oon/off gassing ?

[Alban]

Hello again Doc
I find this most interesting if but probably over my head.
I have read alittle about crushing the microneculie at what pressures would this occur ?

I have also read that O2 degrades surfactant in the aveoli , does O2 in plasma have no effect on the surfactant attached to the micronuclie ?

You mentioned in a previous post that surfactants are present in all of the body's fluids , what purpose do they serve in normal life ?

Do the microneculie collect in families from 0.1 - 3 m even though the pressure around them is the same ?

Is there any reading on this ?

Thank you for taking the time to answer. Alban

 

[The Iceni]

Originally posted by Alban
Thanks for the reply Doc
. . .

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

Hi Alban,

This is basic stuff taught in the first years at medical school and I admit I have forgotten most of it. Arterial pressure dies off towards the periphery and capillariy pressure is very small indeed. Much, much lower than central venous pressure. Venous return is against a pressure gradient and is often also against gravity!

All the small veins of the body, particularly those close to the surface, have semilunar valves at regular intervals along their length, perhaps one every two centimetres or so. However, the majority of the venous return to the heart is by means of the large, deep veins, to which the superficial veins are connected by "perforators" all of which are equipped with one-way valves. In the legs, when these valves fail, varicose veins form as the increased hydrostatic pressure from the deep veins overcomes the effectiveness of those valves lower down - a domino effect.

So the deep veins are not equipped with valves. I now hear you ask yourself, how does blood get from the foot to the vena cava against gravity and what produces the rise in pressure within the central veins? The answer is that all deep veins pass within the large muscles of the body which act like multiple heart chambers pumping the blood towards the centre when they intermittantly contract. I do not know the figures off-hand but I understand that, by such muscle contraction, each step causes a squirt of blood from the calf to shoot up the deep veins of the legs into the abdomen and that the pressure within these deep veins may approach or even exceed that found in the left side of the heart. The pressure changes are certainly very rapid and very large.

So, muscle activity is required for efficient venous return and, I imagine, this is one very good reason that it is thought advisable to fin gently during decompression stops.

This is also one reason micronuclei form in the veins during strenuous exercise after diving such as when climbing the ladder in full kit. The rapid pressure changes produce shock waves and Hydrodynamic cavitation which is one cause for the formation of excessive numbers of micronuclei which are only too happy to take on gas at surface pressures, become permanent and then grow in size to form bubbles.

I hope this helps.

:doctor:

 

[Alban]

Thanks Dr T.

I often feel I am trying to run before I can walk !! As you can guess I have no basic medical knowledge , could you recomend a book that would help me ?? Is there a medical dictionary to help with the correct terminoligy ??

Obviously the pulses would be considerable for a twin set diver with stages .

It seems as allways the body is dynamic in so far as each positive effect seems to cause a negative counter effect .

I am going diving at the weekend so the questions will slow up.

Thank you for your help Alban

 

[Dr Deco]

Dear Alban:

Micronuclei

Micronuclei are those tiny bubbles that form when there are low-pressure regions in small regions in the tissues. These regions are probably the size of a cell or several cells. The nuclei appear to be stabilized against immediate collapse by surfactant. They will become smaller if pressure is applied. In system where they have been measured, seawater, for example, they are present at a depth of at least 60 fsw. In a diver, they do not collapse to any large extent until more that 150 fsw.

When I speak about micronuclei in this FORUM, I am more concerned about the formation of nuclei by physical activity than I am about the crushing of them

Oxygen and surfactant

To my knowledge, surfactant on the bubble interface is not degraded by oxygen that is dissolved. Except for pulmonary problems, oxygen appears to do only good things with respect to decompression.

Purpose of surfactants

This can be confusing. By “surfactant,” I mean a substance that modifies the surface properties of a gas bubble. Virtually all biomolecules have the property of being able to collect on a gas-liquid interface. When this occurs, the surface tension is lowered - or almost always lowered. It is simply intrinsically within the molecule. In general, the surfactant properties per se do not serve any purpose. Only in the lung is a surfactant specially used to keep alveoli from collapsing.

Now, this is in distinction to those molecules specially designed to be “surfactants.” Examples of these are soaps and detergents, wetting agents (found in spot removers in dish washing machines), antifoaming agents (added to rug cleaning detergents), foam enhancers (in beer), stabilizers (in mayonnaise). Other surface-active chemicals are anti wetting agents (such as in the automobile windshield water repellant – “Rain-X”).

Groups of micronuclei

Micronuclei are present in varying concentrations (I believe) in the body’s fluids. They have never been actually seen, but their existence is inferred. It appears that there are a large number of very small ones (less than 0.1 micron), a medium number of medium sized ones (0.5 – 1.0 micron), and a few large ones (larger than 1 micron). The exact concentrations are not known.
I am not aware of any easy access to this material. I found books at a university library in the section on physical oceanography, in books on food science, and the physical chemistry of surfaces

Dr Deco :doctor:

 

[The Iceni]

Originally posted by Dr Deco
Dear Alban:

Micronuclei

Micronuclei are those tiny bubbles that form when there are low-pressure regions in small regions in the tissues. These regions are probably the size of a cell or several cells. The nuclei appear to be stabilized against immediate collapse by surfactant. They will become smaller if pressure is applied. In system where they have been measured, seawater, for example, they are present at a depth of at least 60 fsw. In a diver, they do not collapse to any large extent until more that 150 fsw.

