrodes can be compared with arterial blood gases in several different ways. The relationship between them is commonly expressed by a linear regression equation, and a correlation coefficient, r, calculated. However calculation of the bias and the precision of transcutaneous electrode readings is more helpful in clinical practice. The differences between the two methods are explained by comparing the relationship of three transcutaneous dual electrodes to endtidal gases in adults.

Adult↗
PubMed1987

Drift in vivo of transcutaneous dual electrodes.

TcPO2 and tcPCO2 monitoring is widely used but the in vitro drift of the new combined sensors is unknown. We tested the in vivo stability of 3 such electrodes in six adults, compared to nasal endtidal values from a mass spectrometer. Each electrode was remembraned within 5 days and had a 2 point dry gas calibration at 45 degrees C before fixing to the subjects' right arms. TcPO2, tcPCO2 and endtidal values were averaged over four minutes after 30 minutes equilibration, and then at seven subsequent 20 minute intervals. We observed that (1) Endtidal values remained stable (2) tcPCO2 differed from baseline by less than 3 torr (3) tcPO2 rose significantly in all three electrodes by an average of 16 to 21% and, (4) in vivo drift greatly exceeded separately determined in vitro changes. We discuss the possible explanations for the observed results, and conclude that skin permeability changes may play an important role. In the light of the large in vivo tcPO2 drift, transcutaneous dual electrodes are not reliable trend indicators of blood gases in adults.

Adult↗
PubMed1987

High dose salbutamol in chronic bronchitis: comparison of 400 micrograms, 1 mg, 1.6 mg, 2 mg and placebo delivered by Rotahaler.

Ten patients with chronic bronchitis (Medical Research Council definition) completed a double-blind placebo-controlled study comparing 400 micrograms, 1 mg, 1.6 mg and 2 mg salbutamol powder. Response was measured by spirometry, peak expiratory flow rate, heart rate and tremor at intervals up to 4 hours post-inhalation. Pulmonary function results showed a trend towards higher doses producing improved response and a longer duration of action, with bronchodilatation following 2 mg significantly greater than 400 micrograms. Seven patients developed or had an increase in tremor following a single dose of 2 mg and in one this was considered to be severe. No adverse effects were recorded on ECG.

Administration, Inhalation↗
PubMed1987

Phrenic nerve stimulation in normal subjects and in patients with diaphragmatic weakness.

Phrenic nerve stimulation is often considered to be difficult and unreliable. The time taken for the phrenic nerves to be located and adequately stimulated was measured in 110 subjects, aged 21-89 years, 26 of whom had diaphragmatic weakness; and phrenic nerve conduction time was recorded in 76 of these individuals. Each phrenic nerve was stimulated transcutaneously in the neck with square wave impulses 0.1 ms in duration at 1 Hz and 80-160 volts while diaphragmatic muscle action potentials were recorded with surface electrodes. The time taken to locate either phrenic nerve ranged from two seconds to 22 minutes (median 10s). Both nerves were located in 83 of the 84 control subjects (99%) and in 21 of the 26 patients with diaphragmatic weakness (81%). Mean (SD) phrenic nerve conduction time in the control subjects was 6.94 (0.77) ms on the right and 6.61 (0.77) ms on the left. A weak relationship was found between conduction time and the subjects' age and height. Four out of 24 patients with diaphragmatic weakness had a prolonged phrenic nerve conduction time. Transcutaneous stimulation of the phrenic nerves was not a time consuming procedure, and it was well tolerated, reproducible, and successful in 95% of subjects.

Adult↗
PubMed1987

Comparison of domiciliary nebulized salbutamol and salbutamol from a metered-dose inhaler in stable chronic airflow limitation.

Nineteen patients (12 men) mean age, 63.4 years (range, 32 to 78), with stable chronic airflow limitation, mean FEV, 0.55 L (range, 0.3 to 1.05 L), completed an eight-week, double-blind, double cross-over study comparing nebulized salbutamol and salbutamol from a metered-dose inhaler (MDI). Salbutamol from both delivery systems produced bronchodilation. The doses of salbutamol inhaled via the nebulizer and MDI producing maximal bronchodilation were established by cumulative dose-response curves. The contents of the nebulizer and MDI were inhaled four times a day, one system containing salbutamol and the other a placebo. Cross-over of salbutamol from one system to the other occurred every two weeks. There was no significant difference between the two delivery methods in daily peak expiratory flow rate (PEFR), severity of symptoms, or extra bronchodilator usage. Two weekly laboratory assessments of spirometry, PEFR, and exercise tolerance also showed no significant differences. Careful assessment is recommended before the provision of domiciliary nebulizers.

Adult↗
PubMed1985

The maximal sniff in the assessment of diaphragm function in man.

We studied diaphragm function in a total of 64 normal subjects, who had no past or present respiratory or neuromuscular impairment. We measured transdiaphragmatic pressure (Pdi) during maximal sniffs and compared these values with Pdi during maximal static inspiratory efforts (PImax.). The range of Pdi during maximal sniffs (82-204 cm H2O) had better defined lower limits than Pdi during PImax. (16-164 cm H2O) and a higher mean value: mean +/- SD for maximal sniffs was 137 +/- 28 cm H2O and for PImax. was 90 +/- 37 cm H2O. The reproducibility of sniff Pdi was assessed in eight randomly chosen subjects over 3 days: the mean coefficient of variation was 7.2%. By comparison the coefficient of variation of Pdi during PImax. was 13.0% in seven subjects. The maximal sniff is a spontaneous manoeuvre, easily performed, repeatable without tiring, and reproducible. Its measurement provides a more reliable quantitative method for assessment of diaphragm strength, which has potential in clinical practice.

