Paradoxical bradycardia during exercise and hypoxic exposure. The possible direct effect of hypoxia on sinoatrial node activity in humans.

We describe a patient with pulmonary emphysema who developed paradoxical cardiodeceleration not only during incremental exercise associated with hypoxemia but also during progressive hypoxic challenge. Since coronary angiogram revealed no abnormality, this unique phenomenon seemed to be due to the direct effect of hypoxia on the sinus node activity.