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Biomedical subjects

J Moxham

Publications and source records attributed to J Moxham.

194 records · Page 11Linked to original sources
PubMed1982

Changes in EMG power spectrum (high-to-low ratio) with force fatigue in humans.

During and following high-load fatiguing voluntary contractions, the force response of skeletal muscle to electrical stimulation is altered so that the frequency-force curve is moved to the right. Fatiguing contractions also result in a shift to the left of the electromyographic (EMG) power spectrum. In the quadriceps muscle and the diaphragm of normal subjects the change in the force response to electrical stimulation has been correlated with the EMG changes. After repeated submaximal contractions in the quadriceps and diaphragm, the forces produced by electrical stimulation at low frequencies were reduced, indicating low-frequency fatigue. This type of fatigue persisted for several hours but did not result in any change in the EMG high-to-low ratio. Low-frequency fatigue is probably an important aspect of the failure of skeletal muscle to generate adequate force, and the EMG high-to-low ratio may not recognize this type of fatigue.

Diaphragm↗
PubMed1981

Contractile function and fatigue of the respiratory muscles in man.

Ventilation depends on the proper functioning of the respiratory muscles. These muscles, like other skeletal muscles, can endure high work loads for only short time periods. The work of breathing in patients with lung disease in increased and it has therefore been argued that respiratory muscle fatigue may develop and contribute to respiratory failure. We have studied the contractile function and fatigue of the sternomastoid muscle and the diaphragm in normal subjects and found that these respiratory muscles have the same contractile properties as limb muscles. If subjected to a high load they develop similar patterns of fatigue. Studies on the sternomastoid muscle in patients with lung disease also confirmed that respiratory stress produces fatigue.

Action Potentials↗
PubMed1981

Continuous monitoring of right atrial oxygen tension in patients with myocardial infarction.

Right atrial oxygen tension (RAPvO2) was measured continuously in 26 patients admitted to a coronary care unit with acute myocardial infarction. A catheter incorporating a Clark type oxygen sensor at its tip was inserted percutaneously into the right atrium. Insertion was simple, safe and comparable to the introduction of a standard central venous pressure line. RAPvO2 correlated well with the patients' clinical condition and reflected both cardiac and pulmonary function. When breathing air 11 of the patients had sustained RAPvO2 levels of less than 34 mmHg (4.53 kPa). In this group there were eight deaths. Fifteen patients had an RAPvO2 greater than 34 mmHg (4.53 kPa) except for transient falls related to movement and in this group there were no deaths (p less than 0.002). The correction of arterial hypoxaemia by oxygen therapy raised RAPvO2 and lowered the heart rate. In some patients Dopamine and transvenous pacing raised RAPvO2 and could be adjusted with reference to the continuous recording. Movement often caused marked falls in RAPvO2 especially in the seriously ill. Evidence relating RAPvO2 to mixed venous oxygen and tissue oxygen is reviewed.

Adult↗
PubMed1981

Intravascular mixed venous oxygen tension monitoring. An analysis of electrode performance in 100 patients.

A lengthened umbilical artery catheter incorporating an oxygen electrode (Searle) was flow-guided to the pulmonary artery in 48 out of 62 attempts (77.4%). In the last 70 catheters used, electrode performance was evaluated over a total of 3687 h by comparison with an ABL2 (Radiometer) blood-gas analyser; 654 comparisons were made, of which 255 resulted in recalibration of the electrode output. When sampling intervals were within 6 h, in more than 80% of the comparisons the difference between in vivo and in vitro measurement was within +/- 0.4 kPa (+/- 3 mm Hg). Twenty-four electrodes were removed sooner than clinically indicated (mean useful life 48.5 h) because of failure of oxygen or pressure measurements.

Blood Gas Analysis↗
PubMed1981

Contractile properties and fatigue of the diaphragm in man.

We studied the pressure developed by the diaphragm in response to stimulation of the phrenic nerve in the neck, in three normal men. When the phrenic was electrically stimulated at increasing frequencies the diaphragm responded by increasing transdiaphragmatic pressure to give a frequency-pressure curve similar to the frequency-force curve for other skeletal muscles. The subjects than breathed through an inspiratory resistance for as long as possible and the frequency-pressure curve was repeated. It was found that the diaphragm developed low frequency fatigue, in the same way as previously described for other muscles. We conclude that the diaphragm has contractile properties similar to these of other skeletal muscles. Low frequency fatigue of the diaphragm could contribute to respiratory failure in patients with lung disease.

Adult↗
PubMed1981

Ketotifen in atopic asthma and exercise-induced asthma.

