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This is a multi-part message in MIME format. ------=_NextPart_000_0008_01BE6591.BF516B40 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Chuck, Sorry, I thought you _were_ asking about hydrostatic pressure when you = referred to pressure gradiants. I am getting a little confused about our terminology here, but let me = throw out a few things, to see if we are both speaking the same = language. BTW- thank you, I have not had a stimulating discussion like = this in awhile! >>Hydrostatic pressure (that exerted on and by the liquid due either to = weight, mechanical pressure, or motion) does not effect the pressure of = gasses in solution because the liquid acts as an incompressible = container for the gas within it.<< The fluid is incompressible, but still transmits pressure, does it not? = As in - the weight of the water column over your body determines the = pressure around you. If I have 33ft of water over my head, doesn't that = equal out to 14.7 pounds per square inch of pressure (from the water = alone)? And since I'm at 2 atmospheres absolute of pressure, the gas I'm = now breathing, that is now also at 2ata? And in this gas, the ppO2 is = 0.4ata ? So isn't hydrostatic pressure really the same thing as the gas = pressure? If not, where is the flaw in my logic? When you refer to 'pressure of a gas _in solution_', aren't you = referring to the actual 'quantity' of the gas that has had time to = diffuse into the tissue (since, like you noted, this is not an = instantaneous effect), and if, with infinite time (or a realllllly long = dive), the tissues will either a) become so saturated that they cannot = hold any more gas, or b) reach equilibrium with the hydrostatic = pressure? I must admit, your explanation of how gasses are not dissolved like = solid solutes was a radical shock! It had never occured to me to = question why pressure changes affected gas but not solid solubility. = However, whether or not a solid is soluble is also related to it's = polarity, is it not? I was taught that lipid molecules are non-polar, = and therefore insoluble in water, whereas proteins have a slight = negative charge, making them soluble. No matter, if solubility of gasses is simply a modified version of free = phase, because a gas molecule has more 'molecular collisions' before = exiting out of the fluid, then can't we discard the whole solubility = concept entirely, and view our 'tissue compartments' as being simply = gas-filled cavities enclosed by membranes of varying permeability? Or am = I lagging on this thought? And how does this 'model' fit in with isobaric bubble growth when = switching to a faster diffusing-gas (ie, N to He as diluent)? I would = think that if there was no actual phase change, then changing gas = shouldn't cause bubble growth. >>This is why helium, a relatively small tight entity (single atoms = instead of molecules), continues to exert more pressure on other = molecules of both gas and liquid when in solution and therefore is less = soluble than O2 or N2.<< But doesn't this mean we're back to the 'classical' definition of = solubility, ie, a phase-change?=20 >>I think it is likely that the presence of a high PPO2 in the = capillaries does indeed reduce the amount of O2 ultimately dissociated = from Hb but keep in mind that the Hb carries 70 times the amount of O2 = that the plasma can at 1 ata of air. So, even a little is a lot.<< Right, but Hb is normally almost 98% saturated breathing normal air at = 1ata. Someone (I forget who, some frenchman, I think) did a famous "life = without hemoglobin" experiment where he exsanguinated a pig, replaced = the blood with water, and had it in a hyperbaric chamber down somewhere = below 2ata. The pig lived (until the dive ended, I presume). The gist of = it was that although the plasma-dissolved O2 is minute at sea level, it = rises sharply if you increase the pressure, and at a relatively shallow = depth, enough oxygen _is_ disolved to be significant. So a pO2 high = enough to retard hemoglobin releasing it's oxygen would mean enough is = dissolved, so the Hb didn't _have_ to. If this sounds like I'm thinking out loud, it's because I AM (grin). Wow, if we're not careful, some actual learning might occur here! Rich L ------=_NextPart_000_0008_01BE6591.BF516B40 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD W3 HTML//EN"> <HTML><HEAD> <META content=3Dtext/html;charset=3Diso-8859-1 = http-equiv=3DContent-Type> <STYLE></STYLE> <META content=3D'"MSHTML 5.00.0910.1309"' name=3DGENERATOR></HEAD> <BODY bgColor=3D#ffffff> <DIV><FONT size=3D2>Chuck,</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>Sorry, I thought you _were_ asking about hydrostatic = pressure=20 when you referred to pressure gradiants.</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>I am getting a little confused about our terminology = here, but=20 let me throw out a few things, to see if we are both speaking the same = language.