Ventilatory augmentation by acute intermittent hypoxia in the rabbit.

This study seeks to determine the effects on respiratory function of acute intermittent hypoxia. The experiments were performed on anesthetized, spontaneously breathing rabbits. The experimental protocol consisted of 5 one-minute episodes of hypoxia (14% O(2) in N(2)) interspersed with three-minute normoxic recovery periods. Ventilatory variables, minute ventilation (MV) and its tidal and frequency components, were derived from the continuously recorded airflow signal. We found that MV progressively increased with each next hypoxic-normoxic cycle; the increases were driven by both ventilatory components. Ventilatory augmentation concerned both the stimulus (hypoxic) and recovery (normoxic) periods, but it was significantly greater in the former. The augmented ventilation was sustained for up to 30 min after the last hypoxic run, which suggests the appearance of ventilatory long-term facilitation. The results demonstrate that acute intermittent hypoxia consisting of a few hypoxic-normoxic cycles is capable of inducing appreciable ventilatory changes. Such changes reflect plasticity of the respiratory motor output developing on a short-term basis during ongoing cycles of hypoxia, which, in the present study, correlated with the number of hypoxic cycle. Ventilatory augmentation in response to acute cyclic hypoxic episodes may give insights into the mechanisms of respiratory improvement by intermittent hypoxic training, increasingly used in both sports physiology and medicinal approaches.