Michael C. Schubert

Disorders of Balance and Vestibular Function in US Adults: Data From the National Health and Nutrition Examination Survey, 2001-2004

BACKGROUND Balance dysfunction can be debilitating and can lead to catastrophic outcomes such as falls. The inner ear vestibular system is an important contributor to balance control. However, to our knowledge, the prevalence of vestibular dysfunction in the United States and the magnitude of the increased risk of falling associated with vestibular dysfunction have never been estimated. The objective of this study was to determine the prevalence of vestibular dysfunction among US adults, evaluate differences by sociodemographic characteristics, and estimate the association between vestibular dysfunction and risk of falls. METHODS We included data from the 2001-2004 National Health and Nutrition Examination Surveys, which were cross-sectional surveys of US adults aged 40 years and older (n = 5086). The main outcome measure was vestibular function as measured by the modified Romberg Test of Standing Balance on Firm and Compliant Support Surfaces. RESULTS From 2001 through 2004, 35.4% of US adults aged 40 years and older (69 million Americans) had vestibular dysfunction. Odds of vestibular dysfunction increased significantly with age, were 40.3% lower in individuals with more than a high school education, and were 70.0% higher among people with diabetes mellitus. Participants with vestibular dysfunction who were clinically symptomatic (ie, reported dizziness) had a 12-fold increase in the odds of falling. CONCLUSIONS Vestibular dysfunction, as measured by a simple postural metric, is common among US adults. Vestibular dysfunction significantly increases the likelihood of falls, which are among the most morbid and costly health conditions affecting older individuals. These data suggest the importance of diagnosing, treating, and potentially screening for vestibular deficits to reduce the burden of fall-related injuries and deaths in the United States.

Mechanism of Dynamic Visual Acuity Recovery With Vestibular Rehabilitation

OBJECTIVE To determine why dynamic visual acuity (DVA) improves after vestibular rehabilitation in people with vestibular hypofunction. DESIGN Combined descriptive and intervention study. SETTING Outpatient department in an academic medical institution. PARTICIPANTS Five patients (age, 42-66 y) and 4 age-matched controls (age, 39-67 y) were studied. Patients had vestibular hypofunction (mean duration, 177+/-188 d) identified by clinical (positive head thrust test, abnormal DVA), physiologic (reduced angular vestibulo-ocular reflex [aVOR] gain during passive head thrust testing), and imaging examinations (absence of tumor in the internal auditory canals or cerebellopontine angle). INTERVENTION Vestibular rehabilitation focused on gaze and gait stabilization (mean, 5.0+/-1.4 visits; mean, 66+/-24 d). The control group did not receive any intervention. MAIN OUTCOME MEASURES aVOR gain (eye velocity/head velocity) during DVA testing (active head rotation) and horizontal head thrust testing (passive head rotation) to control for spontaneous recovery. RESULTS For all patients, DVA improved (mean, 51%+/-25%; range, 21%-81%). aVOR gain during the active DVA test increased in each of the patients (mean range, 0.7+/-0.2 to 0.9+/-0.2 [35%]). aVOR gain during passive head thrust did not improve in 3 patients and improved only partially in the other 2. For control subjects, aVOR gain during DVA was near 1. CONCLUSIONS Our data suggest that vestibular rehabilitation increases aVOR gain during active head rotation independent of peripheral aVOR gain recovery.

Prediction of Fall Risk Reduction as Measured by Dynamic Gait Index in Individuals with Unilateral Vestibular Hypofunction

Objective: To determine the effect of vestibular rehabilitation on reduction of fall risk in individuals with unilateral vestibular hypofunction and to identify those factors that predict fall risk reduction. Study Design: Retrospective chart review. Setting: Tertiary referral center. Patients: Forty-seven patients with unilateral vestibular hypofunction, aged 28 to 86 years, who were at risk for falls on initial assessment. Intervention: All patients underwent vestibular rehabilitation including adaptation exercises, designed to improve gaze stability, and gait and balance exercises. Main Outcome Measures: Fall risk (Dynamic Gait Index), visual acuity during head movements (Dynamic Visual Acuity), and subjective complaints were measured initially, at 2-week intervals, and at completion of physical therapy. Results: As a group, the patients had significantly reduced risk for falls (p < 0.001) after rehabilitation. Time from onset of symptoms did not affect the efficacy of vestibular rehabilitation. Both older (≥ 65 yr) and younger (< 65 yr) adults showed significant reductions in fall risk with vestibular rehabilitation (p < 0.001). However, a significantly greater proportion (χ2 = 0.016) of older adults remained at risk for falls at discharge compared with young adults (45% versus 11%). Initial Dynamic Gait Index and Dynamic Visual Acuity scores predicted fall risk reduction in patients with unilateral vestibular hypofunction. A model was developed using initial Dynamic Gait Index and Dynamic Visual Acuity scores to predict fall risk reduction. Conclusions: Vestibular rehabilitation is effective in significantly reducing fall risk in individuals with unilateral vestibular deficit. The model predicts fall risk reduction with good sensitivity (77%) and specificity (90%).

