Non-Invasive Blood Strain in Mice and Rats

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 fee and different blood move parameters in rodents, is of nice scientific worth to the researcher.

Invasive Blood Strain, Rat and Mouse Measurement

Direct blood stress, an invasive surgical process, is the gold customary 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 Strain”, 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 know-how and can also be utilized to match the accuracy of NIBP applied sciences. Telemetry entails the implantation of radio transmitters within the rodent’s physique. This method is properly validated and has glorious correlation with direct blood stress.

The benefit of implantable radio telemetry is the flexibility to repeatedly 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 stage of stress, particularly mice, in relationship to the big, heavy transmitters (2004, ATLA, 4th World Congress, Einstein, Billing, Singh and Chin); (4) irregular habits for the reason that animal can not have social interplay as a result of present know-how requiring the implanted animal to be remoted, one animal per cage; (5) incapacity to carry out excessive throughput screening; (6) excessive value of the preliminary gear set-up and the costly transmitters that require frequent manufacturing unit upkeep; (7) value of fabric and human sources regarding ongoing surgical procedures; and (8) the shortage of a aggressive market leading to excessive product and servicing prices.

Non-Invasive Blood Strain, 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 every of a number of varieties of NIBP sensors, positioned distal to the occlusion cuff, could be utilized to observe the rat BP. There are three (3) varieties of NIBP sensor applied sciences: photoplethysmography, piezoplethysmography and Quantity Strain Recording. Every technique will make the most of an occlusion tail-cuff as a part of the process.

1. Photoplethysmography

The primary and oldest sensor kind is Photoplethysmography (PPG), a light-based know-how. The aim is to file the primary look of the heartbeat whereas deflating the occlusion cuff or the disappearance of pulses upon inflation of the occlusion cuff. Photoplethysmography makes use of an incandescent or LED light supply to file the heartbeat sign wave. As such, this light-based plethysmographic technique makes use of the light supply to light up a small spot on the tail and makes an attempt to file the heartbeat.

Photoplethysmography (PPG) is comparatively inaccurate for the reason that 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 various limitations to a light-based know-how, equivalent to: (1) over-saturation of the BP sign by ambient light; (2) excessive sensitivity to the rodent’s motion (movement artifact); and (3) the issue in acquiring satisfactory mice blood stress alerts in darkish skinned rodents (Pigmentation Differentiation). Light-based sensors additionally trigger tail burns from shut contact and extended publicity.

Diastolic blood stress can’t be measured by photoplethysmography for the reason that know-how data solely the primary look of the heartbeat. If the diastolic BP is displayed on the photoplethysmographic instrumentation, it’s only an estimation that’s calculated by a software program algorithm quite than a real measurement.

Extra 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, file 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 know-how.

The photoplethysmography technique correlates poorly with direct blood stress measurements and is the least advisable sensor know-how for NIBPe in rodents, particularly mice.

2. Piezoplethysmography

The second NIBP sensor know-how is piezoplethys-mography. Piezoplethysmography and photoplethysmography require the identical first look of a pulse within the tail to file the systolic blood stress and coronary heart fee.

Each plethysmographic strategies have related scientific limitations. Whereas photoplethysmography makes use of a light supply to aim to file the heartbeat sign, piezoplethysmography makes use of piezoelectric ceramic crystals to do the identical. From a technical perspective, piezoplethysmography is way extra delicate than photoplethysmography for the reason that sign from the sensor is the speed of change of the heartbeat quite than simply the heartbeat amplitude. Due to this fact, even extraordinarily small mice with excessive velocity pulses will generate a adequate sign to be detected with easy amplifiers.

Piezoelectric sensors are extra correct than light-based/LED sensors however the identical plethysmographic limitations proceed to provide inaccuracies in blood stress measurements. On a optimistic word, the pores and skin pigment of the rodent just isn’t a measurement situation with piezoplethysmography as with photoplethysmography.

Though piezoplethysmography is best than photoplethysmography, each non-invasive tail-cuff blood stress applied sciences correlate poorly with direct blood stress measurements.

3. Quantity Strain Recording

The third sensor know-how is Quantity Strain Recording (VPR). The Quantity Strain Recording sensor makes use of a specifically designed differential stress transducer to non-invasively measure the blood quantity within the tail. Quantity Strain Recording will truly measure six (6) blood stress parameters concurrently: systolic, diastolic, imply, coronary heart pulse fee, tail blood quantity and tail blood move.

Since Quantity Strain Recording makes use of a volumetric technique to measure the blood move and blood quantity within the tail, there are not any measurement artifacts associated to ambient light; motion artifact can also be significantly lowered. As well as, Quantity Strain Recording just isn’t depending on the animal’s pores and skin pigmentation. Darkish-skinned animals don’t have any detrimental impact on Quantity Strain Recording measurements. Very small, 10-gram C57/BL6 black mice are simply measured by the Quantity Strain Recording technique.

Particular consideration is afforded to the size of the occlusion cuff with Quantity Strain Recording with a view to derive essentially the most correct blood stress readings.

