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Biomedical subjects

D Burke

Publications and source records attributed to D Burke.

At least 343 records · Page 19Linked to original sources
PubMed1974

Sensory conduction of the sural nerve in polyneuropathy.

Using surface electrodes, sensory nerve action potentials (SAP) have been recorded in the proximal segment (mid-calf to lateral malleolus) and the distal segment (lateral malleolus to toe 5) of the sural nerve and in the median nerve in 79 control subjects. The values obtained for the distal segment of the sural nerve varied widely and in seven apparently normal subjects no SAP could be distinguished. In the proximal segment conduction velocities were over 40 m/s and there was no significant change with age, unlike the median nerve in which a highly significant slowing occurred with age. Comparison of the results of sural and median sensory conduction studies in 300 consecutive patients screened for sensory polyneuropathy confirms the value of sural nerve sensory studies as a routine screening test, and confirms the belief that the changes in polyneuropathy are usually more prominent in lower limb nerves. It is therefore suggested that studies of sural sensory conduction form the single most useful test in the diagnosis of sensory polyneuropathy.

Adolescent↗
PubMed1974

Isometric contraction of the abductor digiti minimi muscle in man.

Isometric contraction of the abductor digiti minimi muscle (ADM) has been studied in six normal subjects. Twitch contraction times of ADM ranged from 60 to 68 ms and twitch torque ranged from 2·33 to 6·24 × 10(-3) Nm. In three subjects torque declined by an average of 31% after tetanization at 50 Hz for 30 seconds but there was no similar diminution in the evoked muscle action potential suggesting that the fatigue arose from intrinsic muscular mechanisms. A marked decline in tetanic torque occurred with continued tetanization in two subjects for a total of five minutes, but this change was accompanied by a decrease in the muscle action potential. In six subjects threshold stimulation to the ulnar nerve at the wrist and to various sites over the motor point of ADM allowed 55 threshold twitch contractions to be identified after averaging. A unimodal range of contraction times ranging from 40-100 ms was found and this was confirmed by additional experiments in two subjects in whom 30 threshold twitch contractions were identified using a needle electrode to stimulate various sites in the motor point. Tetanization at 50 Hz was performed using threshold stimulus levels. Nine threshold tetanic contractions were evoked in two subjects. In eight tetanic torque progressively fatigued to between 14 and 20% within 60-90 seconds, but, in one tetanic contraction, torque proved relatively fatigue resistant. These results suggest that there is a homogeneous group of motor units in ADM (with respect to contraction time) and that this group contains what are probable fast twitch fatigue sensitive and fatigue resistant motor units. No evidence of a distinct group of slow twitch units was found.

Adult↗
PubMed1974

Contractile properties of the abductor digiti minimi muscle in paramyotonia congenita.

In two subjects with paramyotonia congenita the isometric torque generated by the abductor digiti minimi and the surface EMG recorded over ADM decreased during prolonged or repetitive contractions, whether these were voluntarily or electrically induced. Isometric twitch times did not alter significantly during this muscle fatigue. Cooling greatly accelerated the fatiguing process. It is suggested that this local muscle weakness is due to a progressive decrease in excitability of the muscle cell membrane.

Adult↗
PubMed1974

An analysis of myotonia in paramyotonia congenita.

In two subjects with paramyotonia congenita myotonic delay in muscle relaxation, recorded electromyographically and with a displacement transducer, was found to increase with repeated forceful contractions. Myotonia was elicited readily in warm temperatures, was initially aggravated by cooling, but was invariably lost as muscle fatigue developed. The EMG evidence of myotonia usually subsided before complete muscle relaxation had occurred, suggesting that a defect of the contractile mechanism was present over and above any defect at membrane level.

Adult↗
PubMed1973

Quantitative study of the effect of L-dopa and phenoxybenzamine on the rigidity of Parkinson's disease.

The static and dynamic components of the tonic stretch reflex and shortening reactions have been studied in biceps brachii, triceps, hamstrings, and quadriceps muscles of 19 patients with Parkinson's disease before and during L-dopa therapy. Clinical improvement during L-dopa administration correlated with a reduction in the dynamic component of the tonic stretch reflex in biceps, triceps, and quadriceps but not the hamstrings muscle, and with the static component of the tonic stretch reflex in biceps and triceps but not quadriceps and hamstrings muscles. The only shortening reaction consistently reduced during the L-dopa treatment period was the dynamic shortening reaction of the triceps muscle. The responses of the stretch reflexes to changes in muscle length were not altered by L-dopa therapy. In severely disabled patients the hamstrings and quadriceps stretch reflexes were maximal in a position of partial flexion of the knee joint and this response to muscle length was not altered in these patients despite a dramatic lessening of rigidity in some patients. Shortening reactions commonly remained in some patients after the stretch reflex of the antagonistic muscle was abolished by L-dopa therapy. The administration of phenoxybenzamine to patients being treated with L-dopa reduced the different components of rigidity more than L-dopa alone, and the responses were consistent with phenoxybenzamine suppressing predominantly the descending noradrenergic pathway.

Aged↗
PubMed1972

Tonic vibration reflex in spasticity, Parkinson's disease, and normal subjects.

The tonic vibration reflex (TVR) has been studied in the quadriceps and triceps surae muscles of 34 spastic, 15 Parkinsonism, and 10 normal subjects. The TVR of spasticity develops rapidly, reaching a plateau level within 2-4 sec of the onset of vibration. The tonic contraction was often preceded by a phasic spike which appeared to be a vibration-induced equivalent of the tendon jerk. The initial phasic spike was usually followed by a silent period, and induced clonus in some patients. No correlation was found between the shape of the TVR and the site of the lesion in the central nervous system. The TVR of normal subjects and patients with Parkinsonism developed slowly, starting some seconds after the onset of vibration, and reaching a plateau level in 20-60 sec. A phasic spike was recorded occasionally in these subjects, but the subsequent tonic contraction followed the usual time course. Muscle stretch increased the quadriceps TVR of all subjects, including those with spasticity in whom the quadriceps stretch reflex decreased with increasing stretch. It is suggested that this difference between the tonic vibration reflex and the tonic stretch reflex arises from the selective activation of spindle primary endings by vibration, while both the primary and the secondary endings are responsive to muscle stretch. The TVR could be potentiated by reinforcement in some subjects. Potentiation outlasted the reinforcing manoeuvre, and was most apparent at short muscle lengths. As muscle stretch increased, thus producing a larger TVR, the degree of potentiation decreased. It is therefore suggested that the effects of reinforcement result at least partially from the activation of the fusimotor system. Since reinforcement potentiated the TVR of patients with spinal spasticity in whom a prominent clasp-knife phenomenon could be demonstrated, it is suggested that the effects of reinforcement are mediated by a descending pathway that traverses the anterior quadrant of the spinal cord.

Electromyography↗
PubMed1972

Assessment of cyclobenzaprine in the treatment of spasticity.

The efficacy of cyclobenzaprine 60 mg/day in the treatment of spasticity was assessed in a double-blind crossover trial of two weeks' duration in 15 patients suffering from cerebral or spinal spasticity. Independent clinical and electromyographic methods were used. The effects of cyclobenzaprine did not differ significantly from those of placebo. The administration of a higher dosage, 150 mg/day, to one patient revealed a dose-related response, but the degree of improvement was clinically small. Apart from a skin rash there were no significant untoward effects of therapy.

Adolescent↗