Fig. 2. Cardiovascular response to systemic bupivacaine. (A ) Arterial perfusion of bupivacaine (3 μg/ml, bar ) evoked a prolonged pressor response associated with bradycardia. It was without significant effect on the integrated phrenic nerve activity. (B ) Expansion of the phrenic nerve and heart rate traces demonstrates respiratory sinus arrhythmia before (B1 ) and in the presence of bupivacaine (B2 ). (C ) Frequency distribution of the electrocardiogram R-R interval before (C1 ) and after (C2 ) bupivacaine with a fitted normal distribution (solid line ). bpm = beats/min.