Stable normocapnia during high-frequency body surface oscillation in rabbits

In order to identify the useful range of frequencies and the effect of lung volume on gas exchange during high-frequency ventilation, particularly during high-frequency body surface oscillation (HFBSO), we studied 12 normal, anesthetized, and paralyzed adult rabbits in 2 groups at 1, 3, 5, 8, 12, and 16 Hz in random order. The rabbits were placed in a body box, and a "bias" flow system different from all previously reported systems was used. For a given animal at a given frequency, the oscillation magnitude was adjusted to ensure normocapnia, defined as PaCO2 equal to 40 +/- 2 mmHg, for at least 5 min. For the first group (n = 6) with a mean tracheal pressure of 0.5 cmH2O, the necessary tidal volumes (mean +/- SD) were 3.7 +/- 0.2, 1.9 +/- 0.2, and 1.5 +/- 0.1 ml/kg at 1, 3, and 5 Hz, respectively. Further increases in frequency resulted in only small decreases in the required tidal volumes: 1.4 +/- 0.1, 1.2 +/- 0.1, and 1.2 +/- 0.1 ml/kg at 8, 12, and 16 Hz, respectively. Arterial PO2 values were very similar at all 6 frequencies, with a mean of 78.6 +/- 3.3 mmHg in this group. For the second group (n = 6) with a mean tracheal pressure of 5 cmH2O, arterial PO2 values were again the same at all frequencies applied but were significantly higher (95.5 +/- 2.6 mmHg) than in the first group. No significant difference was observed in the tidal volumes required to maintain normocapnia between the 2 groups, i.e., at the 2 mean tracheal pressures studied.(ABSTRACT TRUNCATED AT 250 WORDS)