Sleep quality under mild hypoxia in men with low hypoxic ventilatory response

The present study evaluated whether slow-wave sleep and whole-night delta power of the non-rapid eye movement (NREM) sleep electroencephalogram (EEG) decrease during sleep at a simulated altitude of 2000 m, and whether such changes related to measures of hypoxic ventilatory response (HVR). This study consisted of two parts; in the first, HVR was measured in 41 subjects and each seven subjects with the lowest or the highest HVR were selected for the subsequent sleep study. In the second part, polysomnogram, arterial oxygen saturation (SpO2) and respiratory events are recorded on the selected subjects under normoxic and hypoxic conditions. Hypoxia decreased SpO2 and increased respiratory disturbances for both groups. The low HVR group, but not the high HVR group, showed decreases in the whole-night delta power of NREM sleep EEG under hypoxia. On the other hand, two subjects in the high HVR group, who showed relatively high apnoea indices, also showed lower SpO2 nadirs and decreases in the whole-night delta power under hypoxia. These results suggest that acute hypoxia equivalent to that at a 2000 m altitude decreases slow-wave sleep in individuals that show low HVR. However, low HVR may not be the only, but one of some factors that decrease the whole-night delta power under hypoxia. Therefore, it was not sufficient to identify individuals likely to be susceptible to deteriorated sleep quality at a simulated altitude of 2000 m only using the HVR test. Other factors, which relate to respiratory instabilities, should be taken into consideration to identify them.