LONG-TERM FACILITATION OF VENTILATION IN HUMANS DURING NREM SLEEP

The purpose of this study was to determine whether episodic hypoxic ex posure would elicit long term facilitation (LTF) of ventilation (V-1) in sleeping humans. Twenty subjects gave written informed consent. Of these, six subjects were unable to maintain stable stage 2 sleep or de eper for a majority of the experiment and their data were excluded fro m the analysis. On night 1 after subjects had reached stable sleep (st age 2 or deeper), the subjects breathed room air for 5 minutes, follow ed by 3 minutes of hypoxia (F1O2 = 8%) This sequence was repeated 10 t imes, and the breathing pattern was observed for a further 60 minutes. Subjects returned to the laboratory for a second visit, which served as a sham night. Instrumentation and study time were the same as on ni ght 1, but subjects breathed room air only. Airflow, tidal volume (V-T ), end tidal O-2 and CO2, and estimation of arterial O-2 saturation (% ) were measured. Seven of the subjects had long-term facilitation (LTF ), which was manifested as a significant increase in V-1 that persiste d for up to 40 minutes following the last hypoxic exposure. In the oth er seven subjects, no substantial increase in V-1 was found. We could not explain this difference based on body size (BMI), gender, level of hypoxemia, or magnitude of the hyperpnea during hypoxia. The differen ce between the two groups was that the LTF group consisted of habitual snorers, and that the NLTF were not inspiratory-flow-limited during t he experiment.