Figure 3.

Hypoxemia and hypercapnia differentially activate post-I activities. A, Recording from urethane-anesthetized Lewis rat illustrating increases in PNA, post-I VNA, and post-I rSNA in response to acute hypercapnia and hypoxemia. B, Phrenic-triggered waveform averages were used to quantify respiratory-related nerve activities. Colored rectangles represent respiratory phases. Insp, Inspiratory; E2, late expiratory. Double-headed arrows indicate quantified parameters. C, Both stimuli progressively recruited PNA, but post-I VNA and rSNA were differentially activated by hypoxemia; phrenic-triggered averages correspond to color-coded epochs indicated in A. D, Pooled data compare hypercapnic and hypoxemic recruitment of PNA, VNA, and rSNA. Significant pairings were identified using Fisher's Least Significant Difference Test. E, Linear regression shows parallel recruitment of rSNA with VNA during hypoxemic trials (r² = 0.84 ± 0.05, p = 0.002, red lines), but not hypercapnic trials (p > 0.3, blue lines). Light red or blue represents individual trials. Bold represents average responses. *p < 0.05. **p < 0.01. ****p < 0.0001.