Decline in semicircular canal and otolith function with age.

Objective To characterize the physiologic nature of the vestibular dysfunction that occurs with the normative aging process. Study Design Cross-sectional study. Setting Tertiary care academic medical center. Patients Fifty individuals age 70 years and above. Interventions Head thrust dynamic visual acuity testing and cervical and ocular vestibular-evoked myogenic potential (VEMP) testing. Main Outcome Measures Semicircular canal function measured by head thrust dynamic visual acuity testing in each of the 3 semicircular canal planes, and saccular and utricular function measured by cervical VEMP and ocular VEMP testing, respectively. Results We observed significant declines in semicircular canal function in each of the canal planes as well as otolith function associated with aging. We found that individuals with impaired horizontal and superior semicircular canal function also were likely to have concomitant deficits in utricular but not saccular function. Overall, we noted that the prevalence of semicircular canal dysfunction was highest followed by saccular then utricular impairment, although we did observe individuals with isolated otolith deficits. Conclusion These data suggest an overall decline in semicircular canal as well as otolith function associated with aging, although the magnitude of impairment was greater for the semicircular canals than the otoliths in this elderly population. A better understanding of the specific vestibular deficits that occur with aging can inform the development of rational screening, vestibular rehabilitation, and fall risk reduction strategies in older individuals.

Diabetes, vestibular dysfunction, and falls: analyses from the National Health and Nutrition Examination Survey.

Objective: Patients with diabetes are at increased risk both for falls and for vestibular dysfunction, a known risk factor for falls. Our aims were 1) to further characterize the vestibular dysfunction present in patients with diabetes and 2) to evaluate for an independent effect of vestibular dysfunction on fall risk among patients with diabetes. Study Design: National cross-sectional survey. Setting: Ambulatory examination centers. Patients: Adults from the United States aged 40 years and older who participated in the 2001-2004 National Health and Nutrition Examination Survey (n = 5,86). Interventions: Diagnosis of diabetes, peripheral neuropathy, and retinopathy. Main Outcome Measures: Vestibular function measured by the modified Romberg Test of Standing Balance on Firm and Compliant Support Surfaces and history of falling in the previous 12 months. Results: We observed a higher prevalence of vestibular dysfunction in patients with diabetes with longer duration of disease, greater serum hemoglobin A1c levels and other diabetes-related complications, suggestive of a dose-response relationship between diabetes mellitus severity and vestibular dysfunction. We also noted that vestibular dysfunction independently increased the odds of falling more than 2-fold among patients with diabetes (odds ratio, 2.3; 95% confidence interval, 1.1-5.1), even after adjusting for peripheral neuropathy and retinopathy. Moreover, we found that including vestibular dysfunction, peripheral neuropathy, and retinopathy in multivariate models eliminated the significant association between diabetes and fall risk. Conclusion: Vestibular dysfunction may represent a newly recognized diabetes-related complication, which acts as a mediator of the effect of diabetes mellitus on fall risk.

Traumatic Brain Injury and Vestibular Pathology as a Comorbidity After Blast Exposure

Blasts or explosions are the most common mechanisms of injury in modern warfare. Traumatic brain injury (TBI) is a frequent consequence of exposure to such attacks. Although the management of orthopedic, integumentary, neurocognitive, and neurobehavioral sequelae in survivors of blasts has been described in the literature, less attention has been paid to the physical therapist examination and care of people with dizziness and blast-induced TBI (BITBI). Dizziness is a common clinical finding in people with BITBI; however, many US military service members who have been exposed to blasts and who are returning from Iraq and Afghanistan also complain of vertigo, gaze instability, motion intolerance, and other symptoms consistent with peripheral vestibular pathology. To date, few studies have addressed such “vestibular” complaints in service members injured by blasts. Given the demonstrated efficacy of treating the signs and symptoms associated with vestibular pathology, vestibular rehabilitation may have important implications for the successful care of service members who have been injured by blasts and who are complaining of vertigo or other symptoms consistent with vestibular pathology. In addition, there is a great need to build consensus on the clinical best practices for the assessment and management of BITBI and blast-related dizziness. The purpose of this review is to summarize the findings of clinicians and scientists conducting research on the effects of blasts with the aims of defining the scope of the problem, describing and characterizing the effects of blasts, reviewing relevant patients’ characteristics and sensorimotor deficits associated with BITBI, and suggesting clinical best practices for the rehabilitation of BITBI and blast-related dizziness.

