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Ian S. Curthoys - One of the best experts on this subject based on the ideXlab platform.
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Suppression Head Impulse Test paradigm (SHIMP) characteristics in people with Parkinson’s disease compared to healthy controls
Experimental Brain Research, 2021Co-Authors: Kim E. Hawkins, Elodie Chiarovano, Hamish G. Macdougall, Jorge Rey-martinez, Serene S. Paul, Ariadna Valldeperes, Ian S. CurthoysAbstract:The suppression Head Impulse Test paradigm (SHIMP) is a newly described indicator of vestibular function which yields two measures: vestibulo-ocular reflex (VOR) gain and a saccadic response. It is an alternative and complementary Test to the Head Impulse Test paradigm (HIMP). Parkinson’s disease (PD) has known saccadic and central vestibular pathway dysfunction. This paper is the first description of SHIMP VOR gain and saccade characteristic in this population. This prospective observational study measured the SHIMP VOR gain and saccade characteristics in 39 participants with idiopathic PD and compared this to 40 healthy controls (HC). The effect of group, demographic variables and SHIMP characteristics were evaluated. SHIMP VOR gains were not significantly different between groups ( p = 0.10). Compared to HC, the PD group mean SHIMP peak saccade velocity was significantly reduced by an average of 77.07°/sec ( p
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Suppression Head Impulse Test paradigm (SHIMP) characteristics in people with Parkinson's disease compared to healthy controls.
Experimental brain research, 2021Co-Authors: Kim E. Hawkins, Elodie Chiarovano, Hamish G. Macdougall, Jorge Rey-martinez, Serene S. Paul, Ariadna Valldeperes, Ian S. CurthoysAbstract:The suppression Head Impulse Test paradigm (SHIMP) is a newly described indicator of vestibular function which yields two measures: vestibulo-ocular reflex (VOR) gain and a saccadic response. It is an alternative and complementary Test to the Head Impulse Test paradigm (HIMP). Parkinson's disease (PD) has known saccadic and central vestibular pathway dysfunction. This paper is the first description of SHIMP VOR gain and saccade characteristic in this population. This prospective observational study measured the SHIMP VOR gain and saccade characteristics in 39 participants with idiopathic PD and compared this to 40 healthy controls (HC). The effect of group, demographic variables and SHIMP characteristics were evaluated. SHIMP VOR gains were not significantly different between groups (p = 0.10). Compared to HC, the PD group mean SHIMP peak saccade velocity was significantly reduced by an average of 77.07°/sec (p
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suppression Head Impulse Test paradigm shimp characteristics in people with parkinson s disease compared to healthy controls
Experimental Brain Research, 2021Co-Authors: Kim E. Hawkins, Elodie Chiarovano, Hamish G. Macdougall, Jorge Reymartinez, Serene S. Paul, Ariadna Valldeperes, Ian S. CurthoysAbstract:The suppression Head Impulse Test paradigm (SHIMP) is a newly described indicator of vestibular function which yields two measures: vestibulo-ocular reflex (VOR) gain and a saccadic response. It is an alternative and complementary Test to the Head Impulse Test paradigm (HIMP). Parkinson's disease (PD) has known saccadic and central vestibular pathway dysfunction. This paper is the first description of SHIMP VOR gain and saccade characteristic in this population. This prospective observational study measured the SHIMP VOR gain and saccade characteristics in 39 participants with idiopathic PD and compared this to 40 healthy controls (HC). The effect of group, demographic variables and SHIMP characteristics were evaluated. SHIMP VOR gains were not significantly different between groups (p = 0.10). Compared to HC, the PD group mean SHIMP peak saccade velocity was significantly reduced by an average of 77.07°/sec (p < 0.001), and SHIMP saccade response latency was longer, with an average delay of 23.5 ms (p = 0.003). SHIMP saccade peak velocity was also associated with both Head Impulse velocity (p = 0.002) and SHIMP VOR gain (p = 0.004) variables, but there was no significant influence of these variables when SHIMP saccade peak velocity was considered as a predictor of PD (p = 0.52-0.91). VOR gains were unaffected by PD. PD-specific saccadic dysfunction, namely reduced peak saccade velocities and prolonged response latencies, were observed in the SHIMP-induced saccade responses. VOR gain using slow phase eye velocity is preferred as the indicator of vestibular function in the SHIMPs paradigm as non-vestibular factors affected saccade peak velocity.
