An instrumented timed up and go: the added value of an accelerometer for identifying fall risk in idiopathic fallers.

The Timed Up and Go (TUG) test is a widely used measure of mobility and fall risk among older adults that is typically scored using a stopwatch. We tested the hypothesis that a body-fixed accelerometer can enhance the ability of the TUG to identify community-living older adults with a relatively high fall risk of unknown origin. Twenty-three community-living elderly fallers (76.0 ± 3.9 years) and 18 healthy controls (68.3 ± 9.1 years) performed the TUG while wearing a 3D-accelerometer on the lower back. Acceleration-derived parameters included Sit-to-Stand and Stand-to-Sit times, amplitude range (Range), and slopes (Jerk). Average step duration, number of steps, average step length, gait speed, acceleration-median, and standard-deviation were also calculated. While the stopwatch-based TUG duration was not significantly different between the groups, acceleration-derived TUG duration was significantly higher (p = 0.007) among the fallers. Fallers generally exhibited lower Range and Jerk (p < 0.01). While TUG stopwatch duration successfully identified 63% of the subjects, an accelerometer-derived three-measure-combination correctly classified 87% of the subjects. Accelerometer-derived measures were generally not correlated with TUG duration. These findings demonstrate that fallers have difficulty with specific TUG aspects that can be quantified using an accelerometer. Without compromising simplicity of testing, an accelerometer can apparently be combined with TUG duration to provide complementary, objective measures that allow for a more complete, sensitive TUG-based fall risk assessment.

A wearable system to assist walking of Parkinson s disease patients.

BACKGROUND: About 50% of the patients with advanced Parkinson's disease (PD) suffer from freezing of gait (FOG), which is a sudden and transient inability to walk. It often causes falls, interferes with daily activities and significantly impairs quality of life. Because gait deficits in PD patients are often resistant to pharmacologic treatment, effective non-pharmacologic treatments are of special interest. OBJECTIVES: The goal of our study is to evaluate the concept of a wearable device that can obtain real-time gait data, processes them and provides assistance based on pre-determined specifications. METHODS: We developed a real-time wearable FOG detection system that automatically provides a cueing sound when FOG is detected and which stays until the subject resumes walking. We evaluated our wearable assistive technology in a study with 10 PD patients. Over eight hours of data was recorded and a questionnaire was filled out by each patient. RESULTS: Two hundred and thirty-seven FOG events have been identified by professional physiotherapists in a post-hoc video analysis. The device detected the FOG events online with a sensitivity of 73.1% and a specificity of 81.6% on a 0.5 sec frame-based evaluation. CONCLUSIONS: With this study we show that online assistive feedback for PD patients is possible. We present and discuss the patients' and physiotherapists' perspectives on wearability and performance of the wearable assistant as well as their gait performance when using the assistant and point out the next research steps. Our results demonstrate the benefit of such a context-aware system and motivate further studies.

Bilateral coordination of gait and Parkinson's disease: the effects of dual tasking.

The aetiology of gait disturbances in Parkinson's disease (PD) is not fully understood. Recently, it was shown that in patients with PD, bilateral coordination of gait is impaired and that walking while being simultaneously engaged in a cognitive task is detrimental to their gait. To assess whether cognitive function influences the bilateral coordination of gait in PD, this study quantified left-right stepping coordination using a phase coordination index (PCI) that evaluates both the variability and inaccuracy of the left-right stepping phase (phi) generation (where the ideal phi value between left and right stepping is 180 degrees ). This report calculated PCI values from data obtained from force sensitive insoles embedded in subjects' shoes during 2 min of walking in a group of patients with PD (n = 21) and in an age matched control group (n = 13). All subjects walked under two walking conditions: usual walking and dual tasking (DT) (ie, cognitive loading) condition. For patients with PD, PCI values were significantly higher (ie, poorer coordination) during the DT walking condition compared with usual walking (p<0.001). In contrast, DT did not significantly affect the PCI of the healthy controls (p = 0.29). PCI changes caused by DT were significantly correlated with changes in gait variability but not with changes in gait asymmetry that resulted from the DT condition. These changes were also associated with performance on a test of executive function. The present findings suggest that in patients with PD, cognitive resources are used in order to maintain consistent and accurate alternations in left-right stepping.

Mental and motor switching in Parkinson's disease.

Switching difficulties in Parkinson's disease (PD) are expressed in both mental and motor tasks. The authors of the present study investigated whether those deficits coexist in the same patient and are positively correlated. They tested 8 nondemented PD patients and 6 age-matched control participants by using the modified Wisconsin Card Sorting Test and a motor switching paradigm that is based on the task of reaching toward visual targets, the location of which could unexpectedly be altered within the reaction time. In both mental and motor tasks, patients performed significantly worse than controls. There were no significant correlations between the two types of pathology in individual patients. Mental and motor switching deteriorate in PD patients, but the deficits are not necessarily of parallel severity.