Dynamic Visual Acuity during Passive Head Thrusts in Canal Planes

We sought to determine whether the dynamic visual acuity (DVA) test, which has been used to measure the function of the two horizontal semicircular canals (SCCs), could be adapted to measure the individual function of all six SCCs using transient, rapid, unpredictable head rotation stimuli (head thrusts) in the direction of maximum sensitivity of each SCC. We examined head-thrust DVA (htDVA) performance in 19 healthy control subjects, five patients before and six patients after plugging of one superior SCC for treatment of superior canal dehiscence, and two subjects with unilateral vestibular deafferentation (UVD) by vestibular neurectomy. We compared htDVA results for each SCC to vestibulo-ocular reflex gains measured using 3-D scleral coil recordings during a passive head-thrust-test paradigm. Individuals with normal vestibular function had similar htDVA scores for each of the six directions (canals) tested (mean 0.058 ± 0.050 LogMAR). Individuals tested after surgical plugging of one superior SCC were similar to normal for all SCCs except the plugged SCC, which had significantly worse htDVA scores (mean 0.270 ± 0.08 LogMAR). Individuals with UVD had significantly worse htDVA scores for head rotations maximally exciting any of the ipsilesional SCC (mean 0.317 ± 0.129 LogMAR) and scores similar to normal subjects for contralesional rotations (0.063 ± 0.051 LogMAR). These findings suggest that the htDVA test, which does not require scleral coil placement, magnetic field coils, or expensive oculography equipment, can provide a useful quantitative measure of individual SCC function.

Evaluation of quantitative head impulse testing using search coils versus video-oculography in older individuals

Objective To evaluate the validity of 2D video-oculography (VOG) compared with scleral search coils for horizontal AVOR gain estimation in older individuals. Study Design Cross-sectional validation study. Setting Tertiary care academic medical center. Patients Six individuals age 70 and older. Interventions Simultaneous eye movement recording with scleral search coil (over right eye) and EyeSeeCam VOG camera (over left eye) during horizontal head impulses. Main Outcome Measures Best estimate search coil and VOG horizontal AVOR gain, presence of compensatory saccades using both eye movement recording techniques. Results We observed a significant correlation between search coil and VOG best estimate horizontal AVOR gain (r = 0.86, p = 0.0002). We evaluated individual head impulses and found that the shapes of the head movement and eye movement traces from the coil and VOG systems were similar. Specific features of eye movements seen in older individuals, including overt and covert corrective saccades and anticompensatory eye movements, were captured by both the search coil and VOG systems. Conclusion These data suggest that VOG is a reasonable proxy for search coil eye movement recording in older subjects to estimate VOR gain and the approximate timing of corrective eye movements. VOG offers advantages over the conventional search coil method; it is portable and easy to use, allowing for quantitative VOR estimation in diverse settings such as a routine office-based practice, at the bedside, and potentially in larger scale population analyses.

Saccade and vestibular ocular motor adaptation

PURPOSE This paper focuses on motor learning within the saccadic and vestibulo-ocular reflex (VOR) oculomotor systems, vital for our understanding how the brain keeps these subsystems calibrated in the presence of disease, trauma, and the changes that invariably accompany normal development and aging. We will concentrate on new information related to multiple time scales of saccade motor learning, adaptation of the VOR during high-velocity impulses, and the role of saccades in VOR adaptation. The role of the cerebellum in both systems is considered. METHODS Review of data involving saccade and VOR motor learning. RESULTS Data supports learning within the saccadic and VOR oculomotor systems is influenced by 1). Multiple time scales, with different rates of both learning and forgetting (seconds, minutes, hours, days, and months). In the case of forgetting, relearning on a similar task may be faster. 2). Pattern of training, learning and forgetting are not similarly achieved. Different contexts require different motor behaviors and rest periods between training sessions can be important for memory consolidation. CONCLUSIONS The central nervous system has the difficult task of determining where blame resides when motor performance is impaired (the credit assignment problem). Saccade and VOR motor learning takes place at multiple levels within the nervous system, from alterations in ion channel and membrane properties on single neurons, to more complex changes in neural circuit behavior and higher-level cognitive processes including prediction.

The modified Romberg Balance Test: normative data in U.S. adults.

Objective: To generate normative values for performance on the modified Romberg Test of Standing Balance on Firm and Compliant Support Surfaces stratified by age, sex, and race/ethnicity and to determine fall risk associated with different levels of performance. Study Design: National cross-sectional survey. Setting: Ambulatory examination centers. Patients: U.S. adults 40 years and older who participated in the 2001-2004 National Health and Nutrition Examination Survey (n = 5,086). Interventions: Time to failure on the modified Romberg Test of Standing Balance on Firm and Compliant Support Surfaces. Main Outcome Measures: History of falling in the previous 12 months. Results: We observed that the time to failure decreased with increasing age across all sex and race/ethnicity categories. We found that once individuals went below a time to failure of 20 seconds, there was a significant greater than 3-fold increase in the odds of falling. In general, participants crossed the 20-second threshold at the age of 60 to 69 years. Conclusion: We established nationally representative normative values for performance on the modified Romberg test and noted differences in the rates of change across demographic groups. In addition, we demonstrated the fall risk associated with different levels of performance. These data will aid the clinician in interpreting and risk stratifying their patients performance on this postural test.