ABSTRACT
Accurate neurophysiological assessment of the respiratory muscles has been hampered by a number of technical problems, especially in conscious humans. In an ideal situation, force, muscle fiber length, and speed of contraction can be measured, the muscles can be stimulated electrically, and the electromyogram can be recorded with minimal far-field interference from surrounding muscles and minimal recording artefact. The latter may be produced by changes in the relationship of the electrodes to the muscle or variation in conductivity of surrounding tissues. The respiratory muscles include the diaphragm, which is largely inaccessible to noninvasive recording techniques, although the phrenic nerves can be stimulated. The intercostal and abdominal muscles present technical difficulties whether studied individually or together because they are layered, and the latter are innervated by multiple ventral roots. Finally, there is no reliable method to derive absolute muscle force produced by any of the individual muscles involved in the generation of respiratory pressures.
