Noninvasive measurement of systolic blood pressure in rats: A novel technique

Anil Gangwar, Pradeep Kumar, Anita Rawat, Sunita Tiwari 
 Department of Physiology, King George's Medical University, Lucknow, Uttar Pradesh, India

Correspondence Address:
Pradeep Kumar
Department of Physiology, King George«SQ»s Medical University, Lucknow, Uttar Pradesh
India

Full Text

Sir,

Essential hypertension affects 95% of hypertensive patients worldwide countries. [1] Animal models are required to understand the physiology of essential hypertension. Intraarterial cannulation is generally considered the most physiological method of blood pressure (BP) recording in animals like rats. The procedure of arterial cannulation in small animals and to maintain the patency of arterial catheter for long time experimentation is very difficult and time consuming. [2],[3] Various studies has reported the strong correlation between tail-cuff and intraarterial BPs measured simultaneously in conscious rats. [4],[5] These comparisons have provided important validations of the BP recorded by tail-cuff method. However, there are various factors including heating and restraint that can alter the BP recorded by noninvasive methods. [6]

Photoplethysmography (PPG), piezoplethysmography and volume pressure recording used in various noninvasive blood pressure (NIBP) techniques for measuring the BP in small animals like a rat and mice are expensive. Systolic BP can be determined by measuring the pressure value in the cuff when PPG pulse reappears during deflation. This is a simple technique and does not need calculations or formulae. [7] In view of the above, we hypothesized that BP in rat can be measured by using pulse transducer with physiograph and an appropriate rat tail-cuff.

In this study, we recorded the systolic BP of rats by an innovated device reproducible and that correlates strongly with BP measured subsequently by NIBP machine from ADinstruments (ADI) (IN125NIBP controller) Australia. This experimental design has the advantage of being simple, convenient and of low cost.

The study was conducted on albino rats (n = 6) weighing 180-250 g obtained from central animal house of King George's Medical University, Lucknow. BP was measured by two devices at 9:30 am daily for 5 days. The device was developed at the Department of Physiology KGMU, Lucknow. Study was done in accordance with the CPCSEA guidelines.

Sphygmomanometer, physiograph with coupler, pulse transducer, triway and noncollapsible rubber tubes were procured from various laboratories and inflatable rat tail-cuff was designed by the authors [Figure 1]. The cuff consists of latex balloon measuring 5 cm × 2 cm with 0.5 mm thickness. This balloon was placed in a circular plastic case having a diameter of 23 mm with a central hole of 12 mm diameter. The balloon was kept in such a fashion that it remains in contact with an inner surface of plastic case around the central hole, so that this balloon encircles the tail. One end of the triway was connected with the balloon (tail-cuff) and other two ends were connected to inflating-deflating pump and sphygmomanometer [Figure 2]. The system measures systolic BP by determining the cuff pressure (reflected on sphygmomanometer) at which blood flow (pulse) to the tail was eliminated. This elimination of blood flow (pulse) was recorded by pulse transducer connected to single-channel physiograph through a suitable coupler.{Figure 1}{Figure 2}

The animals were kept in restrainers after acclimatizing them, the tail was passed through the hole of the newly designed cuff and the pulse transducer was tied around the tail distal to the cuff. As the system was switched on the pulse was recorded on, the physiograph paper; the cuff was inflated by the pump and the pressure in the cuff was raised until the pulse was eliminated. The pressure at which the pulse was eliminated was the systolic BP of the animal. The systolic BP and pulse were also recorded by the NIBP system of ADI for comparison.

Results [Table 1] showed that the new device was able to record the systolic BP in a reproducible and reliable manner. There was no significant difference between the BPs recorded by both devices [Figure 3].{Figure 3}{Table 1}

The BP recording of small animals is necessary to develop strategies for control of hypertension. A number of noninvasive devices are available to record BP in small animals. The costs of these devices are high and may not be affordable the under-resourced physiology laboratories of developing countries like India. Our device needs only one physiograph and a sphygmomanometer, which are usually available in the physiology laboratories. The systolic BP measured by our low cost device is reproducible and comparable with NIBP system of ADI. Serial measurements in a larger number of animals are necessary for further calibration and validation of this novel technique.

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