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The MLS065/6 DMT Normalization Module for Windows provides an easy method for the calculation of optimal
pretension conditions for microvascular or any small tubular tissue research. The DMT Normalization Module is for use with PowerLab, LabChart and DMT Wire Myographs.
The DMT Normalization Module should be used with the latest version of LabChart. Click here for the latest LabChart Update for Windows.
The module:
- automatically calculates tissue length
- provides online and offline determination of effective
pressure
- calculates the pre-tension (micrometer setting) for normalization
The rationale and theory behind normalizing elastic tissues
such as microvessels has been extensively investigated by
Professor Michael Mulvany (for details see Mulvany MJ, Halpern,
W Circulation Research 1977, 41: 19-26). Mulvany determined
that the optimal pre-tension conditions (ie internal circumference)
for microvascular studies is best defined as the size when
the vessel is fully relaxed and under a transmural pressure
of 100 mmHg. Therefore the aim of the normalization procedure
is to determine the internal circumference at which the vessel
would be relaxed and under a transmural pressure of 100 mmHg.
This index is denoted as IC100 and
is calculated for each vessel mounted on the wire myograph.
There are a number of factors which need to be considered
when conducting studies using elastic tissues, these include:
- The size of elastic structures (vessels) which can only have
meaning if the conditions are clearly defined.
- The sensitivity of preparations to agonists is dependent
on the degree of tissue stretch.
- The active response of a vessel is dependent on the
extent of stretch (according to the active tension-internal
circumference relation) it is useful to set vessels to
an internal circumference which gives the maximum response.
It is therefore important to define the experimental conditions
prior to conducting investigations into the properties of
elastic tissues.
The normalization procedure is performed by distending the
vessel stepwise and measuring sets of micrometer readings
whilst recording the developed force using PowerLab and LabChart.
The DMT Normalization Module calculates the internal circumference
from the measured distance between the wires, known diameter
of the wire and length of tissue used. The length of the tissue is determined
using a calibrated eyepiece and microscope. Wall tension
is the measured force divided by the wall length from which
effective pressure is calculated. Effective pressure is an
estimate of the pressure which would be necessary to extend
the vessel to the measured internal circumference.
DMT Normalization window with stepwise distension of the tissue
using the micrometer and the developed force. The graph on the
right
is
automatically generated from the calculated internal
circumference
and resting wall
tension by the module.
A graph of internal circumference versus resting wall tension
is created with each stepwise distension, with the module
ending once the effective pressure exceeds 100 mmHg (13.3
kPa). An exponential curve is then fitted to the internal
circumference pressure data and, using Laplace's equation,
the point on the curve corresponding to 100 mmHg is determined
and denoted IC100. From the IC100 a value IC1 is calculated
(0.9 x IC100) which the module then uses to calculate the
micrometer setting which sets the internal circumference
to this pressure. The module has been set with a default
of 0.9 (rat mesenteric vessels) this ratio (IC1/IC100) should
be determined for different tissue types.
Normalization Settings dialog
The DMT Normalization Module provides a Normalization Settings
dialog box in which microscope eyepiece calibration, target
pressure, IC1/IC100 ratio, online averaging and delay time
can be entered which are used in the calculations which will
be used for each tissue being normalized. Each LabChart channel
has a separate Normalization Window in which the tissue end
points (determination of tissue length) and wire diameter
can be entered. Micrometer values and force determinations
are entered in this window either online (while recording)
or offline. A graph of the measured internal circumference
versus resting wall tension of the vessel is created from
which the IC100 and IC1 are calculated. The module also provides
the user with the micrometer setting for achieving the desired
pre-tension conditions for the tissue being studied.
More Information
For more information download the Software Booklet (5.83 MB) or contact your nearest ADInstruments
Representative.
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