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Biomedical subjects

B Lynn

Publications and source records attributed to B Lynn.

At least 19 recordsLinked to original sources
PubMed2003

Longitudinal sliding of the median nerve in patients with carpal tunnel syndrome.

In nerve compression syndromes restricted nerve sliding may lead to increased strain, possibly contributing to symptoms. Ultrasound was used to examine longitudinal median nerve sliding in 17 carpal tunnel syndrome patients and 19 controls during metacarpophalangeal joint movement. Longitudinal movement in the forearm averaged 2.62 mm in controls and was not significantly reduced in carpal tunnel syndrome (CTS) patients (mean=2.20 mm). In contrast, CTS patients had a 40% reduction in transverse nerve movement at the wrist on the most, compared to least, affected side and nerve areas were enlarged by 34%. Normal longitudinal sliding in the patients indicates that nerve strain is not increased and will not contribute to symptoms.

Adult↗
PubMed2001

The use of cross-correlation analysis between high-frequency ultrasound images to measure longitudinal median nerve movement.

Impaired nerve movement can lead to nerve injury (e.g., carpal tunnel syndrome). A noninvasive method to measure nerve movement in longitudinal section would enable an extensive analysis of nerve entrapment syndromes. A method has been developed using cross-correlation between successive high-frequency ultrasound (US) images to measure longitudinal movement of nerve and muscle. Control "phantom" experiments demonstrated the accuracy and reliability of this method at velocities of 1-10 mm/s. Increasing the frame interval between the compared frames enabled the accurate calculation of slower velocities. The correlation algorithm successfully measured relative movement when the US transducer was moved 1-3 mm over the surface of the forearm. Median nerve movement was repeatedly measured in the forearm during 30 degrees passive wrist extension in three subjects (range 2.63-4.12 mm) and index finger extension in seven subjects (range 1.59-4.48 mm). Median nerve movement values were consistent with those from cadaver studies.

Adult↗
PubMed2001

The use of ultrasound imaging to demonstrate reduced movement of the median nerve during wrist flexion in patients with non-specific arm pain.

Following clinical screening, we examined movement of the median nerve at the wrist using high-resolution (10-22 MHz) ultrasound in 16 controls and 12 patients with non-specific arm pain (also referred to as repetitive strain injury). Imaging was performed just proximal to the carpal tunnel with the wrist in neutral, 30 degrees of extension and 30 degrees of flexion. In control subjects the position of the median nerve was 4.8 (SE=0.4) mm more radial with the wrist flexed than with the wrist extended. In the twelve arm pain patients the average change was only 1.2 (SE=0.5) mm. It appears that ultrasound imaging may be helpful in diagnosing non-specific arm pain, a condition for which there are no well-defined diagnostic tests at present. The reduced nerve movement seen with ultrasound imaging confirms previous work with magnetic resonance imaging.

Adolescent↗
PubMed2000

Acute traumatic myelopathy secondary to a thoracic cyst in a professional football player.

STUDY DESIGN: Case report of acute traumatic myelopathy secondary to thoracic synovial cyst in a professional football player. OBJECTIVE: To emphasize examination for myelopathy and describe the radiographic and magnetic resonance findings of a rare source of traumatic myelopathy. BACKGROUND: Magnetic resonance imaging is the best initial evaluation for myelopathy in a traumatic setting. Heightened awareness during evaluation of a player involved in a traumatic incident allowed the diagnosis of potential cord damage and paralysis. METHODS: A subject with symptoms resulting from a direct blow to the back was evaluated for myelopathy, with diagnosis assisted by magnetic resonance imaging used to pinpoint the source of the disorder. RESULTS: The diagnosis allowed a surgical excision of the traumatic synovial cyst and full recovery of the injured football player. CONCLUSIONS: Awareness during examination for myelopathy in an acutely injured athlete is imperative to prompt the clinician to order the proper diagnostic studies and thereby embark on a surgical correction of the problem.

Adult↗
PubMed1999

The relationship between axonal spike shape and functional modality in cutaneous C-fibres in the pig and rat.

