Name: an instrumented pull test to characterize postural responses
Uploaded: 2019-04-06T15:00:00
Description: Watch this Scientific Journal Video about An Instrumented Pull Test to Characterize Postural Responses at JoVE.com

We thank Angus Begg (The Bionics Institute) for his assistance in the video protocol. We acknowledge Dr. Sue Finch (Statistical Consulting Centre and Melbourne Statistical Consulting Platform, University of Melbourne) who provided statistical support. This work was supported by the funding through the National Health and Medical Research Council (1066565), the Victorian Lions Foundation, and The Victorian Government&#39;s Operational Infrastructure Support Program.

All methods described were reviewed and approved by the local human research ethics committee at Melbourne Health. Informed consent was obtained from the participant prior to the study.
1. Equipment setup
<ol>
	<li>Prepare the electromagnetic motion tracker with 3 miniature motion sensors as per the manufacturer&#39;s guidelines. Prior to data collection, ensure each sensor is sampled at a minimum 250 Hz, displacement is measured in millimeter units and rotations (pitch, roll, and yaw) are i...

<ol>
	<li>Shemmell, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interactions+between+stretch+and+startle+reflexes+produce+task-appropriate+rapid+postural+reactions.">Interactions between stretch and startle reflexes produce task-appropriate rapid postural reactions.</a> Frontiers in Integrative Neuroscience. 9, (2015).</li><li>Kerr, G. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Predictors+of+future+falls+in+Parkinson+disease.">Predictors of future falls in Parkinson disease.</a> Neurology. 75 (2), 116-124 (2010).</li><li>Latt, M. D., Lord, S. R., Morris, J. G. L., Fung, V. S. 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E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Testing+balance+and+fall+risk+in+persons+with+Parkinson+disease,+an+argument+for+ecologically+valid+testing.">Testing balance and fall risk in persons with Parkinson disease, an argument for ecologically valid testing.</a> Parkinsonism &amp; Related Disorders. 17 (3), 166-171 (2011).</li><li>Fahn, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Recent Developments in Parkinson's Disease. , 153-163 (1987).</li><li>Hunt, A. L., Sethi, K. 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A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Early+biomechanical+markers+of+postural+instability+in+Parkinson's+disease.">Early biomechanical markers of postural instability in Parkinson's disease.</a> Gait and Posture. 30 (4), 538-542 (2009).</li><li>Mancini, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Trunk+accelerometry+reveals+postural+instability+in+untreated+Parkinson's+disease.">Trunk accelerometry reveals postural instability in untreated Parkinson's disease.</a> Parkinsonism &amp; Related Disorders. 17 (7), 557-562 (2011).</li><li>Nonnekes, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Are+postural+responses+to+backward+and+forward+perturbations+processed+by+different+neural+circuits?.">Are postural responses to backward and forward perturbations processed by different neural circuits?.</a> Neuroscience. 245, 109-120 (2013).</li><li>Horak, F. B., Dimitrova, D., Nutt, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direction-specific+postural+instability+in+subjects+with+Parkinson's+disease.">Direction-specific postural instability in subjects with Parkinson's disease.</a> Experimental Neurology. 193 (2), 504-521 (2005).</li><li>Colebatch, J. G., Govender, S., Dennis, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Postural+responses+to+anterior+and+posterior+perturbations+applied+to+the+upper+trunk+of+standing+human+subjects.">Postural responses to anterior and posterior perturbations applied to the upper trunk of standing human subjects.</a> Experimental Brain Research. 234, 367-376 (2016).</li><li>Graus, S., Govender, S., Colebatch, J. 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A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+moderate+Parkinson's+disease+on+compensatory+backwards+stepping.">The effect of moderate Parkinson's disease on compensatory backwards stepping.</a> Gait and Posture. 38 (4), 800-805 (2013).</li><li>Valls-Sole, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reaction+time+and+acoustic+startle+in+normal+human+subjects.">Reaction time and acoustic startle in normal human subjects.</a> Neuroscience Letters. 195 (2), 97-100 (1995).</li><li>Carlsen, A. N., Maslovat, D., Lam, M. Y., Chua, R., Franks, I. 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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+surface+electromyography+in+biomechanics.">The use of surface electromyography in biomechanics.</a> Journal of Applied Biomechanics. 13 (2), 135-163 (1997).</li><li>Horak, F. B., Nashner, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Central+programming+of+postural+movements:+adaptation+to+altered+support-surface+configurations.">Central programming of postural movements: adaptation to altered support-surface configurations.</a> Journal of Neurophysiology. 55 (6), 1369-1381 (1986).</li><li>Saito, H., Yamanaka, M., Kasahara, S., Fukushima, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Relationship+between+improvements+in+motor+performance+and+changes+in+anticipatory+postural+adjustments+during+whole-body+reaching+training.">Relationship between improvements in motor performance and changes in anticipatory postural adjustments during whole-body reaching training.</a> Human Movement Science. 37, 69-86 (2014).</li><li>Kam, D. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dopaminergic+medication+does+not+improve+stepping+responses+following+backward+and+forward+balance+perturbations+in+patients+with+Parkinson's+disease.">Dopaminergic medication does not improve stepping responses following backward and forward balance perturbations in patients with Parkinson's disease.</a> Journal of Neurology. 261 (12), 2330-2337 (2014).</li><li>Peterson, D. S., Horak, F. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Effect+of+Levodopa+on+Improvements+in+Protective+Stepping+in+People+With+Parkinson's+Disease.">The Effect of Levodopa on Improvements in Protective Stepping in People With Parkinson's Disease.</a> Neurorehabilitation and Neural Repair. 30 (10), 931-940 (2016).</li><li>Haubenberger, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transducer-based+evaluation+of+tremor.">Transducer-based evaluation of tremor.</a> Movement Disorders. 31 (9), 1327-1336 (2016).</li><li>Elble, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Task+force+report:+scales+for+screening+and+evaluating+tremor:+critique+and+recommendations.">Task force report: scales for screening and evaluating tremor: critique and recommendations.</a> Movement disorders: official journal of the Movement Disorder Society. 28 (13), 1793-1800 (2013).</li><li>Adkin, A. 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Here, we have demonstrated the protocol for instrumentation of the clinical pull test, taking a method widely used in clinical practice and yielding an objective measurement of postural responses in addition to the important aspect of the pull administration. Using semi-portable motion tracking, this method offers a means of measurement that is more accessible compared to conventional laboratory techniques28. Using this method, researchers can explore characteristics of postural responses to a top...

