Over the previous 20 years, analysis scientists have tried to non-invasively measure mice and rat blood stress (BP) with various levels of success.
The power to precisely and non-invasively measure the systolic and diastolic blood stress, along with the center pulse price and different blood move parameters in rodents, is of nice scientific worth to the researcher.
Invasive Blood Stress, Rat and Mouse Measurement
Direct blood stress, an invasive surgical process, is the gold normal to match the accuracy of non-invasive blood stress (NIBP) applied sciences. Direct blood stress ought to be obtained on the rodent’s carotid artery when evaluating to NIBP. “Validation in Awake Rats of a Tail Cuff Methodology for Measuring Systolic Stress”, Bunag, R.D., Journal of Utilized Physiology, Vol 34, Pgs 279-282, 1973.
Radiotelemetry, a extremely invasive surgical process, is a really dependable blood stress expertise and can also be utilized to match the accuracy of NIBP applied sciences. Telemetry includes the implantation of radio transmitters within the rodent’s physique. This system is nicely validated and has wonderful correlation with direct blood pressure monitors.
The benefit of implantable radio telemetry is the power to constantly measure rat and mouse blood stress in free transferring laboratory animals.
The disadvantages of radiotelemetry are: (1) morbidity related to the preliminary surgical implantation of the transmitter; (2) morbidity related to surgical procedure required to switch the battery, which has a brief battery life; (3) enhance within the animal’s degree of stress, particularly mice, in relationship to the massive, heavy transmitters (2004, ATLA, 4th World Congress, Einstein, Billing, Singh and Chin); (4) irregular conduct because the animal can’t have social interplay as a result of present expertise requiring the implanted animal to be remoted, one animal per cage; (5) incapability to carry out excessive throughput screening; (6) excessive value of the preliminary tools set-up and the costly transmitters that require frequent manufacturing unit upkeep; (7) value of fabric and human assets regarding ongoing surgical procedures; and (8) the dearth of a aggressive market leading to excessive product and servicing prices.
Non-Invasive Blood Stress, Rat and Mouse Measurement
The NIBP methodology consists of using a tail cuff positioned on the tail to occlude the blood move. Upon deflation, one in all a number of forms of NIBP sensors, positioned distal to the occlusion cuff, may be utilized to observe the rat BP. There are three (3) forms of NIBP sensor applied sciences: photoplethysmography, piezoplethysmography and Quantity Stress Recording. Every methodology will make the most of an occlusion tail-cuff as a part of the process.
1. Photoplethysmography
The primary and oldest sensor sort is Photoplethysmography (PPG), a light-based expertise. The aim is to document the primary look of the heart beat whereas deflating the occlusion cuff or the disappearance of pulses upon inflation of the occlusion cuff. Photoplethysmography makes use of an incandescent or LED gentle supply to document the heart beat sign wave. As such, this light-based plethysmographic methodology makes use of the sunshine supply to light up a small spot on the tail and makes an attempt to document the heart beat.
Photoplethysmography (PPG) is comparatively inaccurate because the readings are based mostly solely on the amplitude of a single pulse and may solely imprecisely measure the systolic blood stress and the center beat. There are a lot of limitations to a light-based expertise, reminiscent of: (1) over-saturation of the BP sign by ambient gentle; (2) excessive sensitivity to the rodent’s motion (movement artifact); and (3) the problem in acquiring satisfactory mice blood stress indicators in darkish skinned rodents (Pigmentation Differentiation). Gentle-based sensors additionally trigger tail burns from shut contact and extended publicity.
Diastolic blood stress can’t be measured by photoplethysmography because the expertise data solely the primary look of the heart beat. If the diastolic BP is displayed on the photoplethysmographic instrumentation, it’s only an estimation that’s calculated by a software program algorithm slightly than a real measurement.
Further variability and inaccuracy happens in PPG units that depend on acquiring readings throughout occlusion cuff inflation.
Occlusion cuff size can also be one other supply of variability and inaccuracy. Occlusion cuff size is inversely associated to the accuracy of the blood stress. Lengthy cuffs, predominantly in most photoplethysmographic units, document decrease than the precise blood stress measurements.
These limitations severely compromise the consistency, dependability and accuracy of the NIBP measurements obtained by units that make the most of light-based/LED photoplethysmographic expertise.
The photoplethysmography methodology correlates poorly with direct blood stress measurements and is the least really helpful sensor expertise for NIBPe in rodents, particularly mice.
2. Piezoplethysmography
The second NIBP sensor expertise is piezoplethys-mography. Piezoplethysmography and photoplethysmography require the identical first look of a pulse within the tail to document the systolic blood stress and coronary heart price.