ASSESSMENT OF DIAPHRAGM FUNCTION USING MOUTH PRESSURE TWITCHES IN CHRONIC OBSTRUCTIVE PULMONARY-DISEASE PATIENTS

The relative invasiveness of the balloon catheter technique in measuring twitch transdiaphragmatic pressure (Pdi(t)) limits its clinical use. By phrenic stimulation we obtained swings in mouth pressure (Pm(t)) in six COPD patients (age 50 to 72, FEV1 18 to 48% of predicted) at relaxed FRC (rFRC) and during graded inspiratory efforts (IE; twitch occlusion, TO). At rFRC, Pm(t) was damped and time lagged relative to the esophageal pressure twitch (Pes(t)), as if pressure had equilibrated through an RC system. Pm(t) was not correlated with Pdi(t). Conversely, Pm(t) and Pes(t) were always well matched during IE [Pm(t) = 0.971 (SEM +/- 0.028) Pes(t), r > 0.89], possibly in relation to a decrease in upper airway compliance or more uniform pleural pressure swings. Pm(t) decreased with the level of voluntary diaphragmatic contraction (Pdi(vol)) in proportion to Pdi(t), reflecting a progressive increase in the level of diaphragm activation. During IE, Pm(t) was closely related to the voluntary mouth pressure in five subjects but not in the remaining subject, indicating intersubject variability in the level of diaphragmatic recruitment relative to other inspiratory muscles. We submit that measuring Pm during inspiratory efforts upon which bilateral phrenic stimulation is superimposed offers a relatively simple method for the assessment of diaphragm activation, potentially applicable in the clinical field.