The effect of sleep stage change on pulmonary circulation has not been well documented in patients with obstructive sleep apnea syndrome (OSAS). We investigated whether or not stage-specific change can affect pulmonary artery pressure (Ppa) in patients with OSAS. Thirty-one patients with OSAS underwent right cardiac catheterization in the daytime and the following night, including 19 patients in whom Ppa could be measured throughout non–rapid eye movement (NREM) and rapid eye movement (REM) sleep. Ten of the 19 patients had daytime pulmonary hypertension (PH) defined by a mean Ppa (Ppa) ⩾ 20 mm Hg. Then we analyzed Ppa response to hypoxia spontaneously occurring during the period of sleep apnea. The slopes of the regression lines between arterial oxygen saturation measured by pulse oximeter (SpO₂ ) and Ppa curves were almost the same in both NREM and REM patient groups with or without daytime PH, whereas the response curve was significantly shifted upward in REM compared with NREM patients with daytime PH. Furthermore, Ppa was elevated more markedly in association with REM burst, phasic REM, compared with tonic REM. We conclude that vascular tone of pulmonary artery could be elevated in association with REM sleep which is independent of the degree of hypoxia, and that this state-specific change is manifested in patients with daytime PH.

To determine the relationship between periodic breathing (PB) during sleep at high altitude and ventilatory chemosensitivities, we studied nine Japanese climbers who participated in the expedition to the Kunlun Mountains (7,167 m) in China in 1986. At sea level, ventilatory response to hypoxia (HVR) by isocapnic progressive hypoxia test and to hypercapnia (HCVR) by Read's method were examined. At altitude 5,360 m, respiratory movements of the chest and abdominal wall, SaO2, ECG, and HR were monitored. Seven climbers manifested PB during sleep. There was a significant correlation between PB during sleep and HVR and HCVR (p less than 0.05). All the climbers showed severe desaturation during sleep. There was a significant negative correlation between degree of desaturation during sleep and HVR (p less than 0.05). A negative correlation was also detected between PB and the degree of desaturation during sleep. We concluded that ventilatory chemosensitivities play an important role in eliciting PB and that climbers with high HVR can maintain their arterial oxygenation during sleep, due to hyperventilation induced by PB, which is considered an advantageous adaptation for lowland sojourners.

To clarify the heart rate (HR) slowing response during periodic breathing (PB) with apnea and its relationship to hypoxic ventilatory response (HVR), sleep studies were done in seven Japanese climbers at 5,360 m in the Kunlun mountains of China in 1986. Apnea duration (APD), arterial oxygen saturation changes (ΔSaO2), and the percentage of heart rate changes (ΔHR%) during PB with apnea were analyzed. The data were compared with hypoxic heart rate and ventilatory responses assessed at sea level. HR during the apneic period (APD, 10, 8 ± 1.2 s; ΔSaO2, 10.2 ± 1.8%) was significantly smaller than that during the ventilatory period of PB (56.0 ± 5.1/min and 74.6 ± 6.2/min, respectively). This HR slowing or acceleration alternated in accordance with off and on activities in ventilation. The magnitude of ΔHR% had a significant correlation with that of ΔSaO2 (P < 0.01). The sensitivity of HR depression to desaturation (ΔHR%/ΔSaO2) was smaller in low HVR climbers than in high HVR climbers. We concluded that these results can be ascribed to the fact that the primary effect of peripheral chemoreceptors on the cardiovascular center is vagotonia, and the effect is overridden by the vagal pulmonary inflation reflex.