Axonal spike shape was examined in identified cutaneous C-fibres dissected from the saphenous nerves of anaesthetized pigs and rats, and was found to vary with functional class. In the pig, the action potential duration for heat nociceptor units (duration at half peak amplitude, 1.25 +/- 0.16 ms, mean +/- S.E.M., n=32) was significantly longer than the duration for polymodal nociceptive units (0.88 +/- 0.11 ms, n=32). Both classes of nociceptive C-fibre had action potentials of longer duration than the low-threshold mechanoreceptor units (0.49 +/- 0.04 ms, n=24) and the inexcitable C-fibres (0.56 +/- 0.06 ms, n=19). Undershoot durations were also longer in nociceptive than non-nociceptive C-fibres. In contrast, spike amplitudes were similar in all classes of C-afferent. In the rat, as in the pig, the polymodal nociceptor units had action potentials of longer duration (0.75 +/- 0.05 ms, n=73) than the mechanoreceptor units (0.60 +/- 0.01 ms, n=23). C-fibres identified as spontaneously active sympathetic efferent units had wider action potentials (main initial peak: 1.01 +/- 0.12 ms, n=22; undershoot: 4.1 +/- 1.23 ms, n=20) than the afferent C-fibres (main peak: 0.69 +/- 0.03 ms, n=130; undershoot: 1.4 +/- 0.09 ms, n=111). All rat C-fibre types had action potentials with main initial peaks of a similar height. However, cold thermoreceptor units had spikes with significantly smaller undershoots compared to nociceptive or inexcitable C-fibres. It is concluded that there are clear differences in axonal spike shape between the different functional classes of C-fibre and, in particular, that nociceptive C-afferents tend to have axonal action potentials of longer duration than non-nociceptive afferents. The ion channels responsible for the longer duration action potentials may provide a target for the development of highly selective analgesic drugs.

Action Potentials↗
PubMed1999

Schwann cell-derived Desert hedgehog controls the development of peripheral nerve sheaths.

We show that Schwann cell-derived Desert hedgehog (Dhh) signals the formation of the connective tissue sheath around peripheral nerves. mRNAs for dhh and its receptor patched (ptc) are expressed in Schwann cells and perineural mesenchyme, respectively. In dhh-/- mice, epineurial collagen is reduced, while the perineurium is thin and disorganized, has patchy basal lamina, and fails to express connexin 43. Perineurial tight junctions are abnormal and allow the passage of proteins and neutrophils. In nerve fibroblasts, Dhh upregulates ptc and hedgehog-interacting protein (hip). These experiments reveal a novel developmental signaling pathway between glia and mesenchymal connective tissue and demonstrate its molecular identity in peripheral nerve. They also show that Schwann cell-derived signals can act as important regulators of nerve development.

Animals↗
PubMed1999

Dermatofibrosarcoma protuberans. A rare case involving the pediatric foot.

Dermatofibrosarcoma protuberans is a rare, slow-growing, locally destructive, intermediate-grade malignancy that originates in the dermal layer of the skin. Dermatofibrosarcoma protuberans rarely metastasizes and has a marked tendency to recur following local surgical excision. The lesion is found most commonly on the trunk, on the proximal aspect of both the lower and upper extremities, and in the head and neck region. Dermatofibrosarcoma protuberans occurs most commonly in people between the ages of 20 and 50. This article describes the clinical and pathologic features of this rare, malignant neoplasm and describes a rare case of dermatofibrosarcoma protuberans involving the pediatric foot.

Child↗
PubMed1998

Inhibition of forskolin-induced sensitisation of frog skin nociceptors by the cyclic AMP-dependent protein kinase A antagonist H-89.

The role of cAMP and protein kinase A (PKA) in nociceptor sensitisation has been studied in frog skin in vitro. Multifibre nerve responses during noxious heating were enhanced by adding forskolin, an agent that elevates cAMP. H-89, a PKA antagonist, blocked the increased responses due to forskolin, but did not affect baseline responses. Thus, cAMP appears to act via PKA when sensitising nociceptors in frog skin.

Action Potentials↗
PubMed1998

Vibration sense in the upper limb in patients with repetitive strain injury and a group of at-risk office workers.

