The dynamics of the vestibulo-ocular reflex (VOR) were studied in 14 patients at the onset of vestibular neuritis, and at follow-up 1 year later. A velocity step stimulus of 150 degrees/s was used to investigate the VOR time constant and gain, and the results were related to the caloric response. In the acute, vertiginous phase of the disease, the VOR time constant was reduced but was almost normalized 1 year later, both among patients who regained normal caloric side-difference and among those who did not. However, the increase in VOR time constant was greater among those who regained normal caloric excitability, and regression analysis showed a correlation between the prolongation of the VOR time constant and the recovery of caloric excitability. These findings suggest that VOR dynamics are modulated during the acute phase of vestibular neuritis, and that there is recovery with vestibular compensation. Furthermore, the recovery of the VOR time constant is not solely dependent on the recovery of normal caloric excitability. This implies that central storage of velocity information may be involved in the VOR, even in cases of asymmetric vestibular input after vestibular compensation.

Adolescent↗

PubMedDate not supplied

Evaluation of methods for shaded surface display of CT volumes.

There are several ways to compute a shaded surface display of radiological 3D density volumes. In this paper we evaluate 12 methods which are different combinations of principles for detection of the surface to be displayed (gray-value threshold, gradient threshold, zero-crossing of 2nd derivative), localizing this surface in space (grid-point accuracy, subvoxel accuracy) and finally estimating the direction of the surface normal (from the gradient in the 2D depth image, from the gradient in the 3D-volume). The best quality is obtained by zero-crossing detection, subvoxel localization, and 3D-gradient orientation.

Data Display↗

PubMedDate not supplied

Effect of alertness and visual attention on optokinetic nystagmus in humans.

The effect of alertness and visual attention on optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN) was studied in 20 volunteers. Electroencephalographic (EEG) activity was recorded over the occipital lobe. Exposure to sound and vibration caused a significant increase in the mean slow-phase velocity of OKN, whereas its maximum slow-phase velocity remained unaffected. Vibration tended to increase the mean slow-phase velocity of OKN more than sound did, though the difference was not statistically significant. Vibration also significantly increased the OKAN. When alpha rhythm appeared in the occipital EEG during OKN, the velocity of concurrent slow phases was reduced. However, the periods of alpha rhythm did not differ between the different stimulus conditions. The findings suggest that sound and vibration activate the subcortical optokinetic mechanism, thus causing an increase in the mean velocity of OKN. Abatement of visual attention is reflected in temporary reduction of OKN in conjunction with the appearance of alpha waves and is to be interpreted as transient quiescence of the cortical optokinetic mechanism.

Acoustic Stimulation↗

PubMedDate not supplied

Effect of alertness on the vestibulo-ocular reflex and on the slow rise in optokinetic nystagmus in rabbits.

The effect of alertness on the time constant of the vestibulo-ocular reflex (VOR) and the time constant of the slow rise of the optokinetic nystagmus (OKN) was studied in nine pigmented rabbits. When the rabbits were alerted by vibration, the time constant of the VOR was prolonged, and that of the slow rise in OKN was shortened, whereas the gain of VOR and OKN remained largely unaffected. These findings agree with the suggestion that the state of alertness affects the vestibular system by way of the so-called velocity storage mechanism.

Algorithms↗

PubMedDate not supplied

Mycobacterial sensitins: where are we now?

A limited review of the results of using comparative reciprocal intradermal mycobacterial sensitin (CRIS) testing with guinea pigs for the classification and identification of mycobacteria is presented. The technical procedures and the materials used in CRIS testing are referred to only briefly. Strains of mycobacteria that grow well on a synthetic nonimmunogenic medium can be identified or classified at the species level with this method. At present some 50 species of mycobacteria can be identified by CRIS testing. With this method alone, delineation between the genera Mycobacterium and Nocardia (or between subgenera of Mycobacterium proposed earlier) and differentiation between individual strains of Mycobacterium tuberculosis, Mycobacterium bovis, and Mycobacterium africanum are not possible. In a blind study that utilized CRIS testing, a total of 10 strains of Mycobacterium avium complex serovars 1, 2, 4, and 6 and one strain of serovar 9 were identified as M. avium; a total of five strains of serovars 14, 16, 17, and 20 and one strain of serovar 12 were identified as Mycobacterium intracellulare; a total of seven strains of serovars 41, 42, and 43 and two other strains of serovar 9 were identified as Mycobacterium scrofulaceum; and two other strains of serovar 9 appeared to be distinct from M. avium and from the other two species just mentioned (author's unpublished data). CRIS tests cannot be used at present for the identification of mycobacteria that cannot be cultivated.

Animals↗

PubMedDate not supplied

A preliminary study of joint surface changes after an intraarticular fracture: a sheep model of a tibia fracture with weight bearing after internal fixation.

