Chronic intermittent hypoxia enhances ventilatory long-term facilitation in awake rats

This study examined the effect of chronic intermittent hypoxia (CIH: 5 min 11-12% O2/5 min air, 12 h/night, 7 nights) on ventilatory long-term facilitation (LTF) and determined the persistence period of this CIH effect in awake rats. LTF, elicited by 5 or 10 episodes of 5 min 12% O2, was measured four times in the same Sprague-Dawley rats by plethysmography, before and 8 h, 3 days, and 7 days after CIH treatment. Resting ventilation was unchanged after CIH. Five episodes of 12% O2 did not initially elicit LTF but elicited LTF (23.5 +/- 1.4% above baseline) 8 h after CIH, which partially remained at 3 days (11.4 +/- 2.2%, P < 0.05) and disappeared at 7 days. Ten episodes initially elicited LTF (17.7 +/- 1.1%, 45-min duration) and elicited an enhanced LTF (29.1 +/- 1.5%, 75 min) 8 h after CIH. These results demonstrated that CIH enhanced ventilatory LTF in conscious, freely behaving rats in two ways: 1) a previously ineffective protocol induced LTF; and 2) LTF magnitude was increased and LTF duration prolonged, and this CIH effect on LTF persisted for at least 3 days.