Assessment of vestibular ototoxicity of ear drops by recording of vestibular evoked potentials to acceleration impulses.

INTRODUCTION: The cochlear ototoxicity of several ear drops is well documented in the literature, but very few studies exist on the vestibular ototoxicity of these topical drugs. GOAL OF STUDY: To develop an animal model for the assessment of the vestibular ototoxicity of ear drops. MATERIALS AND METHODS: Two animal groups, consisting of five fat sand rats (FSRs) each, underwent unilateral labyrinthectomy. Normal saline was topically applied into the middle ear cavity of rats in the first group for 7 days (control group). Rats in the second group were treated in the same way by topical gentamicin solution. Cochlear function was assessed by the recording of auditory evoked potential (ABPs) thresholds, and vestibular function was assessed by the recording of vestibular evoked potentials (VsEPs) to angular accelerations. RESULTS: In the control group, except for the amplitude of the first wave, there was no significant difference in the VsEPs recorded before and after topical application. In the gentamicin group, VsEPs could not be recorded after 7 days, and ABPs were recorded in one case only, with a threshold of 100 dB sound pressure level (SPL). CONCLUSION: VsEPs seem to be a reliable measure for evaluating the vestibular ototoxicity of topical ear drops.

Development of short latency vestibular evoked potentials in the neonatal rat.

The development of short latency vestibular evoked potentials (VsEPs) was investigated in the neonatal rat. Using the appropriate stimulus (linear or angular acceleration impulses) and head orientation, responses elicited in various vestibular end-organs (utricle: x-VsEP; saccule: z-VsEP; lateral semi-circular canal: a-VsEP) were measured in rat pups at various ages between post-natal days (PND) 5 and 30, and compared to those recorded from adult animals. It was found that the VsEPs initially appeared on PND 6 (x-VsEPs and z-VsEPs) or 7 (a-VsEPs), and that by PND 8 the three responses could be recorded in all animals. The first wave of the responses, generated in the primary sensory nerve and reflecting end-organ activity, reached adult latencies and amplitudes by PND 10, showing rapid maturity of the responses. Auditory responses, on the other hand, develop at a later stage (from PND 11). The possible mechanisms involved in this differential maturation between vestibular and auditory activity are discussed.

The effect of head orientation on the vestibular evoked potentials to linear acceleration impulses in rats.

OBJECTIVE: To investigate the influence of linear acceleration impulses delivered when the head is held in different static head orientations, on the first wave of the short latency vestibular evoked potential (VsEP). The first wave is the compound action potential of the primary vestibular neurons synchronously activated. BACKGROUND: It has been shown previously that the VsEP elicited in response to linear acceleration is initiated mainly in the otolith organs. These organs are responsive to both dynamic and static linear forces, including gravity. METHODS: VsEPs to linear acceleration stimuli (4g) were recorded when the rats head was oriented so that a) the plane of the utricular macula was aligned with the plane of the stimulus, b) in supine position and c) with the head pitched up and down in various angles with respect to gravity (stimulus-head spatial relation remained constant) as compared to a reference position. RESULTS: With the stimulus aligned with the plane of the utricular macula, the amplitude of the first wave of the L-VsEPs was significantly larger than in the reference position. In the supine position, the amplitude of the first wave was significantly larger and the latency was significantly shorter. The amplitude of the first VsEP wave tended to be larger in the "head up" orientations as compared to the "head down" orientations (not statistically significant). CONCLUSIONS: These results demonstrate the influence of head position and gravity on the VsEPs to linear acceleration impulses, which is in accordance with their otolithic origin.

Surgical anatomy of the ear of the fat sand rat.

OBJECTIVE: This study was conducted to investigate and describe the anatomical details of the ear of the fat sand rat (Psammomys obesus). METHODS: Thirty ears (15 in dry skull and 15 in live animals) were dissected with the aid of an operating microscope and microsurgical techniques. Photographs were taken through an operating microscope. RESULTS: The temporal bone of the fat sand rat consists mainly of an unusually large bulla. Three distinct auditory ossicles were visualized and the manubrium of the malleus is relatively long in relation to the size of the ear. Most parts of the inner ear bulge into the bulla cavity and are easily accessible. The cochlea consists of 3.25 turns. The tympanic membrane, facial nerve, stapedial artery, and eustachian tube are described in detail. The large size of the bulla is probably related to the high sensitivity, particularly at low frequencies of the animals ear. CONCLUSION: The fat sand rat was found to be an excellent experimental animal for the investigation of middle and inner ear physiology.

