Ventilatory saving by external chest wall compression or oral high-frequency oscillation in normal subjects and those with chronic airflow obstruction

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Abstract
Oscillation of the air within the lungs at high frequency is associated with an increased clearance of CO2. Because of the high frequency and low volume of these oscillations, spontaneous breathing is unhindered and the technique has potential value as a supplement to ventilation. High-frequency oscillations were superimposed upon tidal breathing by using a loudspeaker attached to a mouthpiece (oral high-frequency oscillation, OHFO) or by external chest wall compression (ECWC). The changes in ventilation and breathlessness were compared by using OHFO and ECWC in normal subjects with those in patients with chronic airflow obstruction (CAO) and the pattern of saving was related to the resonant frequencies of the respiratory system as a whole (for, 5-10 Hz in normal subjects 16-26 Hz in CAO) and those of the ribcage (Foc, 70 Hz). OHFO reduced minute ventilation (.ovrhdot.VE) by up to 46% in normal subjects (P < 0.01) and 29% in CAO (P < 0.01) without any rise in CO2. ECWC reduced .ovrhdot.VE by 27% in normal subjects (P < 0.01) and 16% in CAO (P < 0.01) without a rise in CO2. High-frequency oscillation by either method relieved breathlessness in those with CAO and was comfortable and well tolerated. In normal subjects for was discrete and varied little with respiration. Maximum savings occurred around for (5-10 Hz). In CAO, there was no obvious single resonant frequency and flow and pressure signals were intermittently in phase over a band of about 10 Hz. The reductions in minute ventilation were only loosely related to for (13-26 Hz). Neither group reduced .ovrhdot.VE at fo1r (65-75 Hz). OHFO has considerable potential in the management of patients with CAO, where it may be of value as an assistance to breathing and in the relief of breathlessness. ECWC, although effective in principle, is impractical by these methods and awaits the development of an acceptable delivery system.