Biomedical subjects

K Ming Chan

Publications and source records attributed to K Ming Chan.

10 recordsLinked to original sources

PubMed2006

Transcranial direct current stimulation of the primary motor cortex affects cortical drive to human musculature as assessed by intermuscular coherence.

Intermuscular coherence analysis can be used to assess the common drive to muscles. Coherence in the beta-frequency band (15-35 Hz) is thought to arise from common cortical sources. Intermuscular coherence analysis is a potentially attractive tool for the investigation of motor cortical excitability changes because it is non-invasive and can be done relatively quickly. We carried out this study to test the hypothesis that intermuscular coherence analysis was able to detect cortical excitability changes in healthy subjects following transcranial direct current stimulation (tDCS). tDCS has been shown to increase (anodal stimulation) or decrease (cathodal stimulation) the size of the muscle potential evoked by TMS. We found that anodal tDCS caused an increase in motor evoked potential (MEP) size that was paralleled by an increase in beta-band intermuscular coherence. Similarly, the reduction in MEP size produced by cathodal tDCS was paralleled by a reduction in beta-band intermuscular coherence, while sham stimulation did not result in any change in either MEP amplitude or beta-band intermuscular coherence. The similar pattern of change observed for MEP and intermuscular coherence may indicate similar mechanisms of action, although this cannot be assumed without further investigation. These changes do suggest that at least some of the action of tDCS is on cortical networks, and that combined tDCS and intermuscular coherence analysis may be useful in the diagnosis of pathologies affecting motor cortical excitability.

Adult↗

PubMed2006

Randomized controlled trial of modafinil for the treatment of fatigue in postpolio patients.

The purpose of this study was to test whether modafinil is effective in alleviating the symptoms of fatigue in postpolio patients, because it has been helpful for such symptoms in other neurologic disorders. Using a double-blind, randomized, placebo-controlled cross-over design, 14 postpolio patients with moderate to severe fatigue were assigned to receive modafinil or placebo first. Piper Fatigue Scale, Epworth Sleepiness Scale, digit span, and reaction time tests were done at baseline and then at weekly intervals. The Piper Fatigue Scale scores improved by 27 +/- 40% (mean +/- SD) following modafinil and by 43 +/- 36% following placebo. Scores for most of the other tests did not change during the study. Therefore, we conclude that modafinil was not effective in alleviating the symptoms of fatigue in postpolio patients.

Benzhydryl Compounds↗

PubMed2005

BIONic WalkAide for correcting foot drop.

The goal of this study was to test the feasibility and efficacy of using microstimulators (BIONs) to correct foot drop, the first human application of BIONs in functional electrical stimulation (FES). A prototype BIONic foot drop stimulator was developed by modifying a WalkAide2 stimulator to control BION stimulation of the ankle dorsiflexor muscles. BION stimulation was compared with surface stimulation of the common peroneal nerve provided by a normal WalkAide2 foot drop stimulator. Compared to surface stimulation, we found that BION stimulation of the deep peroneal nerve produces a more balanced ankle flexion movement without everting the foot. A three-dimensional motion analysis was performed to measure the ankle and foot kinematics with and without stimulation. Without stimulation, the toe on the affected leg drags across the ground. The BIONic WalkAide elevates the foot such that the toe clears the ground by 3 cm, which is equivalent to the toe clearance in the unaffected leg. The physiological cost index (PCI) was used to measure effort during walking. The PCI is high without stimulation (2.29 +/- 0.37; mean +/- S.D.) and greatly reduced with surface (1.29 +/- 0.10) and BION stimulation (1.46 +/- 0.24). Also, walking speed is increased from 9.4 +/- 0.4 m/min without stimulation to 19.6 +/- 2.0 m/min with surface and 17.8 +/- 0.7 m/min with BION stimulation. We conclude that functional electrical stimulation with BIONs is a practical alternative to surface stimulation and provides more selective control of muscle activation.

Adult↗

PubMed2004

Double-blind randomized controlled trial of low-level laser therapy in carpal tunnel syndrome.