The efficacy of ketotifen, a tricyclic benzocycloheptathiophene derivative, was assessed in an outpatient clinical trial and in a group of 12 asthmatic subjects with exercise-induced asthma. Subjects in the outpatient trial had mild asthma and consisted of two groups: a group of 24 atopic asthmatics with at least one positive skin test reaction and with an associated history of bronchial reactivity to at least one allergen; and a group of eight asthmatics with one or more positive skin prick tests but not bronchial reactivity to an allergen. Both groups took four weeks medication of ketotifen 1 mg bd and placebo in a randomised double-blind crossover study. There was no difference between ketotifen and placebo for any measurement made during the study and consequently no evidence of drug efficacy. The exercise study followed a standardised protocol and each subject took in random double-blind order, placebo, 1 mg, 2 mg, and 4 mg ketotifen two hours before exercise. There was no difference in the mean decreases in lung function from pre-exercise baseline values after three doses of ketotifen than with placebo. Drug levels suggested ketotifen was well absorbed. It would appear that if given for a period of only four weeks ketotifen had no beneficial effects in the management of mild asthma, and that a single dose before exercise does not modify exercise-induced asthma.

Adolescent↗
PubMed1980

Hydrocortisone suppression test and discriminant analysis in differential diagnosis of hypercalcaemia.

Experience is reported of the hydrocortisone suppression test in 140 hypercalcaemic patients, comprising 98 new cases of hyperparathyroidism and 42 cases of non-parathyroid malignant disease. The diagnostic accuracy of the test was compared in 168 patients with that of discriminant analysis, the discriminant functions being derived from plasma inorganic phosphate, alkaline phosphatase, chloride, bicarbonate, and urea, and the erythrocyte sedimentation rate. The hydrocortisone test and discriminant analysis each achieved a diagnostic accuracy of about 93% in 148 patients with either non-parathyroid malignant disease or hyperparathyroidism without osteitis fibrosa. When both tests pointed to the same diagnosis, they were wrong in less than 1% of cases. The hydrocortisone test was not helpful in patients with osteitis fibrosa. Both tests can be performed in any hospital with reliable standard laboratory services. Used in combination they have a high predictive value in distinguishing hypercalcaemia of parathyroid origin from that due to non-parathyroid malignant disease and have not led to errors of clinical importance. They should continue to play a major role in the differential diagnosis of hypercalcaemia until a prompt and reliable service finally establishes parathyroid hormone assay as the definitive laboratory procedure.

Adult↗
PubMed1980

Sternomastoid muscle function and fatigue in man.

1. A technique has been devised to measure the effect of stimulation frequency on the contraction force in an accessory muscle of respiration, the sternomastoid, in man. The frequency/force curve was found to be very similar to that of the quadriceps and adductor pollicis muscles. 2. Fatigue of the sternomastoid due to inspiratory loading or sustained maximum voluntary ventilation resulted in reduced force generation at low stimulation frequencies compared with maximum force. This type of fatigue frequently persisted for several hours. 3. If low frequency fatigue were to develop in patients with pulmonary disease it could have important consequences for the development of respiratory failure.

Electric Stimulation↗
PubMed1979

A controlled clinical trial comparing disodium cromoglycate and ICI 74,917 in extrinsic asthma.

A controlled clinical trial comparing inhalation of disodium cromoglycate (DSCG) and of ICI 74,917 was carried out using a double-placebo technique in thirty-two patients with extrinsic asthma already shown to be reasonably responsive to DSCG. In view of the fact that ICI 74,917 is 300 times more potent than DSCG in inhibiting antigenic challenge in animals a better effect was anticipated from the new drug in the human asthmatic subject. Whilst this was not obtained, there appeared to be no lesser effect than that of DSCG.

Asthma↗
PubMedDate not supplied

Influence of lung volume and rib cage configuration on transdiaphragmatic pressure during phrenic nerve stimulation in man.

Transdiaphragmatic pressure was recorded during bilateral supramaximal percutaneous phrenic nerve stimulation at 1 Hz (twitch Pdi) to investigate the effect of lung volume and rib cage configuration on diaphragm contractility in man. Stimulations were performed in 5 normal supine subjects at resting end expiration (FRC) and at lung volumes above and below FRC, during relaxation against a closed airway and during isovolume manoeuvres. Twitch Pdi at FRC was 24.4 cm H2O. At lung volumes above FRC, twitch Pdi decreased by 7.04 +/- 3.2 cm H2O per litre of volume change. At lung volumes below FRC, twitch Pdi increased by 12.4 +/- 8.6 cm H2O per litre of volume change. When the diaphragm was lengthened during an isovolume manoeuvre at FRC, twitch Pdi increased. A similar relationship between lung volume and twitch Pdi was obtained during stimulations performed with abdominal binding. These results demonstrate that the pressure developed by the diaphragm during phrenic nerve stimulation is significantly affected both by increases and decreases in lung volume and by the rib cage configuration at which stimulation is performed.

Adult↗