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computing endolymph hydrodynamics during Head Impulse Test on normal and hydropic vestibular labyrinth models
Frontiers in Neurology, 2020Co-Authors: Jorge Reymartinez, Kai Cheng, Ann M Burgess, Xabier Altuna, Ian S. CurthoysAbstract:Hypothesis: Build a biologic geometry based computational model to Test the hypothesis that, in some circumstances, endolymphatic hydrops can mechanically cause enhanced eye velocity responses during clinical conditions of the Head Impulse Test. Background: Some recent clinical and experimental findings had suggested that enhanced eye velocity responses measured with the video Head Impulse Test could not only be caused by recording artifacts or central disfunction but also could be directly caused by the mechanical effect of endolymphatic hydrops on horizontal semicircular canal receptor. Methods: Data from clinical video Head Impulse Test was computed in three biologic-based geometry models governed by Navier-Stokes equations; six Head Impulses of incrementally increasing peak Head velocity were computed in each one of the three different geometric models, depending on absence, canal or utricular hydrops. Results: For all computed Head Impulses an increased endolymphatic pressure was measured at the ampullar region of the horizontal semicircular canal on both canal and utricular hydrops models. The mean of aVOR gain was 1.01 ± 0.008 for the no-hydrops model, 1.14 ± 0.010 for the canal hydrops model was, and 1.10 ± 0.007 for the utricular hydrops model. Conclusion: The results of the physical computation models support-the hypothesis that in endolymphatic hydrops conditions, which are affecting horizontal semicircular canal and utricular region on moderate dilatations, the eye velocity responses output-by the aVOR will be enhanced by a 1.14 factor and aVOR gain values will be enhanced by over 1.1 for Impulses to the right side.
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clinical application of the Head Impulse Test of semicircular canal function
Hearing Balance and Communication, 2017Co-Authors: Ian S. Curthoys, Leonardo ManzariAbstract:AbstractObjective: To review the theory, the validity and the clinical application and the new developments of the video Head Impulse Test (vHIT) of semicircular canal function. vHIT has now superseded the caloric Test as the first-line clinical Test for vestibular patients.Outcomes: This review examines the origin and rationale for vHIT: how it is carried out; pitfalls in Testing; the validation of the Test; the interpretation of overt and covert compensatory saccades in patients with vestibular loss; how the area VOR gain is calculated.Results: The advantages of the Test are considered: it is so innocuous that it can be given to patients even during acute vertigo attacks, and given repeatedly at short intervals; it is very successful for Testing young children; it Tests all six semicircular canals, and, unlike the caloric Test, provides measures of the absolute level of canal function and so is valuable for monitoring the effect of ototoxic antibiotics as well as identifying bilateral vestibular loss. P...
Hamish G. Macdougall - One of the best experts on this subject based on the ideXlab platform.
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Suppression Head Impulse Test paradigm (SHIMP) characteristics in people with Parkinson’s disease compared to healthy controls
Experimental Brain Research, 2021Co-Authors: Kim E. Hawkins, Elodie Chiarovano, Hamish G. Macdougall, Jorge Rey-martinez, Serene S. Paul, Ariadna Valldeperes, Ian S. CurthoysAbstract:The suppression Head Impulse Test paradigm (SHIMP) is a newly described indicator of vestibular function which yields two measures: vestibulo-ocular reflex (VOR) gain and a saccadic response. It is an alternative and complementary Test to the Head Impulse Test paradigm (HIMP). Parkinson’s disease (PD) has known saccadic and central vestibular pathway dysfunction. This paper is the first description of SHIMP VOR gain and saccade characteristic in this population. This prospective observational study measured the SHIMP VOR gain and saccade characteristics in 39 participants with idiopathic PD and compared this to 40 healthy controls (HC). The effect of group, demographic variables and SHIMP characteristics were evaluated. SHIMP VOR gains were not significantly different between groups ( p = 0.10). Compared to HC, the PD group mean SHIMP peak saccade velocity was significantly reduced by an average of 77.07°/sec ( p
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Suppression Head Impulse Test paradigm (SHIMP) characteristics in people with Parkinson's disease compared to healthy controls.
