Window type of ductus arteriosus with shunt reversal.
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Adult↗
Biomedical subjects
A S Wee
Publications and source records attributed to A S Wee.
Acute rheumatic fever and carditis in older adults.
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Adult↗
Anodal block: can this occur during routine nerve conduction studies?
The median nerves of five normal subjects were electrically excited at the wrist with fine-tipped stimulating electrodes in a bipolar fashion. Compound sensory nerve action potentials (CSNAPs) were recorded from the index finger and compound muscle action potentials (CMAPs) from the thenar muscles. Both the cathode and the anode were positioned over the length of the nerve. Recordings were performed with different cathode-to-anode distances of 5, 10, 20, and in some cases, 30 mm. Just supramaximal CSNAPs and CMAPs were obtained initially with the cathode situated distal to the anode and then with the stimulus polarity reversed. There were no significant differences in the amplitude, duration, and morphology of the CSNAPs or CMAPs that were recorded by using different stimulus polarities. There was a consistent increase in the onset latency of the responses when the stimulus polarity was reversed (cathode located proximal to anode). This increase in latency was proportionate to the increase in distance from the cathode to the recording electrode. The effect of anodal block could not be observed from the above experiment.
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Comparison of the shock artifacts induced by tripolar and bipolar electrical stimulation techniques.
Tripolar and bipolar electrical stimulation procedures were performed on the upper limbs of eight subjects. The mid-forearm was stimulated electrically (tripolar or bipolar) by surface electrodes, and the induced stimulus shock artifacts were recorded simultaneously from the wrist and elbow. During tripolar stimulation, two types of stimulating configurations were utilized: with the center electrode designated as the cathode and the two outermost electrodes connected to a common anode, and vice versa. During bipolar stimulation, the center electrode served as one pole of the stimulator, and one of the two outermost electrodes of the tripolar stimulator was disconnected. The stimulus intensity was kept constant in all stimulating procedures. Artifacts were reduced significantly during tripolar compared to bipolar stimulation, if the outermost electrodes of the tripolar stimulator (which were facing the recording electrodes) were also oriented toward the recording sites during bipolar stimulation and had the same stimulus polarity. Artifacts were slightly reduced in amplitude from tripolar stimulation, if the center electrode were oriented toward the recording sites during bipolar stimulation and had the same stimulus polarity as previously used during tripolar stimulation.
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Carpal tunnel syndrome: a system for categorizing and grading electrophysiologic abnormalities.
A system for classifying and grading electrophysiologic abnormalities in carpal tunnel syndrome is described. It is based on criteria for assessing severity of: 1) focal nerve conduction slowing; 2) conduction block or dispersion in the responses; and 3) axonal loss. These criteria are applied separately to each component (sensory or motor) of the median nerve. The focal sensory conduction velocity (CV) slowing across the carpal tunnel is measured from ratios of the wrist-to-palm CVs to palm-to-finger sensory CVs; and motor conduction slowing, from ratios of the wrist-to-palm CVs to elbow-to-wrist motor CVs. The amount of amplitude loss due to dispersion or conduction block at the carpal tunnel is calculated from the amplitude ratios of the responses (sensory or motor) evoked at the wrist to those evoked at the palm. Axonal loss is estimated from reduction in the absolute amplitudes of sensory or motor responses evoked at the palm. This classification scheme is relatively simple, and it not only quantifies the abnormality, but it also suggests the pathophysiology.
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Effects of acute and chronic denervation on human myotonia.
A 32-year-old man with myotonia congenita (Becker type) sustained multiple gunshot wounds. These produced a partial thoracic spinal cord injury and a severe sciatic nerve injury. Six days following the incident, clinical (percussion) and electrophysiologic (EMG) myotonia could be elicited in paretic leg muscles resulting both from the myelopathy and peripheral nerve disruption. Eight months later, the myotonia was no longer present in denervated muscles from the sciatic nerve injury, but was still noted in muscles with upper-motor neuron weakness from the myelopathy. Although myotonia is related principally to abnormalities in the muscle fiber itself, it appears that it is also dependent upon the structural integrity of the peripheral nerve supply to the muscle for myotonia to continue to occur. The findings in this patient suggest that myotonia may well have diminished and disappeared in muscles shortly after the nerves had undergone Wallerian degeneration. Myotonia does not recur if there is no significant reinnervation.
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Ulnar nerve stimulation at the palm in diagnosing distal ulnar nerve entrapment.
