DMT Normalization Add-On Module to LabChart 8

The MLS065/8 DMT Normalization Module Version 8 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.

Features

• Automatically calculates tissue length

• Provides online and offline determination of effective pressure

• Calculates the pre-tension (micrometer setting) for normalization

Elastic Tissues

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.

Normalization Settings

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. 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.

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.

Available as Part of LabChart Pro

The MLS065/8 DMT Normalization Module is also available as part of LabChart Pro. Visit the LabChart Pro information page prior to making a purchasing decision. Existing LabChart users and PowerLab system purchasers can upgrade to LabChart Pro at a special price.