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. 2017 Jul 19;118(4):2194–2215. doi: 10.1152/jn.00170.2017

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Fig. 15. — Recovery to eupnea vs. tachypneic failure after transient interruptions of chemosensory feedback assuming high input drive to the CPG during the interruptions. These simulations are analogous to those shown in Fig. 12, except here g_tonic is set to 0.5 nS (high drive to CPG) rather than 0.1 nS (low drive to CPG) in the absence 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 0.5 nS for 24.5 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 in A, except that the g_tonic = 0.5 nS clamp (blue) is held for 0.1 s 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. The interruption of chemosensory feedback causes a sudden increase in g_tonic since the constant value it is set to during the interruption (0.5 nS) is higher than the values traversed by g_tonic during eupneic bursting (0.12–0.22 nS). This change triggers a barrage of spiking and a large expansion of lung volume that rapidly increases $P a_{O}_{_{2}}$ to 124 mmHg. During the remainder of the g_tonic clamp, the CPG exhibits tonic spiking that does not drive effective lung expansions and $P a_{O}_{_{2}}$ decreases to 83 mmHg. After release of the clamp, 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 (green trace). D: tachypneic failure from B projected onto (h, vol_L, $P a_{O}_{_{2}}$ ) coordinates. Same as in C, except that during the intermediate $P a_{O}_{_{2}}$ oscillations from t = 90 to 120 s the interburst intervals and burst durations gradually shorten and the system descends into tachypnea (red trace).