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Biomedical subjects

G M Allen

Publications and source records attributed to G M Allen.

31 records · Page 2Linked to original sources
PubMed1996

Reduced voluntary drive to the human diaphragm at low lung volumes.

Maximal inspiratory and transdiaphragmatic pressures vary with lung volume but the possibility that some of this variability reflects variable voluntary drive to the diaphragm has not been investigated systematically. We assessed the influence of lung volume on the ability to activate the diaphragm with voluntary effort during maximal Mueller manoeuvres. Voluntary activation of the diaphragm was assessed using twitch interpolation with bilateral phrenic nerve stimulation in 6 subjects. Each performed 10 maximal efforts at lung volumes around functional residual capacity (FRC) and additional efforts at volumes above and below FRC. Voluntary activation of the diaphragm was higher at lung volumes above FRC (> 60% TLC; activation 98.3 +/- 2.6%) than at lung volumes around FRC (45-60% TLC; activation 95.5 +/- 3.5%) and below FRC (< 45% TLC; activation 83.3 +/- 15.8%; p < 0.05). Submaximal diaphragm activation at low lung volumes may reflect differences in the length-tension relationships of the various inspiratory muscles and/or reflex inhibition of phrenic motoneurones at low lung volumes.

Adult↗
PubMed1996

Surgical treatment of emphysema using bovine pericardium strips.

Chronic pulmonary emphysema (CPE) damages lung tissue, causing it to lose elasticity and no longer exchange oxygen and carbon dioxide efficiently. In the past, lung transplantation was the only surgical treatment for CPE. Lung volume reduction surgery (LVRS) using bovine pericardium strips is a surgical approach that removes emphysematous lung tissue, allows healthy lung tissue to reexpand, and improves the functioning of the intercostal muscles and diaphragm. Surgical stapling devices buttressed with strips of bovine pericardium are used in LVRS procedures to reduce air leaks along staple lines. Patients with CPE who have undergone LVRS procedures using bovine pericardium strips have experienced a dramatic increase in their ability to exchange air, allowing them to have more normal lifestyles.

Female↗
PubMed1996

Muscle force, perceived effort, and voluntary activation of the elbow flexors assessed with sensitive twitch interpolation in fibromyalgia.

OBJECTIVE: To measure maximal voluntary strength and central activation without fatigue, and to assess both peripheral and central components of muscle fatigue of the elbow flexor muscles, during exercise, in a group of patients with fibromyalgia (FM) (n = 11). Results are compared with data from control subjects (n = 36). METHODS: Maximal voluntary activation and strength of elbow flexors were quantified using twitch interpolation during attempted maximal isometric contractions both in unfatigued muscles and during fatigue produced by 45 min of submaximal exercise. RESULTS: Maximal voluntary strength of the elbow flexors before and during exercise was within the normal range. Central fatigue did not develop to a greater extent in the patient group. No patient had a decline in twitch amplitude during exercise below the 95% confidence limit for the decline in control subjects. However, the increment in perceived effort (Borg Scale) was abnormally large in 5 patients during the fatiguing exercise. CONCLUSION: Neither poor motivation, reflex pain inhibition, nor muscle contractile failure are important in the pathogenesis of fatigue in patients with FM. However, the subjective response to exercise is commonly excessive.

Adult↗
PubMed1995

Reliability of measurements of muscle strength and voluntary activation using twitch interpolation.

We investigated the reproducibility of measurements of maximal voluntary torque and maximal voluntary activation using twitch interpolation. On 5 days, each of 5 subjects performed 10 maximal voluntary isometric contractions of their elbow flexors. Single supramaximal stimuli were delivered over biceps brachii at the measured peak torque during each effort, and in the relaxed muscle 5 s later. A voluntary activation score was calculated from the size of twitches evoked by the stimuli (resolution < 0.15 Nm). Although all subjects were able to drive the stimulated elbow flexor muscles maximally in some trials, they did not do so in 75% of all contractions. Maximal voluntary torques did not vary significantly within a subject between sessions. There were consistent differences in the level of maximal voluntary activation between subjects (P < 0.01), but no differences in voluntary activation within an individual across days in 4 of 5 subjects. Failure to drive the stimulated elbow flexor muscles maximally was not associated with inadvertent co-contraction of the antagonist muscles.

Adult↗
PubMed1995

Central fatigue. Critical issues, quantification and practical implications.

Central fatigue during exercise is the decrease in muscle force attributable to a decline in motoneuronal output. Several methods have been used to assess central fatigue; however, some are limited or not sensitive enough to detect failure in central drive. Central fatigue develops during many forms of exercise. A number of mechanisms may contribute to its development including an increased inhibition mediated by group III and IV muscle afferents along with a decrease in muscle spindle facilitation. In some situations, motor cortical output is shown to be suboptimal. A specific terminology for central fatigue is included.

Exercise↗
PubMed1994

Muscle performance, voluntary activation and perceived effort in normal subjects and patients with prior poliomyelitis.

Many people previously affected by polio complain of increased fatigue, weakness and pain many years after the initial illness. Although electromyographic abnormalities have been found in these patients, the cause of their increased weakness is not well understood. Previous studies have shown decreased strength and impaired exercise performance in those with prior polio, but the level of voluntary drive to the muscle has not been investigated. The present study investigated maximal voluntary activation without fatigue and both peripheral and central components of muscle fatigue during exercise in 21 subjects with poliomyelitis 20-40 years previously, and 20 healthy, age-matched control subjects. Voluntary activation and strength of the elbow flexors were quantified using twitch interpolation during maximal isometric voluntary contractions both at rest, and during fatigue induced by 45 min of repeated isometric contractions. Compared with the control subjects, patients with prior polio had impaired voluntary activation both when the elbow flexors were not fatigued and during fatiguing submaximal exercise. During exercise, polio subjects also had lower twitch amplitudes and increased subjective fatigue. Central and peripheral fatigue were more marked in those with the post-polio syndrome. The impaired voluntary activation with unfatigued muscles in polio subjects indicates that defective central or reflex drive may contribute to their new weakness.

