41
The stepwise distension is continued until the calculated effective pressure exceeds the target transmural
pressure. The target value needs to be optimized for the individual tissue preparation (optimal active
force as determined by the length-tension relationship for that tissue). For rat mesenteric arteries the
target transmural pressure is normally 100 mmHg (13.3 kPa):
An exponential curve is fitted to the internal circumference pressure data as illustrated in figure 3.9. Now
the isobar corresponding to 100 mmHg is used to calculate the IC
100
value from the point of interception
between the function of the exponential curve and the function of the 100 mmHg isobar.
The normalized internal circumference IC1 is calculated by multiplying the internal circumference
corresponding to 100 mmHg, IC
100
, by a factor k. The factor is for rat mesenteric arteries 0.9. Again, this
value should be optimized for the particular tissue preparation being used by a length-tension curve.
The normalized internal (lumen) diameter is then calculated by:
The micrometer reading X1 at which the internal circumference of the normalized vessel is set to is
calculated by:
T
100 mmHg
= 100 mmHg•
IC
2
( (
IC
1
= k •IC
100
IC
1
d
1
=
(IC
1
– IC
0
)
2
X
1
= X
0
+
