Predictors of Periodic Breathing at Altitude

Periodic breathing is commonly seen during sleep in healthy humans following ascent to high altitude. The hyperventilation induced by hypoxia at altitude leads to hypocapnia which can, during sleep, inhibit respiration yielding apnea. The subsequent fall in P02 and rise in PC02 could then trigger hyperventilation and perpetuate the cycle. This cycling requires sufficient hyperventilation in response to hypoxia and rising PC02 to produce the necessary level of hypocapnia. As a result, these events may be influenced by inter- individual variability in the hypoxic and hypercapnic ventilatory response. To test this theory, we measured hypoxic HVR and hypercapnic HCVR ventilatory responses awake and NREM sleep both at sea level and on nights 1, 4, and 7 following arrival at altitude 14,110 ft in six healthy males. Ventilatory pattern and PC02 were also determined on these nights. On night 1 at altitude, periodic breathing developed in three of the six subjects and correlated significantly with the sea level NREM HVR r.86, P.02, and near-significantly with both the sea level awake HVR r.83, P.08, and sea level NREM HCVR r. 76, P.08. Periodic breathing decreased on nights 4 and 7, but an association persisted between the number of respiratory oscillations and the NREM hypercapnic response determined on the respective night night 4, r.93, P.02 night 7, r.89, P.04. Keywords Hypoxic and hypercapnic ventilatory responses, Acclimatization, Apnea threshold, Periodic breathing.