oon/off gassing ?

[The Iceni]

Hi Alban,

Yes, on balance, during the surface phase of decompression you will exhale more nitrogen than you inhale but this need not necessarily be reflected in the pp NO2 of exhaled air for the following reasons.

Exhaled air contains water vapour, carbon dioxide and oxygen, all of which will vary, often quite independently.

The relative partial pressures of the excreted gasses also depends upon the breathing depth and rate.

Even then, I do not believe it would help me to know the amount of nitrogen I am excreting. What we need be concerned about is the extremely minute amount nitrogen that is not being excreted from a very small region of the body because it is trapped in a few microscopic gas bubbles in the spinal cord, say.

As far as I am aware there are no sensors able to measure the partial pressure of nitrogen, possibly because it is an inert gas and I cannoit think of a practical use for one, at least with respect to diving.

If you think about it, by the time any such changes are detected it would be too late to do anything about it other than to therapeutically recompress the diver.

 

[Dr Deco]

Dear Alban:

Expired partial pressures

It is true that you could see expired nitrogen in the exhaled breathing gas. Since you are breathing in 79% nitrogen, the exhaled nitrogen would be added on top of that. It would not really be all that apparent. When gas washout studies are being performed, the subjects are given 100% oxygen to breathe so that the exhaled inert gas is more observable.

Practical use

The experimental evidence is against the use of whole body gas washout to indicate problems associated with DCS. The pain of DCS is a very limited event and gas is dissolved in the whole of the body. You would effectively be looking at the reduced rate of nitrogen elimination in tissue near a joint while nitrogen is being eliminated from muscle, fat, and organ in the entire body. Laboratory trials of this have never produced much useful information.

This is not unlike information from Doppler bubble detectors. It would be nice to find only gas bubbles emanating from bends-producing tissues, but that is nor the case. In actuality, gas bubbles issue forth from the capillaries of muscle and fat tissue.

Dr Deco :doctor:

 

[Alban]

Thank's Doc's

I did imagine there would be a good reason perhaps I will use this as a marketing ploy for a true Personal Dive Computer.

Thanks again Alban

 

[Dr Deco]

Dear Alban:

Personal dive computer

A personal decompression device was the goal of those of us who worked with ultrasound devices in the early 70s. We found that it was not possible with current technology, and that several things were true.

• gas bubbles form in many tissues (e.g., muscle and fat), not just tendons and ligaments,
• these “bubble formers” produce many more bubbles than tendons and ligaments,
• extra-vascular bubble formation in tissue probably causes the pain of DCS, and these bubbles do not find their way into the circulatory system.

The “features” of bubble detection are not dissimilar to whole-body gas analysis. You really wish to know what is occurring in a very small volume of tissue. Instead you receive information from the whole body, most of which is quite useless.

If I knew how to make an individualized device, I would put it into my mythical "Bends Buster" dive computer.=-)

Dr Deco :doctor:

 

[Alban]

I was thinking that the N2 sensor would go after the exhaust port on the demand valve and be linked to the computer . This would compare actual pp n2 with the theoretical pp n2 calculated by the computer , after completing a deco stop if the actual pp n2 was higher than suggested by the computer it would call for an increased stop time , as Dr T said there are other variables but these are calculable and if the sample rate was often enough perhaps predictable , alas Dr Deco has shot me down before I got the prototype of the drawing board but if any potential backers would care to send $ or £ they will be gratefully accepted.

Thanks Alban