Experimental brain research, 2021Co-Authors: Kim E. Hawkins, Elodie Chiarovano, Hamish G. Macdougall, Jorge Rey-martinez, Serene S. Paul, Ariadna Valldeperes, Ian S. CurthoysAbstract:The suppression Head Impulse Test paradigm (SHIMP) is a newly described indicator of vestibular function which yields two measures: vestibulo-ocular reflex (VOR) gain and a saccadic response. It is an alternative and complementary Test to the Head Impulse Test paradigm (HIMP). Parkinson's disease (PD) has known saccadic and central vestibular pathway dysfunction. This paper is the first description of SHIMP VOR gain and saccade characteristic in this population. This prospective observational study measured the SHIMP VOR gain and saccade characteristics in 39 participants with idiopathic PD and compared this to 40 healthy controls (HC). The effect of group, demographic variables and SHIMP characteristics were evaluated. SHIMP VOR gains were not significantly different between groups (p = 0.10). Compared to HC, the PD group mean SHIMP peak saccade velocity was significantly reduced by an average of 77.07°/sec (p
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suppression Head Impulse Test paradigm shimp characteristics in people with parkinson s disease compared to healthy controls
Experimental Brain Research, 2021Co-Authors: Kim E. Hawkins, Elodie Chiarovano, Hamish G. Macdougall, Jorge Reymartinez, Serene S. Paul, Ariadna Valldeperes, Ian S. CurthoysAbstract:The suppression Head Impulse Test paradigm (SHIMP) is a newly described indicator of vestibular function which yields two measures: vestibulo-ocular reflex (VOR) gain and a saccadic response. It is an alternative and complementary Test to the Head Impulse Test paradigm (HIMP). Parkinson's disease (PD) has known saccadic and central vestibular pathway dysfunction. This paper is the first description of SHIMP VOR gain and saccade characteristic in this population. This prospective observational study measured the SHIMP VOR gain and saccade characteristics in 39 participants with idiopathic PD and compared this to 40 healthy controls (HC). The effect of group, demographic variables and SHIMP characteristics were evaluated. SHIMP VOR gains were not significantly different between groups (p = 0.10). Compared to HC, the PD group mean SHIMP peak saccade velocity was significantly reduced by an average of 77.07°/sec (p < 0.001), and SHIMP saccade response latency was longer, with an average delay of 23.5 ms (p = 0.003). SHIMP saccade peak velocity was also associated with both Head Impulse velocity (p = 0.002) and SHIMP VOR gain (p = 0.004) variables, but there was no significant influence of these variables when SHIMP saccade peak velocity was considered as a predictor of PD (p = 0.52-0.91). VOR gains were unaffected by PD. PD-specific saccadic dysfunction, namely reduced peak saccade velocities and prolonged response latencies, were observed in the SHIMP-induced saccade responses. VOR gain using slow phase eye velocity is preferred as the indicator of vestibular function in the SHIMPs paradigm as non-vestibular factors affected saccade peak velocity.
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Video-Head Impulse Test in superior canal dehiscence.
Acta oto-laryngologica, 2021Co-Authors: Payal Mukherjee, Elodie Chiarovano, Kai Cheng, Leonardo Manzari, Leigh A. Mcgarvie, Hamish G. MacdougallAbstract:BACKGROUND Superior Canal Dehiscence is classically diagnosed with typical abnormalities on Vestibular Evoked Myogenic Potentials (VEMPs) and Computed Tomography (CT) scans. AIM This paper discusses the utility of the video Head Impulse Test (vHIT) in SCD. METHODS Data from 11 ears (8 patients) with SCD were retrospectively reviewed. Results from vHIT, VEMPs and CT and when possible, MRI scans were correlated. An audit of 300 vHIT from patients undergoing routine Testing for any neurotological complaint was also conducted to look at the incidence of isolated abnormal superior canal function. RESULTS 82% of patients (9 ears) with SCD showed abnormal vHIT (reduced gain and catch-up saccades) isolated to the affected superior semicircular canal. CONCLUSION Correlation of the CT and VEMPs are important in forming a diagnosis of SCD. However, if isolated superior canal vHIT abnormalities are demonstrated, it is suggestive of SCD and such patients should be referred for further investigations.
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a new saccadic indicator of peripheral vestibular function based on the video Head Impulse Test
Neurology, 2016Co-Authors: Hamish G. Macdougall, Leonardo Manzari, Leigh A. Mcgarvie, Ian S. Curthoys, Michael G Halmagyi, Stephen J Rogers, Ann M Burgess, Konrad P WeberAbstract:Objective: While compensatory saccades indicate vestibular loss in the conventional Head Impulse Test paradigm (HIMP), in which the participant fixates an earth-fixed target, we investigated a complementary suppression Head Impulse paradigm (SHIMP), in which the participant is fixating a Head-fixed target to elicit anticompensatory saccades as a sign of vestibular function. Methods: HIMP and SHIMP eye movement responses were measured with the horizontal video Head Impulse Test in patients with unilateral vestibular loss, patients with bilateral vestibular loss, and in healthy controls. Results: Vestibulo-ocular reflex gains showed close correlation ( R 2 = 0.97) with slightly lower SHIMP than HIMP gains (mean gain difference 0.06 ± 0.05 SD, p Conclusions: While compensatory saccades indicate vestibular loss in conventional HIMP, anticompensatory saccades in SHIMP using a Head-fixed target indicate vestibular function. SHIMP saccades usually appear later than HIMP saccades, therefore being more salient to the naked eye and facilitating vestibulo-ocular reflex gain measurements. The new paradigm is intuitive and easy to explain to patients, and the SHIMP results complement those from the standard video Head Impulse Test. Classification of evidence: This case-control study provides Class III evidence that SHIMP accurately identifies patients with unilateral or bilateral vestibulopathies.
