Effects of Body Positions on Respiratory Muscle Activation During Maximal Inspiratory Maneuvers

We evaluated the maximal mouth inspiratory pressure and the EMG patterns of major respiratory and accessory muscles used in the generation of voluntary inspiratory maneuvers during different body positions. Ten healthy subjects (F/M-4/6), the mean age 22.0 +/- 0.6 years, participated in the study. The maximal inspiratory mouth pressure (MIP) during Muller's maneuver was measured from residual volume in the standing, sitting, right-sided (RSL) and left-sided lying (LSL), supine, and head-down-tilt (HDT) (-30 degrees relatively horizon) positions. EMG of the diaphragmatic (D), parasternal (PS), sternocleidomastoid (SM), and genioglossus (GG) muscles were assessed in each body position. The baseline MIP was 105.3 +/- 12.0 in men and 59.9 +/- 10.1 cmH(2)O in women in the standing position and did not appreciable differ in the other positions, except the HDT where it was lower by 23 and 27% in men and women, respectively (P < 0.05). During Muller's maneuver, diaphragmatic EMG activity also was similar in all the body positions, but it was significantly enhanced in the HDT. In contrast, PS EMG showed the highest level of activation in the standing position, taken as the control, reference level, and was lower in the HDT. Activation of SM during the maneuver was near the control in the sitting position, lower in the supine (79%), RSL (85%), LSL (80%), and HDT (72%) positions (P < 0.05). GG EMG was significantly greater during maximal inspiratory effort in the supine and HDT positions (125 and 130%, respectively), while it was lower in the sitting, LRS, and LLS positions (76, 57, and 43%) compared with standing (P < 0.05). We conclude that the inspiratory pressure generated during Muller's maneuver is a reflection of complex interactions between several muscle groups during changes in body positions.