Quantity Strain Recording is essentially the most dependable, constant and correct technique to non-invasively measure the blood stress in mice as small as 10 grams to rats higher than 950 grams.

In an unbiased scientific validation research performed in 2003 at Yale College, New Haven, Connecticut, Quantity Strain Recording correlated 99 p.c with direct blood stress:

“Quantity Strain Recording is great. It is extremely correct and reliable. We carried out experiments on temperature-controlled, adult rats and the non-invasive blood stress measurements confirmed virtually good correlation with invasive blood stress measurements. We’re very happy with the outcomes.”

Quite a few printed analysis papers can be found validating the accuracy, reliability and consistency of Quantity Strain Recording. See the Medical Bibliography part.

Rodent Holders, Rat and Mouse

The best animal holder ought to comfortably restrain the animal, create a low-stress setting and permit the researcher to continually observe the animal’s habits. A educated rat or mouse can comfortably and quietly stay within the holder for a number of hours.

It is extremely helpful to include a darkened nostril cone into the rodent holder to restrict the animal’s view and scale back the extent of animal stress. The animal’s nostril will protrude by means of the entrance of the nostril cone permitting for snug respiration. The tail of the animal ought to be totally prolonged and exit by means of the rear hatch opening of the holder.

The correct dimension animal holder is crucial for correct blood stress measurements. If the holder is simply too small for the animal, the restricted lateral area is not going to enable the animal to breathe in a relaxed trend. The animal will compensate by elongating its physique, thereby making a respiration artifact. A respiration artifact will trigger extreme tail movement and undesirable blood stress readings.

Animal Physique Temperature, Rat and Mouse

A NIBP system ought to be designed to comfortably heat the animal, scale back the animal’s stress and improve blood move to the tail.

The rodent’s core physique temperature is essential for correct and constant blood stress measurements. The animal will need to have satisfactory blood move within the tail to amass a blood stress sign. Thermo-regulation is the tactic by which the animal reduces its core physique temperature, dissipates warmth by means of its tail and generates tail blood move.

Anesthetized animals could have a decrease physique temperature than awake animals so extra care should be administered to keep up the animal’s correct core physique temperature. An infrared warming blanket or a re-circulating water pump with a heat water blanket is the popular technique to keep up the animal’s correct core physique temperature. The animal ought to be heat and cozy however by no means sizzling. Excessive care should be exercised to by no means overheat the animal.

Warming units equivalent to sizzling air heating chambers, warmth lamps or heating platforms that apply direct warmth to the animal’s toes are usually not advisable to keep up the animal’s core physique temperature. These heating units will overheat the animal and enhance the animal’s respiratory fee, thereby rising the animal’s stress stage. These situations will elicit poor thermo-regulatory responses and create inconsistent and inaccurate blood stress readings.

Environmental Temperature

The correct room temperature is crucial for correct blood stress measurements. The room temperature ought to be at or above 26C. If the room temperature is simply too cool, equivalent to beneath 22C, the animal is not going to thermo-regulate, tail blood move might be lowered and it could be troublesome to acquire blood stress alerts. A chilly metal table or a close-by air-con duct are undesirable throughout animal testing.

Animal Preparation

The animal ought to be positioned within the holder not less than 10 to fifteen minutes previous to acquiring stress measurements. Acclimated animals will present quicker BP measurements than non-acclimated animals. Correct animal dealing with is crucial to constant and correct blood stress measurements. A nervous, burdened animal could have diminished circulation within the tail.

Best Blood Pressure Monitors In 2022

Most rodents will shortly adapt to new situations and really feel snug in small, darkish and confined areas. Coaching just isn’t crucial to acquire correct blood stress readings, nevertheless, some researchers choose coaching periods. Rodents can simply be educated in roughly three days, 15-minutes every day earlier than starting your experiment.

The animal ought to be allowed to enter the holder freely. After the animal is within the holder, modify the nostril cone so the animal is snug however not capable of transfer excessively. The animal ought to by no means have its head bent sideways or its physique compressed towards the again hatch. The animal’s temperature ought to be monitored all through the experiment.

Conclusion

Tail-cuff NIBP measurements could be constant, correct and reproducible when learning awake and anesthetized mice and rats. As well as, a number of animal testing may be very cost-effective for big scale, excessive throughput screening. Care should be exercised to correctly deal with the animals. Coaching the animals and monitoring the animal’s temperature might also be helpful.

The volumetric stress recording technique gives the best diploma of correlation with telemetry and direct blood stress and is clearly the popular tail-cuff sensor know-how.
NIBP units that make the most of Quantity Strain Recording are a priceless device in analysis and can proceed to be helpful in lots of research protocols. The principle benefits are: (1) they require no surgical procedure; (2) they’re considerably cheaper than different blood stress gear, equivalent to telemetry; (3) they will display screen for systolic and diastolic BP modifications over time in massive numbers of animals; and (4) they supply the researcher with the flexibility to acquire correct and constant blood stress measurements over time in long-term research.