Konrad P Weber - One of the best experts on this subject based on the ideXlab platform.
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a new saccadic indicator of peripheral vestibular function based on the video Head Impulse Test
Neurology, 2016Co-Authors: Hamish G. Macdougall, Leonardo Manzari, Leigh A. Mcgarvie, Ian S. Curthoys, Michael G Halmagyi, Stephen J Rogers, Ann M Burgess, Konrad P WeberAbstract:Objective: While compensatory saccades indicate vestibular loss in the conventional Head Impulse Test paradigm (HIMP), in which the participant fixates an earth-fixed target, we investigated a complementary suppression Head Impulse paradigm (SHIMP), in which the participant is fixating a Head-fixed target to elicit anticompensatory saccades as a sign of vestibular function. Methods: HIMP and SHIMP eye movement responses were measured with the horizontal video Head Impulse Test in patients with unilateral vestibular loss, patients with bilateral vestibular loss, and in healthy controls. Results: Vestibulo-ocular reflex gains showed close correlation ( R 2 = 0.97) with slightly lower SHIMP than HIMP gains (mean gain difference 0.06 ± 0.05 SD, p Conclusions: While compensatory saccades indicate vestibular loss in conventional HIMP, anticompensatory saccades in SHIMP using a Head-fixed target indicate vestibular function. SHIMP saccades usually appear later than HIMP saccades, therefore being more salient to the naked eye and facilitating vestibulo-ocular reflex gain measurements. The new paradigm is intuitive and easy to explain to patients, and the SHIMP results complement those from the standard video Head Impulse Test. Classification of evidence: This case-control study provides Class III evidence that SHIMP accurately identifies patients with unilateral or bilateral vestibulopathies.
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the video Head Impulse Test vhit detects vertical semicircular canal dysfunction
PLOS ONE, 2013Co-Authors: Hamish G. Macdougall, Leigh A. Mcgarvie, Ian S. Curthoys, G M Halmagyi, Konrad P WeberAbstract:Background The video Head Impulse Test (vHIT) is a useful clinical tool to detect semicircular canal dysfunction. However vHIT has hitherto been limited to measurement of horizontal canals, while scleral search coils have been the only accepted method to measure Head Impulses in vertical canals. The goal of this study was to determine whether vHIT can detect vertical semicircular canal dysfunction as identified by scleral search coil recordings. Methods Small unpredictable Head rotations were delivered by hand diagonally in the plane of the vertical semicircular canals while gaze was directed along the same plane. The planes were oriented along the left-anterior-right-posterior (LARP) canals and right-anterior-left-posterior (RALP) canals. Eye movements were recorded simultaneously in 2D with vHIT (250 Hz) and in 3D with search coils (1000 Hz). Twelve patients with unilateral, bilateral and individual semicircular canal dysfunction were Tested and compared to seven normal subjects. Results Simultaneous video and search coil recordings were closely comparable. Mean VOR gain difference measured with vHIT and search coils was 0.05 (SD = 0.14) for the LARP plane and −0.04 (SD = 0.14) for the RALP plane. The coefficient of determination R2 was 0.98 for the LARP plane and 0.98 for the RALP plane and the results of the two methods were not significantly different. vHIT and search coil measures displayed comparable patterns of covert and overt catch-up saccades. Conclusions vHIT detects dysfunction of individual vertical semicircular canals in vestibular patients as accurately as scleral search coils. Unlike search coils, vHIT is non-invasive, easy to use and hence practical in clinics.
