Biomedical subjects
Publications and source records attributed to A Struppler.
Stereotactic interventions at the thalamic or subtalamic level for treatment of pathological hyperkinesias provide a good model for investigation of the systems controlling tonic innervation in the alert subject. It is suggested that the poststereotactic muscular hypotonia observed contralaterally to the lesion is due to changes in the tonic innervation pattern caused by interruption of a proprioceptive feedback loop.
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In order to analyse the EMG pattern during unloading of brachial biceps muscle, the interference EMG and single motor unit activity were investigated. The measurements were done on seven healthy subjects with two types of unloading techniques: a) active unloading, when the subjects resisted against an external load (10, 20, 30 and 40 N) which is suddenly released, and b) passive unloading, performed by low inertia torque motors with independently adjustable background extension and suddenly applied flexion torques. Following active unloading the silent period duration, the amplitude of the rebound and its segmentation into consecutive bursts is changing with initial load, whereas the silent period latency remains constant. Following passive unloading the acceleration influences predominantly the amplitude of the rebound, without changing its latency and silent period duration. The initial voluntary activity influences both silent period duration and rebound parameters (latency, amplitude and duration).
Response patterns of single muscle spindle primary afferents to abrupt load perturbations inflicted upon the contracting finger flexors were investigated in awake human subjects using the technique of microneurography. Units showed a transient high-frequency discharge in the rising phase of the stretch. No repeated burst activity attributable to irregularities of the stretch velocity or to mechanical oscillations of the muscle could be detected.
Thirty-three patients with complete median, ulnar or digital nerve transections were studied 4 months to 13 years subsequent to suture or nerve grafting. In all cases, sensory disturbances, in terms of paraesthesia or hypaesthesia, were encountered. Painful or unpleasant symptoms, allodynia or hyperpathia, were observed most frequently in patients with poor recovery. The clinical findings and the patients' subjective complaints were correlated to microneurographic single fibre recordings of regenerated cutaneous mechanoreceptors. In more than 80% of the recordings, discharge properties of regenerated receptors, thresholds and a variety of other electrophysiological data were similar or equal to normal controls. Less than 20% of the receptors exhibited atypical properties suggesting defective steady-state regeneration. The ratio of rapidly adapting (RA-units) to slowly adapting mechanoreceptors (SA-units) was inverse in relation to normals. The density of regenerated RA-receptors was higher in the proximal than in the distal part of the reinnervated area. This paralleled the clinical finding of reduced sensory discrimination in these cases and suggests that SA-units may regenerate preferentially. In painful conditions no single fibres could be recorded, reflecting the relative paucity of fibres and probably the atrophy of the nerve. The results of the microstimulation experiments, although less reliable, revealed some evidence that the central processing of regenerated units is abnormal. Clinical and electrophysiological data supported this concept of central changes underlying some of the phenomena observed during peripheral nerve regeneration.
In experiments on adult human subjects we examined the effect on passive mechanical properties of a muscle by conditioning it with either an isometric contraction or passive muscle extension. The test measurement was the amount of muscle displacement (stiffness) and the accompanying EMG in response to a brief torque pulse. Two muscles were tested, flexor digitorum profundus (FDP) and brachialis. In FDP the discharge of single muscle spindles was recorded as well. After muscle extension and return to the initial length, passive stiffness was less than after an isometric contraction. The changes in stiffness were accompanied by changes in pattern of EMG and in the responses of muscle spindles. It is suggested that in resting muscle there are stable cross bridges between actin and myosin filaments of muscle fibres which largely determine the passive stiffness. Muscle extension leads to detachment of these cross bridges which then re-form at the longer length. Return of the muscle to its starting length leads to development of slack in muscle fibres because, stiffened by the presence of the stable cross bridges, they are unable to shorten. Slack in muscle fibres lowers their measured stiffness. Muscle contraction, on the other hand, will result in any preexisting slack being taken up by the actively shortening muscle fibres, thereby raising muscle stiffness. Stiffness in intrafusal fibres is likely to follow a similar pattern to that in extrafusal fibres, leading to changes in stretch responsiveness of muscle spindles and consequently in the reflex EMG. It is concluded that the changes in stiffness and accompanying reflexes observed in this study are likely to be seen, at least under some conditions, in normal movements.
The treatment of acute and chronic low back pain is a problem frequently encountered in the doctor's office. Selective drug therapy has a useful role to play within the framework of the overall therapeutic strategy. Indications and practical application of the major analgesic agents in various low back pain conditions are discussed.
