VENTILATORY RESPONSE TO ARM ELEVATION - ITS DETERMINANTS AND USE IN PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

During arm elevation, normal individuals predominantly recruit the dia phragm, whereas chronic obstructive pulmonary disease (COPD) patients use more the accessory inspiratory and abdominal expiratory muscles. T o test that arm elevation is useful to study the ventilatory muscle re sponse in COPD, and to define the factors that determine this response , we studied 34 patients (FEV(1) 0.95 +/- 0.08 L) during 2 min of arm elevation. Transnasal balloons were used to determine end-inspiratory and endexpiratory gastric (Pg), pleural (Ppl) and transdiaphragmatic ( Pdi) pressures. The slope of Delta Pg/Delta Ppl (= Pg(i) - Pg(e)/Ppl(i ) - Ppl(e)) was used to infer respiratory muscle recruitment. With lin ear regression, the Delta Pg/Delta Ppl during arm elevation significan tly correlated with resting Delta Pg/Delta Ppl (r = 0.68), hyperinflat ion (FRC/TLC, r = 0.52), and diaphragmatic tension time index (TTldi) (r = 0.47). With multiple regression, resting Delta Pg/Delta Ppl, perc entage predicted FRC (FRC %pred) and TTldi influenced Delta Pg/Delta P pl during arm elevation (r = 0.84). Over the 2 min of arm elevation, t he dependency upon resting breathing pattern decreased, while hyperinf lation and TTldi became increasingly important. Higher resting TTldi v alues were associated with a faster and shallower breathing pattern (f /V-T greater than or equal to 38) during arm elevation. We conclude th at the pattern of respiratory muscle recruitment during arm elevation depends primarily on the resting breathing pattern. Over 2 min, the de gree of hyperinflation and the force reserve of the diaphragm increasi ngly impact on the ability to recruit the diaphragm. Measurement of f/ V-T during arm elevation is useful to determine functional reserve of the diaphragm in severe COPD.