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the video Head Impulse Test diagnostic accuracy in peripheral vestibulopathy
Neurology, 2009Co-Authors: Hamish G. Macdougall, Leigh A. Mcgarvie, Konrad P Weber, G M Halmagyi, Ian S. CurthoysAbstract:Background: The Head Impulse Test (HIT) is a useful bedside Test to identify peripheral vestibular deficits. However, such a deficit of the vestibulo-ocular reflex (VOR) may not be diagnosed because corrective saccades cannot always be detected by simple observation. The scleral search coil technique is the gold standard for HIT measurements, but it is not practical for routine Testing or for acute patients, because they are required to wear an uncomfortable contact lens. Objective: To develop an easy-to-use video HIT system (vHIT) as a clinical tool for identifying peripheral vestibular deficits. To validate the diagnostic accuracy of vHIT by simultaneous measures with video and search coil recordings across healthy subjects and patients with a wide range of previously identified peripheral vestibular deficits. Methods: Horizontal HIT was recorded simultaneously with vHIT (250 Hz) and search coils (1,000 Hz) in 8 normal subjects, 6 patients with vestibular neuritis, 1 patient after unilateral intratympanic gentamicin, and 1 patient with bilateral gentamicin vestibulotoxicity. Results: Simultaneous video and search coil recordings of eye movements were closely comparable (average concordance correlation coefficient rc 0.930). Mean VOR gains measured with search coils and video were not significantly different in normal (p 0.107) and patients (p 0.073). With these groups, the sensitivity and specificity of both the reference and index Test were 1.0 (95% confidence interval 0.69 –1.0). vHIT measures detected both overt and covert saccades as accurately as coils. Conclusions: The video Head Impulse Test is equivalent to search coils in identifying peripheral vestibular deficits but easier to use in clinics, even in patients with acute vestibular neuritis. Neurology ® 2009;73:1134 –1141
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Horizontal Head Impulse Test detects gentamicin vestibulotoxicity
Neurology, 2009Co-Authors: Konrad P Weber, Leigh A. Mcgarvie, Michael J. Todd, Ian S. Curthoys, G M HalmagyiAbstract:Background: Parenteral antibiotic therapy with gentamicin, even in accepted therapeutic doses, can occasionally cause bilateral vestibular loss (BVL) due to hair cell toxicity. Objective: To quantify in patients with gentamicin vestibulotoxicity (GVT) the extent of acceleration gain deficit of the horizontal vestibulo-ocular reflex at different accelerations with a graded Head Impulse Test (HIT) in comparison with standard caloric and rotational Testing. To characterize the corresponding HIT catch-up saccade pattern to provide the basis for its salience to clinicians. Methods: Horizontal HIT of graded acceleration (750°–6,000°/sec 2 ) was measured with binocular dual search coils in 14 patients with GVT and compared with 14 normal subjects and a control subject with total surgical BVL. Results: Patients showed mostly symmetric HIT gain deficits with a continuous spectrum from almost normal to complete BVL. Gain deficits were present even at the lowest Head accelerations. HIT gain correlated better with caloric (Spearman ρ = 0.85, p = 0.0001) than rotational Testing (ρ = 0.55, p = 0.046). Cumulative amplitude of overt saccades after Head Impulses was 5.6 times larger in patients than in normal subjects. Compared with previously published patients after unilateral vestibular deafferentation, GVT patients with BVL generated only approximately half the percentage of covert saccades during Head rotation (23% at 750°/sec 2 to 46% at 6,000°/sec 2 ). Conclusions: Head Impulse Testing is useful for early bedside detection of gentamicin vestibulotoxicity because most patients, even those with partial bilateral vestibular loss (BVL), have large overt saccades. Covert saccades, which can conceal the extent of BVL, are only approximately half as frequent as in unilateral patients, but may be present even in total BVL.
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Head Impulse Test in unilateral vestibular loss vestibulo ocular reflex and catch up saccades
Neurology, 2008Co-Authors: Konrad P Weber, Leigh A. Mcgarvie, Ian S. Curthoys, M J Todd, G M HalmagyiAbstract:Background: Quantitative Head Impulse Test (HIT) measures the gain of the angular vestibulo-ocular reflex (VOR) during Head rotation as the ratio of eye to Head acceleration. Bedside HIT identifies subsequent catch-up saccades after the Head rotation as indirect signs of VOR deficit. Objective: To determine the VOR deficit and catch-up saccade characteristics in unilateral vestibular disease in response to HIT of varying accelerations. Methods: Eye and Head rotations were measured with search coils during manually applied horizontal HITs of varying accelerations in patients after vestibular neuritis (VN, n = 13) and unilateral vestibular deafferentation (UVD, n = 15) compared to normal subjects (n = 12). Results: Normal VOR gain was close to unity and symmetric over the entire Head-acceleration range. Patients with VN and UVD showed VOR gain asymmetry, with larger ipsilesional than contralesional deficits. As accelerations increased from 750 to 6,000 °/sec 2 , ipsilesional gains decreased from 0.59 to 0.29 in VN and from 0.47 to 0.13 in UVD producing increasing asymmetry. Initial catch-up saccades can occur during or after Head rotation. Covert saccades during Head rotation are most likely imperceptible, while overt saccades after Head rotation are detectable by clinicians. With increasing acceleration, the amplitude of overt saccades in patients became larger; however, initial covert saccades also became increasingly common, occurring in up to about 70% of trials. Conclusions: Head Impulse Test (HIT) with high acceleration reveals vestibulo-ocular reflex deficits better and elicits larger overt catch-up saccades in unilateral vestibular patients. Covert saccades during Head rotation, however, occur more frequently with higher acceleration and may be missed by clinicians. To avoid false-negative results, bedside HIT should be repeated to improve chances of detection.
