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Biomedical subjects

J T Mortimer

Publications and source records attributed to J T Mortimer.

At least 55 records · Page 3Linked to original sources
PubMed1984

Conditioning of the diaphragm with phrenic nerve stimulation after prolonged disuse.

We studied the effect of electrical stimulation of the phrenic nerve on the force frequency relationship of the disused diaphragm. A high quadriplegic who had been totally ventilator dependent for 6 months following a C2 fracture received bilateral phrenic nerve stimulators. During a 6-wk period of conditioning by electrical stimulation, the force of diaphragm contraction was assessed by measurement of transdiaphragmatic pressures during stimulation of each nerve over a range of frequencies. Tidal volume as well as rib cage and abdominal motion were studied. There was an upward shift of the force frequency relationship of the diaphragm over the 4-month period of phrenic nerve pacing using repetitive stimulus trains of 14 to 28 Hz. This improvement appeared to plateau at about 11 wk. The increase in contractility was accompanied by a progressive diminution in the stimulus frequency at which fusion of the contraction occurred. The disused diaphragm, like other skeletal muscle, may be conditioned with electrical stimulation.

Aminophylline↗
PubMed1983

Diaphragm activation with intramuscular stimulation in dogs.

We studied in 10 supine anesthetized dogs diaphragm contraction produced by electrical activation with intramuscular electrodes surgically implanted in the ventral surface of the diaphragm and compared this with activation of the ipsilateral phrenic nerve (C5, 6, and 7) before it entered the thorax. Repetitive 40-Hz pulse trains with supramaximal current stimulus were used after hyperventilation of the animals to apnea. A single intramuscular electrode within 1 to 2 cm of the site of phrenic nerve entry into the diaphragm produced a mean transdiaphragmatic pressure of 12.0 cm H2O +/- 0.97 SE and mean tidal volume of 0.27 L +/- 0.04 SE. Mean values observed with phrenic nerve stimulation were not statistically different, and both electrode systems produced equivalent outward abdominal motion and upper rib cage paradox, as monitored by inductive plethysmography. There was no difference in gas exchange during stimulation with a single hemidiaphragm electrode and mechanical ventilation compared at the same tidal volume and respiratory rate. Blockade of neuromuscular transmission with curare eliminated intramuscular and phrenic nerve stimulation proportionately, suggesting that activation of the diaphragm is dependent in both cases on the phrenic nerve. This technique does not entail manipulation of the phrenic nerve and may have clinical application as an alternative technique for diaphragm pacing.

Animals↗
PubMed1981

The relationship between receptor occlusion and the frequency sweep electromyogram during competitive neuromuscular blockade.

The purpose of this study was to correlate the frequency sweep electromyogram (FS-EMG) responses to various levels of receptor occlusion during partial neuromuscular blockade by d-tubocurarine (dTC). The FS-EMG represents the integrated compound muscle action potential induced by intra-muscular electrical stimulation as the stimulus frequency increases exponentially from 1 to 100 Hz. The FS-EMG response was recorded from the tibialis anterior muscles of six adult cats at different levels of neuromuscular blockade during recovery from intravenously injected dTc, 0.25 mg/kg. The fraction of receptors blocked was estimated by measuring the depolarization produced by proximate intraarterial injection of graded doses of succinylcholine. The FS-EMG became diminished for driving frequencies greater than 50 Hz when receptor occupancy was about 25-30 per cent. The responses corresponding to lower stimulus rates declined only at increasing levels of occlusion. The FS-EMG response to low-frequency stimulation did not diminish until 70 per cent of the available receptor pool was blocked. Simultaneous measurement of muscle force demonstrated a depressed response equivalent to that of the FS-EMG. These data were compared with the sensitivities reported for other tests of neuromuscular block. The frequency sweep electromyogram appears to be about as sensitive as determination of responses to sustained 5-second tetanic stimulation at 200 Hz, but more sensitive than determination of responses to tetanic stimulation at 100 Hz or twitch responses, or train-of-four measurements.

