The American Heart Association (AHA) Scientific Sessions will be held in Orlando, Florida, November 4 - 7th, 2007.

Visit Scisense at Booth 459 and drop off your ballot for a chance to win a Canon Powershot A560 camera. Click here for more information and a copy of the ballot.

Six months ago in this newsletter we announce that Scisense had doubled in size to serve our large and growing numbers of customers. This rapid rate of expansion has continued over the summer and further personnel are being added every month, both on staff and in the field through new distributors and resellers..

Some important points to remember about Scisense Inc:

• All Scisense FV series pressure-volume amplifiers, FP series pressure amplifiers and FT series pressure and pressure-volume catheters conform to EU EMC Directive 89/336/EEC and meet CE standards.
• All products are tested to the highest standards of quality with each item being subjected to a wide range of tests, a superior process to the statistical sampling technique that other companies use for quality control.
• Our focus is to provide complete solutions and we will work with you to maximize your results in any difficult or unusual application for our sensors.

Can saline be used in place of blood to perform a cuvette volume calibration?

A common method of calibrating a conductance measurement into volume units is to perform a cuvette calibration using blood.  Ideally, this calibration should be performed before each experiment to take into account the ability of the rings to measure conductance (which can change from day to day depending on cleaning and maintenance of the catheter).  For some species, it might be feasible to withdraw a large enough sample to perform this calibration before every experiment; however, this is not possible with small rodents.  Typically, a small subset of animals is used to establish a calibration curve.  These calibration values are then applied to data collected for the rest of the group.  Some labs will simply perform this calculation when a catheter is used for the very first time. 

There is a way to calibrate the catheter before measuring from EACH animal without withdrawing any blood.  Blood has a specific resistivity which is important in solving for volume using Baan’s equation.  Any other fluid can, in theory, be used as long as the resistivity is the same as the blood sample being used.  Thus, a saline/distilled water mixture could be made up to “mimic” the resistivity of blood.

A typical scenario follows:

1. A number of mice (e.g. n=4) are used to determine the resistivity value of blood.  The resistivity of blood can be determined using a conductance meter or a Rho cuvette
2. It is important to determine the resistivity while maintaining the temperature of your sample at body temperature
3. Mix a batch of saline with distilled to match the resistivity of blood
4. Use this mixture before every experiment

A typical example would be as follows:

1. Conductivity of blood equals 7,600 micro-Siemens at 37 deg. C.
2. Conductivity of 0.9% normal saline equals 15,200 micro-Siemens at room temperature (22 deg. C)
3. A mixture of 50% normal saline and 50% distilled water (at room temperature) would provide you with a suitable blood replacement for cuvette calibration

Advantages of this method include:

1. Being able to perform a calibration before every experiment
2. Taking into account conductance ring sensitivity
3. Not having to immerse the cuvette in a water bath to maintain at 37 deg C.

Dr. Marc Feldman, Professor of Medicine and Engineering and Director, Cardiac Catheterization Laboratory, UTHMC, San Antonio, Texas, USA, has recently completed a validation study comparing the Scisense pressure sensor to a another commercially available solid-state pressure sensor.  Preliminary results were recently presented at the Total Solutions for Laboratory Animal Science (TSLAS) meeting in Tokyo, Japan.  Dr. Feldman performed a number of in vitro tests as well as in vivo comparisons.  The in vivo pressure data was acquired with both the Scisense catheter and the other pressure catheter inserted into the same LV of a number of mice via apical puncture.  In other words, pressure data was acquired simultaneously at the same site within the same mouse.  Dr. Feldman was able to confirm that:

“both sensors had equivalent in vitro swept frequency response over time, frequency response at 100mmHg, and catheter step response to transient pressure drop. Both sensors also performed similarly during in vivo dose-response studies to iv isoproterenol, and simultaneous placement of both micro-manometer pressure sensors in the same intact murine heart.”
Source: TSLAS Presentation, August 2007

Two advantages of all Scisense rodent catheters over its competitor are the uniform and smooth profile at the tip of the catheter and a uniquely designed recessed pressure sensor window.  This benefits customers because it minimizes trauma during insertion and minimizes signal artifacts during use.  This is particularly important when measuring ventricular pressures in the mouse where at end-systole the internal short axis dimension is only a few millimeters in diameter and the endocardium can sometimes come into contact with the sensor.

A summary of Dr. Feldman’s data can be found on our web-site at:

http://www.scisense.com/techinfo/Scisense_Pressure_Sensor_Comparison.pdf (currently not available to download)

Some of the upcoming events where you will find Scisense Include:

• AHA Scientific Sessions 2007, Orlando, Florida. November 4 – 6, 2007 (BOOTH 459)

• “Data Acquisition and Analysis in Small Animals”, IRCM, Montreal, Quebec. December 6, 2007

• Experimental Biology 2008, San Diego, California. April 5 – 9, 2008 (BOOTH 330)