THE EFFECT OF LUNG-MECHANICS ON GAS-TRANSPORT DURING HIGH-FREQUENCY OSCILLATION

With the general aim of obtaining clinically relevant information on the use of high-frequency oscillation (HFO), we examined the effects of altering oscillatory frequency (f), tidal volume (V(T)), and mean airway pressure (P(aw)) on gas exchange in rabbits, both before and after altering the animal's pulmonary mechanics by saline induced lung injury. Twenty-seven combinations of f (5, 8, 12 Hz), V(T) (0.5, 1, 2 mL/kg), and P(aw) (5, 10,13 cm H2O) were used. Acute pulmonary injury was induced by instilling 10 mL/kg of warm saline into the lung. Gas exchange was assessed by steady-state levels of arterial oxygen tension (Pa(O2)) and carbon dioxide tension (Pa(CO2)). Arterial Pa(O2) was independent of f or V(T) before or after lung injury; it was independent of P(aw) before injury but highly dependent on P(aw) after lavage. The difference was presumably related to lung volume recruitment. Arterial Pa(CO2) was dependent on f and V(T) but independent of P(aw) at any time. The relationship was modeled by the equation Pa(CO2) is-proportional-to f(a) . V(T)b where the exponents a = -0.4 and b = -0.6. Our technique of a standardized saline instillation gave a reproducible and stable model of lung injury. In damaged rabbit lungs the principles of HFO appear to be similar to conventional mechanical ventilation: oxygenation depends on P(aw) and inspired oxygen concentration, while CO2 removal is determined by f and V(T).