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Twenty eight patients with severe, intractable spasticity have been treated by chronic intrathecal administration of baclofen. An implantable programmable drug-administration-device (DAD) was used with a permanent intrathecal catheter. Infusion of 50 to 800 micrograms/day of baclofen completely abolished spasticity. Follow-up was up to two years. Therapeutic effect was documented by clinical assessment of tone, spasms and reflexes and by electrophysiological recordings of mono- and polysynaptic reflex activity. Complications and untoward side-effects of the procedure were few. This procedure is recommended for spasticity of spinal origin refractory to physiotherapy and oral medication. It is a preferable alternative to ablative surgical intervention.
Within the target area used for the stereotactic treatment of pathological tremor, recording of somatosensory evoked potentials and single units and also electrical stimulation were performed. The data were correlated with anatomical sites as demonstrated in the stereotactic atlas of Schaltenbrand and Wahren by using a computer system. The affected anatomical area was predominantly the prelemniscal radiation and adjacent thalamic nuclei. The recordings and stimulation effects indicate that a direct spinal input is involved in the control of muscle tone and manifestation of tremor.
Following therapeutic stereotactic lesions in the ventrolateral subthalamus and adjacent nuclei there are two phenomena concerning muscle tone: decreased muscle stiffness and failure in load compensation. In order to clarify whether hypotonia is due to decreased reflex activity and/or reduced nonreflex muscle stiffness, torque-induced stretch responses in the forearm flexor muscles and muscle spindle afferent discharge were investigated. In hypotonia following these lesions, the immediate compensation of abrupt external perturbations was diminished prior to reflex onset. A special feedback system is presented which originates in skeletal muscles and which continuously controls the muscle stiffness during movements. This afferent fiber system probably has a greater representation at the thalamic level as compared to the peripheral nerve. It is assumed that the decrease in muscle stiffness as well as the failure in load compensation are due to diminished static gamma-drive. This lack in somatosensory feedback can be compensated voluntarily by changing the mode of innervation.
Computer vision (CV), a computerized method to analyze digital images (e.g., CT scans), and computer graphics (CG), a set of computer programs for displaying two, three- or four-dimensional data, are recent computer techniques which are appropriate to assist functional stereotactic surgery. CV and CG are useful for the evaluation of spatial relations between anatomical structures and the sites of spontaneous neuronal noise or of electrophysiological stimulation data gathered during stereotactic interventions for movement disorders. CV and CG can be employed for stereotactic operation planning, during the operation for target point evaluation and for further postoperative data analysis.
We studied paired discharges (PDs) of single motor units (MUs) of the first dorsal interosseus muscle in parkinsonian and essential tremor. The number of PDs increased with increasing tremor strength and the duration of their intervals shortened. The amplitudes of the single tremor beats showed a significant negative correlation to the duration of the intervals of the preceding PDs. It is concluded that PDs play an important role as tremor amplifiers. The basic mechanism is probably the more than linear summation of two twitch contractions with short interval which is known from animal experiments.
The activity of single motor units (MUs) of the orbicularis oculi muscle was recorded in normal volunteers. While the subject maintained a constant firing rate, electrical stimuli were applied to the ipsilateral supraorbital nerve. Peristimulus histograms were constructed showing 2 periods of discharge accumulation at times corresponding to the R1 and R2 component of the blink reflex, each followed by a silent period, called SP1 and SP2, respectively. Whereas SP1 may merely result from the synchronisation of discharges in the preceding R1, SP2 can only be explained by an inhibition of the motoneurone activity. These findings confirm the existence of silent periods in the orbicularis oculi muscle in spite of the absence of mechanisms probably responsible for silent periods in load-bearing muscles.
We evaluated the concentration of the neuropeptide somatostatin (SOM) in the CSF of patients with several neurologic diseases. Since SOM is localized in high concentrations in primary sensory pathways, such as the dorsal root ganglia and dorsal horn of the spinal cord, it might be involved in conditions of chronic pain due to functional alterations of nociceptive neurons, such as postinfectious zoster neuralgia. Our study indicated a marked elevation of SOM in patients suffering from postzoster neuralgia compared with controls. Comparison with other neurologic diseases revealed decreased CSF SOM levels in Parkinson's and Alzheimer's disease, unchanged values in patients with amyotrophic lateral sclerosis, and increased concentrations in patients with brain tumors. In neurodegenerative disorders, SOM levels in CSF seemed to reflect the anatomic distribution as well as a reduction or preservation of the peptide in certain brain areas affected by the disease process. In postzoster patients, postinfectious degeneration of dorsal root ganglia cells might cause deafferentation of dorsal horn neurons and activation of SOM-containing systems with increased release either locally from neurons in the dorsal horn of the spinal cord or from descending fiber projections. The results suggested that SOM may take part in the modulation of nociceptive responses.
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