High frequency chest wall oscillation in patients with chronic air-flow obstruction.

In order to assess high frequency chest wall oscillation (HFCWO) as a way to assist spontaneous breathing in obstructive lung disease, we studied 12 patients with severe and stable COPD. HFCWO at 5 Hz were applied by means of an inflatable vest. In order to avoid any discomfort, oscillations were applied only during the expiratory phase of the spontaneous breathing cycle. We compared gas exchange and pattern of breathing during control and HFCWO periods, each lasting 15 min. Minute ventilation did not change, but the pattern of breathing was markedly altered during HFCWO: breathing frequency decreased (p less than 0.001) from 18 +/- 6/min during control to 14 +/- 5/min, whereas tidal volume increased (p less than 0.01) from 600 +/- 200 ml during control to 860 +/- 400 ml. Secondary to this change in the pattern of breathing, arterial PO2 increased slightly (p less than 0.01) from 54 +/- 7 mm Hg during control to 57 +/- 8 mm Hg during HFCWO, and arterial PCO2 significantly (p less than 0.01) decreased from 46 +/- 6 mm Hg during control to 43 +/- 7 mm Hg during HFCWO. In addition, duty cycle (Ti/Ttot) decreased (p less than 0.001) from 0.37 +/- 0.03 s during control to 0.29 +/- 0.05 s during HFCWO. Such a decrease in duty cycle suggest that inspiratory muscle work was facilitated under HFCWO. In 8 patients, we obtained the tension-time index (TTdi), or the product of duty cycle and Pdi/Pdimax, and found that this index significantly decreased (p less than 0.05) from 0.06 +/- 0.03 during control to 0.04 +/- 0.02 during HFCWO.(ABSTRACT TRUNCATED AT 250 WORDS)