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On Jul 30, 9:56 pm, Tim McNamara <[email protected]> wrote:
> In article <[email protected]>,
>
>
>
> [email protected] wrote:
> > On Jul 30, 2:53 pm, Tim McNamara <[email protected]> wrote:
> > > In article <[email protected]>,
>
> > > [email protected] wrote:
> > > > On Jun 7, 11:57 am, Andy Coggan <[email protected]> wrote:
>
> > > > > In fact, mild-to-moderate arterial desaturation tends to occur
> > > > > during maximal exercise in a significant portion of the
> > > > > population (at least discounting young, healthy, untrained
> > > > > men!), indicating that, at least to some extent, aerobic
> > > > > capacity (i.e., VO2max) is limited, in part, by pulmonary
> > > > > function.
>
> > > > Phoeey. A small arterial desaturation is most likely explained by
> > > > increased left to right shunting
>
> > > Left to right shunting from where to where through what? This term
> > > is usually used to indicate left to right shunting through an
> > > atrial septal defect or cases of tricuspid atresia. There should
> > > be little or no left to right shunting through a patent foramen
> > > ovale and should be no shunting at all in a normal heart. So I am
> > > not clear to what you refer. Thanks.
>
> > My bad, I should have said increased right to left shunting although
> > this is not so much as a physiological shunt but as a ventilation
> > perfusion defect behaving as a shunt.
>
> That didn't really clarify. Ventilation defects are generally caused by
> obstructions somewhere in the airway; perfusion defects are generally
> caused by emboli in the pulmonary vasculature. What is the cause of the
> "ventilation perfusion defect" you are pointing towards? Does this
> occur in non-pathological individuals?
>
> I trimmed the rest of your previous post in an over-zealous fit of good
> netiquette, unfortunately. It would appear that Nielsen (2003) found
> that arterial desaturation during exercise is multifactoral and that
> large lung capacity does offer some protection from this. Perhaps this
> link offers some light on the subject:
>
> http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_...
> =14617055&dopt=AbstractPlus
By the way, I found the Nielsen article (the link didn't work for me)
that I think you referred to. It supports what I said ("A widening of
the PAO2-PaO2 difference does indicate that a diffusion limitation, a
ventilation-perfusion mismatch and/or a shunt influence the transport
of O2 from alveoli to the pulmonary capillaries."), although I am not
sure the author fully understands all the variables contributing to
these possibilities. Further, I found this sentence very interesting:
"During maximal exercise, an extreme lactate spill-over to blood
allows pH decrease to below 7.1 and according to the O2 dissociation
curve this is critical for SaO2." This finding supports the view that
"exercise is limited by the periphery" over the "exercise is centrally
limited" argument. something I have always maintained to the constant
derision of some of the so-called "experts" here and elsewhere, like
Dr.Coggan. I will add it to my quiver. Thanks for the link
> In article <[email protected]>,
>
>
>
> [email protected] wrote:
> > On Jul 30, 2:53 pm, Tim McNamara <[email protected]> wrote:
> > > In article <[email protected]>,
>
> > > [email protected] wrote:
> > > > On Jun 7, 11:57 am, Andy Coggan <[email protected]> wrote:
>
> > > > > In fact, mild-to-moderate arterial desaturation tends to occur
> > > > > during maximal exercise in a significant portion of the
> > > > > population (at least discounting young, healthy, untrained
> > > > > men!), indicating that, at least to some extent, aerobic
> > > > > capacity (i.e., VO2max) is limited, in part, by pulmonary
> > > > > function.
>
> > > > Phoeey. A small arterial desaturation is most likely explained by
> > > > increased left to right shunting
>
> > > Left to right shunting from where to where through what? This term
> > > is usually used to indicate left to right shunting through an
> > > atrial septal defect or cases of tricuspid atresia. There should
> > > be little or no left to right shunting through a patent foramen
> > > ovale and should be no shunting at all in a normal heart. So I am
> > > not clear to what you refer. Thanks.
>
> > My bad, I should have said increased right to left shunting although
> > this is not so much as a physiological shunt but as a ventilation
> > perfusion defect behaving as a shunt.
>
> That didn't really clarify. Ventilation defects are generally caused by
> obstructions somewhere in the airway; perfusion defects are generally
> caused by emboli in the pulmonary vasculature. What is the cause of the
> "ventilation perfusion defect" you are pointing towards? Does this
> occur in non-pathological individuals?
>
> I trimmed the rest of your previous post in an over-zealous fit of good
> netiquette, unfortunately. It would appear that Nielsen (2003) found
> that arterial desaturation during exercise is multifactoral and that
> large lung capacity does offer some protection from this. Perhaps this
> link offers some light on the subject:
>
> http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_...
> =14617055&dopt=AbstractPlus
By the way, I found the Nielsen article (the link didn't work for me)
that I think you referred to. It supports what I said ("A widening of
the PAO2-PaO2 difference does indicate that a diffusion limitation, a
ventilation-perfusion mismatch and/or a shunt influence the transport
of O2 from alveoli to the pulmonary capillaries."), although I am not
sure the author fully understands all the variables contributing to
these possibilities. Further, I found this sentence very interesting:
"During maximal exercise, an extreme lactate spill-over to blood
allows pH decrease to below 7.1 and according to the O2 dissociation
curve this is critical for SaO2." This finding supports the view that
"exercise is limited by the periphery" over the "exercise is centrally
limited" argument. something I have always maintained to the constant
derision of some of the so-called "experts" here and elsewhere, like
Dr.Coggan. I will add it to my quiver. Thanks for the link