Figure 4. (A) Percent compound action potential (CAP) amplitude during diaphragm pacing. Note decreases in percent CAP amplitude are not affected by aminophylline dose. (B) Percent transdiaphragmatic pressure (Pdi) during diaphragm pacing. Note rapid and significant decrease in percent Pdi during saline administration in contrast to preservation of percent Pdi during the first 5 min of pacing and only modest fatigue after 25 min, which recovers completely in the A40 group. Intermediate reductions in percent Pdi occur in the A10 and A20 groups. S = saline; A10 = aminophylline 10 mg/kg followed by 1 mg *symbol* kg sup -1 *symbol* h sup -1; A20 = 20 mg/kg followed by 2 mg *symbol* kg sup -1 *symbol* h sup -1; and A40 = 40 mg/kg followed by 4 mg *symbol* kg sup -1 *symbol* h sup -1.