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Biomedical subjects

C W Hess

Publications and source records attributed to C W Hess.

At least 109 records · Page 6Linked to original sources
PubMed1988

Evaluation of proximal facial nerve conduction by transcranial magnetic stimulation.

A magnetic stimulator was used for direct transcutaneous stimulation of the intracranial portion of the facial nerve in 15 normal subjects and in patients with Bell's palsy, demyelinating neuropathy, traumatic facial palsy and pontine glioma. Compound muscle action potentials (CMAPs) thus elicited in the orbicularis oris muscle of controls were of similar amplitude but longer latency (1.3 SD 0.15 ms) compared with CMAPs produced by conventional electrical stimulation at the stylomastoid foramen. No response to magnetic stimulation could be recorded from the affected side in 15 of 16 patients with Bell's palsy. Serial studies in two patients demonstrated that the facial nerve remained inexcitable by magnetic stimulation despite marked improvement in clinical function. In the patient with a pontine glioma, the CMAP elicited by transcranial magnetic stimulation was of low amplitude but normal latency. In six of seven patients with demyelinating neuropathy, the response to intracranial magnetic stimulation was significantly delayed. Magnetic stimulation produced no response in either patient with traumatic facial palsy. Although the precise site of facial nerve stimulation is uncertain, evidence points to the labyrinthine segment of the facial canal as the most likely location.

Adult↗
PubMed1988

Somatosensory evoked potentials following nerve and segmental stimulation do not confirm cervical radiculopathy with sensory deficit.

Twenty eight patients with unilateral cervical radiculopathy were studied by somatosensory evoked potentials (SEPs) from nerve stimulation at the wrist and from skin stimulation at the first, third or fifth finger depending on the root involved. In order to evaluate the reliability of various "radicular SEP patterns" as described in the literature, absolute latencies and side-to-side differences of the brachial plexus component from the supraclavicular fossa (N9), the medullary component (N13) from the cervical vertebra Cv7, and the primary cortical component (N20, P25) were assessed. Side-to-side differences of the amplitudes of N20/P25 and of the conduction times across the intervertebral fossa (interval N9-N13) were analysed. After nerve stimulation, 68% of the patients had false negative findings on the symptomatic, while 36% had positive findings on the asymptomatic side. After segmental stimulation, 72% of the patients had false negative findings on the symptomatic, while 22% had positive findings on the asymptomatic side. It is concluded that SEPs following nerve and segmental stimulation do not reliably confirm clear-cut already established diagnoses of unilateral radiculopathy with sensory and motor deficit. Therefore, they will not be helpful in the electrophysiological investigation of cervicobrachialgias of unknown origin.

Adolescent↗
PubMed1988

Central motor conduction in degenerative ataxic disorders: a magnetic stimulation study.

Central motor conduction to small hand muscles was measured using magnetic stimulation of the motor cortex and electrical stimulation of proximal motor roots in 11 patients with Friedreich's ataxia, 10 patients with early onset cerebellar ataxia with retained tendon reflexes (EOCA) and 13 patients with late onset degenerative cerebellar disease (LOCD). Central motor conduction was abnormal in 91% with Friedreich's ataxia, 70% with EOCA and 38% with LOCD. Central motor conduction abnormalities were not specific to individual disorders but were more severe and were related to disease duration in Friedreich's ataxia and EOCA.

Adult↗
PubMed1988

Brainstem auditory-evoked potentials studied with paired stimuli in multiple sclerosis patients.

In 19 patients with definite multiple sclerosis (MS) brainstem auditory-evoked potentials (BAEP) with paired stimuli were recorded. Only hearing pathways without abnormalities in usual BAEP were examined. The latencies of wave III and wave V were significantly increased with the paired-stimulus technique (using paired-click intervals of 1.5 and 4.0 ms duration) compared to single clicks. In 4 patients (21%) paired-click BAEP latencies exceeded the critical values of normal subjects. This technique might give new possibilities in detecting minor lesions in MS patients.

Adult↗
PubMed1988

Knee effusion and reflex inhibition of the quadriceps. A bar to effective retraining.

In order to investigate the difficulty of quadriceps training in the presence of an effusion into the knee we examined 13 patients with chronic effusions by recording isometric muscle strength. Maximal strength was markedly lower in the presence of an effusion, and aspiration of the effusion produced a 13.6% increase in strength (p less than 0.01). A further, small increase of 8% was recorded after intra-articular lignocaine injection. Isometric strength and surface integrated EMG correlated well in six patients. Two reflex mechanisms seem to inhibit quadriceps innervation in the presence of a persistent knee effusion, one mediated by pressure sensitive receptors, the other still unknown. Joint aspiration and systemic or intra-articular anti-inflammatory drug treatments are advised before any programme of quadriceps training to allow maximum effects to be achieved.