Postural reflexes act to maintain&#160;balance and upright stance in response to perturbations1. Impairment of these postural responses in disorders such as Parkinson&#39;s disease results in postural instability, and commonly leads to falls, reduced walking confidence and diminished quality of life2,3,4. In clinical practice, postural reflexes are typically assessed with the pull test, where an examiner briskly pulls the patient backward at the shoulders and visually grades the response5,6,7,8. Postural instability is usually scored using the Unified Parkinson&#39;s Disease Rating Scale (UPDRS) (0 - normal to 4 - severe), as published by the International Movement Disorder Society5. This method has been used extensively in the assessment of individuals with Parkinson&#39;s disease but suffers poor reliability and very limited scaling (score/4)6,7,9. Pull test scores often do not correlate with important clinical endpoints such as falls and the integer-based rating lacks sensitivity to detect fine postural changes10,11.
Laboratory-based objective measures offer precise information about the nature of balance response by quantifying kinetic (e.g., the center of pressure), kinematic (e.g., joint goniometry/limb displacement) and neurophysiological (e.g., muscle recruitment) endpoints12. These methods may identify abnormalities before postural instability is clinically evident and track changes over time, including responses to treatment13,14.
Tools for Quantifying Postural Instability
Conventional techniques of dynamic posturography commonly employ moving platforms. Resulting postural responses are quantified using a combination of posturography, electromyography (EMG), and accelerometry12,15,16. However, the bottom-up responses of platform perturbations - which evoke a response like slipping on a wet floor, are fundamentally different from the top-down postural responses of the clinical pull test - as may occur when being bumped in a crowd. Emerging evidence suggests truncal perturbations yield different postural characteristics to those of moving platforms17,18,19. Accordingly, others have attempted truncal perturbations in the laboratory using complex techniques including motors, pulleys, and pendulums15,20,21,22. Methods of measurement are often expensive and inaccessible and comprise of video-based motion capture that requires dedicated space in specialized laboratories20,21. Ideally, an objective method to characterize pull test responses should have excellent psychometric properties, be easy to administer, simple to operate, widely accessible, and portable. This is important to facilitate widespread adoption of the technique as an alternative assessment tool to assess postural responses within research and potentially, clinical settings.
The Instrumented Pull Test 
The aim of this protocol is to offer researchers a technique for objective assessment of postural responses to the pull test. A semi-portable and widely available electromagnetic motion capture system underpins the technique. The perturbation involves manual pulls that do not require specialized mechanical systems. This method has sufficient sensitivity to detect small differences in postural reaction times and response amplitudes; therefore, it is suited to capturing potential abnormalities rated from normal up to grade 1 postural instability according to the UPDRS (postural instability with unassisted balance recovery)5. This method may also be utilized to explore the effects of therapy on postural instability. The protocol described here is derived from that in Tan et al.23.

