Imposed power of breathing associated with use of an impedance threshold device.

OBJECTIVE To measure the imposed power of breathing (imposed work of breathing per minute) associated with spontaneous breathing through an active impedance threshold device and a sham impedance threshold device. DESIGN Prospective randomized blinded protocol. SETTING University medical center. PATIENTS Nineteen healthy, normotensive volunteers (10 males, 9 females, age range 20-56 y, mean +/- SD weight 54.8 +/- 7.7 kg for females, 84 +/- 8 kg for males). METHODS The volunteers completed 2 trials of breathing through a face mask fitted with an active impedance threshold device set to open at -7 cm H(2)O pressure, or with a sham impedance threshold device, which was identical to the active device except that it did not contain an inspiratory threshold pressure valve diaphragm. Spontaneous breathing frequency (f), tidal volume (V(T)), exhaled minute ventilation, inspiratory pressure, and inspiratory time were measured with a respiratory monitor, and the data were directed to a laptop computer for real-time calculation of the imposed power of breathing. RESULTS There were no significant differences in heart rate, respiratory rate, tidal volume, and minute ventilation, with and without inspiratory impedance. For the sham and active impedance threshold device groups, respectively, the mean +/- SD imposed power of breathing values were 0.92 +/- 0.63 J/min and 8.18 +/- 4.52 J/min (p < 0.001), the mean +/- SD inspiratory times were 1.98 +/- 0.86 s and 2.97 +/- 1.1 s (p = 0.001), and the mean +/- SD inspiratory airway/mouth pressures were -1.1 +/- 0.6 cm H(2)O and -11.7 +/- 2.4 cm H(2)O (p < 0.001). CONCLUSIONS Breathing through an active impedance threshold device requires significantly more power than breathing through a sham device. All subjects tolerated the respiratory work load and were able to complete the study protocol.