Help for SwayStar™ (4.7.3.265)
The goal of the SwayStar™ measurements is to make direct comparisons between the amplitudes of trunk instabilities in different groups of subjects for both stance and gait tasks. Including task duration as a measurement makes it possible to weight the information content of duration relative to trunk-sway variables. Clinicians will want to compare a test subject’s values to normal reference values and then decide, based on the pattern of the deviations from the reference values, whether the subjects’ values are likely to be similar to those of a specific patient group. Examples of this procedure for different patient groups are provided in the following list of clinical-scientific literature. The reviews provide up-to-date summaries.
Reviews:
Clinical Scientific (Sway Star™):
Basta D, Todt I, Scherer H, Clarke A, Ernst A. Postural control in otolith disorders. Hum Mov Sci, 2005, 24:268-279
Basta D, Clarke A, Ernst A, Todt I. Stance performance under different sensorimotor conditions in patients with post-traumatic otolith disorders. J Vest Res, 2007, 17:25-31
Ernst A, Basta D, Seidl RO Todt I, Scherer H, Clarke A. Management of posttraumatic vertigo. Otolaryngol Head Neck Surg. 2005, 132:554-558
Grimbergen YA, Knol MJ, Bloem BR, Kremer BP, Roos RA, Munneke M. Falls and gait disturbances in Huntington’s disease. Mov Disord 2008, 23;970-976
Hegeman J, Shapkova E, Honegger F, Allum JHJ. Effect of age and height on trunk sway during stance and gait. J Vest Res 2007,17:75-87.
Horlings GC, Drost G, Bloem BR, Trip J, Pieterse AJ, Van Engelen BGM, Allum JHJ. Trunk sway analysis to quantify the warm-up phenomenon in myotonia congenita patients. J Neurol Neurosurg Psychiatry. 2008 (in press).
Horlings GC, Kueng UM, Honegger F, Bloem BR, Van Alfen N, Van Engelen BGM, Allum JHJ. Identifying vestibular and proprioceptive loss using posturographic analysis of stance tasks. Clinical Neurophysiology 2008, 119:2338-2346.
Horlings CGC, Carpenter MG, Kueng UM, Honegger F, Yun M, Wiederhold B, Allum JHJ
Influence of virtual reality on postural stability during quiet stance. Neuroscience Lett 2009, (in press)
Visser JE, Voermans NC, Oude Nijhius LB, van der Eijk M, Nijk R, Munneke M, Bloem BR. Quantification of trunk rotations during turning and walking in Parkinsons’s disease. (in press)
Clinical Scientific (Balance Freedom™)
Allum JHJ, Davis JR, Carpenter MG, Tschanz R, Meyes S, Debrunner D, Burger J. Neurofeedback in der Rehabilitation von Gleichgewichtsstörungen. at-automatiserungstechnik 2008, 56:467-475.
Basta D, Singbartl F Todt I, Clarke A, Ernst A. Postural control in otolith disorders. Vestibular rehabilitation by auditory feedback in otolith disorders. Gait and Posture, 2008, 28:397-404
Davis JR, Carpenter MG, Tschanz R, Meyes S, Debrunner D, Burger J, Allum JHJ. Trunk sway reduction in the young and elderly using vibrotactile and auditory biofeedback. Submitted to J Gerontology
Horlings CGC, Honegger F, Allum JHJ, Carpenter MG. Vestibular and proprioceptive contributions to human balance corrections: aiding those with prosthetic feedback. Proc NYAS 2009(in press)
Janssen LJF, Verhoeff LL, Horlings CGC, Allum JH. Directional effects of biofeedback on trunk sway during gait tasks in healthy young subjects. Gait and Posture 2009 (in press)
Verhoeff LL, Janssen LJF, Horlings CGC, Allum JHJ. Effects of biofeedback on trunk sway during dual tasking in healthy young and elderly. Gait and Posture 2009(in revision)
SwayStar™ directly measures the angular deviations of the trunk near the centre of mass (around L3-L5) without relying on indirect calculations obtained from measuring forces imposed on strain gauges embedded within a support surface or body marker information supplied by motion analysis systems. The measurement system of SwayStar™ is mounted on a belt. This mode of measurement makes the system portable, quick and easy to use.
Measuring trunk angular motion near the centre of gravity is probably the most effective way to quantify a falling tendency. It is independent of the linear motion of the body, that is, how fast one is walking. Measuring at another body segment might not quantify a balance instability. For example, motion of the head alone would not, because head movements are often independent from those of the trunk.
With the Bluetooth communication system SwayStar™ employs, the test subject can be up to 100 m away from the base measuring system at the PC. Other systems using camera, ultra-sonic or magnetic based sensor systems lack this huge field of operation.
Current camera-based, linear-displacement, motion analysis systems have limitations for analyzing body sway. They lack the sensitivity to accurately monitor small angular movements, they operate within frequency bandwidths that are too low (less than 50 Hz) to quantify a range of angular velocities accurately and the subject is often confined to a pre-defined test area making it difficult to perform and record gait tasks. Such motion analysis systems require repeated calibration to ensure that angles calculated from marker movements on the body are accurate. SwayStar™ avoids the limited accuracy, narrow bandwidth of such systems, and intensive operator costs. The SwayStar™ system measures as accurately as the earth’s rotation (0.01 deg/sec) how the trunk is moving during different real-time tasks without significantly limiting the subject’s movements. One of the prime disadvantages of motion analysis system is the need for dedicated technical personnel to operate the system and to produce the angular measurements that SwayStar™ produces automatically.
Thus one of the main advantages of SwayStar™ is that it can be used to measure the small movements of body sway during stance tasks, and it can be used to measure large sway movements of gait tasks, for example the getting up off a stool phase as part of the get-up-and-go task.
Stance tests can be performed in many forms with SwayStar™. One of the most common is on two legs, with and without vision, and like with computerised dynamic posturography (CDP) with an unstable surface. A foam pad is used as the unstable surface with SwayStar™. By comparing the values of sway under different visual and support surface conditions it is possible to assess the visual, somatosensory and vestibular contributions to stance control just as with CDP, however, not just in the pitch direction. The assessment can be made for the roll direction too which standard CDP equipment cannot perform.
A new addition to SwayStar™ is the combined vibro-tactile and auditory feedback system – Balance Freedom™. Signal transducers mounted on a head-band are driven by the sensors of SwayStar™. Thereby acoustic and vibratory feedback is provided to the patient on the status of his balance control, that is, the leaning motion of his trunk. Thresholds for the activation of vibro-tactile and auditory feedback are set at low and medium angles of trunk sway. A visual warning signal is also activated when the patient leans more than a higher set threshold.
The use of vibro-tactile feedback at head reduces the transmission time of these signals to the CNS. Furthermore this system used bone-conducting acoustic transducers to provide auditory feedback thereby opening up the air conduction pathway for normal hearing instead of blocking it with loudspeakers or in-ear speakers. Finally combined bone-conducting acoustic transducers and vibro-tactile devices mounted on the head may also excite otolith pathways and provide a means of artificial feedback.
The Balance Freedom™ system replaces the Auditory Feedback System Model 1. This system used 4 loudspeakers to provide auditory feedback (see Hegeman et al 2005 in reference list section 2.2.) produced by BII and now obsolete. The Auditory Model 1 system is still software supported.