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	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Analog to Digital Convertor &#38; Software</td>
			<td style="width:140px;">CED</td>
			<td style="width:159px;">Micro 1401-3</td>
			<td style="width:357px;">Any suitable digital acquisition system can be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Load Cell</td>
			<td>Omegadyne</td>
			<td>LCM201-100N</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MATLAB Software</td>
			<td>MathWorks Inc.</td>
			<td>NA</td>
			<td>Any data science platform can be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Motion Sensor</td>
			<td>Ascension</td>
			<td>6DOF, type-800</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Motion Tracker</td>
			<td>Ascension&#160;</td>
			<td>3D Guidance trakSTAR</td>
			<td>Mid-range transmitter</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">S&#38;F Technical Harness and Belt</td>
			<td>Lowepro</td>
			<td>LP36282</td>
			<td></td>
		</tr>
	</tbody>
</table>

an instrumented pull test to characterize postural responses

Impairment of postural reflexes, termed postural instability, is a common and disabling deficit in Parkinson's disease. To assess postural reflexes, clinicians typically employ the pull test to grade corrective responses to a backward perturbation at the shoulders. However, the pull test is prone to issues with reliability and scaling (score/4). Here, we present an instrumented version of the pull test to more precisely quantify postural responses. Akin to the clinical test, pulls are manually administered except pull force is also recorded. Displacements of the trunk and feet are captured by a semi-portable motion tracking system. Raw data represent distance traveled (in millimeter units), making subsequent interpretation and analysis intuitive. The instrumented pull test also detects variabilities influencing pull test administration, such as pull force, thereby identifying and quantifying potential confounds that can be accounted for by statistical techniques. The instrumented pull test could have application in studies seeking to capture early abnormalities in postural responses, track postural instability over time, and detect responses to therapy.

The instrumented pull test (Figure 1) was used to investigate trunk and step responses in a young, healthy cohort23. Thirty-five trials were presented serially, with an auditory stimulus delivered concurrently with each pull (Figure 2). The auditory stimulus was either 90 dB (normal) or 116 dB (loud). The loud stimulus has been demonstrated as sufficient to trigger StartReact effects, where pre-prepared re...

Watch this Scientific Journal Video about An Instrumented Pull Test to Characterize Postural Responses at JoVE.com

An Instrumented Pull Test to Characterize Postural Responses

Impairment of postural reflexes, termed postural instability, is difficult to quantify. Clinical assessments such as the pull test suffer issues with reliability and scaling. Here, we present an instrumented version of the pull test to objectively characterize postural responses.

Impairment of postural reflexes, termed postural instability, is a common and disabling deficit in Parkinson's disease. To assess postural reflexes, ...

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