=20 BTW- thank you, I have not had a stimulating discussion like this in=20 awhile!</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>>>Hydrostatic pressure (that exerted on and by = the=20 liquid due either to weight, mechanical pressure, or motion) does not = effect the=20 pressure of gasses in solution because the liquid acts as an = incompressible=20 container for the gas within it.<<</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>The fluid is incompressible, but still transmits = pressure,=20 does it not? As in - the weight of the water column over your body = determines=20 the pressure around you. If I have 33ft of water over my head, doesn't = that=20 equal out to 14.7 pounds per square inch of pressure (from the water = alone)? And=20 since I'm at 2 atmospheres absolute of pressure, the gas I'm now = breathing, that=20 is now also at 2ata? And in this gas, the ppO2 is 0.4ata ? So isn't = hydrostatic=20 pressure really the same thing as the gas pressure? If not, where is the = flaw in=20 my logic?</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>When you refer to 'pressure of a gas _in solution_', = aren't=20 you referring to the actual 'quantity' of the gas that has had time to = diffuse=20 into the tissue (since, like you noted, this is not an instantaneous = effect),=20 and if, with infinite time (or a realllllly long dive), the tissues will = either=20 a) become so saturated that they cannot hold any more gas, or b) reach=20 equilibrium with the hydrostatic pressure?</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>I must admit, your explanation of how gasses are not = dissolved=20 like solid solutes was a radical shock! It had never occured to me to = question=20 why pressure changes affected gas but not solid solubility. However, = whether or=20 not a solid is soluble is also related to it's polarity, is it not? I = was taught=20 that lipid molecules are non-polar, and therefore insoluble in water, = whereas=20 proteins have a slight negative charge, making them = soluble.</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>No matter, if solubility of gasses is simply a = modified=20 version of free phase, because a gas molecule has more 'molecular = collisions'=20 before exiting out of the fluid, then can't we discard the whole = solubility=20 concept entirely, and view our 'tissue compartments' as being simply = gas-filled=20 cavities enclosed by membranes of varying permeability? Or am I lagging = on this=20 thought?</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>And how does this 'model' fit in with isobaric = bubble growth=20 when switching to a faster diffusing-gas (ie, N to He as diluent)? I = would think=20 that if there was no actual phase change, then changing gas shouldn't = cause=20 bubble growth.</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>>>This is why helium, a relatively small tight = entity=20 (single atoms instead of molecules), continues to exert more pressure on = other=20 molecules of both gas and liquid when in solution and therefore is less = soluble=20 than O2 or N2.<<</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>But doesn't this mean we're back to the 'classical' = definition=20 of solubility, ie, a phase-change? </FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>>>I think it is likely that the presence of a = high PPO2=20 in the capillaries does indeed reduce the amount of O2 ultimately = dissociated=20 from Hb but keep in mind that the Hb carries 70 times the amount of O2 = that the=20 plasma can at 1 ata of air. So, even a little is a = lot.<<</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>Right, but Hb is normally almost 98% saturated = breathing=20 normal air at 1ata. Someone (I forget who, some frenchman, I think) did = a famous=20 "life without hemoglobin" experiment where he exsanguinated a = pig,=20 replaced the blood with water, and had it in a hyperbaric chamber down = somewhere=20 below 2ata. The pig lived (until the dive ended, I presume). The gist of = it was=20 that although the plasma-dissolved O2 is minute at sea level, it rises = sharply=20 if you increase the pressure, and at a relatively shallow depth, enough = oxygen=20 _is_ disolved to be significant. So a pO2 high enough to retard = hemoglobin=20 releasing it's oxygen would mean enough is dissolved, so the Hb didn't = _have_=20 to.</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>If this sounds like I'm thinking out loud, it's = because I AM=20 (grin).</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>Wow, if we're not careful, some actual learning = might occur=20 here!</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>Rich L</FONT></DIV></BODY></HTML> ------=_NextPart_000_0008_01BE6591.BF516B40-- -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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