Share thisThe general non invasive blood pressure methodology consists of utilizing a tail cuff placed proximally on the tail to occlude the blood flow. Upon deflation, one of several types of non invasive blood pressure sensors, placed distal to the occlusion cuff, will attempt to measure the blood pressure. There are three types of non invasive blood pressure sensor technologies: photoplethysmography, piezoplethysmography, and volume pressure recording. Each method will utilize an occlusion tail-cuff as part of the methodology.
Direct blood pressure, an invasive surgical procedure, is the gold standard used to compare the accuracy of non invasive blood pressure technologies. Direct blood pressure should be performed on the rodent’s carotid artery, rather than the femoral artery.
Radiotelemetry, a minimally invasive surgical procedure, is a very reliable blood pressure technology and is also utilized to compare the accuracy of non invasive blood pressure technologies. Telemetry involves the use of implanted radio transmitters in the rodent’s body. This technique is well validated and has excellent correlation with direct blood pressure. The advantage of implantable radiotelemetry is the ability to continuously measure blood pressure in free moving laboratory animals. The disadvantages of radiotelemetry include: morbidity associated with surgical implantation; increase in the animal’s level of stress; and the high cost of the equipment.
Non Invasive Blood Pressure Technologies
Photoplethysmography: The first and oldest sensor type is a light-based technology, photoplethysmography (PPG). The aim is to record the first appearance of the pulse when it re-enters the tail artery during the deflation cycle of the proximal occlusion cuff. Photoplethysmography utilizes a standard light source or a LED light source to record the pulse signal wave. As such, this light-based plethysmographic method uses the light source to illuminate a small spot on the tail and attempts to record the pulse.
Photoplethysmography is relatively inaccurate and can only imprecisely measure the systolic blood pressure and the heart beat. There are many limitations to a light-based technology, such as: over-saturation of the blood pressure signal by ambient light; extreme sensitivity to the rodent’s movement (motion artifact); and the difficulty in obtaining adequate blood pressure signals in dark skinned rodents (pigmentation differentiation).