Adolescent↗
PubMed1988

[Transcranial cortex stimulation with magnetic field pulses: methodologic and physiologic principles].

The recently introduced method of painless transcranial brain stimulation using magnetic pulses has proved to be particularly suitable for exciting the motor cortex in conscious humans. The magnetic pulse is generated by a brief current pulse which passes through the stimulating coil, and the time varying magnetic field induces stimulating currents within the brain. Experimental evidence indicates that transcranial magnetic stimulation as opposed to electrical brain stimulation activated corticospinal neurones transsynaptically. With a circular stimulating coil centered near the vertex, upper limb muscles of the right side are preferentially activated with the inducing current clockwise viewed from above and vice versa. For the leg muscles the optimal position of the coil on the scalp is more critical and varies from subject to subject. Voluntary contraction of the target muscle reduces the threshold stimulus intensity, increases the amplitude and shortens the latency of the evoked compound muscle action potentials (CMAPs). This facilitatory effect of background muscle activity is most pronounced in the small hand muscles, where only a slight contraction is sufficient to greatly enhance the responses. In a relaxed small hand muscle facilitation of the responses can also be achieved by contraction of either the homologous contralateral or a neighbouring ipsilateral muscle. Even in relaxed state, the CMAPs show an inherent variability which is not related to the subject's motor readiness or mental state in any obvious way, provided the muscles' relaxed state is ascertained. The stimulus strength affects the amplitudes but not the latencies of the responses over a relatively wide range of suprathreshold intensities.

Electric Stimulation↗
PubMed1988

[Characteristics of electrical discharges by transcranial cortex stimulation activated motor units of the hand muscles of the human].

Using concentric needle electrode recording from hand muscles (abductor digiti minimi, first dorsal interosseus, or abductor pollicis brevis muscle) the latencies of single motor unit potentials in response to threshold magnetic brain stimuli were studied under different conditions. It has been shown that the motor units activated by threshold brain stimuli had the lowest threshold for voluntary activation (A = vol. activated, B = brain stim.). Onset latencies of 23 motor unit potentials from different sites in the relaxed muscles of four healthy subjects ranged from 22.4 to 32.4 ms (average: 26.4 ms; SD: 2.80 ms) but proved to be relatively stable when stimulating and recording conditions were kept constant (variation less than 0.5 ms, see poststimulus time histogram in Fig. 2). With concurrent contraction of an ipsilateral neighbouring or of the contralateral homologous muscle the motor unit potentials from the relaxed target muscle jumped to an earlier latency by 1.2 to 1.7 ms (C in Fig. 3 and B-2 in Fig. 4). On one occasion another motor unit of higher threshold was alternatively activated by this procedure (B-3 in Fig. 4). Since the same procedures are known to enhance the compound muscle action potentials as recorded from the relaxed muscle with surface electrodes, the shorter latencies of single motor units are considered to be caused by a facilitatory influence on the motoneurones. A possible explanation for these latency shifts would be that the motor units discharge later in response to the brain stimulus induced repetitive cortico-spinal impulses when there is no facilitation, whereas during facilitation the firing level is reached earlier.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Latissimus dorsi transfer for the treatment of massive tears of the rotator cuff. A preliminary report.

Symptomatic irrepairable rotator cuff tears usually entail complete loss of the substance of the supraspinatus and infraspinatus tendons. Loss of external rotation control and cranial migration of the humeral head on attempted flexion or abduction of the shoulder are the functional hallmarks. Transfer of the latissimus dorsi tendon from the humeral shaft to the superolateral humeral head provides a large, vascularized tendon that can be used to close a massive cuff defect and that exerts an external rotation and head-depressing moment that allow more effective action of the deltoid muscle. This procedure was carried out in 14 patients without any significant complications. Pain relief and functional results in those four cases with a minimum follow-up period of one year (average, 14 months) compared favorably with alternative treatment methods and warrant further anatomic, electromyographic, and clinical investigation.

Adult↗
PubMed1987

Excitability of the human motor cortex is enhanced during REM sleep.

