Fig. 12.

Recovery to eupnea vs. tachypneic failure after transient interruption of chemosensory feedback. A: time course of $P{a}_O{}_{{}_2}$ before (black), during (blue), and after (green) interruption of chemosensory feedback. Black, eupneic breathing in closed-loop model; blue, chemosensory feedback is interrupted by holding g_tonic fixed at 0.1 nS for 49.2466 s; green, chemosensory feedback is reestablished by again making g_tonic a function of $P{a}_O{}_{{}_2}$. System recovers to eupnea. B: same as A, except the g_tonic = 0.1 nS clamp (blue) is held for 0.1 ms longer. After reestablishing chemosensory feedback the system ultimately descends into tachypnea (red) rather than recovering to eupnea. C: eupneic recovery from A projected onto (h, vol_L, $P{a}_O{}_{{}_2}$) coordinates. During the g_tonic clamp (blue curve), the CPG is quiescent and $P{a}_O{}_{{}_2}$ decreases to 42 mmHg. After release of the clamp (green curve), g_tonic increases rapidly, causing a barrage of spiking and a large expansion of lung volume that rapidly increases $P{a}_O{}_{{}_2}$ to 82 mmHg. From t = 120 to 180 s the system exhibits bursts of spiking with shorter interburst intervals and shorter burst durations than eupneic breathing. This leads to intermediate $P{a}_O{}_{{}_2}$ values (76–80 mmHg) as the interburst intervals and burst durations gradually lengthen and the system returns to eupneic breathing. D: tachypneic failure from B projected onto (h, vol_L, $P{a}_O{}_{{}_2}$) coordinates. Same as C, except that during the intermediate $P{a}_O{}_{{}_2}$ oscillations from t = 120 to 180 s the interburst intervals and burst durations gradually shorten and the system descends into tachypnea (red curve).