Mechanical chest-wall vibration does not relieve air hunger.

Mechanical vibration of the chest wall can reduce dyspnea. It is unclear which sensations of respiratory discomfort are modulated by vibration (work/effort, air hunger, tightness). We performed two experiments to test whether vibration modifies air hunger: Experiment 1-eight adults performed six breath holds and rated their uncomfortable 'urge to breathe.' Vibration was applied separately at four chest-wall and two control sites, using two amplitudes. Breath-hold duration and ratings were unchanged by vibration at any site or amplitude. Experiment 2-nine adults were mechanically ventilated (mean 8.73 L/min) at constant hypercapnia (mean 48 mmHg) to produce mild to moderate ratings of air hunger (mean 37% of scale) with minimal respiratory muscle work. Vibration at 2nd or 3rd intercostal spaces during either inspiration or expiration did not change air hunger compared to triceps vibration. These experiments demonstrated that vibration does not relieve air hunger; we postulate that the effect of vibration is specific to the form of dyspnea.