Adult↗
PubMed1994

Impaired voluntary drive to breathe: a possible link between depression and unexplained ventilatory failure in asthmatic patients.

BACKGROUND: Although psychological distress predicts mortality in asthma, an underlying physiological link has not been shown. This study examined relations between impaired voluntary drive to breathe and measures of mood states. METHODS: The level of maximal voluntary activation of the diaphragm and elbow flexors was measured in a previous study using a sensitive modification of the twitch interpolation technique in 11 asthmatic and 10 control subjects. In this study psychological distress was assessed using the Profile of Mood States questionnaire and measures of distress were compared with the muscle voluntary activation results. RESULTS: For the asthmatic subjects, depressed mood increased the risk of impaired maximal voluntary activation of the diaphragm by 3.5 times (95% CI 1.09 to 11.3). No such association was observed in control subjects. CONCLUSIONS: These results suggest that depressed mood may predispose an asthmatic patient to impaired voluntary activation of the diaphragm. Such individuals would be at increased risk of rapidly developing ventilatory failure if faced with severe airway narrowing.

Asthma↗
PubMed1993

Reduced voluntary drive to breathe in asthmatic subjects.

Maximal voluntary drive to the diaphragm and a non-respiratory muscle group (elbow flexors) was compared in 10 control subjects and 11 asthmatics who were studied when well. The degree of voluntary activation during repeated attempted maximal quasi-static efforts was determined using the twitch interpolation technique in the absence of contractile fatigue under both control conditions and following bronchial challenge with histamine. Diaphragm activation was assessed using bilateral phrenic stimulation at the normal resting end-expiratory lung volume after exhalation from TLC. Asthmatic subjects showed lower and more variable voluntary activation than control subjects for both diaphragm (82.0% +/- 18.4 [SD], vs 87.8% +/- 12.0, P < 0.01) and elbow flexors (91.3% +/- 7.6 vs 95.8% +/- 4.1, P < 0.01). Histamine challenge decreased FEV1 in asthmatic subjects to 50% of the initial value, but had no significant effect on voluntary activation in either subject group. The decreased voluntary drive to the diaphragm observed in some asthmatic subjects may predispose to rapid development of ventilatory failure during severe airway narrowing.

Adult↗
PubMed1993

Respiratory sensations, cardiovascular control, kinaesthesia and transcranial stimulation during paralysis in humans.

1. To determine whether discomfort associated with breathing (dyspnoea) is related to the chemical drive to breath, three subjects were totally paralysed while fully conscious. Subjective responses to a rising CO2 stimulus were obtained during rebreathing, rebreathing with CO2 added, and breath holding. Dyspnoea was measured with a 10-point Borg scale. 2. Following nasotracheal intubation and ventilation (oxygen saturation, O2,Sat, 98-100% and end-tidal CO2, PET,CO2, 30-40 mmHg), total neuromuscular blockade was induced by a rapid injection of atracurium (> 2.5 mg kg-1) and complete paralysis was maintained with an infusion (5 mg (kg h)-1). Paralysis was confirmed by abolition of the compound muscle action potentials of both the diaphragm and abductor hallucis evoked by supramaximal electrical stimulation of the relevant nerves. Communication via finger movement was preserved for the first 20-30 min following paralysis by inflation of a sphygmomanometer cuff on one arm. 3. Before and during complete paralysis, dyspnoea increased progressively during hypercapnia produced by rebreathing (with or without CO2 added to the circuit at 250 ml min-1). The mean PET,CO2 eliciting 'severe' dyspnoea was 46 mmHg during rebreathing, 42 mmHg during 'breath holding', and 52 mmHg during rebreathing with added CO2. There were no significant differences between the values obtained during paralysis and in the control study immediately before paralysis. The duration of breath holding was not prolonged by paralysis and the PET,CO2 at the 'break point' was not altered by paralysis. 4. Thus, dyspnoea is preserved following total neuromuscular blockade. This suggests that chemoreceptor activity, via the central neuronal activity which it evokes, can lead to discomfort in the absence of any contraction of respiratory muscles. 5. During paralysis, attempted contraction of arm, leg and trunk muscles increased heart rate and blood pressure. For attempted handgrip contractions, the increases in heart rate (range, 7-15 beats min-1) and mean arterial pressure (range, 20-32 mmHg) were similar to those recorded with actual contractions in trials immediately before paralysis. In one subject, graded increases in heart rate and blood pressure occurred for attempted contractions of 45 s duration over a range of intensities (0-100% maximal effort). 6. During complete paralysis, transcranial electromagnetic stimulation of the motor cortex produced illusory twitch-like movements of the wrist and digits. This also occurred in separate studies during complete ischaemic paralysis and anaesthesia of the forearm and hand.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMedDate not supplied

Post-polio syndrome: assessments, pathophysiology and progression.

While there have been many reports of the decline in motor function in patients with prior-polio, there have been few reports of quantitative changes in muscle function and the pathophysiological mechanisms for the deterioration are poorly understood. This paper describes the establishment of a postpolio clinic and the principles adopted in quantitative muscle testing using twitch interpolation. Peripheral endurance and/or voluntary drive to muscles is impaired in about 30% of prior-polio patients attending the clinic. Progression of these deficits is slow and not easily predicted by factors associated with the original illness.

Ambulatory Care Facilities↗