OBJECTIVES: To investigate in patients with repetitive strain injury (RSI) and in office workers using computer keyboard equipment (a) whether the vibration threshold in the hand was altered, (b) the immediate effects of keyboard use on vibration thresholds and (c) whether the tolerance of suprathreshold vibration was normal. METHOD: A vibrametre (Somedic Ab, Stockholm Sweden) was used to obtain threshold vibration measurements, by the method of limits, for all peripheral-nerve cutaneous distributions in the hand. Tolerance of suprathreshold stimulation was obtained by stimulation of the soft tissues of the forearm by increasing the amplitude of vibration. RESULTS: Thresholds for vibration were significantly raised for the median nerve in both the patient and office-worker groups. The patient group additionally had raised thresholds for the ulnar nerve. Following use of the keyboard, thresholds for the median nerve were further elevated in the patient group, but not in the other groups, demonstrating a work-related exacerbation. At suprathreshold stimulation. 14 members (82%) of the patient group experienced an allodynic response to vibration, indicating, possible changes in the central processing of non-noxious sensory information. This changed sensory response was not seen in either the office-worker or control groups. CONCLUSION: Patients may have a minor polyneuropathy, whereas the office workers demonstrate early signs of the condition. Quantitative measurement of vibration perception may prove useful in patient assessment and for detection of the early onset of RSI in the work environment.

Adult↗
PubMed1997

The relationship between cutaneous C fibre type and antidromic vasodilatation in the rabbit and the rat.

1. Skin blood flow was monitored during antidromic stimulation of identified cutaneous C fibres in fine filaments dissected from the saphenous nerve of anaesthetized rabbits and rats. The techniques used to monitor skin blood flow were laser Doppler perfusion imaging and laser Doppler flowmetry. 2. In the rabbit filaments a total of thirty-three C fibres were tested for their ability to produce antidromic vasodilatation. The only C fibres found to have vasodilator actions were of the polymodal nociceptor afferent class, and fourteen (50%) of the twenty-eight polymodal nociceptor units tested were vasoactive. The afferent receptive fields of polymodal nociceptor afferents were mapped carefully using suprathreshold mechanical stimuli, and there was a good correlation between afferent receptive field area and area of vasodilatation. 3. In the rat, eleven of the fifty-four C fibres antidromically stimulated had vasodilator actions. All eleven vasoactive C fibres were nociceptive and comprised seven polymodal nociceptor units, two heat nociceptor units and two incompletely classified nociceptor units. The area of increased blood flow was always coincident with the afferent field of the stimulated unit. 4. In the rat the vasodilator units were not evenly distributed over the saphenous nerve receptive field. Nine of the eleven vasoactive C fibres had receptive fields located on the foot or the digits, and only two were on the ankle or lower leg. Overall, the population of nociceptive C fibres was evenly distributed over the saphenous nerve receptive field. 5. In both the rabbit and the rat, a subclass of polymodal nociceptor afferents form the majority of the vasoactive units and will make the main contribution to axon reflex flare and other neurogenic inflammatory responses involving vasodilatation. The vasoactive polymodal nociceptor units tend to have relatively low mechanical sensitivity, although they have typical heat thresholds. In the rat heat nociceptor units also have vasodilator actions. However, such heat nociceptor units form a minor functional class of afferent C fibre in the rat saphenous nerve, and are not found in the rabbit saphenous nerve. 6. The findings from this study in the rabbit and the rat are compared with the situation in pig skin. The close relationship between afferent receptive field area and spread of flare across species is noted, and the way these measures increase with body size is discussed.

Afferent Pathways↗
PubMed1997

The effect of topical turpentine on the functional properties of cutaneous afferents in the anaesthetized rat.

Turpentine was applied to the rat dorsal hindpaw over 1.5-3.5 h and afferent activity was recorded for 1.5-7 h after its removal. Increased spontaneous activity from both A- and C-fibres was observed. There was an increase in units with no response to natural stimuli and a reduction in the numbers of all types of afferent unit, with some recovery of the C- and A delta-classes during the recording period. Surviving C-polymodal nociceptor units had normal sensitivity to noxious heat, but higher mechanical thresholds. Thus turpentine application caused no nociceptor sensitization. Instead, the many insensitive units plus the generalized spontaneous firing may be signs of non-specific axonal damage. A general division of irritant chemicals into those that are predominately damaging, like turpentine, and those that generate specific nociceptor firing or sensitization, is proposed.

