Effects of paralysis with pancuronium on chest wall statics in awake humans.

The influence of tonic inspiratory muscle activity on the relaxation characteristics of the chest wall, rib cage (RC), and abdominal wall (ABW) has been investigated in four highly trained subjects. Chest wall shape and volume were estimated with magnetometers. Pleural pressure (Pes) and abdominal pressure were measured with esophageal and gastric balloons, respectively. Subjects were seated reclining 30 degrees from upright, and respiratory muscle weakness was produced by pancuronium bromide until RC inspiratory capacity was decreased to 60% of control. Only minor changes were observed for Konno-Mead relaxation characteristics (RC vs. ABW) between control and paralysis. Similarly, although RC relaxation curves (RC vs. Pes) during paralysis were significantly different from control (P less than 0.05), the changes were small and not consistent. The differences between paralysis-induced changes in resting end-expiratory position of the chest wall and helium-dilution functional residual capacity (FRC) suggested changes in volume of blood within the chest wall. We conclude that 1) although tonic inspiratory activity of chest wall muscles exists, it does not significantly affect the chest wall relaxation characteristics in trained subjects; 2) submaximal paralysis produced by pancuronium bromide is likely to modify either spinal attitude or the distribution of blood between extremities and the thorax; these effects may account for the changes in FRC in other studies.