Welcome to DB, Tom!
There are many studies about diving reflex and diving response available on the Internet, and in academic libraries. Some of them are listed for example here:
reflex OR response @ APNEA.cz
Also many other documents address the topic. Check for example works of Dr. Lindholm (
Lindholm @ APNEA.cz), and many other documents in the medical category of the Freediving Media Base:
documents medical @ APNEA.cz