Kim E. Hawkins - One of the best experts on this subject based on the ideXlab platform.
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Suppression Head Impulse Test paradigm (SHIMP) characteristics in people with Parkinson’s disease compared to healthy controls
Experimental Brain Research, 2021Co-Authors: Kim E. Hawkins, Elodie Chiarovano, Hamish G. Macdougall, Jorge Rey-martinez, Serene S. Paul, Ariadna Valldeperes, Ian S. CurthoysAbstract:The suppression Head Impulse Test paradigm (SHIMP) is a newly described indicator of vestibular function which yields two measures: vestibulo-ocular reflex (VOR) gain and a saccadic response. It is an alternative and complementary Test to the Head Impulse Test paradigm (HIMP). Parkinson’s disease (PD) has known saccadic and central vestibular pathway dysfunction. This paper is the first description of SHIMP VOR gain and saccade characteristic in this population. This prospective observational study measured the SHIMP VOR gain and saccade characteristics in 39 participants with idiopathic PD and compared this to 40 healthy controls (HC). The effect of group, demographic variables and SHIMP characteristics were evaluated. SHIMP VOR gains were not significantly different between groups ( p = 0.10). Compared to HC, the PD group mean SHIMP peak saccade velocity was significantly reduced by an average of 77.07°/sec ( p
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Suppression Head Impulse Test paradigm (SHIMP) characteristics in people with Parkinson's disease compared to healthy controls.
Experimental brain research, 2021Co-Authors: Kim E. Hawkins, Elodie Chiarovano, Hamish G. Macdougall, Jorge Rey-martinez, Serene S. Paul, Ariadna Valldeperes, Ian S. CurthoysAbstract:The suppression Head Impulse Test paradigm (SHIMP) is a newly described indicator of vestibular function which yields two measures: vestibulo-ocular reflex (VOR) gain and a saccadic response. It is an alternative and complementary Test to the Head Impulse Test paradigm (HIMP). Parkinson's disease (PD) has known saccadic and central vestibular pathway dysfunction. This paper is the first description of SHIMP VOR gain and saccade characteristic in this population. This prospective observational study measured the SHIMP VOR gain and saccade characteristics in 39 participants with idiopathic PD and compared this to 40 healthy controls (HC). The effect of group, demographic variables and SHIMP characteristics were evaluated. SHIMP VOR gains were not significantly different between groups (p = 0.10). Compared to HC, the PD group mean SHIMP peak saccade velocity was significantly reduced by an average of 77.07°/sec (p
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suppression Head Impulse Test paradigm shimp characteristics in people with parkinson s disease compared to healthy controls
Experimental Brain Research, 2021Co-Authors: Kim E. Hawkins, Elodie Chiarovano, Hamish G. Macdougall, Jorge Reymartinez, Serene S. Paul, Ariadna Valldeperes, Ian S. CurthoysAbstract:The suppression Head Impulse Test paradigm (SHIMP) is a newly described indicator of vestibular function which yields two measures: vestibulo-ocular reflex (VOR) gain and a saccadic response. It is an alternative and complementary Test to the Head Impulse Test paradigm (HIMP). Parkinson's disease (PD) has known saccadic and central vestibular pathway dysfunction. This paper is the first description of SHIMP VOR gain and saccade characteristic in this population. This prospective observational study measured the SHIMP VOR gain and saccade characteristics in 39 participants with idiopathic PD and compared this to 40 healthy controls (HC). The effect of group, demographic variables and SHIMP characteristics were evaluated. SHIMP VOR gains were not significantly different between groups (p = 0.10). Compared to HC, the PD group mean SHIMP peak saccade velocity was significantly reduced by an average of 77.07°/sec (p < 0.001), and SHIMP saccade response latency was longer, with an average delay of 23.5 ms (p = 0.003). SHIMP saccade peak velocity was also associated with both Head Impulse velocity (p = 0.002) and SHIMP VOR gain (p = 0.004) variables, but there was no significant influence of these variables when SHIMP saccade peak velocity was considered as a predictor of PD (p = 0.52-0.91). VOR gains were unaffected by PD. PD-specific saccadic dysfunction, namely reduced peak saccade velocities and prolonged response latencies, were observed in the SHIMP-induced saccade responses. VOR gain using slow phase eye velocity is preferred as the indicator of vestibular function in the SHIMPs paradigm as non-vestibular factors affected saccade peak velocity.
