An Instrumented Pull Test to Characterize Postural Responses

Summary

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.

Abstract

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.

Introduction

Postural reflexes act to maintain balance and upright stance in response to perturbations¹. Impairment of these postural responses in disorders such as Parkinson's disease results in postural instability, and commonly leads to falls, reduced walking confidence and diminished quality of life^2,3,⁴. 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 response^5,6,

Protocol

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

1. Prepare the electromagnetic motion tracker with 3 miniature motion sensors as per the manufacturer'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 in degrees. Ensure that all internal filterings are disabled, and the position of the sensors set to reference a static origin (usually the electromagn....

Results

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.......

Discussion

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.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Analog to Digital Convertor & Software	CED	Micro 1401-3	Any suitable digital acquisition system can be used
Load Cell	Omegadyne	LCM201-100N
MATLAB Software	MathWorks Inc.	NA	Any data science platform can be used
Motion Sensor	Ascension	6DOF, type-800
Motion Tracker	Ascension	3D Guidance trakSTAR	Mid-range transmitter
S&F Technical Harness and Belt	Lowepro	LP36282