When I speak about micronuclei in this FORUM, I am more concerned about the formation of nuclei by physical activity than I am about the crushing of them

Dr Deco :doctor:

Dear Alban,

One thing about medicine is you can never know it all. That is why we have to practice (joke). In the UK we are required to do at least nine years of training and then we often get it wrong. I am not sure that a basic natomy or physiology text book will help but I'll have a peek in the library.

I am not sure if that is what Dr Deco is suggesting about my ideas on the muscle pump's role in the formation of more micronuclei during exercise. I may be wrong, but it was my understanding that the effects of the muscle pump on the blood were two-fold. Firstly the pressure in the dep veins is increased by muscle contraction and then it is released as the muscles relax.

Clearly an increased pressure wil not generate micronuclei but I think the subsequent rapid reduction in pressure will. In any case, the muscular action does produce pressure waves and it is very likely indeed that this energy will be transmitted to the nascent bubbles.

Blood is not an easy thing to study in real life under the electron microscope!

As for surfactant as Dr Deo rightly states it is essential in the lungs to keep the alveoli open because it reduces the surface tension (like the lower tension in the walls of an an inflated baloon with thinner walls). One problem very premature (male) babies face is insufficient surfactant in their immature lungs, the alveoli of which are unable to remain inflated even under positive pressure ventilation.

Natural surfactants normally increase bubble size by a similar reduction in the surface tension of the micronuclei and bubbles. Soaps and detergenst form bubbles in air because they lower the surface tension so much that the film of water is not disrupted by the lower increased pressure within the bubble. Without the surfactant the surface tension and consequential internal pressure is too great for the bubble to be stable or even to form at all.

Anyawy, that's how I remember it.

 

[Dr Deco]

Dear Dr T:

Muscle pump

The possibility my well exist that the muscle pump creates decompression gas bubbles in the venous return. The essential point, however, for the pathophysiology of DCS is that bubbles in the veins do not produce joint-pain decompression sickness . It is true that if too many are present, they can cause problems with the pumping action of the heart and even arterialize. That, obviously, is a very severe problem. I doubt, though, that bubbles would grow if nuclei were formed in the veins.

The reason that I favor the capillaries for bubble formation, aside from the fact that this is were you see the growth, is that the dissolved inert gas tension is highest in the region of the extravascular tissue and capillary. The strong possibility exists that the contractions of the muscles cause the capillary walls to collapse and endothelial cells to come into contact. The muscle relaxes, the capillary springs open and the endothelial cell walls separate. This allows the possibility of embryos to grow into the micronuclei. (We are trying to get the associated web site up and running to explain this in more detail.)

Dr Deco :doctor:

 

[The Iceni]

Thanks, Dr Deco.

You are of course right that venous bubbles are not so much of a problem unless the diver has a right-to-left shunt but these are pretty common.

The muscle bed is highly vascularised and stuffed full with capillaries of course.

Kind regards,

 

[Alban]

Thank you Dr T and Dr D

This has been most enlightening I have found some further reading at the Abyss site but asking specific questions here has cleared up many things . It must be frustrating at times trying to explain Biophysics at the molecular level to someone who wouldn't know a protein from a proton and I much appreciate your patience with this.

A web page explaining the causes and effects would be an excellent idea and I look forward to it .

Until then and the Deco board seems quiet ?? can I ask a few more questions ?

The micronuclei are formed within the body fluids which would contain nitrogen I assume this is what is in the bubbles ?? is it possible for them to contain O2 , He , or water ?

During exercise this will not only create new micronuclei but will increase the size of existing which may exceed their critical value at which point they will continue to grow during decompression if they remain in a tissue site . During mild exercise ( walking ) the viscous adhesive forces will not be as great ??

As always thank you for your time. Alban

 

[Dr Deco]

Dear Alban:

Gases in the micronuclei

The gases in the microbubbles are in equilibrium with the dissolved gases in the liquids. The microbubbles will contain inert gas (nitrogen, helium, etc), water vapor, oxygen, and carbon dioxide. In diving, it is only the inert gas that contributes to the size of the bubbles. It is present in the greatest partial pressure. In altitude exposures, however, the other components can add up quickly and become appreciable players in this game. In fact, at an altitude of 63,000 feet, the external (ambient) pressure is equal to the vapor pressure of water at body temperature. This pressure is often referred to as the “altitude at which blood boils.”

Exercise and micronuclei

Musculoskeletal exercise will increase the incidence of decompression sickness. One postulated manner by which this can occur is through the production of reduced pressures in the body (“Stress Theory”). This was first proposed by E. N. Harvey during the 1940s. [Another hypothesis advanced by pothers was that of the increased production of carbon dioxide by muscle activity, the so-called “Work Theory.”]

Theories will come and go and there are definite historical reasons for their rise and fall. It has only been in the recent decade that interest has revived in this area of barophysiology.

Exercise and off gassing

If the exercise is mild, such as walking, post dive activity will encourage the increase of perfusion (= blood flow) through the tissue and promote the elimination of inert gas. This is naturally to be looked upon as a good thing.

Dr Deco :doctor:

 

[Alban]

Hi Doc an excellent web site .

Something has been puzzling me ?? I am sure someone here can put me straight on this one.
At the surface we are saturated with N2 at P.P. 0.79 , after a dive our tables allow us to exit the water with some tissues supersaturated but within critical values this allows us to continue our decompression in a more comfortable environment . Will our exhaled gas now contain a higher P.P. N2 than inspired until equilibrium is restored ?

If so is it not possible or beneficial to calculate the theoretical expired P.P. N2 during decompression and to monitor it ??

Thank you Alban