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I would like to pose a different question to the entire group for
brainstomring and learning:
In relation to drug delivery and particularly to pharmacokinetics, what would
be the definition of "Blood flow" versus "perfusion"? Are they the same? Or
are they different? If different what is their relationship or
interdependecne?
I will refrain for now in expressing my opinion, I would like to here from
you all...
Thank you,
Alfredo R. Sancho,
USC PK-Imaging Ctr.
Los Angeles, CA
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Hi,
From a clinical point of view, you could have blood flowing through a vessel
which is distally obstructed and therefore have no perfusion beyond the
obstruction. So, you can have blood flow without perfusion. The converse
however is not possible.
Interesting question.
Lisergicus
----------
From: david.aaa.pharm.cpb.uokhsc.edu on behalf of Alfredo R. Sancho
Sent: Thursday, April 24, 1997 12:10 PM
To: Multiple recipients of PharmPK - Sent by
Subject: Blood flow - Perfusion
I would like to pose a different question to the entire group for
brainstomring and learning:
In relation to drug delivery and particularly to pharmacokinetics, what would
be the definition of "Blood flow" versus "perfusion"? Are they the same? Or
are they different? If different what is their relationship or
interdependecne?
I will refrain for now in expressing my opinion, I would like to here from
you all...
Thank you,
Alfredo R. Sancho,
USC PK-Imaging Ctr.
Los Angeles, CA
Back to the Top
About the question on blood flow and perfusion it should be noted that are
two different concepts. One is related to the passage of blood trough a
vessel, that is a necesary condition, but not sufficient to have perfusion,
since an adecuate pressure is needed to achieve perfussion. So both are
physical terms related to cardiovascular physiology, but by no means have
clinical or physiological equivalence
Fermin Valenzuela
Dept. of Pharmacology
Faculty of Medicine
Universidad Nacional Autonoma de Mexico
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>In relation to drug delivery and particularly to pharmacokinetics,
what would be the definition of "Blood flow" versus "perfusion"?
Blood flow: The movement of blood within the blood system as a direct
result of cardiac output.
Perfusion: The movement of blood from the CV system into and through
organs / tissues.
> Are they the same? Or are they different?
They are different.
> If different what is their relationship or interdependecne?
Perfusion is dependent upon blood flow supplying the perfusate (blood,
plasma, leukocytes, etc.) to the organ or tissue being perfused.
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Hi, I am very interested in these questions as I am working on a study
of peripheral vascular disease using fluorescent dyes.
In relation to drug delivery, I think blood flow and perfusion can be
very different. Perfusion is dependent on factors such as
permeability, diffusion, and the surface area of the capillaries, in
addition to the flow to the region. Blood flow would be dependent on
cardiac output and heart rate, and local autonomic control of
vasoconstriction.
I am now interested in whether combined pharmacokinetic information
from an intravascular indicator dye and a permeable dye can give
information on both flow and permeability. Any comments on this idea
would be appreciated. Specifically I am working with sodium
fluorescein (permeable) and indocyanine green (intravascular).
Deborah OhGenevad-oh.at.uiuc.edu >I would like to pose a different question to the entire
University of Illinois at Urbana-Champaign
group for
>brainstomring and learning:
>
>
>In relation to drug delivery and particularly to pharmacokinetics,
what would
>be the definition of "Blood flow" versus "perfusion"? Are they the
same? Or
>are they different? If different what is their relationship or
>interdependecne?
>
>I will refrain for now in expressing my opinion, I would like to here
from
>you all...
>
>Thank you,
>
>Alfredo R. Sancho,
>USC PK-Imaging Ctr.
>Los Angeles, CA
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From the perspective of a cardiovascular physiologist, blood flow is
well-defined. It is a measure of the volume of blood passing a given
point in the circulation per unit time. It has units of, say, ml/min.
When a "perfused organ" preparation is used, we mean simply that we are
(or an anesthetized animal is) pumping blood into the arterial side of
an organ's or tissue's vascular system.
So I would ask, when used in the context of pharmacokinetics, what are
the units of "perfusion"? Or even, what is the definition of perfusion?
Oscar's point is well-taken in that some portion of a tissue may not be
perfused because of an upstream obstruction, but I'd argue that that
portion of the tissue is also without blood flow.
So you cannot deliver a drug (at least by a vascular route) to a tissue
that receives no blood flow and is thus "unperfused".
Regards,
Bob
--
Robert D. Phair, Ph.D. rphair.-at-.ix.netcom.com
BioInformatics Services http://www.webcom.com/rphair
Partnering and Outsourcing for Computational Biology
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Webster definition of perfusion: the act of pouring over or through,
especially the passage of a fluid through the vessels of a specific organ.
Not being a pharmacokineticist but a radiologist working on perfusion
measurement from images, I do not know the field enough to answer your
question-the pharmacokinetic sense of perfusion.
The concept of perfusion has become controversial, especially with the growing
application of MR and CT for perfusion measurement.
Perfusion to an organ is determined by complex physiologic/anatomic processes:
blood pressure, velocity, capillary morphology, capillary permeability, oxygen
and nutrient demands. The definition of perfusion has varied depending on the
field of interest: physiologist, radiologist, pathologists, cardiologist, etc.
Perfusion in the classical physiological sense is blood circulation: it is
measured by total blood flow per a unit mass or volume of tissue (e.g.
ml/min/100g). For example, a single organ such as the kidney with a single
blood supply, the blood flow into the kidney is measured and divided by its
mass. In this definition, blood flow may be synonymous with perfusion. But
we must remember that classical perfusion measurement techniques are based on
terminal deposition (microsphere) or washout (radionuclide) of tracers and
hence only considering the component of blood flowing in the capillary bed.
