Info IPE may be more prevalent than previously thought, click through to find out why!

[Nemrod]

- The overwhelming majority of snorkels tested had a negative inspiratory pressure of less than 8 cm H2O. The highest was 12.7 cm H2O, which is roughly the performance of a US Divers Conshelf XIV at 70 fsw. Can someone speak to modern tolerances for inspiratory pressures for scuba regulators?

Interested to hear others' thoughts on this.

Best regards,
DDM

There is a difference between a regulator and a snorkel that may not be on first glance apparent. A regulator may have a momentary high negative inspiration pressure ( as it cracks) but then the Venturi takes over and the reduced negative inspiration pressure to sustain demand flow is evident with simple Magnehelics. But the snorkel has no Venturi and requires a high negative inspiration pressure for the entire cycle. And the center of the lungs is more than a few inches below the surface and a good regulator like the Conshelf will crack at well under 1.5 inches of water. Most single hose (second stage) regs will tune as low as 1.0 inches of water give or take but due to case fault will be unstable at less or free flow slightly. The G250 for example and by the way the Conshelf have effective Venturi action which lower the inhalation effort once flow is initiated and in some cases may go momentarily positive.

James

 

[Duke Dive Medicine]

There is a difference between a regulator and a snorkel that may not be on first glance apparent. A regulator may have a momentary high negative inspiration pressure ( as it cracks) but then the Venturi takes over and the reduced negative inspiration pressure to sustain demand flow is evident with simple Magnehelics. But the snorkel has no Venturi and requires a high negative inspiration pressure for the entire cycle. And the center of the lungs is more than a few inches below the surface and a good regulator like the Conshelf will crack at well under 1.5 inches of water. Most single hose (second stage) regs will tune as low as 1.0 inches of water give or take but due to case fault will be unstable at less or free flow slightly. The G250 for example and by the way the Conshelf have effective Venturi action which lower the inhalation effort once flow is initiated and in some cases may go momentarily positive.

James

Fair point, and the breathing resistance curves in the link support your statement. Still, it would be interesting to see if there's any correlation between snorkeling incidents and type of snorkel used. Also read your previous post - props for not losing it under water in a frightening situation and glad you're hear to have this conversation.

Best regards,
DDM

 

[Nemrod]

I want to recant a poorly worded statement of mine in post 10. I did not mean this line of research would not be valuable, I was meaning or intending how can this research be used or applied. I wanted to set that straight. I was not intending to devalue the work or subject if it came across that way.

Yes, I would be curious how free diver snorkels or for example the old (decades old) Scubapro Shotgun snorkel would compare to some of todays snorkels with the various contraptions to prevent water entry and the full face snorkel masks. I would also like to see a WOB comparisons, the full inhale and exhale cycle, comparing snorkels to regulators and taking into account the delta between the position of the center of lungs/diaphragm of the snorkeler and water surface.

James

 

[pauldw]

the reduced negative inspiration pressure to sustain demand flow is evident with simple Magnehelics.

Indeed. I have long thought that we need to pay a lot more attention to Magnehelics.

 

[Nemrod]

Indeed. I have long thought that we need to pay a lot more attention to Magnehelics.

Hmmm. What I mean is that using a test mouthpiece that has a port for a Magnehelic or manometer it is easy to observe the second stage reach a cracking value (typically 1.2 inches) and then watch the needle drop as the Venturi takes over and with an instrument that can measure both positive and negative pressure observe a positive reading in some cases. Whereas a snorkeler would be working against the delta between the center of his/her lungs and the water surface continuously. Which may explain the difference in the study between the results of scuba divers and snorkelers observed. Well, I will leave it to the smart people to see what it means and how to apply the results.

James

 

[cerich]

- The authors noted that it was not possible to diagnose pulmonary edema in the victims of fatal drowning. It is reasonable to assume that the incidence of people susceptible to some sort of swimming-induced pulmonary edema has not changed, so what is behind the roughly seven-fold increase in snorkeling deaths from 1995 to 2019? Has there been that much of an influx of visitors who snorkel?

yes, cruise ship travel has exploded since then and snorkeling is among the most popular port activity in survey after survey
Also, Dry snorkels, more specifically out of asia with high WOB in design, now even worse with the full face snorkel masks. In the 80's- early 90's the top snorkels like the Scubapro twin were designed all about WOB, CO2 elimination on exhale so doesn't recycle , then well, along came .. dry snorkels that did not spend as much attention to those important details andaspects came on market, and many of them when shut so well when water comes over the top that there is still plenty of CO2 in the tube, that get's inhaled as soon as the dry top opens again. The WOB on most is..poor if not shutting off water all the time, add in frequent shut down by water conditions and technique (lack of) by the swimmer/snorkeler.. and all the airway conditions that can contribute to IPE are there in spades.
No offense to anyone, but this isn't a secret, I have know it for literally decades and watched in dismay