Several studies have suggested that low-level laser therapy (LLLT) is effective in patients with carpal tunnel syndrome (CTS). In a double-blind randomized controlled trial of LLLT, 15 CTS patients, 34 to 67 years of age, were randomly assigned to either the control group (n = 8) or treatment group (n =7). Both groups were treated three times per week for 5 weeks. Those in the treatment group received 860 nm galium/aluminum/arsenide laser at a dosage of 6 J/cm2 over the carpal tunnel, whereas those in the control group were treated with sham laser. The primary outcome measure was the Levine Carpal Tunnel Syndrome Questionnaire, and the secondary outcome measures were electrophysiological data and the Purdue pegboard test. All patients completed the study without adverse effects. There was a significant symptomatic improvement in both the control (P = 0.034) and treatment (P =0.043) groups. However, there was no significant difference in any of the outcome measures between the two groups. Thus, LLLT is no more effective in the reduction of symptoms of CTS than is sham treatment.

Adult↗

PubMed2003

Electrical stimulation of the human common peroneal nerve elicits lasting facilitation of cortical motor-evoked potentials.

Motor-evoked potentials (MEP) in the tibialis anterior (TA) muscle were shown to be facilitated by repetitive electrical stimulation of the common peroneal (CP) nerve at intensities above motor threshold. The TA electromyogram (EMG) and ankle flexion force were recorded in response to transcranial magnetic stimulation (TMS) of the leg area of the motor cortex to evaluate the excitability of cortico-spinal-muscular pathways. Repetitive stimulation of the CP nerve at 25 Hz for 30 min increased the MEP by 50.3 +/- 13.6% (mean +/- S.E.) at a TMS intensity that initially gave a half-maximum MEP (MEPh). In contrast the maximum MEP (MEPmax) did not change. Ankle flexion force (103 +/- 21.9%) and silent period duration (75.3 +/- 12.9%) also increased. These results suggest an increase in corticospinal excitability, rather than total connectivity due to repetitive CP stimulation. Facilitation was evident after as little as 10 min of stimulation and persisted without significant decrement for at least 30 min after stimulation. The long duration of silent period following CP stimulation (99.2 +/- 14.8 ms) suggests that this form of stimulation may have effects on the motor cortex. To exclude the possibility that MEPh facilitation was primarily due to sensory fibre activation, we performed several control experiments. Preferentially activating Ia muscle afferents by vibration in the absence of motor activity had no significant effect. Cutaneous afferent activation via stimulation of the superficial peroneal nerve increased the amplitude of responses at MEPmax rather than MEPh. Concurrent tendon vibration and superficial peroneal nerve stimulation failed to facilitate TA MEP responses. In summary, repetitive electrical stimulation of the CP nerve elicits lasting changes in corticospinal excitability, possibly as a result of co-activating motor and sensory fibres.

Adult↗

PubMed2003

Randomized controlled trial of strength training in post-polio patients.

Many post-polio patients develop new muscle weakness decades after the initial illness. However, its mechanism and treatment are controversial. The purpose of this study was to test the hypotheses that: (1) after strength training, post-polio patients show strength improvement comparable to that seen in the healthy elderly; (2) such training does not have a deleterious effect on motor unit (MU) survival; and (3) part of the strength improvement is due to an increase in voluntary motor drive. After baseline measures including maximum voluntary contraction force, voluntary activation index, motor unit number estimate, and the tetanic tension of the thumb muscles had been determined, 10 post-polio patients with hand involvement were randomized to either the training or control group. The progressive resistance training program consisted of three sets of eight isometric contractions, three times weekly for 12 weeks. Seven healthy elderly were also randomized and trained in a similar manner. Changes in the baseline parameters were monitored once every 4 weeks throughout the training period. The trained post-polio patients showed a significant improvement in their strength (P < 0.05). The magnitude of gain was greater than that seen in the healthy elderly (mean +/- SE, 41 +/- 16% vs. 29 +/- 8%). The training did not adversely affect MU survival and the improvement was largely attributable to an increase in voluntary motor drive. We therefore conclude that moderate intensity strength training is safe and effective in post-polio patients.

Aged↗

PubMed2003

Compression of the ulnar nerve at the elbow by an intraneural ganglion.

