Intermittent hypoxia (IH) conditioning alters tachycardiac responses to hypoxia

Objective To examine hypoxia‐stimulated tachycardiac responses before and after IH conditioning. Methods IH (10% O 2 ) 5 min X5 on Day 1 and gradually increased to 6 min X10 on Day 14, with 4‐min room air between IH exposures (N = 8, 25±2 yrs). Heart rate (HR), mean arterial pressure (MAP), minute ventilation (V), end‐tidal O 2 (P ET O 2 ) and CO 2 (P ET CO 2 ), were determined during Day 1 and Day 14 IH exposures (Table). Results Acute, repeated IH exposures (Bout 5 vs 1) (− significantly augmented the slopes of HR/P ET O 2 in both Day 1 1.35±0.11 vs −0.51±0.06 bpm/mmHg) and Day 14 (−1.18±0.16 vs −0.39±0.05 bpm/mmHg) although MAP was constant during IH exposures. These chemo‐reflex stimulated tachycardia tended to be attenuated (P = 0.060) following 14‐d IH exposures. Conclusions Hypoxia‐stimulated tachycardiac responses were augmented during acute, repeated IH exposures, but tended to be diminished following 14‐d IH conditioning.