Effect of white noise "masking" on vestibular evoked potentials recorded using different stimulus modalities.

Short latency vestibular evoked potentials (VsEPs) to linear acceleration impulses (L-VsEPs) are initiated in the otolith organs (saccule and utricle). Some of the saccule afferents have been reported to respond not only to linear acceleration, but also to high intensity acoustic stimuli. If so, the L-VsEP recorded from the saccule (elicited with the stimulus orientated relative to the head so as to optimally activate the saccule, i.e. stimulus in the vertical plane, Z-VsEP) should be reduced during high intensity broad band noise (BBN) "masking". Conversely, the utricular afferents have been reported to be less auditory-sensitive. Therefore, an L-VsEP which is mainly utricular in origin (stimulus in the horizontal plane, X-VsEP) should be less affected by this noise "masking". This was investigated in rats by recording X-VsEPs and Z-VsEPs and angular VsEPs (A-VsEPs), originating in the lateral semi-circular canals, before, during and after exposure to short duration, high intensity (113 dB SPL) BBN. This intensity completely masked auditory nerve evoked responses. The Z-VsEP did appear to be slightly more affected by the noise "masking" than the X-VsEP, implying the presence of more auditory-sensitive elements in the saccule. The A-VsEP was also affected by the BBN. The overall effect was relatively small (on average, 10-25% depression of the first wave of the different VsEPs). The responses showed recovery 5 min later.

Origins of the short latency vestibular evoked potentials (VsEPs) to linear acceleration impulses.

OBJECTIVE: To verify the vestibular origin of the short latency (t < 12.5 msec) vestibular evoked potentials (VsEPs) in response to linear acceleration impulses (L-VsEPs) and to differentiate between the contributions of the otolith organs and the semi-circular canals (SCCs) to their initiation. DESIGN AND METHODS: L-VsEPs (stimulus intensity, 3 g; rise time, 1.0 to 1.5 msec) were recorded in fat sand rats (Psammomys obesus) before and after unilateral labyrinthectomy, plugging of the SCCs in the remaining ear, and bilateral labyrinthectomy. Auditory nerve brainstem evoked responses (ABRs) and VsEPs to angular acceleration impulses (A-VsEPs) were also recorded. Wave amplitudes and latencies were statistically analyzed (MANOVA, repeated t-tests). RESULTS: In the intact animal, the linear VsEPs consisted of 5 to 6 waves, several mV in amplitude, with short latencies. The latency of the first wave was 2.0 msec. These waves were abolished after bilateral labyrinthectomy. Before and after plugging of the SCCs, linear acceleration VsEP wave latencies did not change, although amplitudes were slightly reduced. Similar results were obtained with respect to ABRs recorded from the same ear. Angular acceleration VsEPs were abolished after SCC plugging. CONCLUSIONS: These and other results confirm that the linear VsEPs are compound action potentials of the vestibular pathway, the first wave is the response of the vestibular nerve, and they are initiated mainly in the otolith organs.

Differential effect of the loop diuretic furosemide on short latency auditory and vestibular-evoked potentials.

OBJECTIVE: This study aimed to investigate the differential effect of the loop diuretic furosemide on the auditory and vestibular (otolith) end organs in the same animals simultaneously. DESIGN AND METHODS: Auditory nerve-brain stem-evoked responses (ABR-generated in the cochlea) and short latency vestibular-evoked responses to linear acceleration impulses (L-VsEP-generated in the otolith organs) were recorded from albino Sabra rats both before and at minute intervals after intravenous injections of the loop diuretic furosemide. In some animals, an equal volume of saline was injected to control for the effect of the injection itself. In most animals, more than one injection of saline or furosemide was possible (furosemide, N = 17 injections in 10 rats; saline, N = 18 injections in 9 rats). Peak-to-peak amplitude and peak latency changes in the first wave in each recording (representing end-organ activity) as a function of postinjection time were compared between the two evoked potentials using analysis of variance and repeated t-tests. RESULTS: Saline injections caused only minor changes in the amplitude of the ABR and the L-VsEP. After administration of furosemide, the amplitude of the L-VsEP hardly changed. However, there was a noticeable decrease in the amplitude of the ABR. CONCLUSIONS: Although furosemide has a major depressant effect on cochlear function, vestibular end-organ activity is hardly altered.

Effect of noise on the vestibular system - Vestibular evoked potential studies in rats.

