Pulmonary Oxygen toxicity

[chuckrt]

Dear canuckton,

After doing some quick calcuations I came up with the harvesters breathing at slightly less than 60%. (54) and that is considered the safe area for no llung damage. This is an interesting question but they should have known the outcome. I don't think they would do a study that would cause injury to humans as this is not legal I believe. I no I no the Goverment does not abide by the laws it generates.

chuckrt

 

[chuckrt]

Dear Doc,

I believe you are right, with the shift in A/a gradient it might inhibit the process. You are going to make me dig out my textbooks, Doc I hate reading textbooks!!

Bottom line is nobody should ever have to worry about this issue if diving by following thier tables and computer. If commercial divers and/or companies put themselves or employees at risk the courts will have a field day on them.

Time to dig out Resp. Disease book and look it up.

chuckrt

 

[Dr Deco]

Dear chuckrt:

Doing a test that carries some risk is not out of the question. It would naturally need to be designed such that the risk was within reasonable limits. This can be accomplished, for example, by checking the lung function of the test subjects every few hours. They could be removed from the study at some agreed upon limit.

What rather is the limiting factor is the cost. Most people are not aware of how research work is conducted. It is necessary for a scientist to obtain money by means of a research grant. Granting agencies, public or private, have only so much money to dole out. Unless the problem is one of great interest to a large number of people (or is endorsed by a “personality” or is politically correct), it will never see the light of day.

Because people rarely, if ever, encounter a scientist in their lifetimes, it is not possible to inquire from them how the “everyday business” of their work is conducted. The idea persists that scientists will just study something because it is worth studying. That is an interesting concept, but America is not that wealthy. :box:

Dr Deco :doctor:

 

[chuckrt]

Dr. Deco,

I agree with you but I thought that if a study was done they would use the usual study subjects and probably did ie:animals. WE probably will never no, as you said, it is not endorsed by a celebrity etc. All the medical study around here is done at Upstate med. part of the state university of NY. It is an interesting topic though. It has me wondering how they would set up the testing and monitoring of human subjects.

chuckrt

 

[Dr Deco]

Dear chuckrt:

Human trials

Human trials in all research endeavors involve minimizing the risk to the subject. I have seen tests that were discussed where I believed that the greatest risk was driving you car from home to the test site. While that is real, it does not count.

In the testing of Pulmonary Oxygen Toxicity in the laboratory of Dr Lambertsen, the test subjects were exposed to a given pressure of oxygen for several hours. Every few hours, each subject was tested for several aspects of their pulmonary function. Vital Capacity was found to vary in a predictable fashion over a period of many hours.

Subjects were also queried regarding their symptoms. These ranged from mild irritation to uncontrollable coughing. The subjects were removed from the chamber when they reached a certain level of reduction in vital capacity. They breathed room air and the course of recovery was monitored, again using the same pulmonary function tests.

It was found that all subjects would recover if they went no further than the test limits. It is known from medical treatment, however, the lung fibrosis will occur if too much oxygen is administered and this is irreversible.

A physician always supervises these tests. Unfortunately, sometimes things go awry, and the subject is injured. This is very rare.

Dr Deco :doctor:

 

[chuckrt]

Dear Doc,

Thanks for the info and study.

chuckrt

 

[The Iceni]

Originally posted by Dr Deco
Dear DiveDoc:

Saturation Diving

Saturation diving refers to exposures of an individual to pressure such that all of the inert gas has been taken into the body for that depth (pressure) and the tissues are not saturated. Some will saturate faster than other (blood is the fastest, brain and cord are next). The process is complete after a couple of days. Saturation according to a dive table is after six halftimes of the longest compartment. This means that, after this duration, the table maker does not believe that the incidence of the biomarker for DCS will change

Dr Deco :doctor:

I believe the not should not be there. I know. I know!

As you say Dr Deco, a tissue will be fully saturated after 6 half times. The Buhlmann algorith assumes the slowest compartment has a half time of 635 minutes for nitrogen so become saturated after 6 x 635 mins or 2.6 days of exposure to that pressure.

As it is saturated the body cannot take on any more inert gas at that particular pressure so the decompression profle for any saturation dive can be used regardless of the duration of the dive. The deco penalty of a week or even a month, at that pressure, will be the same as it was for a dive of 2.6 day's duration.

This had considerable commercial implications and was routinely used during the exploration phase during the extraction of North Sea oil and gas and one can understand why, when the deco profiles extended over many days.

 

[Dr Deco]

Dear Dr T:

Ouch! :upset:

Where did that “not” come from? Yes, indeed, after a period of time, all of the tissues will be filled with all of the dissolved nitrogen (or helium) that is possible for that pressure (in accordance with Henry’s Law).

Long Half times

I do not have all of the information concerning the Buhlmann dives, but I will suspect that some decompresses needed such slow decompressions that they indicated a half time of 600 minutes. I can imagine that this was indeed an artifact and it resulted from the slow off gassing from nitrogen (or helium) in the gaseous state. When nitrogen is in the gaseous state, the driving force for elimination is very slow. The bubble will expand and the nitrogen inside will come to ambient pressure (plus some pressure from surface tension). This internal pressure, being equivalent to ambient will actually take on dissolved nitrogen from the tissues. When the uptake is complete, then that nitrogen will re-diffuse into the tissue and eventually into the capillaries. This process will have a long half time.

As I have indicated often on the Board, musculoskeletal activity will contribute to the formation of microbubbles. Since these saturation divers are in a chamber, they are walking around a bit over the several days it requires for decompression (about 100 feet/day).

When I speak of diving conservatively, I am not referring strictly to reducing gas loading. That does not greatly change the incidence of DCS if it is a small amount. Heavy physical activity will modify the outcome.

Dr Deco :doctor: