Figure 1. Abdominal motor activity patterns during high central respiratory drive.

Effect of increased respiratory drive on integrated phrenic (PN), hypoglossal (HN), lumbar abdominal (AbN) and central vagus (cVN) outflows recorded simultaneously. A, during eupnoea in the juvenile rat (a₁) AbN activity exhibits low amplitude post-I discharge. The response to anoxia (95% N₂ and 5% CO₂) was divided into 3 phases: inspiratory excitation (a₂), inspiratory depression (a₃) and gasping (a₄). During phases a₂ and a₃ augmenting AbN discharge emerged with variable amplitudes. The pattern transformed into biphasic-E AbN activity during gasping (phase a₄). Note that the appearance of a single doublet inspiratory burst (third burst prior to a₄) was predicted by the model of Wittmeier et al. (2008). B, neonatal rats (n= 3) presented similar motor outflows during gasping with biphasic-E AbN discharges. This activity continued longer (in comparison with juvenile rats) without suffering respiratory arrest. C, bolus injections of NaCN (100 μl, 0.03%) into the perfusate to activate peripheral chemoreceptors also induced biphasic-E activity in the AbN in juvenile rats.