Phrenic LTF at 60 min post-hypoxia in TC, SH and IH groups before, during and after hypercapnic test without PEEP (white column) or with PEEP (black column). Left panel: Effect of 5% CO2 on LTF, n=3 for TC, n=4 for SH and IH control and n=5 for IH PEEP. Right panel: Effect of 10% CO2 on LTF, n=3 for TC, n=4 for SH and n-5 for IH. Data (means ± SE) expressed as percentage above baseline. n=4 in all groups except IH with PEEP (n=5). * indicates significant difference from baseline; † indicates significant difference from non-PEEP.