Results on gas-exchange and cerebral hemodynamics. CMV, conventional mechanical ventilation; HFO, high-frequency oscillation; TGI, tracheal gas insufflation; pre-HFO-TGI CMV corresponds to either the baseline CMV period of study day 1, or the 60-minute period that followed the 11-hour period of post-HFO-TGI CMV of the preceding study day (see also Figure 1 and corresponding legend). Left: results on PaO2/fractional inspired oxygen (FiO2) (top diagram), PaCO2 (middle diagram), and arterial pH (bottom diagram) obtained, during CMV1 (that is, just before HFO-TGI initiation), HFO-TGI at 4, 8, and 12 hours, and CMV2 (that is, at 30 minutes after HFO-TGI discontinuation; see also Figure 1 and corresponding legend). Right: results on intracranial pressure (top diagram) and cerebral perfusion pressure (bottom diagram) also obtained at the previously mentioned time points. Squares and error bars represent mean and SD, respectively. *P < 0.01 versus pre-HFO-TGI CMV. †P < 0.01 versus post-HFO-TGI CMV. §P < 0.05 versus pre-HFO-TGI CMV and post-HFO-TGI CMV. ‡P < 0.05 versus pre-HFO-TGI CMV.