Distal entrapment of the ulnar nerve at the wrist and hand (Guyon's syndrome) is a relatively uncommon condition. It may present with a confusing permutation of sensory and motor symptoms, depending on which branches of the ulnar nerve are involved Electrodiagnostic test procedures are often helpful in sorting out this quandary. Electrophysiologic studies that include electrical stimulation of the nerve at the palm, in addition to stimulation of the ulnar nerve at other locations, are useful in demonstrating the focal nerve conduction abnormality that is involved in the entrapment. Sensory and motor recordings from palmar stimulation of the ulnar nerve are not technically difficult procedures, and can be performed routinely.
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Correlation between the size of the compound muscle and sensory nerve action potentials recorded from the foot in distal axonopathy.
Nerve conduction study was performed on 71 diabetic patients with distal sensorimotor axonopathy. Of 76 lower limbs studied, 46.1% showed no recordable sural compound sensory nerve action potential (CSNAP), and 55.3% no superficial peroneal CSNAP. Only 2.6% revealed no recordable compound muscle action potential (CMAP) from the abductor hallucis (AH) muscle, and 9.2% showed no obtainable CMAP from the extensor digitorum brevis (EDB) muscle. There were fairly good positive correlations between the amplitudes of the sural CSNAPs and AH CMAPs (r = 0.66), and between the superficial peroneal CSNAP and EDB CMAP amplitudes (r = 0.63). There were no instances in which a CSNAP could be obtained from the sural or superficial peroneal sensory nerve, but a CMAP could not be recorded from the AH or EDB muscle. If the CMAP amplitudes of the AH and EDB muscles were reduced to less than 0.3 mV, usually a CSNAP could longer be recorded from the sural and superficial peroneal sensory nerves. The size of the CSNAP is a more sensitive measure compared to the CMAP in revealing the presence of distal sensorimotor axonopathy.
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Correlation between the biceps brachii muscle bulk and the size of its evoked compound muscle action potential.
This study was to determine if the size of the compound muscle action potential (CMAP) recorded from a large muscle, such as the biceps brachii, can be correlated with the muscle mass or volume that is generating the electrical response. Supramaximal CMAPs were obtained from 32 normal biceps brachii muscles to electrical stimulation of the musculocutaneous nerve at the axilla. Upper-arm circumference was measured with biceps muscle relaxed (elbow extended) and during muscle contraction (elbow flexed). For all muscles, mean CMAP duration was 16.45 ms, amplitude was 10.50 mV, and area was 96.13 mVms. Body mass index and absolute upper-arm circumference (biceps muscle relaxed or contracted) did not correlate with CMAP duration, amplitude, and area; Pearson correlation coefficients (r) ranged from -0.24 to 0.16. However, the difference (increment) in upper-arm circumference due to biceps muscle contraction correlated with CMAP duration (r = 0.47), amplitude (r = 0.67), and area (r = 0. 75). CMAP size (amplitude and area) correlated well with biceps brachii muscle volume as estimated by the increase from baseline in upper-arm circumference during muscle contraction. The difference (increment) in upper-arm circumference due to biceps muscle contraction reflects mainly the underlying biceps muscle bulk, and eliminates other variables such as thickness of the subcutaneous tissues and triceps brachii muscle.
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Carpal tunnel syndrome: comparison of the compound muscle action potentials recorded at the thenar region from ulnar and median nerve stimulation.
Thenar muscles are primarily innervated by the median nerve. However, compound muscle action potentials (CMAPs) evoked by ulnar nerve stimulation can be recorded at the thenar region due to proximity of some ulnar-innervated muscles, and from volume conduction events. This study was to determine if loss of thenar muscle mass from carpal tunnel syndrome (CTS) could alter the size of ulnar CMAPs obtained at the thenar region, because of changes in the physical surroundings and electrical conductivity. Supramaximal CMAPs were recorded over the thenar eminence to electrical stimulation of the ulnar nerve at the wrist and median nerve at the palm in 102 hands with CTS. Needle EMG was done in the thenar muscles. Severity of needle EMG abnormality was negatively correlated with median-evoked CMAP amplitude (r = -0.76), but not with ulnar-evoked CMAP amplitude (r = -0.12). There was no correlation between the absolute amplitudes of the median and ulnar CMAPs (r = -0.13). Needle EMG abnormality had modest negative correlation (r = -0.43) with median/ulnar CMAP amplitude ratio. Mean median/ulnar CMAP amplitude ratios for normal EMG and for mild, moderate, and severe needle EMG abnormalities were 3.72, 3.31, 1.56, and 0.37, respectively. The absolute amplitude of the ulnar CMAP recorded at the thenar area does not seem to be influenced significantly by the degree of thenar muscle loss (atrophy) from median nerve pathology. However, if the median/ulnar CMAP amplitude ratio falls below 0.5, the study suggests severe loss of motor units in the thenar muscles.