A rare cause of ulnar nerve compression at the elbow is presented in this report. A 42 year old right-handed mechanic developed subacute, progressive numbness, tingling and weakness in his right hand. Electrophysiologic studies demonstrated a severe conduction block affecting the ulnar nerve in the retrotrochlear groove but without any sign of major axonal loss. His hand functions were carefully studied prior to surgery. While fine motor tasks were not affected, the hand strength was markedly diminished. At surgery, a 1-cm diameter intraneural ganglion at the site of the conduction block was found and excised. The patient made a dramatic recovery within 6 weeks post-surgery. The conduction block completely resolved and the hand functions also returned to normal. This and other reported cases point to the importance of early diagnosis and intervention.

Adult↗

PubMed2003

Applicability, validity, and reliability of the Piper Fatigue Scale in postpolio patients.

OBJECTIVE: To identify a scale that is potentially applicable for measuring the fatigue in postpolio patients and to evaluate its validity and reliability in this population. DESIGN: Interview survey of 64 individuals with postpolio syndrome and 25 healthy controls of similar age range, with retest in a subset of postpolio patients. The sample was recruited from a postpolio support group, a postpolio clinic, and the general community. Subjects completed the Piper Fatigue Scale, the Beck Depression Inventory, and the Chalder Fatigue Questionnaire during the interview. RESULTS: Face and content validity of the Piper Fatigue Scale was established by a team of experts and by a group of postpolio patients. The postpolio subjects had significantly higher Piper Fatigue Scale scores than the healthy control subjects (P < 0.001), demonstrating extreme groups validity. Convergent validity was shown with a strong positive correlation between Piper Fatigue Scale scores and Chalder Fatigue Questionnaire scores (r = 0.80). Reliability was also demonstrated with the Piper Fatigue Scale's high internal consistency (alpha = 0.98) and strong test-retest agreement (intraclass correlation coefficient = 0.98). CONCLUSIONS: The Piper Fatigue Scale is a valid and reliable tool for measuring postpolio fatigue. This scale may be useful in other studies of postpolio fatigue, including those gauging the effectiveness of various treatments for this fatigue.

Activities of Daily Living↗

PubMed2003

The impact of ulnar nerve compression at the elbow on the hand function of heavy manual workers.

The objectives of this article were to study the impact of the hand function disability due to ulnar neuropathy at the elbow (UNE) on workers engaged in occupations requiring heavy hand use. Four patients (42.5 +/- 7 years old), all engaged in heavy-duty jobs, with severe conduction block but without severe axonal loss were recruited. The severity of ulnar nerve compression was quantified based on electrophysiologic studies, Jebsen-Taylor Hand Function Test, Jamar dynamometer, and Semmes-Weinstein Monofilaments Test. UNE resulted in a reduction in hand strength without any significant impact on fine motor dexterity. The 4 laborers whose work required strong hand grip found this debilitating. Severe UNE affects the hand function of heavy manual workers by impeding their grip and pinch strengths. However, UNE does not affect tasks requiring fine hand dexterity.

Adult↗

PubMed2000

Use of the collision technique to improve the accuracy of motor unit number estimation.

OBJECTIVE: To evaluate the risk of stimulating the same motor axon at different points along the median nerve when using the multiple point stimulation (MPS) technique and how this affects the accuracy of the motor unit number estimate (MUNE). METHODS: Using the MPS technique, MUNE in the median innervated intrinsic hand muscles was done on two normal subjects, a patient with carpal tunnel syndrome and one with prior poliomyelitis. The collision technique was then used to confirm whether two motor unit action potentials (MUAPs) with similar configurations and sizes were generated by the same motor unit. A new MUNE was recalculated after the repeated inclusion of the same motor unit had been excluded. RESULTS: While the risk of stimulating the same motor axon at widely separate locations of the median nerve was negligible in normal subjects, this risk was much higher in patients with a depleted motor neuron pool. This resulted in marked distortion of the calculated size of the average single MUAP and, consequently, inaccuracy of the MUNE. CONCLUSIONS: The inadvertent inclusion of the same motor units, if not recognized, can markedly affect the accuracy of the MUNE. The collision technique can be useful in minimizing this risk.

Action Potentials↗