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ASSOCIATION BETWEEN ULTRASOUND-DETERMINED CHARACTERISTICS OF THE DIAPHRAGM AND RESPIRATORY FUNCTION IN YOUNG ADULTS: PRELIMINARY STUDY

Abstract

C.R. Mortimer, G.C. Smilanich, L.E. Merifield, J.J. Dickinson, R.C. Pritchett, L.J. D’Acquisto, A.P. Freire, J.M. Dickinson, FACSM

Central Washington University, Ellensburg, WA

Ultrasound (US) is a non-invasive imaging technique that can be used to examine functional and morphological characteristics of the diaphragm. This technique is utilized to predict weaning success in mechanically ventilated patients, however, to what extent US-determined characteristics of the diaphragm are related to respiratory function in healthy adults is much less explored. PURPOSE: To examine the association between US-determined characteristics of the diaphragm and measures of respiratory muscle strength (maximal inspiratory and expiratory pressures). METHODS: Seventeen healthy individuals volunteered (10M, 7F; 23±3yr; 174±8cm; 74±15kg). While lying supine, US (Terason 3200T) images of the right hemidiaphragm were obtained to determine diaphragm thickness (B-mode, mid-axillary line) and diaphragm excursion (m-mode, between mid-clavicular and axillary lines, below right costal margin) during tidal expiration, tidal inspiration, and maximal inspiration. Respiratory muscle strength was assessed by maximal inspiratory (MIP) and expiratory pressures (MEP, Cosmed Pony FX). All measures were collected on the same day. RESULTS: Collapsed across both sexes, diaphragm thickness assessed at end of expiration and at end of maximal inspiration showed moderate correlations with MIP (r=0.556 and 0.489, respectively, P<0.05). While a moderate association between maximal diaphragm excursion and MIP was observed, this did not reach statistical significance (r=-0.466, P<0.1). Diaphragm thickness at end of expiration was moderately correlated with MEP (r=0.491, P<0.05), however, no other US-determined characteristic correlated with MEP. Interestingly, males showed greater diaphragm thickness at expiration compared to females (2.1±0.3 vs.1.5±0.3 mm, P<0.05) and stronger correlations between US-determined diaphragm thickness and MIP. CONCLUSION: These preliminary findings suggest that US-determined characteristics of the diaphragm are related to respiratory muscle strength in healthy young adults (primarily MIP), and that US may be capable of identifying sex-based differences. Future research is needed to identify the impact of exercise or other interventions on morphological and functional characteristics of the diaphragm.

Supported by CWU School of Graduate Studies and Research

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