Effect of inspiratory flow rate on the esophageal pressure gradient in upright humans

We measured pressures in 2 lung regions in 5 seated subjects with 2 esophageal balloons placed 7.2 +/- 0.6 cm (mean +/- SE) apart in the mid-thorax in order to obtain the esophageal pressure gradient (EPG). Pressure differences between the lower thoracic balloon and a balloon placed in the stomach were obtained to measure transdiaphragmatic pressure (pdi). Inspiratory maneuvers were made from functional residual capacity (FRC) at either low inspiratory flow rates (slow VI) (mean slow VI: 0.22 +/- 0.05 L/sec) or at rapid flow rates (fast VI) (2.15 +/- 0.15 L/s). At FRC the mean EPG was 0.19 +/- 0.04 cm H2O/cm. The mean EPG was consistently lower at 500 cc above FRC during fast VI (0.14 +/- 0.03 cm H2O/cm) than during slow VI (0.28 +/- 0.05 cm H2O/cm) (P less than 0.001, paired 't' test). Fast VI results in amplification of pressure in the lower as compared to the upper region wih reduction in EPG. Diaphragmatic contraction appears to influence alterations in EPG during fast VI.