Chondroblastoma of the foot.

A total of 322 cases of chondroblastoma were referred to the Armed Forces Institute of Pathology between 1960 and 1990. Ten additional cases of chondroblastoma were treated at Walter Reed Army Medical Center between 1985 and 1993. Forty-two of these involved the foot, two of which were treated at Walter Reed Army Medical Center. Patients with chondroblastoma of the foot were male in 35 (81%) cases, with a mean age of 25.5 years, which was significantly different from the mean age of 17.3 years in patients with chondroblastoma of the long bones (P < 0.0001). Chondroblastoma of the foot is most commonly found in the posterior subchondral areas of the talus and calcaneus as well as in the calcaneal apophysis. Radiographically, the lesion was associated with an articular surface or apophyseal area in all cases and appeared radiolucent, with little to no matrix production. The margins were generally well defined. Cystic features were noted grossly and histologically in 24 (57%) specimens, a feature seen in only 21% of all chondroblastomas overall. Treatment consists of thorough curetting and bone grafting with good oncologic and functional results.

Acoustical effects of endotracheal intubation.

Certain acoustical consequences of endotracheal intubation were examined in 13 male cardiovascular-surgery patients. Each subject recorded three tokens of a sustained vowel 1 day before intubation, 1 day after, upon discharge, and during a follow-up visit. Eight acoustical measures were obtained from the audio-recorded vowels: (a) mean fundamental frequency (Fo), (b) Fo standard deviation, (c) Fo perturbation quotient, (d) mean sound pressure level (SPL), (e) SPL standard deviation, (f) SPL perturbation quotient, (g) spectral flatness of the residue signal, and (h) coefficient of excess. Mean Fo, Fo standard deviation, mean SPL, SPL standard deviation, and coefficient of excess did not differ significantly across recording sessions, although certain predictable trends were apparent. Fo perturbation quotient, SPL perturbation quotient, and spectral flatness of the residue signal varied significantly across sessions, implying that these acoustical measures may be useful in the identification and monitoring of even minor intubation-related laryngeal trauma.

The position and the state of the larynx during general anesthesia and muscle paralysis.

Based on a chance observation in two patients in whom the larynges could be visualized during direct laryngoscopy using topical anesthesia but not after general anesthesia and muscle paralysis, the authors postulated that there will be a shift in the position of the larynx with the onset of general anesthesia and muscle paralysis. To verify this the authors measured the position of larynx in lateral radiographs of necks taken in human volunteers when they were awake, and after induction of general anesthesia and muscle paralysis. The authors found that the hyoid bone and epiglottis were shifted anteriorly and the supraglottic region or the vestibule of the larynx was enlarged with the onset of general anesthesia and muscle paralysis. In addition, the larynx was also stretched longitudinally with wide separation of the vestibular and vocal folds. The authors conclude that consciousness is associated with tonic muscular activity that folds the larynx and partially closes it and that onset of general anesthesia and muscle paralysis opens the larynx wider and shifts it anteriorly, which might make visualization of the larynx during direct laryngoscopy difficult in some patients.

Orientation of fibers in human dorsal lumbar dura mater in relation to lumbar puncture.

Longitudinal insertion of a lumbar puncture needle bevel is less likely to cause post-lumbar puncture headache than is transverse insertion. The reason for this has not been entirely clear. We investigated the direction of dural fibers in posterior L3-4 dura mater obtained from three autopsies and tallied it in three orthogonal planes. Under low-power light microscopy the tissue appeared to be composed of lamellae branching irregularly and directed concentrically to the spinal cord. Electron micrographs (x5000) revealed that the lamellae consisted mainly of bundles of collagen fibers that pursued wavy courses in various directions. The lamellae also contained branching elastic fibers, many of which were directed longitudinally. This arrangement of fibers probably minimizes the tendency of a dural puncture hole to gape under tension if the needle bevel is directed longitudinally.

Mechanisms of differential axial blockade in epidural and subarachnoid anesthesia.

The mechanisms of persistent differential blocks that accompany subarachnoid and epidural anesthesia are clarified here with the aid of two principles derived from in vitro study of individual myelinated axons: 1) conduction can leap two consecutive blocked nodes but not three, and 2) a fiber length with more than three consecutive nodes bathed by weak anesthetic may block by decremental conduction, the requisite concentration varying inversely with the number of nodes bathed by anesthetic. Principle 1 applies in epidural blockade, where anesthetic bathes only a few millimeters of segmental nerve extradurally in the intervertebral foramen. Here, three-node block will be rare in large, long-internode fibers but likely in small, short internode fibers, thus explaining the differential retention of motor power in the presence of block of pain, which is achieved in epidural anesthesia when relatively weak solutions are used, as in obstetrics. Principle 2 may intervene in subarachnoid blockade where, cephalad to the site of puncture, increasingly concentrated anesthetic bathes increasing lengths of fibers in the craniocaudal succession of spinal nerve roots. This will produce decremental conduction block in increasingly long internode fibers in successive roots, reflected in a corresponding craniocaudal segmental sequence of blocked physiological functions: vasoconstriction, cutaneous temperature discrimination, pinprick pain sensibility, and skeletal motor activity. The segmental spatial differential sequence migrates with time but resembles the temporal differential sequence of loss seen at the onset of peripheral nerve blocks. Several other previously disparate clinical observations follow logically from the new interpretation.

Differential use-dependent (frequency-dependent) effects in single mammalian axons: data and clinical considerations.