Leigh A. Mcgarvie - One of the best experts on this subject based on the ideXlab platform.
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Video-Head Impulse Test in superior canal dehiscence.
Acta oto-laryngologica, 2021Co-Authors: Payal Mukherjee, Elodie Chiarovano, Kai Cheng, Leonardo Manzari, Leigh A. Mcgarvie, Hamish G. MacdougallAbstract:BACKGROUND Superior Canal Dehiscence is classically diagnosed with typical abnormalities on Vestibular Evoked Myogenic Potentials (VEMPs) and Computed Tomography (CT) scans. AIM This paper discusses the utility of the video Head Impulse Test (vHIT) in SCD. METHODS Data from 11 ears (8 patients) with SCD were retrospectively reviewed. Results from vHIT, VEMPs and CT and when possible, MRI scans were correlated. An audit of 300 vHIT from patients undergoing routine Testing for any neurotological complaint was also conducted to look at the incidence of isolated abnormal superior canal function. RESULTS 82% of patients (9 ears) with SCD showed abnormal vHIT (reduced gain and catch-up saccades) isolated to the affected superior semicircular canal. CONCLUSION Correlation of the CT and VEMPs are important in forming a diagnosis of SCD. However, if isolated superior canal vHIT abnormalities are demonstrated, it is suggestive of SCD and such patients should be referred for further investigations.
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a new saccadic indicator of peripheral vestibular function based on the video Head Impulse Test
Neurology, 2016Co-Authors: Hamish G. Macdougall, Leonardo Manzari, Leigh A. Mcgarvie, Ian S. Curthoys, Michael G Halmagyi, Stephen J Rogers, Ann M Burgess, Konrad P WeberAbstract:Objective: While compensatory saccades indicate vestibular loss in the conventional Head Impulse Test paradigm (HIMP), in which the participant fixates an earth-fixed target, we investigated a complementary suppression Head Impulse paradigm (SHIMP), in which the participant is fixating a Head-fixed target to elicit anticompensatory saccades as a sign of vestibular function. Methods: HIMP and SHIMP eye movement responses were measured with the horizontal video Head Impulse Test in patients with unilateral vestibular loss, patients with bilateral vestibular loss, and in healthy controls. Results: Vestibulo-ocular reflex gains showed close correlation ( R 2 = 0.97) with slightly lower SHIMP than HIMP gains (mean gain difference 0.06 ± 0.05 SD, p Conclusions: While compensatory saccades indicate vestibular loss in conventional HIMP, anticompensatory saccades in SHIMP using a Head-fixed target indicate vestibular function. SHIMP saccades usually appear later than HIMP saccades, therefore being more salient to the naked eye and facilitating vestibulo-ocular reflex gain measurements. The new paradigm is intuitive and easy to explain to patients, and the SHIMP results complement those from the standard video Head Impulse Test. Classification of evidence: This case-control study provides Class III evidence that SHIMP accurately identifies patients with unilateral or bilateral vestibulopathies.
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the video Head Impulse Test vhit detects vertical semicircular canal dysfunction
PLOS ONE, 2013Co-Authors: Hamish G. Macdougall, Leigh A. Mcgarvie, Ian S. Curthoys, G M Halmagyi, Konrad P WeberAbstract:Background The video Head Impulse Test (vHIT) is a useful clinical tool to detect semicircular canal dysfunction. However vHIT has hitherto been limited to measurement of horizontal canals, while scleral search coils have been the only accepted method to measure Head Impulses in vertical canals. The goal of this study was to determine whether vHIT can detect vertical semicircular canal dysfunction as identified by scleral search coil recordings. Methods Small unpredictable Head rotations were delivered by hand diagonally in the plane of the vertical semicircular canals while gaze was directed along the same plane. The planes were oriented along the left-anterior-right-posterior (LARP) canals and right-anterior-left-posterior (RALP) canals. Eye movements were recorded simultaneously in 2D with vHIT (250 Hz) and in 3D with search coils (1000 Hz). Twelve patients with unilateral, bilateral and individual semicircular canal dysfunction were Tested and compared to seven normal subjects. Results Simultaneous video and search coil recordings were closely comparable. Mean VOR gain difference measured with vHIT and search coils was 0.05 (SD = 0.14) for the LARP plane and −0.04 (SD = 0.14) for the RALP plane. The coefficient of determination R2 was 0.98 for the LARP plane and 0.98 for the RALP plane and the results of the two methods were not significantly different. vHIT and search coil measures displayed comparable patterns of covert and overt catch-up saccades. Conclusions vHIT detects dysfunction of individual vertical semicircular canals in vestibular patients as accurately as scleral search coils. Unlike search coils, vHIT is non-invasive, easy to use and hence practical in clinics.
