The impact of arousal state, sex, and sleep apnea on the magnitude of progressive augmentation and ventilatory long-term facilitation.

The impact of arousal state, sex, and sleep apnea on the magnitude of progressive augmentation and ventilatory long-term facilitation. J Appl Physiol 114: 52-65, 2013. First published November 8, 2012; doi:10.1152/japplphysiol.00985.2012.-We examined the impact of arousal state, sex, and obstructive sleep apnea (OSA) on the magnitude of progressive augmentation of the hypoxic ventilatory response and ventilatory long-term facilitation (vLTF). We also examined whether exposure to intermittent hypoxia during sleep has an impact on the apnea-hypopnea index (AHI) in individuals with OSA. Ten men and seven women with OSA, along with ten healthy men and ten healthy women, were exposed to twelve 2-min episodes of hypoxia (end-tidal PO2: 50 Torr) in the presence of sustained hypercapnia (end-tidal PCO2: 3 Torr above baseline), followed by a 30-min recovery period during wakefulness and sleep. The OSA participants completed an additional sham study during sleep. The AHI during the first hour of sleep following the intermittent hypoxia and sham protocols were compared. Progressive augmentation was only evident during wakefulness and was enhanced in the OSA participants. vLTF was evident during wakefulness and sleep. When standardized to baseline, vLTF was greater during wakefulness and was enhanced in the OSA group (men: wakefulness 1.39 +/- 0.08 vs. sleep 1.14 +/- 0.03; women: wakefulness 1.35 +/- 0.03 vs. sleep 1.16 +/- 0.05 fraction of baseline; P <= 0.001) compared with control (men: wakefulness 1.19 +/- 0.03 vs. sleep 1.09 +/- 0.03; women: wakefulness 1.26 +/- 0.05 vs. sleep 1.08 +/- 0.04 fraction of baseline; P <= 0.001). The AHI following exposure to intermittent hypoxia was increased (intermittent hypoxia 72.8 +/- 7.3 vs. sham 56.5 +/- 7.0 events/h; P <= 0.01). Sex-related differences were not observed for the primary measures. We conclude that progressive augmentation is not evident, and the magnitude of vLTF is diminished during sleep compared with wakefulness in men and women. However, when present, the phenomena are enhanced in individuals with OSA. The AHI data indicate that, under the prevailing experimental conditions, vLTF did not serve to mitigate apnea severity.