With a high normal PaCO2 (greater than 6.0 kPa) and high PaO2 (greater than 30 kPa), HFV and PEEP (0.5 kPa) decreased PNA by a mean of only 30%. When PaO2 was decreased to physiological values (less than 13.3 kPa), with a low normal PaCO2 (less than 5.3 kPa), the decrease in ...