Figure 3. Original tracings of compound action potential (CAP), abdominal pressure (Pab), and esophageal pressure (Pes) during diaphragm pacing with aminophylline 40 mg/kg (A40) (A) compared with saline control (SAL) (B). Note decrease in CAP amplitude in both animals, but Pab and Pes (and hence Pdi) are nearly preserved in the animal given aminophylline but decrease rapidly and persistently throughout pacing in the control animal. (The offset of the CAP baselines does not imply differences in resting potential.) REC = recovery.