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Transmission of acoustic or vibratory signals from a contracting muscle to relatively distant tissues.
In 20 normal subjects, acoustic or vibratory signals generated during sustained voluntary isometric contraction of the biceps brachii muscle were recorded directly over the muscle belly. The signals were also recorded simultaneously at a distance from the contracting biceps muscle over the posterior upper arm near the triceps muscle. Frequency amplitude spectra (FAS) of the recordings were determined. The amount of transmission of the most dominant vibratory signal from the biceps muscle to the posterior arm was estimated from the amplitude ratio of similar frequency peaks in the FAS obtained from recordings in these two separate regions. The mean amplitude ratio was 0.46. This finding suggests that when several groups of muscles are contracting simultaneously, there may be significant transmissions of acoustic signals from one muscle to the other. These transmissions could potentially interfere with the selective recording of sounds produced by a specific muscle.
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Effect of interelectrode recording distance on morphology of the antidromic sensory nerve action potentials at the finger.
In 15 normal subjects, antidromic median sensory compound nerve action potentials (SCNAPs) were recorded supramaximally from the middle finger with ring electrodes, using different interelectrode recording distances. The onset latencies were identical in all recording instances. The peak latency and amplitude of the major negative deflection continued to increase with increasing interelectrode distance. At and beyond a 4 cm interelectrode recording separation, they both achieved maximum values and did not increase further. On the other hand, the duration and area did continue to increase with increasing interelectrode separation. These findings suggest that in normal individuals, the true onset latency, peak latency, and amplitude are well reflected in the median SCNAP when it is recorded with an interelectrode distance of 4 cm or more at the finger; thus, they can easily be standardized. The SCNAP duration and area, however, are more variable since they both continue to change with increasing interelectrode recording separation without approaching a saturation value.
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Relationship between the size of the recording electrodes and morphology of the compound muscle action potentials.
To determine the effect of recording electrode size on the compound muscle action potentials (CMAPs), maximally evoked CMAPs were obtained from the abductor digiti minimi muscle in ten normal subjects with circular-shaped surface recording electrodes of different diameters (4, 6, 8, 10, 12, and 14 mm). The electrodes were concentrically located on the same recording point on the muscle at its endplate zones when obtaining the CMAPs. The CMAP onset latency remained unchanged for all recording electrode sizes. The CMAP amplitude decreased with increasing electrode size. The mean absolute amplitude difference between CMAPs recorded with a 4-mm diameter electrode and those with a 14-mm diameter electrode was 1.22 mV, representing an amplitude decrement of 10% with this increase in electrode size. The general shape or morphology of the CMAPs was relatively well preserved.
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Vibrations and sounds produced during sustained voluntary muscle contraction.
In 20 normal subjects, sounds or vibrational signals were recorded from the biceps brachii muscle during voluntary isometric contraction. Fourier analysis showed presence of predominantly low frequency components with little contributions beyond 60 or 70 Hz. Relatively high amplitude peaks occurring below 20 Hz were seen in the frequency spectrum with the most prominent of these peaks occurring at a mean frequency of 11.3 Hz. A majority of subjects had one or two additional peaks, each appearing on either side of the major peak with mean frequencies of 7.3 and 16.2 Hz. In general, subjects who could not sustain a very steady contraction had more peaks compared to those who were able to maintain a smoother contraction. Between 20 and 50 Hz, several well-defined but much smaller peaks were also seen. The frequencies of some of these small peaks can be expressed as exact harmonics of the previously described larger peaks in 85% of subjects.
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Radial sensory innervation to index and middle fingers: electrophysiologic considerations.
Antidromic radial and median compound sensory nerve action potentials (CSNAPs) were recorded from the index and middle fingers in 20 subjects. No appreciable radial sensory response can be seen at the middle finger. Seventy-five percent of subjects had radial CSNAPs at the index finger, seen to a variable extent along the finger, with 40% having a response limited only to the base of the first phalanx. Radial CSNAP amplitude was small compared to median CSNAP (ratio = 0.16). Because of the small size and wide variability among individuals, radial CSNAPs from index and middle fingers seem to have limited direct clinical utility. Contamination of median CSNAPs by radial CSNAPs is negligible or absent (when there is unavoidable spread of the stimulus to the radial nerve), if median sensory responses are recorded from the distal half of the index or middle finger.
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Where is the ideal reference site for recording the thenar compound muscle action potential.
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The sinus node in cor pulmonale.
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Adult↗