A, four superimposed sweeps of the discriminated active unit. B-D, histograms of the activity of a cardiac vagal C fibre efferent triggered from: integrated phrenic nerve activity (B, Integ. phrenic; 20 ms bins, 131 sweeps), the femoral arterial blood pressure wave (C, BP; 5 ms bins, 1665 sweeps), and tracheal pressure (D, TP; 20 ms bins, 214 sweeps). Above each histogram is an average of the respective trigger input.