Oxygen Window and deeper stops

[Dr Deco]

Kendall:

Thanks for the comments on your studies. They sound quite methodical and complete. I many cases, I would imagine that advanced amateurs could provide some very useful information at a very attractive price – since it is all volunteer.

I do hope that one is always cautious since these are - after all is said and done – human testing programs.

Best of success. I look forward to hearing more in the future.

Mike P. :doctor:

 

[Saturation]

Kendall Raine once bubbled...
Thank you, Mike. I see where my remarks about deep stops addressing free gas phase may have been expressed simplistically and inartfully.

I started using the Doppler nine years ago out of curiosity. When I switched from deco schedules based on Buhlmann to RGBM, I did so gradually with the Doppler serving as a safety blanket. ...

I was still seeing large variations in post dive bubbles based on work load, so started using a scooter for any significant distances at depth. As you would certainly expect, this had the result of reducing post dive bubbles.

As with deep stops, nothing new here. I'm simply finding out for myself what others, e.g. yourself, George Irvine, Bruce Wienke and others have been saying for a long time. I'll also try to never forget Dr. Hamilton's First Law of Decompression: S**t Happens!

Hi KR:

Where you ever tested for a PFO? And if not, have you ever put the doppler on your carotids or any of your buddies?

Again the Doppler scores are not 1:1, and people have been bent with doppler scores of zero.

 

[Kendall Raine]

I have been tested and the result was negative. Nevertheless, I assume the opposite and use a 2 fpm ascent from 20 fsw along with short surface deco before heavy lifting. Also, no bounce diving!

Readings are typically at the subclavian site since this is the easiest to get a clean return off of. The precordial would obviously be better, but getting a clean signal while on a dive boat is more difficult. I had not thought of monitoring an arterial site; however. My understanding was that the kind of thoracic back pressure (valsalva or other strain) needed to force bubbles through any but the largest shunt would define arterial bubbles as purely transitory making resting arterial measurements not meaningful. I also understand current thinking is that inert gas bubbles are not formed on the arterial side. Are you suggesting monitoring the carotid while trying to force the back pressure? I'm not sure I want to do that on myself.

I agree with the predictive limitations of the Doppler. It is one indicator of deco stress, not Dr. Powell's to-be-invented Bendometer. Just as a clean reading is no insurance against a hit, a Grade IV is no guarantee of getting bent.

 

[Saturation]

Kendall Raine once bubbled...
..I had not thought of monitoring an arterial site; however. My understanding was that the kind of thoracic back pressure (valsalva or other strain) needed to force bubbles through any but the largest shunt would define arterial bubbles as purely transitory making resting arterial measurements not meaningful. I also understand current thinking is that inert gas bubbles are not formed on the arterial side. Are you suggesting monitoring the carotid while trying to force the back pressure? I'm not sure I want to do that on myself.

HI KR:

No back pressure on purpose please. Such pressures can exists spontaneously in heavy bubbling. As its simple to get a carotid reading, and if any bubble were making it through a shunt for anyone in your group, you may hear a carotid tweap in the Grade 1-2 range during a subclavian or right atrial Grade 3-4 swossh. PFOs are a common anatomical defect, but less common are lung shunts. The high grades are need for a transient pulmonary hypertension to occur and push bubbles accross. Checking your carotids is one way to verify that no bubbles are crossing over for whatever reason, i.e., arterializing. if not everyone was tested for a PFO, you may be able to make a screening diagnosis this way [for verification later by a TEE]. Even a TEE has a a 2-3% false negative diagnosis level, so even among those who tested negative, here's a simple way to verify nothing indeed is getting through.

 

[Kendall Raine]

Fascinating. I'll check the carotid artery next time. Thank you.

 

[Saturation]

Welcome, K. Please let us know if you hear anything!