HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 102/5/1883    most recent 00694.2006v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Ross, E. Z. Articles by McConnell, A. K. Search for Related Content PubMed PubMed Citation Articles by Ross, E. Z. Articles by McConnell, A. K.

Influence of acute inspiratory loading upon diaphragm motor-evoked potentials in healthy humans

¹Centre for Sports Medicine and Human Performance, ²School of Health Sciences and Social Care, Brunel University, Uxbridge, Middlesex, United Kingdom

Submitted 20 June 2006 ; accepted in final form 21 December 2006

Acute prior activity of the inspiratory muscles can enhance inspiratory muscle strength and reduce effort perception during subsequent inspiratory efforts. However, the mechanisms subserving these changes are poorly understood. Responses to magnetic stimulation in 10 subjects were studied after an acute bout of nonfatiguing inspiratory muscle loading (IML), corresponding to 40% of subjects’ initial maximal inspiratory pressure (MIP), and after an acute bout of nonloaded, forced inspiration (NLF). Motor-evoked potentials elicited by cortical stimulation (MEP_c) and by phrenic nerve stimulation (MEP_p) were recorded transcutaneously from the diaphragm before, immediately after, and 15 min after two sets of 30 inspiratory efforts, at rest and during an MIP effort. After IML, MIP increased to 113 ± 3% (SE) of baseline and diaphragm MEP_p (during MIP) significantly increased (129 ± 10% of baseline). Diaphragmatic MEP_c (during MIP), expressed as a percentage of maximal MEP_p, decreased after IML (from 29 ± 9% to 20 ± 6%; P = 0.017) and after NLF (from 43 ± 5% to 31 ± 5%; P = 0.032). Observations from the biceps brachi demonstrated that changes after IML and NLF were specific to the inspiratory muscle, since no significant changes were observed in biceps force generation or in MEP_p or MEP_c amplitudes. These data indicate that after IML increased global inspiratory strength is accompanied by increased peripheral excitability and by a dampening of corticospinal excitability of the diaphragm.

transcranial magnetic stimulation; inspiratory muscles; end-tidal carbon dioxide