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Biomedical subjects

D J Ireland

Publications and source records attributed to D J Ireland.

At least 19 recordsLinked to original sources
PubMed1999

Subjective visual vertical in patients with benign paroxysmal positional vertigo.

The ocular tilt reaction leads to an alteration in the subjective visual vertical (SVV). Nonsurgical peripheral vestibular dysfunction only rarely leads to changes in the SVV. To our knowledge, no studies have examined the effects on the SVV in patients with benign positional paroxysmal vertigo (BPPV) post Hallpike and Semont maneuvers. Sixteen patients with posterior canal BPPV were assessed in the vestibular clinic in Winnipeg, Manitoba. These patients had assessment of their SVV at baseline, post Hallpike and Semont maneuvers, and at follow-up 2 weeks later. These patients were also compared to a control group (n = 9). Ten of 16 patients showed a statistically significant change in SVV post Hallpike maneuver. An even larger number of patients, 14 of 16, showed a significant difference when compared to the control group post Hallpike. These findings suggest that the inferior vestibular nerve may to some degree influence the ocular tilt reaction.

Adult↗
PubMed1996

Post-treatment instructions in the nonsurgical management of benign paroxysmal positional vertigo.

Benign paroxysmal positional vertigo (BPPV) is the commonest peripheral vestibular disorder seen in dizziness clinics. It was long believed that the condition was caused by inorganic particles in the cupula of the posterior semicircular canal (PSC). More recently it has been suggested that BPPV may result from free-floating densities in the endolymph of the long arm of the PSC. Among the various treatment modalities used, two maneuvers, each based on a different theory of pathogenesis, have reported equally high success in the control of this disorder. These maneuvers are customarily followed by strict post-treatment instructions. We studied patients with BPPV prospectively by comparing the therapeutic effectiveness of these two modalities and studying the importance of post-treatment instructions in affecting the final outcome in each modality. We showed that both maneuvers were equally successful in controlling the symptoms and that post-treatment instructions were not necessary.

Adult↗
PubMed1996

Ocular torsion monitoring in chemical labyrinthectomy.

OBJECTIVE: To study the usefulness of ocular torsion analysis as an adjunct to examining central vestibular compensation. DESIGN: Prospective evaluation. SETTING: The Vestibular Disorders Clinic, University of Manitoba Health Sciences Centre. METHODS: Seven patients with intractable Meniere's disease underwent elective transtympanic gentamycin labyrinthectomy. Serial examination of patient progress was performed using fundus photography, subjective visual vertical estimations, electronystagmography, and audiometry. RESULTS: Ocular torsion analysis reveals unexpected initial and early contraversive torsion behaviour in some patients, which may represent an early irritative phenomenon stemming from either the gentamicin or the Meniere's disease itself. CONCLUSION: Despite the sensitivity of the ocular torsion measures, there appears to be no useful predictive correlation between ocular torsion and audiometric functioning that might predict impending hearing loss. Nevertheless, ocular torsion analysis reveals subtle changes in vestibular system functioning and may provide useful adjunctive information in the assessment of vestibular ototoxicity.

Adult↗
PubMed1996

Decision matrix analysis for tonic ocular torsional abnormalities with posturography abnormalities.

Tonic ocular torsions can arise from a variety of central or peripheral, vestibular, and nonvestibular lesions. However, the role of tonic ocular torsions in neurotology has been limited to surgical patients after unilateral vestibular deafferentation. By using 12 patients with a spectrum of well-defined unilateral peripheral vestibular lesions confirmed by electronystagmography (ENG), we identified a link between ipsiversive tonic ocular torsion compensation and vestibulospinal compensation, as measured by computerized dynamic posturography. In the context of ENG findings and posturography, the differential diagnosis of ocular torsions may be localized to the otoliths by using a decision matrix. Specifically, conditions of absent vision and sway-referenced support on computerized dynamic posturography associated with concurrent static ocular torsional abnormalities may suggest an otolith disorder. Furthermore, static ocular torsion assessment provides another important window on central vestibular compensation.

Adult↗
PubMed1995

Dizziness Handicap Inventory correlates of computerized dynamic posturography.

To assess the handicapping effect of dizziness related to posture and balance, the Dizziness Handicap Inventory (DHI) and Computerized Dynamic Posturography (CDP) were used to assess 101 consecutive patients referred for neurotologic evaluation of dizziness. Most patients, regardless of diagnosis, related some level of preexisting handicap, most often in the DHI Physical subscale. Generally, females and patients with bilateral lesions scored higher in all DHI subscales. No clinically useful correlations emerged between DHI and CDP testing, although DHI scores were marginally higher for patients failing CDP conditions. Functional balance ability could not be correlated with patient handicap, but a literature review suggests that the desynchrony between dizziness signs and symptoms may be related to underlying patient anxiety and differences in coping strategies.