A conspicuous feature of rapid eye movement (REM) sleep is atonia of postural muscles due to a powerful brainstem inhibitory effect on spinal motoneurones. However, small myoclonic jerks occur during REM sleep and increased activity of cortical neurones is suggested by the EEG. Transcranial cortical stimulation with magnetic pulses has been used to investigate motor excitability during sleep in man. Motor responses were evoked during sleep using stimuli identical to those used in wakefulness. Response amplitudes were depressed during slow wave sleep (SWS) and enhanced or the same during REM sleep. These findings suggest that the susceptibility of the human motor cortex to stimulation is enhanced during REM sleep.

Electric Stimulation↗
PubMed1987

Magnetic brain stimulation: central motor conduction studies in multiple sclerosis.

Central motor conduction (CMC) was evaluated in 32 normal subjects and 83 patients with multiple sclerosis, and the findings were correlated with clinical signs and evoked potential data. CMC time was obtained from the latency difference in responses from the abductor muscle of the little finger to magnetic stimulation of the motor cortex and electrical stimulation at the C-7/T-1 interspace. Mean CMC time in normal subjects was 6.2 msec (SD 0.86 msec), and amplitudes of responses to cortical stimuli were at least 18% of those obtained with stimuli at the wrist. CMC was abnormal in 60 patients with multiple sclerosis (72%); this correlated well with brisk finger flexor jerks (p less than 0.005). CMC was abnormal in 79% of patients with weakness of the abductor muscle of the little finger and in 54% with a normal muscle. Neurological examination was normal in 7 arms with abnormal CMC. Visual evoked potentials were abnormal in 67%, somatosensory evoked potentials in 59%, and brainstem auditory evoked potentials in 39% of those tested. For each procedure more subjects had abnormal CMC and normal evoked potentials than the reverse. The technique is of value for demonstrating and documenting central motor pathway lesions in multiple sclerosis, especially when physical signs are equivocal.

Action Potentials↗
PubMed1987

Auditory brain-stem potentials studied with paired stimuli in normals.

Brain-stem auditory evoked potentials (BAEPs) to paired stimuli of various intervals were recorded using a subtraction technique to cancel the first and facilitate recognition of the second response. In a pilot series of 12 experiments, no latency change was encountered with paired click intervals (PCI) of 8 and 6 ms. Thirty healthy subjects were then investigated by presenting single and paired stimuli with a PCI of 4, 3.1, 2.3 and 1.5 ms at a repetition rate of 10/s to each subject. With diminishing PCIs, identification and latency measurement of waves IV and V became increasingly difficult because of marked amplitude reduction. Component III remained identifiable in all but two recordings and showed a statistically significant latency increase and amplitude reduction only when the stimuli were presented 1.5 ms apart. Component I did not show a consistent latency change with any PCI but its amplitude was significantly reduced with 4 ms PCI. These findings differ from those reported when using PCIs of 5 ms or more and when using single stimuli at a high repetition rate, where component V was the most stable. The alterations of evoked potentials found only with a PCI of 1.5 ms are probably of central origin.

Acoustic Stimulation↗
PubMed1987

Magnetic and electrical transcranial brain stimulation: physiological mechanisms and clinical applications.

The human brain can be stimulated by electric shocks or by brief intense magnetic fields. The latter cause only a trivial scalp sensation. Stimuli exciting the motor cortex cause contralateral muscle responses, but the threshold for excitation is markedly reduced by slight voluntary contraction of the target muscle. For small hand muscles, the overall latency from scalp to muscle is shorter by 1.8 ms when electrical stimuli are used than when stimuli are magnetic. Central motor conduction time (CMCT) can be estimated by stimulating over the scalp and then over the cervical area. In healthy subjects, the CMCT is 6.1 +/- 0.8 (SD) (n = 29). Physiological studies have shown that the facilitation of responses in hand muscles produced by voluntary contraction is also present when contralateral muscles are used, but not when a leg muscle is contracted. The mechanism of facilitation may involve neural activity at both spinal and cortical levels. Single motor units can be caused to discharge by threshold brain stimuli. These motor units are the same ones activated first during weak voluntary contractions. Clinical studies have shown that the CMCT may be greatly prolonged in patients with multiple sclerosis and that subclinical motor pathway lesions can be detected. Central conduction may also be abnormal in patients with motor neuron disease and cervical myelopathy. Side effects have not been encountered with either type of stimulator.

Electric Stimulation↗
PubMed1987

Responses in small hand muscles from magnetic stimulation of the human brain.

