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

Abstract

We measured pressures in 2 lung regions in 5 seated subjects with 2 esophageal balloons placed 7.2 ± 0.6 cm (mean ± 1 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 V̇ I) (mean slow V ̇ I : 0.22 ± 0.05 L/sec ) or at rapid flow rates (fast V̇ I) (2.15 ± 0.15 L/s). At FRC the mean EPG was 0.19 ± 0.04 cm H 2O/cm. The mean EPG was consistently lower at 500 cc above FRC during fast V̇ I (0.14 ± 0.03 cm H 2O/cm) than during slow V̇ I (0.28 ± 0.05 cm H 2O/cm) ( P < 0.001, paired ‘ t’ test). Fast V̇ I results in amplification of pressure in the lower as compared to the upper region with reduction in EPG. Diaphragmatic contraction appears to influence alterations in EPG during fast V̇ I.