Adaptation, Psychological↗
PubMed1995

Vestibular evoked myogenic potentials.

A pilot study was undertaken in our Vestibular Disorders Clinic to re-evaluate the clinical benefits of vestibular evoked myogenic potentials (VEMP). In seven normal subjects and 20 documented unilateral peripheral vestibular disorder patients, electromyograms were recorded from surface electrodes over the sternomastoid muscles and averaged in response to 0.1-millisecond clicks played through headphones. Control patients demonstrated EMG positive-negative potentials (p14-n21) of equivalent latencies and amplitudes both ipsilateral and contralateral to the stimuli. In patients with documented unilateral peripheral vestibular disorders, the p14-n21 potentials were preserved in the presence of sensorineural hearing loss and absent in those patients with partial or total vestibular loss. A high directional correlation is noted between the p14-n21 potential and gold-standard caloric testing. We suspect the origin of the response may be in the saccule and suggest that VEMP testing may be useful in assessing intact vestibulocollic pathways in humans.

Adult↗
PubMed1994

Unilateral vestibular deafferentation: a model of adaptation.

After acute loss of peripheral vestibular function, a centrally adaptive process takes place. Clinical measurements of vestibular adaptation are useful, both diagnostically and as a means of following patients after acute vestibular deficits. Ocular torsion is one measurement that can be used to follow these acutely disabled patients. The measurement is made from fundus photographs and is technically easy to perform and interpret. We present a pilot study from our Vestibular Disorders Clinic using fundus photography to measure the optic nerve head-foveal angle in six patients undergoing unilateral vestibular neurectomy, with subsequent analysis resulting in a speculative mathematical model of vestibular compensation in the roll plane. While the identification or selection of patients with significant ocular torsions from the vestibular population remains ill-defined, fundus photography remains an easy and useful method of following compensation in postoperative patients.

Adaptation, Physiological↗
PubMed1994

Human vertical optokinetic nystagmus and after-response, and their dependence upon head orientation with respect to gravity.

Characteristics of human vertical optokinetic nystagmus (VOKN) and afternystagmus (VOKAN) were examined by electro-oculography in 18 normal human subjects by means of the analysis of slow phase velocity (SPV) and area under the regression curve of the VOKAN decay. Under normal gravity, subjects were tested in upright and left ear down (90 degrees roll) positions, respectively, using a hemisphere onto which stripes were projected at a velocity of 40 degrees/s in left, right, up and down directions. Analysis of the VOKN and VOKAN revealed a significant asymmetry of vertical eye movements in the subjects' sagittal plane, ie, stronger upward SPV than downward in both VOKN and VOKAN decay. This asymmetry became even more prominent when the head was in the 90 degrees roll position. It is postulated that the asymmetry of VOKN and VOKAN in humans, as in animals, is due to the asymmetrical storage capability of the vertical velocity storage mechanism which mainly contributes to upward eye movements. In addition, it is postulated that the vertical storage mechanism is modified by the action of gravity on the otolith organs. However, only two out of our 18 subjects demonstrated cross-coupling, as reported in animals, from the horizontal to the vertical mode of storage when the head was tilted away from the spatial vertical.

Adult↗
PubMed1992

Stimulus velocity dependence of human vertical optokinetic nystagmus and afternystagmus.

Stimulus velocity dependence of human VOKN and VOKAN was investigated using 20 degrees, 40 degrees, 60 degrees, and 80 degrees/s optokinetic stimulation. In our experimental conditions, 40 degrees/s was found to be the most appropriate stimulus velocity for inducing reliable VOKN and VOKAN based on the analysis of SPV, gain, and the area under the VOKAN decay curve. There was a clear trend toward up/down asymmetry of VOKN gain, with higher upward OKN SPV than downward at 40 degrees/s. VOKAN with both short and long time constant components was induced in 5 of 11 subjects, but only when the stimulus was upgoing. Stimulation at 20 degrees/s in either direction produced a decay with only a short time constant. VOKN-SPV and the area under VOKAN decay curve at 40 degrees/s showed no significant difference from the corresponding values at 60 degrees/s or 80 degrees/s, indicating that following and the velocity storage mechanism had saturated at 40 degrees/s. However, the gain at 60 degrees/s and 80 degrees/s became low and eye movement regularity was poor. Stimulation at 20 degrees/s may activate mainly the vertical pursuit mechanism, as it did not produce up/down asymmetry. It is proposed that, as in the horizontal case, two kinds of mechanisms are involved in vertical stripe-following eye movements, which represent smooth pursuit and optokinetic systems respectively.