This approach excludes the blood which transits without exchanging with the
organ.
This definition also should exclude physiologic blood-tissue exchange which is
frequently confused with perfusion. In practice, however, the blood-tissue
exchange is an important part of drug transport to an organ and very difficult
to separate from overall drug transport measurements.
K. Ty Bae, MD, PhD
bae.-at-.mirlink.wustl.edu
_______________________________________________________________________________
PharmPK - Discussions about Pharmacokinetics
Pharmacodynamics and related topics
I would like to pose a different question to the entire group for
brainstomring and learning:
In relation to drug delivery and particularly to pharmacokinetics, what would
be the definition of "Blood flow" versus "perfusion"? Are they the same? Or
are they different? If different what is their relationship or
interdependecne?
I will refrain for now in expressing my opinion, I would like to here from
you all...
Thank you,
Alfredo R. Sancho,
USC PK-Imaging Ctr.
Los Angeles, CA
Back to the Top
My understanding is that perfusion relates to flow of blood to exchanging
capillary beds and total blood flow is exactly that. The difference is
particularly important in tissues such as the skin where there are
considerable numbers of a-v shunting vessels.
----------
From: PharmPK
To: Multiple recipients of PharmPK - Sent by
Subject: Blood flow - Perfusion
Date: Thursday, April 24, 1997 11:10AM
Subject: Blood flow - Perfusion
PharmPK - Discussions about Pharmacokinetics
Pharmacodynamics and related topics
I would like to pose a different question to the entire group for
brainstomring and learning:
In relation to drug delivery and particularly to pharmacokinetics, what
would
be the definition of "Blood flow" versus "perfusion"? Are they the same?
Or
are they different? If different what is their relationship or
interdependecne?
I will refrain for now in expressing my opinion, I would like to here from
you all...
Thank you,
Alfredo R. Sancho,
USC PK-Imaging Ctr.
Los Angeles, CA
Back to the Top
There is an extensive literature on using permeable and inpermeable
markers to get information on blood flow and permeability (as well as
markers that enter parenchymal cells). You could start with names like
Carl Goresky, Ken Zierler, and Jim Bassingthwaighte. As you might
imagine it is easy to spell Jim's last name incorrectly, and I probably
have done so here. You could also look at an old book by Niels Lassen
and William Perl titled Tracer Kinetic Methods in Medical Physiology,
Raven, 1979.
Regarding your distinction between blood flow and perfusion, I would
argue you are using perfusion to signify extraction. I personally don't
think perfusion is well-defined, but if it were it ought to have the
same units as blood flow and might represent the fraction of cardiac
output that is delivered to a particular tissue or organ.
I suspect, however, that this debate is going to generate more heat than
light.
Regards,
Bob
--
Robert D. Phair, Ph.D. rphair.at.ix.netcom.com
BioInformatics Services http://www.webcom.com/rphair
Partnering and Outsourcing for Computational Biology
Back to the Top
Dr TyBae says, in part:
"Perfusion to an organ is determined by complex physiologic/anatomic
processes:
blood pressure, velocity, capillary morphology, capillary permeability,
oxygen
and nutrient demands. The definition of perfusion has varied depending
on the
field of interest: physiologist, radiologist, pathologists,
cardiologist, etc.
Perfusion in the classical physiological sense is blood circulation: it
is
measured by total blood flow per a unit mass or volume of tissue (e.g.
ml/min/100g). For example, a single organ such as the kidney with a
single
blood supply, the blood flow into the kidney is measured and divided by
its
mass. In this definition, blood flow may be synonymous with perfusion.
But
we must remember that classical perfusion measurement techniques are
based on
terminal deposition (microsphere) or washout (radionuclide) of tracers
and
hence only considering the component of blood flowing in the capillary
bed.
This approach excludes the blood which transits without exchanging with
the
organ.
This definition also should exclude physiologic blood-tissue exchange
which is
frequently confused with perfusion. In practice, however, the
blood-tissue
exchange is an important part of drug transport to an organ and very
difficult
to separate from overall drug transport measurements."
Two points can be made here. First, if perfusion is defined as "organ
blood flow", then it's determined by arterial pressure, venous pressure,
and the organ's vascular resistance. Resistance is usually dominated by
the arterioles. Under this definition, perfusion is independent of
velocity, capillary morphology, capillary permeability, and oxygen and
nutrient demands. Second, classical perfusion measurement techniques are
not entirely limited to microspheres, or radionuclide washout. It would
be reasonable to ague that perfusion could also be measured by a
flowmeter on the incoming artery.
So, it seems to me that perfusion is organ blood flow, perhaps corrected
for a-v shunts as was pointed out by another post in this thread. As
such it has little (I would say nothing) to do with blood-tissue
exchange. This may be what Dr TyBae means by, "This definition also
should exclude physiologic blood-tissue exchange which is frequently
confused with perfusion." Organ blood flow or perfusion is, of course, a
crucial determinant of drug delivery to the capillary beds. Once there,
however, the drug's chemical properties and the available transport
mechanisms will determine its extraction. At a very detailed level, one
must also be concerned with the issues of flow-limitation, but once in
the interstitial space, cellular uptake, too, is independent of blood
flow. Thus Dr TyBae is correct that blood tissue exchange is an
important element of drug delivery, but mixing the concepts of perfusion
and extraction can only lead to unending semantic wars, as is apparently
the case in radiological usage currently.
Regards,
Bob
--
Robert D. Phair, Ph.D. rphair.aaa.ix.netcom.com
BioInformatics Services http://www.webcom.com/rphair
Partnering and Outsourcing for Computational Biology
PharmPK Discussion List Archive Index page
Copyright 1995-2010 David W. A. Bourne (david@boomer.org)