Mailing List Archive Mailing List Archive
On Mon, 08 Jul 96 00:50:21 EDT, you wrote: >>Peter wrote: > >>> My point is this: You cannot accurately model the distribution and >>> elimination of a drug without knowing the volume of distribution (Vd) in >>> the body of that drug. You can't determine the Vd unless >>> you know something about the size of that "body" i.e.,person. If the >>> relative concentration of the drug is small in relationship to the volume > >Peter, > >You keep making this claim but have not supplied any proof. > >So in the case of *dissolved* N2, just how is it that it's >distribution and elimination depend on Vd ? > John, The statement about drug elimination is correct.I'm still not sure if it is correct to consider N2 as a drug (waiting for some clarification from Pete myself on this) but his premise on volume of distribution is a known pharmacological relationship. Volume of distribution is based on a known quantity of a drug divided by the concentration achieved when that drug is dissolved. Example: say you had 10 grams of a drug,and a swimming pool of unknown volume.you dissolve the drug in the pool & then take a sample and assay it for concentration.Let's say it shows a concentration of 01grams/liter.You can then determine that the volume of the pool is 1,000 liters by a simple math relationship.In the body,the fluid sampled is blood.Now here's where Vd comes into play.Not all of a dissolved drug is contained in the bloodstream.Sometimes the drug is taken up in the tissues,resulting in a higher than expected Vd.For instance,disolve that same 10 grams of a particular drug in the body,and you might find a concentration of .001 grams/liter,giving you an APPARENT volume of distribution of 10,000 liters.Now we all know that the body does not contain 10,000 liters of fluid;what has happened is some of the drug has been taken up by the tissues,and does not show up as concentration in the bloodstream.In order for this concentration to be eliminated,it must first move out of the tissues & into the bloodstream.Clearance is defined as the rate the drug is eliminated ( in liters/hour) and is equal to Vd times k (k being an elimination constant for that particular drug). There can be many other factors that influence the rate at which a drug is absorbed/eliminated in the body,but Vd and k are two of the major ones FOR A DRUG. Carl pointed out to me that a high PPN2 can cause rigidity of red blood cells,which then results in microcirculatory damage & may precipitate a case of the bends.If this is true,then the analogy of N2 absorption to drug absorption may have some validity.Any one who can clarify this aspect,please do so. John L. Dunk Tallahassee,Fl. screwloose@ne*.co*
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]