Achard-Lévi syndrome: pupil-sparing oculomotor nerve palsy due to midbrain stroke.
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Aged↗
Biomedical subjects
M Schüttler
Publications and source records attributed to M Schüttler.
Separating different contributions to the shear force in near-field microscopy.
The shear force between a gold and a graphite sample and an approaching near-field optical probe using tuning fork detection is studied in detail. The adiabatic and dissipative contributions are clearly distinguished by monitoring the amplitude as well as the phase of the tip vibration when approaching the surfaces. Their relative strengths vary differently but characteristically with the distance. The interaction starts in case of graphite at a much larger distance. The adiabatic contribution is larger in the case of gold, whereas graphite shows mostly dissipative interaction. Measurements at various temperatures are performed using a gold sample, showing a dependence of the shear force on the temperature.
Journal Article↗
Selective fascicular stimulation of the rat sciatic nerve with multipolar polyimide cuff electrodes.
PURPOSE: To assess a new flexible, multicontact spiral-cuff electrode made of polyimide with integrated platinum contacts for selective stimulation of nerve fascicles. METHODS: Polyimide cuff electrodes with 12 Pt sites in the spiral cuff were acutely implanted around the sciatic nerve of rats. Stimulation was applied through each one of the four tripoles of the cuff as single pulses of 10 microsec duration of increasing intensity. The motor responses were monitored from EMG recordings of gastrocnemius medialis (GM; innervated by the tibial nerve) and tibialis anterior (TA; innervated by the peroneal nerve) muscles. The torque developed in tbc ankle was simultaneously measured by means of a purposely designed apparatus. Recruitment curves were constructed for the CMAP of the GM and TA muscles and for the torque. RESULTS: In all nerves evaluated stimulation through one or two of the tripoles initially evoked a dorsiflexion with parallel recruitment of the TA muscle at low stimulation intensity; at higher stimulation amplitude activation of the tibial innervated muscles prevailed and led to predominant plantarflexion. On the other hand, stimulating through the other two or three tripoles evoked plantarflexion from the beginning, with increasing force from low to high stimulus intensity. The effectiveness of selective stimulation was mildly increased by applying a simultaneous transverse steering current. The threshold for torque dorsiflexion decreased and the dynamic range of stimulation that resulted in a net dorsiflexion expanded. The effects of steering currents were more noticeable with pulses of 80% than 40% of threshold value, and when applied from an opposite than from an adjacent anode. CONCLUSIONS: Despite the relative small size of the rat sciatic nerve and the close apposition of tibial and peroneal fascicles, we proved the feasibility of using multipolar polyimide cuff electrodes to produce selective fascicular nerve stimulation.
Animals↗
Polyimide cuff electrodes for peripheral nerve stimulation.
This paper describes a new tripolar spiral cuff electrode, composed of a thin (10 microm) and flexible polyimide insulating carrier and three circumneural platinum electrodes, suitable for stimulation of peripheral nerves. The cuffs were implanted around the sciatic nerve of two groups of ten rats each, one in which the polyimide ribbon was attached to a plastic connector to characterize the in vivo stimulating properties of the electrode, and one without a connector for testing possible mechanical nerve damage by means of functional and histological methods. The polyimide cuff electrodes induced only a very mild foreign body reaction and did not change the nerve shape over a 2-6 month implantation period. There were no changes in the motor and sensory nerve conduction tests, nociceptive responses and walking track pattern over follow-up, and no morphological evidence of axonal loss or demyelination, except in one case with partial demyelination of some large fibers after 6 months. By delivering single electrical pulses through the cuff electrodes graded recruitment curves of alpha-motor nerve fibers were obtained. Recruitment of all motor units was achieved with a mean charge density lower than 4 microC/cm(2) for a pulse width of 50 micros at the time of implantation as well as 45 days thereafter. These data indicate that the polyimide cuff electrode is a stable stimulating device, with physical properties and dimensions that avoid nerve compression or activity-induced axonal damage.
Animals↗
[Optimal dosage strategies in total intravenous anesthesia using propofol and ketamine].
The combination of propofol and ketamine for total intravenous anesthesia was investigated; the intention was to minimize the side effects of each drug by the concomitant application of the other drug. METHODS. Twenty patients scheduled for lower abdominal interventions were divided into two groups. In the first group anesthesia was induced and maintained by a simple administration regimen based upon pharmacokinetic principles. Ketamine and propofol were given as bolus injections (60 mg each) with a time interval of 60 s for induction followed by a two-step infusion regimen for propofol (15.5 mg/min) and later on by an additional ketamine infusion (1-2 mg/min). Bolus injections (20 mg) of ketamine were administered to increase the depth of anesthesia if necessary (Fig. 1). The second group received propofol and ketamine by microprocessor-controlled infusion pumps requiring the anesthetist to operate a single dial to preset the desired blood levels of both drugs according to the needs of the individual patient (Fig. 2). RESULTS. There were no difference (Table 1) between the two groups in the demographic data of the patients or duration of surgery (30-120 min). The total doses of propofol (750 +/- 262 vs 624 +/- 468 mg) and ketamine (158 +/- 41 vs 99 +/- 48 mg) were smaller in the computer-controlled infusion group, though this difference just failed to be significant. The hemodynamic changes during induction were minor, with a small nonsignificant increase in all parameters (Fig. 3) for 10 min. The controllability of the pharmacodynamic effects of both drugs during anesthesia was very satisfactory in the computer-assisted infusion group and quite satisfactory in the first group. There were no psychic disturbances during induction of or recovery from anesthesia. Respiration was adequate within a few minutes after the end of surgery. The patients were awake about 10 min later and fully oriented after 20 min. No major side effects were observed with this anesthetic technique. CONCLUSION. Total intravenous anesthesia with propofol and ketamine proved to be very satisfactory from a clinical point of view. The major known side effects of propofol (reduced hemodynamics during induction) and ketamine (psychic disturbances and cardiovascular stimulation) were absent and respiratory function was adequate after the end of surgery. This technique, therefore, can be used in risk patients and under disaster conditions when i.v. access is the only possible route of drug administration. The use of computer-assisted infusion pumps markedly enhances handling and controllability of total i.v. anesthesia.
Adult↗