Stromme S B, Blix A S
Aviat Space Environ Med. 1976 Jun;47(6):597-9.
It has been demonstrated that the usual diving bradycardia can be greatly intensified when face immersion is superimposed on a state of apneic exercise. This intensification is neither due to chemoreceptor stimulation, or to face immersion per se. It is concluded that the intensification is caused by chemoreceptor reflex facilitation, due to stimulation of trigeminal receptors in the face.