Valsalva-induced syncope during apnea diving

A young man had two dangerous episodes of transient loss of consciousness d uring apnea diving in a swimming pool. Medical and neurologic examination r esults were normal. Standard autonomic test results (including heart rate v ariability, baroreflex sensitivity, tilt-table test, and Valsalva ratio) we re unremarkable, with the exception of an increased blood pressure decrease during early phase II of the Valsalva maneuver. Syncope with arrhythmic my oclonic jerks could be evoked by a strong straining maneuver. Simultaneous physiologic recordings showed extreme blood pressure and cerebral blood flo w velocity decreases and electroencephalographic slowing during syncope, Th e electrocardiogram showed a continuous sinus rhythm with a progressive tac hycardia. The authors' findings were not compatible with baroreflex failure or vasovagal mechanisms (Bezold-Jarisch reflex activation) as the underlyi ng causes. The authors concluded that mechanical factors (strong reduction of blood reflux to the heart) in combination with a reduced threshold of th e brain for developing ischemia-related arrhythmic myoclonic jerks were res ponsible for Valsalva-induced syncope in the patient.