The potential clinical scope of use-dependent block of conduction (UDB) was assessed by studying characteristics of UDB in vitro in individual mammalian axons. Single and repetitive stimulation was applied to rabbit cervical sympathetic and vagus nerves exposed to solutions containing lidocaine 0, 0.3, or 0.6 mmol/l (9.1 or 18.2 mg/dl) at 37 degrees C. Unit responses were recorded in dissected filaments or extracellularly in the vagus nodose ganglion. With lidocaine 0.3 mM, equilibrium conduction block, tested by single shocks, was rare. 40-Hz trains produced a significantly greater increase in latency (slowing of conduction) and a much greater incidence of UDB in the sympathetic units than in myelinated vagus axons of equivalent control conduction velocities or in unmyelinated axons. 10-Hz stimulation did not produce UDB. With lidocaine 0.6 mM, the incidence of equilibrium conduction block was too high among sympathetic axons to assess UDB, and significantly higher than among nonsympathetic myelinated and unmyelinated units. The observations support the hypothesis that the differential block of sympathetics observed clinically with spinal anesthesia may be, at least in part, a use-dependent (frequency-dependent) effect. UDB seems unlikely to contribute to local anesthetic block of pain impulses.

Lack of size-related differential sensitivity to equilibrium conduction block among mammalian myelinated axons exposed to lidocaine.

This study sought to evaluate the sensitivity of individual, relatively thick myelinated axons of mammalian nerve to equilibrium conduction block by lidocaine, and to compare this to the incidence of conduction block previously measured in individual thinner myelinated axons. The incidence of conduction block by lidocaine 0.3 and 0.6 mM (8.1-16.2 mg/dl) was determined on 35 individual axons in dissected filaments of rabbit recurrent laryngeal nerve (RLN) in which the control conduction velocity ranged from 28 to 77 m/sec. Thirty-four axons (97%) remained excitable in lidocaine 0.3 mM; 2 axons (6%) remained excitable in lidocaine 0.6 mM. These proportions did not differ significantly (P greater than 0.2) from those in thinner axons of vagus, either in comparisons with previous data from extracellular recordings or with new data from filament recordings. The results imply that differential blocks observed under clinical conditions probably depend on factors other than a size-related difference in the minimal equilibrium blocking concentration among myelinated axons. Equilibrium depression of the amplitude of RLN compound action potentials by lidocaine 0.3 and 0.6 mM was disproportionately great relative to the incidence of equilibrium conduction block in individual axons, confirming that depression of the compound action potential is not a reliable measure of nerve conduction block.

[Protective effect of lidocaine in maintaining the function of peripheral nerves]. / Der protektive Effekt von Lidocain auf die Funktionserhaltung der peripheren Nerven.

The conduction preserving effect of lidocaine was investigated in sheathed vagus nerves of the rabbit. The nerves were preincubated for one hour in solutions containing either 5 (group I, n = 12) or 20 mmol/l glucose (group II, n = 12). Subsequently, the nerves were deprived of glucose, one half of each group being exposed to 0.1 mmol/l (ca. 0.0025 g/dl) lidocaine hydrochloride. Lidocaine prolonged significantly the 50% and 100% extinction times of compound action potentials of both myelinated A and unmyelinated C axons: In group I, conduction was blocked within 120 +/- 11 and 123 +/- 9 minutes (mean +/- SEM) respectively, whereas in group II conduction block occurred within 174 +/- 16 resp. 183 +/- 17 minutes. In contrast, A and C compound action potentials of nerves incubated without lidocaine were extinguished within 69 +/- 5 and 78 +/- 6 minutes, respectively (group I, p less than 0.001) or 106 +/- 9 minutes (group II, p less than 0.005). The results suggest that administration of subblocking concentrations of lidocaine by standard Bier block technique may increase the margin of safety during operations employing a pneumatic tourniquet, especially if the blood flow to the nerves is impaired by vascular diseases or local anaesthetics containing adrenaline.

[Differential block of peripheral nerve fibers: the effect of lidocaine and potassium deficiency]. / Der Differentialblock der peripheren Nervenfasern: Die Effekte von Lidocain und Kaliummangel.

The combined effects of lidocaine and lack of glucose and potassium on conduction in A and C axons were investigated in vitro in rabbit vagus nerve. Extinction times of compound action potentials of A and C axons were determined in glucose and potassium deficient medium in the absence (group I, n = 6) or presence (group III, n = 6) of 0.1 mmol/l lidocaine hydrochloride. In group I, A fibers lost excitability within 120 +/- 9 min (mean +/- SEM) and the C axons within 133 +/- 6 min. In group III lidocaine prolonged significantly extinction times of both A and C axons (p less than 0.001); however, the conduction ceased in the unmyelinated (C) axons about 120 min later than in the myelinated (A) ones (p less than 0.05). In group II (n = 6) nerves were exposed to lidocaine for the same length of time as group I; these nerves exhibited an amplitude depression of the A and C potentials of less than 50%. In group IV, where 2 or 4 mmol/l KCl was present (n = 6 with each concentration) but no lidocaine, the extinction times decreased; the decrease was statistically significant for C axons but not for A axons. The analysis of nerve core electrolytes at the end of the exposures revealed the highest sodium and the lowest potassium contents in group III nerves. The controls (group I) contained more sodium and potassium than the nerves of group II. Thus a low concentration of lidocaine prolonged excitability in A and C axons deprived of glucose (group III).(ABSTRACT TRUNCATED AT 250 WORDS)