34
Dynamics
of the
Vascular
System
HematocritRatio
x
1
O3
RBCcount(106
lmm3)
MCV
=
Mean corpuscular hemoglobin is defined as
Hemoglobin(g
I
L)
RBCcount(106
lmm3)
MCH
=
(2.3.9)
(2.3.10)
Blood volume is normally determined by the sum of the red blood
cell volume
(Vrbc)
and the plasma volume
(V,):
(2.3.1
1)
The total blood volume in a normal
70
Kg adult is about
5
liters. This
value is not constant and changes according to properties of the vascular
system and activity.
Although total blood volume
(TBV)
can be obtained from dilution
techniques, an estimate of the total blood volume can be obtained from
a
single determination of red blood cell volume
or
plasma volume and
corrected venous hematocrit from the following expressions:
VP
BV
=
(100
-
Hct)
x
Fc~
v,,
BV
=
Hct
x
Fcr
(2.3.12)
(2.3.13)
Indicator
dilution
techniques, are commonly employed in the
determination
of
blood volume. For instance, for the determination
of
plasma volume, small amount
(5
microcurie) of radioactively isodinated
(I'25)
serum albumin (RISA) is injected into the circulation and its
concentration sampled.
For determination of red blood cell volume,
radioactive labeling (e.g. chromium "Cr)
of
red blood cells have been
used and again, concentration of injected sample determined for
a
prescribed intervals.
