• Susana Pinto, Pedro Alves, Bernardo Pimentel, Michael Swash, and Mamede de Carvalho.
• Institute of Physiology, Instituto de Medicina Molecular, Faculty of Medicine, University of Lisbon, Portugal.
• Clin Neurophysiol. 2016 Jan 1; 127 (1): 892-897.

ObjectiveTo evaluate the correlation between diaphragm thickness assessed by ultrasound (US) with respiratory function tests and the diaphragm motor responses, in patients with amyotrophic lateral sclerosis (ALS).Methods42 consecutive ALS patients were studied (11 with bulbar-onset), excluding patients with marked orofacial paresis. Investigation included: revised ALS functional rating scale (ALSFRS-R), forced vital capacity (FVC), maximal voluntary ventilation (MVV), maximal inspiratory (MIP) and expiratory (MEP) pressures, nasal inspiratory pressure during sniff (SNIP); peak-to-peak amplitude of the diaphragmatic motor response to phrenic nerve stimulation (Diaphragm-CMAP), diaphragmatic thickness measured by ultrasound during maximal inspiration and during maximal expiration. Patients were analysed in bulbar or spinal subgroups. Correlations and multiple linear regression models were studied.ResultsThe mean age at disease onset was 58.4 ± 11.1 years and with a mean disease duration of 17.8 ± 13.6 months. Ultrasound studies of diaphragm thickness in full inspiration correlated with diaphragm CMAP in the whole population and in spinal-onset patients; and were similar in the two groups. Multiple linear modelling showed that FVC, SNIP and MVV were dependent on the change of thickness (p=0.001, 0.001 and 0.020, respectively) and that MIP and MEP were related to diaphragm CMAP p=0.003 and p=0.025, respectively).ConclusionDiaphragm thickness correlates with Diaphragm-CMAP, except in bulbar-onset patients. Respiratory tests are dependent on both diaphragm thickness and Diaphragm-CMAP.SignificanceUS thickness of the diaphragm correlates with the number of functional motor units as assessed by the phrenic nerve motor amplitude.Copyright © 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

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