USE OF MOUTH PRESSURE TWITCHES INDUCED BY CERVICAL MAGNETIC STIMULATION TO ASSESS VOLUNTARY ACTIVATION OF THE DIAPHRAGM

There is a need for a simple method to assess the adequacy of diaphrag m activation during voluntary inspiratory efforts in patients with sus pected respiratory muscle weakness. We have compared mouth (Pmo,t), oe sophageal (Poes,t) and transdiaphragmatic (Pdi,t) twitch pressure elic ited bl cervical magnetic stimulation (CMS) in five normal men (mean ( SD) age 32.2 (1.8) yrs) On two Separate study days, Single magnetic st imuli mere delivered at functional residual capacity during relaxation and during graded voluntary inspiratory efforts against a closed airw ay, As voluntary-effort transdiaphragmatic and oesophageal pressure in creased, Pdi,t and Poes,t decreased linearly (r range, respectively, 0 .82-0.98 and 0.87-0.95), During relaxation, Pmo,t was unreliable due t o the poor transmission of intrathoracic pressure, but during inspirat ory efforts, the relation between voluntary mouth pressure and Pmo,t w as also linear (r range 0.83-0.95), On average, our subjects voluntari ly generated 99, 100 and 102% of the maximum transdiaphragmatic, oesop hageal and mouth pressures predicted by the respective linear regressi on equations. Pmo,t was correlated to both Poes,t and Pdi,t during ins piratory efforts, but not during relaxation. These studies confirm tha t twitch pressures induced by CMS during inspiratory efforts can be as sessed at the mouth in normal subjects, providing a simple and noninva sive technique for assessing diaphragm activation during voluntary ins piratory efforts, Potentially, this technique could be made more sensi tive and accurate and applied to detect submaximal efforts in patients .