VENTILATION BY HIGH-FREQUENCY CHEST WALL COMPRESSION IN DOGS WITH NORMAL LUNGS

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Abstract
In 6 anesthetized and paralyzed supine dogs, ventilation by high-frequency chest wall compression (HFCWC) was accomplished by a piston pump rapidly oscillating the pressure in a modified double blood pressure cuff wrapped around the lower thorax. Testing applied frequencies at 3, 5, 8 and 11 Hz applied peak cuff pressures ranged from 30-230 cm H2O. This produced swings of esophageal pressure as high as 18 cm H2O and peak oscillatory air flow ranging from 0.7-1.6 l/s. Oscillatory tidal volume declined with increasing frequency and ranged from a mean of 61-45 ml. After 30 min of applied HFCWC, arterial blood gas determinations revealed a mean PaCO2 [arterial partial pressure of CO2] of 29.3 mm Hg at 5 Hz, 35 mm Hg at 3 Hz, 36 mm Hg at 8 Hz and 51 mm Hg at 11 Hz. Mean PaO2 [arterial partial pressure of O2] improved from ventilator control values at 3 Hz, remained unchanged at 5 and 8 Hz, and declined at 11 Hz. In 2 dogs breathing spontaneously, HFCWC applied at 5 and 11 Hz resulted in a reduction in spontaneous minute ventilation, mainly by a reduction in spontaneous tidal volume; arterial blood gas values changed slightly. One dog ceased to breathe spontaneously within 5 min of application of HFCWC as the PaCO2 fell below control values. In dogs with normal lungs, HFCWC may assist spontaneous ventilation. In paralyzed dogs HFCWC may be of sufficient magnitude to cause hyperventilation.

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