The Cressi Neon is a plucky little computer perfectly suited to the needs of recreational scuba divers and freedivers. While it might not boast all the bells and whistles more expensive models do, the Neon is a solid, entry-level computer at a very wallet-friendly price.
A long-standing paradigm for patterns of change in arterial oxygen (O2) and carbon dioxide (CO2) in free diving holds that despite apnea, compression of the lungs and gas contained therein by increasing water pressure during descent would actually increase the alveolar and arterial pressures of O2 (PAO2 and PaO2, respectively) while having little effect on arterial pressure of CO2 (PaCO2) because of its markedly greater solubility in blood and tissue. Conversely, after continued consumption of O2 during the deeper phase of the dive, there would be a precipitous fall in PAO2 and PaO2 as the lungs expand during ascent, rendering the diver prone to loss of consciousness as they approach the surface (3, 4). The increase in PaO2 at depth coupled with the relatively small increase in PaCO2 (which many divers lower before diving by hyperventilating) could blunt respiratory drive at depth and encourage the diver to dangerously prolong their dive.
Stephanie Williams from the Waitemata District Health Board Point of Care Testing Laboratories loaned two i-Stat Alinity blood gas analyzers for this work and provided invaluable assistance in training team members in the use of these devices and advising on data collection. Free diving New Zealand loaned their competition free diving platform, and Brad James participated in data collection as their representative and deep safety free diver. Malcolm Bird provided a boat and acted as the shallow safety free diver. Paul Scott provided a boat and surface support activity. Jake Williams documented the operation via surface photography. The Motutere Bay TOP 10 Holiday Park allowed the use of shore facilities for logistic purposes. The Slark Hyperbaric Unit facilitated a test of syringe plunger sealing integrity at 6 atmospheres absolute pressure. The Bevin family allowed use of pool facilities for immersed tests of arterial line sampling.
On his first-ever night dive, Sam, an uncertified and inexperienced diver with fewer than 15 lifetime dives, descended to catch lobsters with two other uncertified divers (Dave and Tim). The three descended, while a fourth diver (Ron) planned to freedive and assist with hauling in the anticipated lobster catch. A fifth diver (Eric) remained on the boat. (Note: All names are fictitious.) 781b155fdc