1. The magnetic field generated by a brief current in a 9 cm diameter flat circular coil varies rapidly with time and when applied over the human scalp it is capable of exciting motor structures subserving the small hand muscles. With a peak magnetic field at the centre of the coil of 0.9-1.6 Tesla, single scalp stimuli produced twitches in the right abductor digiti minimi (a.d.m.), first dorsal interosseous (f.d.i.) and adductor pollicis muscles. Compound muscle action potentials (c.m.a.p.s) and single motor units from these muscles were recorded. 2. The twitch force and corresponding c.m.a.p. were greatly enhanced by voluntary background contraction of the muscle and depended on the direction and intensity of the magnetic field. Response amplitude was maximal with the stimulating coil centred near the vertex but precise coil position was not critical. 3. When the orthodromic volley set up in the peripheral nerve by magnetic stimulation of the brain collided with a maximal antidromic volley set up by stimulation at the wrist, remaining electromyographic (e.m.g.) activity gave evidence of multiple firing of some spinal motoneurones, provided that the muscle exerted a slight voluntary background contraction and the stimulus intensity was above threshold for relaxed muscle. 4. When the muscle changed from total relaxation to a slightly contracted state the onset latency of the c.m.a.p. was shortened by about 3 ms without further change when the background contraction increased. In slightly contracted muscle, c.m.a.p. onset latency was little affected over a wide range of stimulus intensities and was unaffected by the position of the stimulating coil within an area of 6 X 6 cm over the vertex. 5. Single motor units, recorded with needle electrodes in the a.d.m. or f.d.i. muscle, could be caused to discharge at a constant latency by threshold brain stimuli. Different single motor units had latencies varying from 22.4 to 32.1 ms. The same motor unit was activated from different coil positions up to 7 cm apart. These motor units had the lowest thresholds for voluntary activation. Stronger stimuli caused the same motor unit to discharge 1.5 ms earlier. 6. The threshold for excitation of pathways to the a.d.m. muscle was reduced by voluntary contraction of the contralateral a.d.m. and by contraction of the ipsilateral f.d.i. muscles. Using these procedures, the c.m.a.p. of totally relaxed a.d.m. muscle showed a more than 2-fold amplitude increase, a shortening of onset latency to a similar degree as with contraction of the muscle itself, and single motor units in the a.d.m. muscle discharged 1.5 ms earlier.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

[Electrically induced cutaneo-muscular reflex from the m. extensor digitorum brevis].

We recorded the cutaneo-muscular reflexes in 90 normal subjects from the extensor digitorum brevis muscle following electrical stimulation at the second toe. In 88 subjects an early and a late EMG response were obtained. The mean latency of the second reflex response was 91.9 +/- 12.1 ms and the mean duration was 27.3 +/- 11.6 ms. However, there was considerable variability of the interindividual amplitudes. Comparison of the age related changes in the latencies of the first and second reflexes yielded results consistent with the transcortical or spino-bulbo-spinal hypothesis.

Adult↗
PubMed1986

Magnetic stimulation of the human brain: facilitation of motor responses by voluntary contraction of ipsilateral and contralateral muscles with additional observations on an amputee.

An intense rapidly changing magnetic field generated in a coil over the scalp can excite motor pathways to hand muscles. With a suprathreshold stimulus, the amplitude of the muscle action potential of the abductor digiti minimi is increased: by weak contraction of the muscle itself, by weak contraction of the ipsilateral first dorsal interosseus, by stronger contraction of the contralateral abductor digiti minimi, but not by contraction of the contralateral first dorsal interosseus, nor by the ipsilateral quadriceps muscle. This facilitation of response to brain stimulation may occur by two mechanisms, one related to the focussing of attention onto a particular hand, the second involving a rise in excitability of homologous motor pathways.

Amputation Stumps↗
PubMed1986

Measurement of central motor conduction in multiple sclerosis by magnetic brain stimulation.

Central motor conduction time (CMCT) to abductor digiti minimi was measured in 18 healthy subjects and in 15 patients with multiple sclerosis. A novel percutaneous magnetic stimulator was used to stimulate the motor cortex painlessly and CMCT was calculated by subtracting the onset latency of muscle responses obtained by electrical stimulation over the C7/T1 interspace from that obtained from stimulation over the scalp. In healthy subjects CMCT was 6.0 +/- 0.76 ms. In multiple sclerosis patients with pyramidal signs in the arms, CMCT was almost always prolonged, the longest conduction time being 39 ms. In 10 patients CMCT was prolonged despite normal strength in the muscle.

Action Potentials↗