Heart rate depression during sleep apnea depends on hypoxic chemosensitivity. A study at high altitude

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 (delta SaO2), and the percentage of heart rate changes (delta HR%) 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; delta SaO2, 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 delta HR% had a significant correlation with that of delta SaO2 (p less than 0.01). The sensitivity of HR depression to desaturation (delta HR%/delta SaO2) 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.