Animals↗
PubMed1979

Generation of unidirectionally propagated action potentials in a peripheral nerve by brief stimuli.

Single, unidirectionally propagated action potentials can be elicited in peripheral nerves by electrical stimuli of short duration. Propagation in one direction is blocked anodically by means of a quasi-trapezoidal stimulus wave form and a modified tripolar electrode configuration. Propagation in the other direction proceeds unhindered. This technique may be applicable to collision blocking of motor nerves for neural prostheses.

Action Potentials↗
PubMed1979

Frequency sweep analysis of neuromuscular junction continuity.

A new technique for measuring neuromuscular junction continuity is described. Junctional transmission is evaluated by integration of the electromyographic (EMG) response induced by intramuscular electrical stimulation. The unique characteristics of this monitoring technique are the use of intramuscular stimulation and a varying stimulation rate. The stimulus frequency is made to increase exponentially from 1 to 100 pulses per second over a period of 10 or 15 seconds. Thin coiled wire electrodes are used for stimulation and recording of the EMG response. The frequency sweep electromyogram (FS-EMB) response was measured in uncurarized and curarized tibialis anterior muscle of cat. In the uncurarized preparation, the FS-EMG response was only slightly decreased with an increasing stimulus frequency. During neuromuscular blockade with d-tubocurarine the FS-EMG response diminished with increasing frequency. The response failed at successively lower frequencies during deeper levels of neuromuscular block. Recovery proceeded in the reverse order. The frequency sweep technique provides quantitative assessment of neuromuscular junction continuity over a broad spectrum of driving frequencies without inducing fatigue. This method does not require force measurements nor voluntary effort. Intramuscular stimulation minimises painful stimuli thus making the frequency sweep technique suitable for evaluating neuromuscular transmission in either conscious or unconscious individuals.

Action Potentials↗
PubMed1977

Frequency sweep electromyogram and voluntary effort in volunteers after d-tubocurarine.

A new method for monitoring the effect of muscle relaxants on the myoneural junction was tested in unanesthetized volunteers. Evoked electromyographic responses to stimulation, sweeping exponentially from 1 to 100 Hz over 10 seconds, were recorded from the hand and abdominal muscles. d-Tubocurarine (dTc) was given intravenously in incremental doses until head lift was abolished. Thumb twitch tension, vital capacity, peak expiratory flow, maximal inspiratory force, and hand grip strength were recorded during partial paralysis and recovery. The frequency sweep electromyogram (FS-EMG) of the musculus rectus abdominis was more depressed than the FS-EMG of the musculus abductor digiti V at the time head lift was abolished. The abdominal muscle recovered faster from dTc paralysis than did the hand muscle. The latter failed to respond normally to the highest frequencies of stimulation during the entire period of observation lasting 72 minutes after dTc injection. At the time of maximal neuromuscular blockade, respiratory function showed less depression than the FS-EMG of the abdominal muscle.

Abdomen↗
PubMed1976

Upper and lower motor neuron lesions in the upper extremity muscles of tetraplegics.

Paralysed upper extremity muscles of 24 tetraplegic patients were examined to determine whether their lower motor neuron was intact. Primary emphasis was placed on the forearm finger flexor muscles (Flexor Digitorum Superficialis and Flexor Digitorum Profundus) and finger extensor muscles (Extensor Digitorum Communis and Extensor Indicis). It was found that the vast majority of these muscles in C4, C5 and C6 subjects retained some or all of their lower motor neurons intact. In C5 subjects, examination was performed on additional muscles that were potentially most useful in an orthosis utilising functional stimulation. Similar to the results of the finger flexor and extensor muscles, the muscles of the wrist and thumb generally had the lower motor neuron at least partially intact. A muscle that often was an exception was M. Flexor Carpi Radialis. These studies indicate that most of the forearm muscles of the upper extremity in high level spinal cord injury patients which are paralysed have the lower motor neuron totally or partially intact. With electrically induced exercise, such muscles are strengthened to functional levels of contraction. Subsequent electrical activation enables the quadriplegic patients to use the muscle functionally.

Adolescent↗