Pulmonary gas exchange during high-frequency ventilation in dogs

Abstract

Steady-state gas exhange was studied in anesthetized paralyzed dogs subjected to high-frequency ventilation (HFB) to determine the effects of oscillation frequency (f 10–40 Hx) and stroke volume (Vs 20–40 ml) on gas exchange efficiency. Alveolar gas fractions were measured by rapid withdrawal of lung gas while oscillations and the bias flow circuit were interrupted. Alveolar ventilation (V̇ A) calculated from steady-state CO 2 elimination and F A co 2 was found to exhibit a frequency-dependent maximum. Similarly, Pa CO 2 increased and Pa O 2 decreased again when f exceeded a critical level. V̇ A was 13% of total ventilation (f · Vs) at 10 Hz (40 ml Vs) decreasing to about 4% at 40 Hz. Blood — gas differences for O 2 (P A - Pa) were about 6 torr and close to zero for CO 2 (Pa - P A). Lung volume assessed from He wash-out was increased with f and Vs. O 2 uptake and CO 2 elimination were significantly enhanced by HFV as a function of Vs. Because the effective V T was essentially unknown, the apparent gas exchange inefficiency at high f and Vs values may be due to the functional characteristics of the apparatus rather than a general feature of HFV.