The direct method is straightforward, but requires catheterization of a major artery. The catheter is connected to a blood pressure transducer and suitable amplifier to produce an analog signal. This signal can be observed on an oscilloscope, or fed into a data acquisition system for recording and analysis.
The NIBP method uses an inflatable cuff around the tail of the animal, a means of inflating/deflating the cuff, and a means of detecting pulsatile blood flow. Depending on the equipment, special software is required to monitor the results, or the measurements can be sent serially to a computer for data collection.
Important note: NIBP systems differ in the means of pulse detection. Mice and rats increase blood flow to their tails as a means of thermoregulation; as the body temperature increases, blood flow is diverted to the tail for heat radiation. The less-sensitive piezo-electric transducers require this heating to get an adequate signal. The more sensitive photoplethysmographic technique normally does not require heating above ambient temperature. It has long been known that heating the animal produces thermostress, and actually increases BP. Thus the well-established photoplethysmographic method produces the most accurate measurements.
The table below lists the major features and advantages of each of these methods of measuring BP. Click on the highlighted link to go directly to that page.
Note: The photoplethysmographic NIBP systems sold by CWE are inherently more sensitive than piezo sensor systems, and do not normally require animal heating.
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