Effect of External Chest Wall Oscillation on Gas Exchange in Healthy Subjects

¹ From West Park Hospital, Wellesley Hospital, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada

Effective gas exchange can be maintained in animals without the need for endotracheal intubation using external chest wall oscillation (ECWO). The clinical application of this technique has been limited by equipment which was either impractical or uncomfortable. We evaluated a prototype of a new oscillator in which an oscillatory profile of negative and positive pressure was imposed on a negative baseline pressure within a cuirass. In seven healthy subjects, we identified an oscillatory cuirass pressure that could effectively ventilate but would not result in severe hypocapnia over 5 min. We then measured the influence of changing the frequency of oscillation (fo) on PaCO₂ and spontaneous ventilation. Lastly, we evaluated the capability of this prototype to achieve targeted changes in chamber pressure. Subjects were ventilated with an inspiratory chamber pressure of 20±4 cm H₂O, an expiratory chamber pressure of 5 cm H₂O and an inspiratory-expiratory ratio of 1:1 at 9 oscillatory frequencies (fo: 1 to 5 Hz at 0.5-Hz increments). Each subject was ventilated for 5 min with consecutive periods of ECWO being separated from each other by 10 min of unassisted breathing. Oscillatory tidal volume (Vo) was sampled and PaCO₂ was determined from the expired carbon dioxide concentration (FECO₂) measured at the mouth. The change in PaCO₂ (PaCO₂) was the difference in PaCO₂ immediately before and after ECWO. We found that PaCO₂ and Vo were inversely related to fo. At 1 Hz the PaCO₂ was 13±1 mm Hg and Vo was 344±34 mL in the absence of spontaneous breathing (fb=0). At 3 Hz and above, at the chamber pressures used, the PaCO₂ was small (1 to 2 mm Hg) and the Vo was less than the predicted dead space. Subjects breathed spontaneously but at a frequency below that of their resting fb. With this prototype, chamber pressure changes up to 30 cm H₂O could be accurately achieved at 1, 2.5, and 4 Hz. In conclusion, ECWO can provide effective ventilation among healthy adults in the presence or absence of spontaneous breathing, and further studies are warranted to explore its effectiveness in a variety of clinical circumstances.

Key Words: external chest wall oscillation • gas exchange

Submitted on November 18, 1993
Accepted on June 10, 2007

This article has been cited by other articles:

				S. E. Scholz, J. Sticher, G. Haufler, M. Muller, O. Boning, and G. Hempelmann Combination of external chest wall oscillation with continuous positive airway pressure Br. J. Anaesth., September 1, 2001; 87(3): 441 - 446. [Abstract] [Full Text] [PDF]