Administration, Topical↗
PubMed1996

The vasodilator component of neurogenic inflammation is caused by a special subclass of heat-sensitive nociceptors in the skin of the pig.

1. Skin blood flow has been imaged during stimulation of fine nerve filaments containing small numbers of identified C fibre units. Filaments were dissected from the saphenous nerve of anaesthetized pigs. 2. Stimulation of filaments containing C heat nociceptor units gave small areas of elevated blood flow (average increase 96%, n = 11) restricted to the afferent receptive field. The extent of the areas of raised blood flow was imaged completely for 8 units. The average extent of vasodilatation in the direction of greatest spread was 8 mm and the maximum spread in any unit was 13 mm. 3. Stimulation of C polymodal nociceptor units never caused increases in blood flow in or near their receptive fields. 4. Localized noxious stimuli (55 degrees C or intradermal injection of capsaicin) caused flare extending 7-15 mm in the same skin region. 5. In agreement with the axon reflex model, spread of flare was restricted to the zone innervated by the terminals of single C fibre units. 6. It is concluded that the C heat nociceptor units are the major class of afferent involved in the flare reaction in the skin of the pig. C polymodal nociceptor units do not appear to be involved in flare in this species. The probable situation in human skin, which is also innervated by heat nociceptors, is discussed.

Animals↗
PubMed1996

Activity-dependent slowing of conduction velocity provides a method for identifying different functional classes of C-fibre in the rat saphenous nerve.

Repetitive firing of nerve fibres results in the slowing of their conduction velocity. The extent of conduction velocity slowing throughout a standard electrical stimulus (20 s, 20 Hz, 2 x electrical threshold) was examined in identified C-fibres dissected from the saphenous nerve of anaesthetized rats. The aim of this study was to establish whether the different functional classes of C-fibre could be identified on the basis of their activity-dependent slowing of conduction velocity. Following 20 s of stimulation at 20 Hz, nociceptive C-fibres showed a significantly greater slowing of conduction velocity (mean +/- S.E.; polymodal and heat nociceptors = 29.2% +/- 0.7, n = 53; mechanical nociceptors = 27.7% +/- 1.7, n =13) than cold thermoreceptive fibres (10.8% +/- 0.6, n = 10), mechanoreceptors (14.4% +/- 0.8, n = 17) and spontaneously active sympathetic efferent units (14.9% +/- 0.8, n = 24). The degree of conduction velocity slowing shown by a unit was not correlated with its resting conduction velocity. There was little overlap of the degree of conduction velocity slowing between the nociceptive and non-nociceptive fibres. Also, there was little overlap of conduction velocity slowing between the mechanoreceptors and the cold units, particularly after just 6 s of stimulation at 20 Hz. Units for which no receptive field to mechanical or thermal stimuli could be found showed a bimodal distribution of conduction velocity slowing. In the saphenous nerve, such inexcitable units will be of three main types--sympathetic efferent units, "sleeping" or "silent" nociceptors and non-cutaneous afferent fibres. Those inexcitable units slowing in conduction velocity by greater than 20% showed a similar distribution to the polymodal nociceptors and those inexcitable units slowing by less than 20% showed a similar distribution to the spontaneously active sympathetic units. Twenty-three of the 61 units without mechanical or thermal receptive fields were investigated using electrical skin stimulation and topical application of 5 or 10% mustard oil. Afferent fields could not be found for any of the nine units that slowed in conduction velocity by less than 20%. Afferent fields were detected for 11 of the remaining 14 insensitive units, which all showed a greater than 20% slowing from resting conduction velocity. Therefore, one can distinguish nociceptive and non-nociceptive afferent fibres simply by looking at the axonal property of activity-dependent slowing of conduction velocity. Moreover, it is possible to use this axonal property to separate the two classes of non-nociceptive afferent C-fibre (i.e. mechanoreceptors and cold thermoreceptors). In addition, one can also use this parameter to differentiate between the afferent and non-afferent populations of inexcitable C-fibres. The ability to identify a particular fibre type on the basis of an axonal property provides a useful tool for the functional classification of fibres in experiments where axons are separated from their terminals.

Afferent Pathways↗