Voluntary and involuntary adaptation of gait in Parkinson's disease

Voluntary and involuntary adaptation of gait in Parkinson's disease (PD) were studied in two separate experiments. In the first experiment, effects of changes in voluntary control were studied by asking PD patients and age-matched healthy subjects to adapt their walking pattern to visual cues resulting in spatial constraints, and auditory cues resulting in temporal constraints on stepping movements. In the second experiment, the adaptation to increases in speed during overground and treadmill walking was studied. Most patients were able to adapt their walking patterns in accordance with instructions. Notwithstanding consistent differences in step length, the adaptation to different conditions under study was highly similar in PD patients and healthy subjects. Only during walking with visually guided step length were the observed adaptations in PD patients less consistent. Contrary to these dissimilarities, the involuntary adaptation of timing of support and swing phases within the stride cycle was very similar between groups. In all conditions, only with changes in step length could a change in relative timing be observed. Our findings show that voluntary adaptation of gait is possible in PD and that basic involuntary coordination mechanisms are preserved. The observed disturbances in stride length regulation probably reflect an inability to perform fast movements in PD. (C) 1998 Elsevier Science B.V

Hemifacial spasm:Intraoperative electromyographic monitoring as a guide for microvascular decompression

OBJECTIVE: Microvascular decompression is the logical and well-accepted treatment of choice for hemifacial spasm (HFS). In experienced hands, good to excellent results can be obtained. However, sometimes the exact site of the vascular compression is unclear. The aim of this study was to analyze whether intraoperative monitoring by stimulated electromyography of the facial nerve may help to improve the results of vascular decompression for HFS. METHODS: In a series of 74 patients operated for HFS, the impact of intraoperative facial nerve monitoring on the surgical procedure was analyzed by use of the clinical and operative patient records. The role of this type of monitoring, with assessment of the so-called abnormal muscle response, was broken down into four categories: a guiding, a confirming, an indirect confirming, or an inconclusive role. The relationship between abnormal muscle response monitoring results and final surgical outcome was analyzed. RESULTS: The overall cure rate was 87.8%, including patients who had previously undergone unsuccessful operations. Complications were minor, and hearing impairment was found in 2.7% of patients. A guiding role of intraoperative monitoring was apparent in 33.8% of patients, and a confirming role was demonstrated in 52.7% of patients, which resulted in a positive contribution of approximately 87% for intraoperative facial monitoring in microvascular decompression for HFS. In patients defined as guiding cases, the cure rate was 92%. CONCLUSION: This study demonstrates the applicability and usefulness of intraoperative facial nerve monitoring in microvascular decompression operations for HFS

Long‐lasting supernormal conduction velocity after sustained maximal isometric contraction in human muscle

Local muscle fatigue (1 min maximal voluntary contraction) and recovery were studied by means of surface and invasive EMG on elbow flexors to record the changes in muscle fiber conduction velocity (MFCV), median power frequency (MPF), integrated EMG (IEMG), and force. The main finding was a long-lasting ''supernormal'' MFCV during recovery, for at least 1 hour. After a normalization phase, the MFCV and MPF continued to increase reaching a steady state at supernormal values after 10-12 min. Mean MFCV increase at 20% MVC after 15-min recovery was 0.58 m . s-1 (12%). Postfatigue IEMG values were increased at all contraction levels. In combination with near normal force levels, this resulted in a decrease in ''neuromuscular efficiency'' (force/IEMG). We suggest that this IEMG increase is mainly a result of the MFCV increase. The MFCV changes in fastest and slowest fibers found with the invasive method indicate a relatively equal effect on type I and II fiber types. A possible explanation of the supernormal MFCV is muscle fiber swelling, in combination with altered membrane properties

Muscle Fiber Conduction Velocity in Amyotrophic Lateral Sclerosis and Traumatic Lesions of the Plexus Brachialis

Muscle fiber conduction velocity (MFCV) in biceps brachii was studied in traumatic brachial plexus lesions (16 patients) and amyotrophic lateral sclerosis (ALS) (22 patients) by means of an invasive (S-MFCV) and a surface (S-MFCV) method. After complete denervation an exponential decrease of the mean I-MFCV was found, T-1/2 =1.1 month. After 4-5 months this resulted in severely reduced conduction velocities (mean 1.4 m/sec, range from 0.5 to 2 m/sec). Simultaneous with signs of reinnervation, fibers with faster conduction velocities were seen. In ALS, a decrease of the mean I-MFCV was found, and slow conducting fibers were found in every patient on at least one side. At the same time muscle fibers with increased I-MFCVs were found. This increased range of velocities seems based on a combination of slow conducting, atrophic fibers, with fast conducting, hypertrophic fibers, compensating the force loss. In some subjects we found these disturbances without clear abnormalities with concentric needle EMG, and with unimpaired muscle force. The surface EMG measurements in the ALS patients revealed increased S-MFCV values in combination with a decrease of the median frequency (F-med). We suggest that the opposite finding of an increased S-MFCV is a consequence of the muscle fiber hypertrophy in the surviving, voluntarily recruited, motor units. The simultaneous decrease of the F-med seems to be caused mainly by the change in shape of the motor unit potential