Studies have shown that in order for sound to affect the vestibular end organs in the inner ear, very high intensities are required. Furthermore, in patients with noise induced hearing loss, vestibular signs, if present, are subclinical. In order to study possible auditory-vestibular interactions in a more controlled fashion, using physiological sound intensities, the present study used short latency vestibular evoked potentials (VsEPs) to impulses of angular (15,000 degrees /sec(2), risetime 1.5 msec) and linear (3-5 g, risetime 1.5 msec) acceleration were used to study the possible effects of sound on peripheral vestibular function in rats. Four different paradigms were used: a - an intense (135 dB pe SPL) click stimulus was presented 5 msec before the linear acceleration impulse and the VsEP to 128 stimuli were recorded with and without this click stimulus. There was no effect of the preceding intense click on the first wave (reflecting end organ activity) of the linear VsEP. b - 113 dB SPL white noise "masking" was presented while the VsEPs were elicited. A 10-20% reduction in the amplitude of the first VsEP wave was seen during the noise exposure, but 5 minutes after this exposure, there was almost complete recovery to pre-exposure amplitude. c - 113 dB SPL noise was presented for one hour and VsEPs were recorded within 15 minutes of cessation of the noise. The auditory nerve-brainstem-evoked response showed a temporary threshold shift while there was no effect on the VsEP. d - 113 dB SPL white noise was presented for 12 hours per day for 21 consecutive days. Auditory nerve-brainstem-evoked responses and vestibular (VsEPs) function were studied one week after the conclusion of the noise exposure. Auditory function was severely permanently depressed (40 dB threshold elevation and clear histological damage) while the amplitude of wave 1 of the VsEP was not affected. It seems therefore that even though intense noise clearly affects the cochlea and may have a "masking" effect on the vestibular end organs, the intensities used in this study (113 dB SPL) are not able to produce a long-term noise induced vestibular disorder in the initially normal ear. These differences between the response of the cochlear and vestibular end organs to noise may be due to dissimilarities in their acoustic impedances and/or their electrical resting potential.

Motor switching abilities in Parkinson's disease and old age: temporal aspects.

OBJECTIVES: To investigate capabilities of arm trajectory modification in patients with Parkinson's disease and elderly subjects using a double step target displacement paradigm. METHODS: Nine patients with Parkinson's disease and seven age matched control subjects were instructed to move a stylus towards visual targets presented on a digitising table. Within each session, in some trials the target location was changed before initiation of movement and the subjects were to modify their movements towards the new target (switching trials). In other trials the target location was not changed (control trials). This procedure was repeated for four different target configurations, using interstimulus time intervals of six different durations. The subjects' hand trajectories were recorded and their kinematic characteristics were analysed. RESULTS: In switching trials, about 40% of the movements were aimed directly toward the final target location in both groups. When the trajectories were initially directed toward the first target and then modified toward the second, the reaction time (RT) to the second stimulus (RT2) was longer than to the first stimulus (RT1). The RT2/RT1 ratio was significantly larger in patients with Parkinson's disease than in healthy elderly subjects. CONCLUSIONS: Patients with Parkinson's disease and elderly subjects are substantially slower in responding to a required modification of their movement than in responding to the required movement initiation. Patients with Parkinson's disease have impaired capabilities in processing simultaneously the motor responses to two visual stimuli presented in rapid succession.

Short latency vestibular evoked potentials (VsEPs) to linear acceleration impulses in rats.

In this study, short latency (t < 12.7 ms) vestibular evoked potentials (VsEPs) in response to linear acceleration impulses were recorded in 37 rats. A new technique (based on a solenoid) was used for generating linear force impulses that were delivered to the animal's head. The impulse had a maximal peak acceleration of 12 g. During the impulse, the displacement was 50 microns (at 4 g) and the rise time was 1.0 ms. A stimulation rate of 2/s was usually used. The VsEPs (averaged responses to 128 stimulations, digital filter: 300-1500 Hz) were recorded with electrodes on pinna and vertex, and were composed of 4-6 clear waves with mean amplitudes (for a 4 g stimulus) of 1-5 microV. The VsEPs were resistant to white noise masking, and were significantly suppressed (P < 0.05) following bilateral application of a saturated KCl solution to the inner ear, showing that contributions of the auditory and somatosensory systems are negligible. The latency of the response decreased as a power law function of stimulus magnitude, and the amplitude of the first wave increased as a sigmoid function of stimulus magnitude. VsEP responses were still present at the lowest intensities attainable (0.06-0.4 g) and reached saturation at 9 g. The amplitude of the later components was reduced when stimulus rate was elevated to 20/s. These results suggest that VsEPs in response to linear accelerations are similar in their nature to VsEPs in response to angular acceleration impulses that were previously recorded. These VsEPs to linear accelerations are most likely initiated in the otolith organs.