Well, there are many scientific documents listed in the Freediving Media Base (
medical documents @ APNEA.cz), and even more interesting literature can be found within the references in those documents, but I think the best would be contacting some of the authors, like for example Dr. Lindholm. There are also several websites, more focused on freediving physiology (
medical websites @ APNEA.cz), and you may also try registering at WFDMA (World Freediving Medical Association -
WFDMA @ APNEA.cz) and posting your question on their forum.
