oon/off gassing ?

[Alban]

Hello

Are the Bulmann tables based on prefusion ( blood flow ) to the different tissues and the on/off gassing rate the same expotentially ? If so during the dive would we not use our leg muscles continually and to some degree excercise which would increase the blood flow. then on a deco stop we hang quite still ?
Would it be benificial to gently fin along on a stop ?

Also at the start of the dive I can be quite warm in a dry suit and get quite chilled at the end on a long stop wouldn't this also effect off gassing.

Sorry for my confusion I feel like one step forward and two back.

Alban

 

[Dr Deco]

Dear Alban:

The rates in most models are governed by perfusion, blood flow, to the various “compartments.” These are exponential functions that contain the halftimes or rates at which dissolved gas in taken up or eliminated.

These algorithms do not have provisions for the changing of the halftime “compartments” as the perfusion changes. As a matter of fact, it would be of value to move your legs during the deco stop. This assists in increasing the blood flow during decompression. In a similar manner it is a good idea to move about somewhat during the surface portion of the decompression. We do not generally think of decompression occurring on the surface, but it does!

Likewise it is a good idea to be warm during the decompression phase, especially if you were warm during the gas uptake portion of the dive.

Dr Deco :doctor:

 

[Alban]

Thanks for the reply Doc

As you said the deco continues after the diver has popped his head out of the water , i am sure most people on a stop continue breathing their deco mix on the surface until the boat picks them up. if we take such care with our final ascent does it then make much difference that we exit the water into a boat quickly , again I am thinking of the legs going from 2mts to the surface so quickly.

May I also ask another question ? The arterial and venous blood supplies are conected via capplillaries yet they have different pressures is this because the cappilaries are so small they can be described as independant ?

I understand the venous supply has a series of one way valves to aid blood return to the heart , how many does it have ? will each section have a different pressure ?

Thank you for your patience Alban

 

[Dr Deco]

Dear Alban:

What concerns me is the fact that a diver climbs aboard the boat with his dive gear and generates or enlarges micronuclei by the process of “hydrodynamic cavitation.” This surface problem concerning decompression has little to do with the fact that the legs are 2 meters underwater and then on the surface. Rather it is STRESS-ASSISTED NUCLEATION that concerns me.

The pressure in the artries is determined by the heart, while that in the veins is primarily hydrostatic in nature. In veins above the neck, the pressure is less than atmospheric, for example.

The number of valves in the legs is variable (I believe). The pressure is different in each section, because of the hydrostatic pressure. However, gas bubbles do not form in the veins and those bubble there (from the capillaries) do not do any damage.

Dr Deco :doctor:

 

[Alban]

Thanks once again Doc

Is it possible to explain ( simply ) “hydrodynamic cavitation.”
Are micro nuclei present in the artieries at all stages of the dive ?
Are they actually in the artieries , do they move with the blood flow in the micro form , I assume it is N2 ??

Thank you for the explainations so far.

Alban

 

[Dr Deco]

Dear Alban:

HYDRODYNAMIC CAVITATION refers to the formation of microbubbles or “cavities” in the liquid itself. It is what would be called bubble formation. Because of surface tension, the inward-directed force causes a microbubble to collapse. To overcome this collapsing force during the few microseconds of bubble formation , additional energy must be supplied. This comes in the form of mechanical energy from the movement of the liquid (water in the case of your body) itself. Because this process involves motion, it is termed “hydrodynamic cavitation.” It is also referred to as "stress-assisted nucleation."

This was first studied by Reynolds (about 1895) for the case of pitting of the large props on ships. He traced the problem to the formation of microbubbles and then their collapse a few milliseconds later. Associated with the collapse is a considerable pressure pulse that can actually pit the metal of the prop.

In the case of the diver, the bubbles are stabilized for short periods by virtue of the fact that biomacromolecules can adsorb on the gas-liquid surface and provide some degree of stability. That is the theory at any rate.

The microbubbles appear to be formed in tissues that can move (again, the "stress-assisted" mechanism. Most are formed in the capillaries of muscle tissue. There do not appear to be any nuclei in arteries (surprisingly). Most are in capillaries, but some are also outside of the circulatory system, and these cause a local increase of tissue pressure that leads to the pain of DCS.

There is some speculation here, but the actual truth is probably close to this (in my opinion). If one waits for a few hours and does not treat DCS, then other biochemical and pathological events can ensue. These are lesions (=injuries) not containing gas and do not repond well to reconmpression therapy.

Dr Deco :doctor:

 

[Alban]

Thank you again Doc it has been most enlightening It will take time to take this all in . I hope it has been of interest to others . I will let you help others now , but I am sure to have more questions !!

P.S. many of the hard boats where I dive do have lifts on them .

Take care Alban

 

[Alban]

This link may be of interest www.fivestartech.com/cfctech/cfcmovie.htm

Check out the frame speed of these photo's

Alban

 

[Alban]

Hello , another question if I may

I understand how swimming running ect excite the bubbles but I am a little unsure when lifting . Does pascals principle play a part or is it the muscles require more O2 which is met by the increase in blood flow ?

as I said earlier the hard boats I use usually have a diver lift which can only be good . But I also dive with a club usually within N.D.C. limits , we use a r.i.b. and as soon as the last diver is up and aboard we set back this can quite often be a bumpy ride if it is wind against tide , in order for the boat to be effient the divers need to be at the front where they take most of the impact from waves , they are in effect holding on quite tight and being shaken up . In the event of an emergency the Coast Guard would request the boat make it's way back to port and the Helicopter would meet it on the way. I would think perhaps it might be better to stay where you are and let the helicopter come to you.Does anyone have any thoughts on this ??

Alban

 

[Dr Deco]

Dear Alban:

Hydrodynamic cavitation

This will occur any time there is sufficient motion of liquids. It can also occur when surfaces touch each other and are quickly pulled apart. This is one form of hydrodynamic cavitation referred to as “viscous adhesion.” It probably occurs (I am guessing) most frequently in the capillaries of your circulatory system. These processes will cause a sudden expansion of micronuclei (<< 1 micron) into the 1 micron-sized ones that can grow to cause DCS. :boom:

Muscle activity

Lifting or any form of muscle activity, such as walking or climbing, will cause hydrodynamic cavitation to occur. This is, no doubt, because extra cellular fluids move when muscles contract. Sometimes this fluid movement is through confined channels and Reynolds cavitation can occur because of the Bernoulli effect (low pressures when fluid moves through a constriction).

The effect of muscle activity on bubble formation is probably not one of oxygen utilization, blood flow, or carbon dioxide production. During the Second World War, CO2 production was thought by some to be the mechanism for increased bubble formation with muscle active; this was termed the “Work Theory.” This was countered by EN Harvey who proposed hydrodynamic cavitation; this was the “Stress Theory.”

Pascal’s principle does not play a role in this.

Pick up

If the diver has pain-only DCS (the bends), then returning to harbor is possibly OK. If the individual has neurological problems, quicker action is necessary.

Dr Deco :doctor: