Figure 3. Changes of P–P intervals provoked by brief neck suction, applied at different times in the breathing cycle.

The stippled boxes show the times and durations of applications of baroreceptor stimulation. Changes of P–P intervals were calculated by subtracting measurements made during breathing from those made at the same times in the breathing cycle after neck suction. Respiratory gating of vagal-cardiac motoneurone responsiveness is continuously variable throughout the breathing cycle. Adapted from Eckberg et al. (1980).