OBJECTIVE: To evaluate the changes in the articular cartilage and subchondral bone after an osteotomy designed to simulate an articular fracture. DESIGN: The contribution of the cartilage and subchondral bone was evaluated twelve weeks after creating a 1.0-millimeter step-off in the medial plateau of the tibia of twelve adult domestic sheep. All animals surviving were labeled with fluorescent markers for bone production, oxytetracycline (fifty milligrams per kilogram), and calcein (twelve milligrams per kilogram) nine and 11.5 weeks after surgery. The knees were loaded in compression using an Instron materials tester with pressure-sensitive film to record joint contact pressures above and below the medial meniscus. SETTING: The studies were performed in the research laboratories of the Orthopaedic Laboratory at Harborview Medical Center in Seattle, Washington and the Madigan Army Medical Center in Tacoma, Washington. ANIMALS: Twelve adult domestic sheep. INTERVENTION: An intraarticular osteotomy of the medial tibial plateau with 1.0 millimeter of displacement was performed. The osteotomy was stabilized with 3.5-millimeter lag screws. MAIN OUTCOME MEASURES: The contact pressures of the knee joint and articular histology were evaluated twelve weeks after surgery. Samples of the articular cartilage were analyzed by light microscopy and electron microscopy to evaluate the response of the articular cartilage and subchondral bone of the differential joint loading because of the irregularity in the articular surface caused by the osteotomy. RESULTS: The knees with an intraarticular step-off had two major contact areas with an intervening zone of reduced load corresponding to the edge of the depressed fragment. Coronal histologic sections through the articular surface showed the presence of thinning and fibrillation on the high side of the step-off and some compensatory hypertrophy of the cartilage. The subchondral bone was not responsible for restoring articular congruity because the rate of bone production was similar between the low side of the articular fracture (1.85 micrometers per day) and the high side of the fracture (1.67 micrometers per day). Scanning electron microscopy showed partial cartilage remodeling by deformation of the high side cartilage with bending of the vertical collagen fibrils, even in the unloaded state. CONCLUSIONS: In this model with a small fracture displacement (1.0 millimeter), which was less than the thickness of the articular cartilage (1.5 millimeters), the contour of the joint improved despite residual articular surface incongruency after the fracture healing.

Animals↗

PubMedDate not supplied

Adaptation to vibratory perturbations in postural control.

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Adaptation, Physiological↗

PubMedDate not supplied

Intraoperative blood transfusions and hyperacute renal allograft rejection in a presensitized recipient.

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Blood Transfusion↗

PubMedDate not supplied

Transtympanic electrocochleography in the assessment of perilymphatic fistulas.

An objective method for the pre-operative diagnosis and the post-operative assessment of a presumed perilymphatic fistula (PLF) using transtympanic electrocochleography is presented. Three cases are reported in which the history of the disease and the symptoms strongly suggested the presence of a PLF. Pre-operative transtympanic electrocochleography (TT ECoG) recordings at rest showed changes similar to those of endolymphatic hydrops and signs of instability of the inner ear hydrodynamic system during raised intrathoracic pressure. Surgery revealed a visible leak in two of the three cases. Both windows were repaired in all the patients. All patients were relieved from their vestibular symptoms at the time when the post-operative TT ECoG was conducted 3-6 months later. The post-operative recordings were stable during raised intrathoracic pressure and the previously elevated summating potentials decreased which was interpreted as an objective indication of the recovery of the hydrodynamic system. However, later one of the patients again developed recurrent vertigo. Twenty patients with well-documented Ménière's disease were used as a control group. TT ECoG was conducted during raised intrathoracic pressure. The Ménière patients showed stable recordings. It is suggested that among patients with suspected PLF and signs of hydrops in TT ECoG, a dependence on the intrathoracic pressure reflected in the recordings may indicate a possible fistula.

Adult↗

PubMedDate not supplied

The relationship of optokinetic nystagmus to pursuit eye movements, vestibular nystagmus and to saccades in humans. A clinical study.

The relationship of mean velocity of optokinetic nystagmus (OKN) to pursuit eye movements (PEM), to vestibular nystagmus and to voluntary saccades was analysed in 10 patients with peripheral vestibular lesions and in 30 patients with central vestibular lesions. PEM and vestibular nystagmus were significantly correlated to OKN, suggesting that a common neural pathway is used in the generation of these eye movements. Weak or no correlation was found between saccadic peak velocity and slow phase velocity of OKN. Using multiple linear regression analysis, it was found that 78.5% of the variation in the slow-phase velocity of OKN could be explained by a synthesis of PEM and vestibular test data. PEM test data were more powerful than those of vestibular nystagmus in deduction of OKN. The possible appearance of slow build-up of OKN could not be deduced from the reduction of PEM. Hence, the relationship between PEM and OKN in man is not a simple linear one, but is more complex.

Adolescent↗