Raising end-expiratory volume relieves air hunger in mechanically ventilated healthy adults

Abstract

Air hunger is an unpleasant urge to breathe and a distressing respiratory symptom of cardiopulmonary patients. An increase in tidal volume relieves air hunger, possibly by increasing pulmonary stretch receptor cycle amplitude. The purpose of this study was to determine whether increasing end-expiratory volume (EEV) also relieves air hunger. Six healthy volunteers (3 women, 31 ± 4 yr old) were mechanically ventilated via a mouthpiece (12 breaths/min, constant end-tidal Pco2) at high minute ventilation (V̇e; 12 ± 2 l/min, control) and low V̇e (6 ± 1 l/min, air hunger). EEV was raised to ∼150, 400, 725, and 1,000 ml by increasing positive end-expiratory pressure (PEEP) to 2, 4, 6, and 8 cmH2O, respectively, for 1 min during high and low V̇e. The protocol was repeated with the subjects in the seated and supine positions to test for the effect of shifting baseline EEV. Air hunger intensity was rated at the end of each breath on a visual analog scale. The increase in EEV was the same in the seated and supine positions; however, air hunger was reduced to a greater extent in the seated position (13, 30, 31, and 44% seated vs. 3, 9, 23, and 27% supine at 2, 4, 6, and 8 cmH2O PEEP, respectively, P < 0.05). Removing PEEP produced a slight increase in air hunger that was greater than pre-PEEP levels ( P < 0.05). Air hunger is relieved by increases in EEV and tidal volume (presumably via an increase in mean pulmonary stretch receptor activity and cycle amplitude, respectively).