Adult↗
PubMed1988

Convergent effects from vestibulospinal tract and primary cutaneous afferent fibers on motoneurons to proximal lower limb flexor and extensor muscles in humans.

In human subjects, the latency and magnitude of cutaneomuscular test reflexes, evoked by stimulation of the sural nerve in the contralateral and ipsilateral quadricep and hamstring muscles, were investigated during static tilts in the pitch axis. The ANOVA demonstrated a highly significant, tilt-dependent modulation of the magnitude of the test reflex for the initial phase of both ipsilateral quadriceps and ipsilateral hamstrings. These results are consistent with results from a similar study on human ankle muscles and provide further evidence that the tilt-dependence of these cutaneomuscular reflexes originates from activity in the otolith receptors.

Afferent Pathways↗
PubMed1988

Effect of active head movements about the pitch, roll, and yaw axes on human optokinetic afternystagmus.

Effects of active head movements about the pitch, roll, or yaw axes on horizontal optokinetic afternystagmas (OKAN) were examined in 16 subjects to test the hypothesis that otolith organ mediated activity induced by a change in head position can couple to the horizontal velocity storage in humans. Active head movements about the pitch axis, forwards or backwards, produced significant OKAN suppression. Pitch forward head movements exerted the strongest effect. Active head movements about the roll axis towards the right also produced OKAN suppression but only if the tilted position was sustained. No suppression was observed following sustained yaw. However, an unsustained yaw left movement after rightward drum rotation significantly enhanced OKAN. Sustained head movement trials did not significantly alter subsequent control trials. In contrast, unsustained movements about the pitch axis, which involve more complex interactions, exerted long-term effects on subsequent control trials. We conclude that otolith organ mediated activity arising from pitch or roll head movements couples to the horizontal velocity storage in humans, thereby suppressing ongoing OKAN. Activity arising from the horizontal canals during an unsustained yaw movement (observed mainly with yaw left), following drum rotation in a direction contralateral to the movement, may also couple to the velocity storage, resulting in increased activity instead of suppression.

Adolescent↗
PubMed1987

The polyclonal antibody responses of Lewis rats to the synthetic encephalitogenic neuropeptide S55S (residues 72-84 of guinea pig myelin basic protein) and its analogs.

Immunochemical analysis of polyclonal antisera from Lewis rats immunized with peptide analogs and subpeptides of residues 72-84 of guinea pig myelin basic protein (MBP) indicated that there were four main epitopic specificities involved: one represented by residues 76-80, one by residues 72-74, one by 81-84-Gly, and one involving 74-76 in a heteroclitic way even when the immunogen contained a tetraleucine spacer between residues 74 and 75. The affinities were all relatively low, ranging from 3 x 10(4) M-1 to 7.2 x 10(6) M-1, and each affinity population was very restricted with respect to heterogeneity. The results were commensurate with our hypothesis that autoimmune responses to homologous encephalitogenic neuropeptide determinants reflect an evolutionarily imposed degeneration of the overall response, and were also in agreement with our hypothesis that the affinities of autoantibodies against epitopes in the molecular neighborhood of an encephalitogen would be necessarily low. It was also found that peptide 69-81-Gly (S67) in solution would not interact in liquid phase radioimmunoassays with any of the above antibody populations, thus indicating that its preferred conformation did not allow the expression of autoreactive epitopes. There was no evidence that S67 in solution. even in the presence of S53, would express any epitopes reactive with autoantibodies. How this finding for a B cell product correlates with T cell-mediated immunologic responses is not totally understood, but it will be recalled that S67 by itself does not induce T cell-mediated experimental allergic encephalomyelitis (EAE), that S53 (residues 75-84-Gly) induces only clinical symptoms of EAE without attendant pathological disease, but that the two together induce classical EAE.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1987

Convergent effects from vestibulospinal tract and primary cutaneous afferent fibers on motoneurons to ankle extensor and flexor muscles in humans.

The latency and magnitude of cutaneomuscular reflexes, evoked by stimulation of the sural nerve in the contralateral and ipsilateral tibialis anterior and soleus, were investigated in normal human subjects during static tilts in the pitch axis. For all subjects the test reflex consisted of oscillating sequences of excitation and inhibition, each muscle exhibiting a characteristic pattern defined by its latency and sign of the initial phase. The latency of the various components and the sign of the initial phase did not vary with angle of tilt. However, the results of an ANOVA demonstrate a highly significant tilt-dependent modulation of the amplitude of the test reflex for the initial inhibitory phase of the contralateral tibialis anterior. We propose that this tilt-dependent effect on the crossed cutaneomuscular reflex originates from activity in the otolith organ receptors.

