Fig. 4. Transdiaphragmatic pressure (Pdi) expressed as percentage of Pdi at normocapnia (baseline) obtained at 100 Hz stimulation at each level of capnia. (  A ) Induction of hypercapnia phase (n = 8). Pdi was significantly lower (*  P < 0.05) at 100 Hz between the third (T2), fourth (T3), and fifth (T4) levels of capnia and the initial value of Pdi (T0: normocapnia–baseline). (  B ) Recovery phase (n = 5 piglets). Pdi was significantly lower (*  P < 0.05) at 100 Hz stimulation between the recovery points (R1 and R2: 30 and 60 min after the return to normocapnia, respectively) and the baseline point (normocapnia). Data are expressed as percentage (mean ± SD).