Pattern of breathing and obstruction pressure in patients with airway obstruction after inhalation of bronchodilators

The neuromuscular drive is increased in patients with an airway obstruction. The aim of the study was to estimate an influence of beta-agonist on breathing pattern and mouth occlusion pressure (P0.1) in patients with reversible and nonreversible airway obstruction. Ventilatory function tests, pattern of breathing analysis, mouth occlusion pressure (P0.1) and inspiratory impedance (P0.1/Vt/Ti) were measured in 23 obstructive patients and 20 healthy subjects. In all patients these measurements were repeated 20 minutes after bronchodilator inhalation (0.2 mg fenoterol). During quiet room-air breathing in patients we observed increased Vt, Vt/Ti comparing with healthy persons. The time of inspiration (Ti) and total time (Ttot) were shortened in comparison to our control group. P0.1 and inspiratory impedance were significantly increased (P0.1 3.6 +/- 1.6 vs 1.6 +/- 0.3 cm H2O, p < 0.01 and P0.1/Vt/Ti 6.6 +/- 2.3 vs 3.8 +/- 1.0 cm H2O/L/s). Measurements performed after bronchodilator inhalation revealed decrease of P0.1 and P0.1/Vt/ Ti in patients responsive to beta-agonist (delta FEVI > 15%). In unresponsive patients (delta FEVI < or = 15%) such decrease in neuromuscular respiratory drive was not observed. We conclude that diminishing of increased neuromuscular respiratory drive in patients with reversible obstruction is a consequence of airway resistance decreasing. It seems to be an additional, advantageous for a patient, effect of bronchodilator inhalation.