The Necessity of Calibration to Obtain Accurate & Repeatable Maximal Lingual Pressure Measurements

Transcription

1 The Necessity of Calibration to Obtain Accurate & Repeatable Maximal Lingual Pressure Measurements Kunal Potnis and Harrison Jones, PhD Duke University Department of Surgery Division of Speech Pathology and Audiology Durham, NC November 20, 2014

2 Disclosures The authors have no disclosures

3 References Adams V, Mathisen B, Baines S, Lazarus C, Callister R. A Systematic Review and Meta-analysis of Measurements of Tongue and Hand Strength and Endurance Using the Iowa Oral Performance Instrument (IOPI). Dysphagia Eisenhart C. Realistic Evaluation of the Precision and Accuracy of Instrument Calibration Systems. Journal of Research of the National Bureau of Standards 1963;67C(2): IOPI Medical. IOPI User Manual 2.2. Redmond, WA. Jones HN, Crisp KD, Moss T, Strollo K, Robey R, Sank J, Canfield M, Case LE, Mahler L, Kravitz RM, Kishnani PS. Effects of respiratory muscle training (RMT) in children with infantile-onset Pompe disease and respiratory muscle weakness. J Pediatr Rehabil Med 2014;7(3): Potter NL, Short R. Maximal Tongue Strength in Typically Developing Children and Adolescents. Dysphagia 2009;24(4):

4 Background Historically, speech-language pathologists (SLPs) have primarily used perceptual assessment techniques in research and clinical practice Increasingly, perceptual assessment is supplemented with quantitative techniques (e.g. lingual strength measures) Quantitative assessment techniques offer benefits to the clinician-scientist including: Standardization of methodology Improved statistical power Improved accuracy and repeatability within and across raters

5 Background, cont. In order to obtain accurate and repeatable data, most instrumentation used for quantitative measurement requires calibration Insufficient attention to calibration is often present in both the clinic and laboratory

6 What is calibration? Test during which known values are applied to a transducer and corresponding output readings are recorded under specified conditions (ASTM, 2009) Calibration is essential to maintain accurate, repeatable measurements with transducer-based measurement systems

7 Important calibration terms Pressure transducer: device that consists of a sensing element and a transduction element that modifies the signal to produce an output Accuracy: the closeness of a measurement relative to a reference, often expressed as ratio of error Repeatability: the ability of a transducer to reproduce output readings under the same conditions

8 Iowa Oral Performance Instrument (IOPI) IOPI is used to provide quantitative measurements of maximal lingual strength (kpa) Pressure-transducer based system Used by SLPs in the clinic and laboratory Standard instrumentation and methodology with normative database

9 IOPI Manufacturer Accuracy Checks Subtle differences between the methodology endorsed by manufacturer in manual over the years: Model 2.1 accuracy check (syringe) Model 2.2 accuracy check (scale) Model 2.2 accuracy check (syringe) Model 2.3 accuracy check (syringe)

10 IOPI Model 2.3 Accuracy Check Method: 1. Attach IOPI to 30 cc syringe via connecting tube 2. Push to 15 cc over 5 sec time interval 3. Record kpa value on IOPI 4. Check to see if it is in acceptable range for appropriate elevation

11 Alternative calibration approach Comprises three principal components to create a closed gas pressure circuit: 1) an air delivery system to introduce positive pressure 2) differential atmospheric pressure reference meter/gauge 3) the IOPI itself (Jones, Crisp, Moss, et al., 2014) As pressure is added, the value on the reference meter is compared to the value displayed on the IOPI over a specified operating range

12 Alternative calibration approach

13 Experimental Method The purpose of this study was to compare the accuracy and repeatability of data obtained from the two different calibration approaches IOPI Model 2.3 Accuracy Check performed on three new, unused IOPIs; 20 accuracy checks performed consecutively on each device Calibration performed on same three IOPIs utilizing alternative approach at three points across measurement range (25, 50, and 75 kpa); 20 times each, consecutively

14 Results IOPI Model 2.3 Accuracy Check IOPI Mean (kpa) Median (kpa) sd (kpa) Range (kpa) IOPI # IOPI # IOPI # Acceptable range (123 m) = 96 kpa ± 3

15 Results, cont. Alternative calibration method IOPI Calibration point (kpa) Mean (kpa) Median (kpa) sd (kpa) Range (kpa) IOPI # IOP1 # IOPI #

16 Discussion IOPI Model 2.3 Accuracy Check Benefits: Less costly Overall decent approximation Limitations: May be sufficient in many circumstances but not for others Less intuitive; may obfuscate understanding of calibration Does not allow for calibration across full range of measurement Dependent upon technique of user

17 Discussion, cont. Alternative calibration approach Benefits: More intuitive; allows user to understand key principles of calibration Allows for calibration across full range of measurement Increased accuracy/repeatability Less dependent upon technique of user Limitations: More costly Dependent upon pressure gauge used Need to void warranty of IOPI to adjust sensitivity

18 Implications Without proper calibration, limitations in usefulness and credibility of quantitative data Differences in clinic vs. research Quantification and thus calibration will become increasingly important in speech pathology

19 Questions? Special thanks to Harrison Jones, PhD and the Duke University Department of Surgery, Division of Speech Pathology and Audiology