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the video Head Impulse Test diagnostic accuracy in peripheral vestibulopathy
Neurology, 2009Co-Authors: Hamish G. Macdougall, Leigh A. Mcgarvie, Konrad P Weber, G M Halmagyi, Ian S. CurthoysAbstract:Background: The Head Impulse Test (HIT) is a useful bedside Test to identify peripheral vestibular deficits. However, such a deficit of the vestibulo-ocular reflex (VOR) may not be diagnosed because corrective saccades cannot always be detected by simple observation. The scleral search coil technique is the gold standard for HIT measurements, but it is not practical for routine Testing or for acute patients, because they are required to wear an uncomfortable contact lens. Objective: To develop an easy-to-use video HIT system (vHIT) as a clinical tool for identifying peripheral vestibular deficits. To validate the diagnostic accuracy of vHIT by simultaneous measures with video and search coil recordings across healthy subjects and patients with a wide range of previously identified peripheral vestibular deficits. Methods: Horizontal HIT was recorded simultaneously with vHIT (250 Hz) and search coils (1,000 Hz) in 8 normal subjects, 6 patients with vestibular neuritis, 1 patient after unilateral intratympanic gentamicin, and 1 patient with bilateral gentamicin vestibulotoxicity. Results: Simultaneous video and search coil recordings of eye movements were closely comparable (average concordance correlation coefficient rc 0.930). Mean VOR gains measured with search coils and video were not significantly different in normal (p 0.107) and patients (p 0.073). With these groups, the sensitivity and specificity of both the reference and index Test were 1.0 (95% confidence interval 0.69 –1.0). vHIT measures detected both overt and covert saccades as accurately as coils. Conclusions: The video Head Impulse Test is equivalent to search coils in identifying peripheral vestibular deficits but easier to use in clinics, even in patients with acute vestibular neuritis. Neurology ® 2009;73:1134 –1141
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Horizontal Head Impulse Test detects gentamicin vestibulotoxicity
Neurology, 2009Co-Authors: Konrad P Weber, Leigh A. Mcgarvie, Michael J. Todd, Ian S. Curthoys, G M HalmagyiAbstract:Background: Parenteral antibiotic therapy with gentamicin, even in accepted therapeutic doses, can occasionally cause bilateral vestibular loss (BVL) due to hair cell toxicity. Objective: To quantify in patients with gentamicin vestibulotoxicity (GVT) the extent of acceleration gain deficit of the horizontal vestibulo-ocular reflex at different accelerations with a graded Head Impulse Test (HIT) in comparison with standard caloric and rotational Testing. To characterize the corresponding HIT catch-up saccade pattern to provide the basis for its salience to clinicians. Methods: Horizontal HIT of graded acceleration (750°–6,000°/sec 2 ) was measured with binocular dual search coils in 14 patients with GVT and compared with 14 normal subjects and a control subject with total surgical BVL. Results: Patients showed mostly symmetric HIT gain deficits with a continuous spectrum from almost normal to complete BVL. Gain deficits were present even at the lowest Head accelerations. HIT gain correlated better with caloric (Spearman ρ = 0.85, p = 0.0001) than rotational Testing (ρ = 0.55, p = 0.046). Cumulative amplitude of overt saccades after Head Impulses was 5.6 times larger in patients than in normal subjects. Compared with previously published patients after unilateral vestibular deafferentation, GVT patients with BVL generated only approximately half the percentage of covert saccades during Head rotation (23% at 750°/sec 2 to 46% at 6,000°/sec 2 ). Conclusions: Head Impulse Testing is useful for early bedside detection of gentamicin vestibulotoxicity because most patients, even those with partial bilateral vestibular loss (BVL), have large overt saccades. Covert saccades, which can conceal the extent of BVL, are only approximately half as frequent as in unilateral patients, but may be present even in total BVL.