Adult↗
PubMed1985

Effect of aminophylline on the human diaphragm.

The effect of intravenous aminophylline on the contractile function of the diaphragm was studied in four normal subjects. The contractility of the diaphragm was assessed by the measurement of transdiaphragmatic pressure (Pdi) after right phrenic nerve stimulation at 1 Hz. Pdi was measured before and during aminophylline infusion (6 mg/kg over 30 minutes), during which therapeutic concentrations of theophylline were attained (mean 13.8 mg/l, range 8.5-20.2). The Pdi achieved was not affected by aminophylline. This result suggests that theophylline at therapeutic concentrations has little effect on the contractility of the normal human diaphragm.

Adult↗
PubMed1985

Action of abdominal muscles on rib cage in humans.

To assess the actions of the rectus abdominis and external oblique muscles on the rib cage in humans, these two muscles were stimulated with surface electrodes in four normal supine subjects at functional residual capacity. Changes in anteroposterior and transverse rib cage diameters and changes in xiphipubic distance were measured with pairs of magnetometers. Stimulation of rectus abdominis produced a marked decrease in the xiphipubic distance and in the anteroposterior diameter, thus making the rib cage more elliptic. In contrast, stimulation of the external oblique caused a decrease in the transverse diameter, making the rib cage more cylindrical. When both muscles were stimulated simultaneously, the resultant rib cage distortion depended on the relative voltage at which each muscle was stimulated. Electromyogram recordings showed that there was no cross contamination or activity of the diaphragm during the muscle stimulations. Transdiaphragmatic pressure increased with the voltage of stimulation, suggesting passive lengthening of the diaphragm. X-ray studies were performed in two subjects and confirmed the main magnetometer findings. These studies thus confirm that the rib cage in humans is more easily distortable than conventionally thought. The abdominal muscles can distort it in either direction depending on which muscles are contracting.

Abdominal Muscles↗
PubMed1985

Effect of rifampicin administration on theophylline pharmacokinetics in humans.

Theophylline pharmacokinetics were studied before and after rifampicin administration (600 mg daily for 1 wk). Rifampicin reduced the area under the concentration-time curve by 18% after the oral administration of sustained release aminophylline (450 mg) to 7 normal subjects (p less than 0.05) and increased the metabolic clearance and volume of distribution by 45% (p less than 0.05) and 17% (p less than 0.05), respectively, after the intravenous administration of aminophylline (5 mg/kg over 30 min) to 8 normal subjects. These findings are consistent with an inducing and choleretic effect of rifampicin on theophylline disposition. In patients receiving theophylline, blood levels should be monitored closely and dosage adjusted if rifampicin therapy is introduced or withdrawn.

Adult↗
PubMed1984

Sternomastoid muscle function and fatigue in normal subjects and in patients with chronic obstructive pulmonary disease.

Four normal subjects and 5 patients with chronic obstructive pulmonary disease (COPD) (mean FEV1, 1.03 L) had frequency:force curves of their sternomastoid muscle measured before and 5 min after a 12-min walk on a flat treadmill, a progressive exercise test (normal subjects only), and a 10-min period of sustained maximal voluntary ventilation (SMVV). Before each test, all subjects had a normal frequency:force curve, and the ratio of the force response at 20 Hz to that at 50 Hz was normal. After SMVV, all the normal subjects and 4 of the 5 patients developed a greater than 15% fall in 20:50 ratio, and this was taken to indicate the presence of low frequency fatigue (LFF). During SMVV, all the subjects achieved minute ventilation greater than 70% of predicted maximal breathing capacity (MBC). During the 12-min walk, all the patients exceeded 70% MBC, and 4 developed LFF. The normal subjects performing progressive exercise also exceeded 70% MBC, and all showed LFF. The 12-min walk did not cause LFF in the normal subjects, but no subject reached 70% of MBC. Despite the presence of LFF in the sternomastoid muscle, the patients were all able to walk the same distance during a second 12-min walk. In both the normal and patient groups, the ventilatory response to CO2 was not changed by the presence of LFF. There were no changes in maximal inspiratory and expiratory mouth pressures or spirometry with LFF. High, sustained levels of minute ventilation cause sternomastoid LFF, but the clinical significance of this phenomenon is not yet certain.

Adult↗
PubMed1983

Aminophylline and fatigue of adductor pollicis in man.

1. The effect of intravenous aminophylline on the contractility of adductor pollicis has been studied in three subjects both in the fresh state and following the induction of muscle fatigue. 2. Aminophylline had no influence on the frequency-force relationship and relaxation rate of adductor pollicis in the fresh state. 3. Fatigue resulted in a selective depression of the force response to low and moderate frequencies of stimulation and a slight effect on maximum force production 10 and 35 min afterwards. 4. Aminophylline given prior to, during and/or after fatigue did not influence this selective low-frequency fatigue at 10 or 35 min. 5. Aminophylline at the concentrations obtained has no significant effect on muscle contractility or fatiguability in man.

Adult↗