Adult↗
PubMed1986

Heteroclitic antibodies in Fischer 344 rats to a synthetic encephalitogenic myelin basic protein peptide.

Fischer 344 rats, immunized with the synthetic encephalitogenic myelin basic protein peptide YS49 (YGSLPQKAQRPQDENG), produced heteroclitic antibodies that reacted much more extensively and with a much higher affinity with the cross-reacting encephalitogenic guinea pig sequence S49S (GSLPQKSQRSQDENG) than they did with the immunogenic YS49. On the other hand, antisera against S49S reacted in a normal manner with homologous S49S and cross-reacted only poorly with YS49. The phenomenon of heteroclisis in Fischer 344 rats correlated with the greater encephalitogenic potency of the cross-reacting entity. Kibler et al. (J. Exp. Med., 146 (1977) 1323-1331), by comparing the encephalitogenic guinea pig sequence to a less potent analog, had also previously observed what now would be termed a heteroclitic phenomenon at the T cell level in Lewis rats. In their hands, however, as well as in ours Lewis rat antisera against the encephalitogenic peptide region were much too complex to be analyzed with respect to heteroclisis. It was shown in the present experiments that by utilizing the Fischer 344 system one may also readily obtain heteroclisis at the B cell level against encephalitogenic peptides. Neither YS49 nor S49S as immunogen produced detectable antibody in Brown Norway (BN) rats with exception of two immunized with YS49. In those two cases heteroclitic antibodies were obtained that had a very low significant (greater than 3 SD above baseline) antigen binding capacity for S49S and no detectable reactivity for the homologous YS49 ligand.

Amino Acid Sequence↗
PubMed1986

Polyclonal antibodies to the encephalitogenic neighborhoods of myelin basic protein: singular affinity populations neutralized by specific synthetic peptide probes.

Specific ligand neutralization was used to probe the extent to which singular antibody affinity populations signified specific determinants in the neighborhood myelin basic protein (MBP) encephalitogens. The probes were individual members of a panel of synthetic peptide analogs subsuming encephalitogenic regions. Comparative Scatchard analyses of neutralized and unneutralized antisera helped to identify the particular peptide determinants involved in the original polyclonal antibody responses to the multiple antigenic determinants of encephalitogenic peptides. The range of affinities for an antibody population against a singular MBP peptide determinant was found to be relatively restricted while the range of affinities overall for all populations within a given antipeptide antiserum was found to be relatively wide and invariably discontinuous. Consequently, the individual discontinuous affinity populations could readily be dissected by application of the Rosenthal method of Scatchard curve analysis. It was found that the singular high affinity antibody population (5.6 x 10(7) M-1) of a Lewis rat antiserum to rat encephalitogenic GSLPQKAQRPQDENG (S49) was against a determinant near the N-terminal non-encephalitogenic end of the peptide. Only the low affinity antibody populations were found that had reactivity for determinants within the encephalitogenic region itself. The singular high affinity antibody population (5.97 x 10(7) M-1) of a rabbit antiserum to rabbit encephalitogenic TTHYGSLPQKAQGHRPQDEG (S82) was against a determinant centered about the tyrosyl residue, within the encephalitogenic region for the rabbit, but was completely cross-reactive with a specific circulating endogenous inhibitor. The results obtained with the rat and rabbit EAE sera were consistent with a previously advanced hypothesis that antibodies to determinants within encephalitogenic neighborhoods would effectively block the onset of EAE if high enough in affinity and not neutralized by an endogenous inhibitor.

Animals↗
PubMed1984

Symmetrical optokinetic after-nystagmus loss in Wallenberg's syndrome and multiple sclerosis.

We have demonstrated abolition of OKAN in either horizontal direction with retention of caloric responses in 3 patients with unilateral brain stem infarcts. In one further patient with diffuse brain stem disease, we have been able to show bilateral loss of horizontal OKAN in the acute phase, with recovery during remission. These findings support the conclusion that the velocity storage mechanism or connections to it, are permanently disabled by unilateral medullary infarcts and may be temporarily disabled by demyelinating disease. Retention of caloric responses in the absence of OKAN would appear to be of assistance in the differential diagnosis between peripheral and central vestibular pathway lesions.

Humans↗