A simple and reliable means for accurate, chronic measurement of pulsatile blood pressure (BP) from conscious, freely moving laboratory mice was developed and validated. The newly developed device consists of a small (1.9 ml, 3.4 g), fully implantable radiotelemetry transmitter. Initial frequency response tests showed an adequate dynamic response; the average -3-dB point found in five transmitters was 145 +/- 14 (SD) Hz. BP, heart rate, and locomotor activity were recorded from 16 chronically (30-150 days) implanted mice. Mean arterial and pulse pressure, checked at regular intervals, ranged from 90-140 mmHg and from 30-50 mmHg, respectively, throughout the study. Transmitter BP measurements were validated against a Millar 1.4-Fr. transducer-tipped catheter. The mean error of the transmitters for diastolic pressures was +1.1 +/- 6.9 mmHg (n = 7). The error for systolic pressures was, on average, 2.7 +/- 3.9 mmHg larger. This new device accurately monitors BP, heart rate, and locomotor activity in conscious, untethered, freely moving mice living in their home cages for periods of at least 150 days.

Accurate continuous chronic measurements of blood pressure from conscious laboratory rats are critical to many experimental protocols but have been difficult or impossible to acquire. A system consisting of an implantable radio-telemetry device, receiver, and computer-based data acquisition system that allows such measurements to be easily obtained has been developed. This system is capable of monitoring and recording arterial pressure (waveform, systolic, diastolic, and mean), heart rate, and activity from rats weighing greater than 175 gm for periods in excess of 6 months. Chronic patency has been achieved through a patented design which includes an antithrombogenic film and a gel membrane located at the catheter tip. Validation of telemetered measurements via carotid catheter has demonstrated the accuracy to be better than +/- 5 mmHg in 85% (N = 20) tested at 3 weeks post implantation, 86% (N = 15) tested at 8 weeks, and 78% (N = 9) at 12 weeks. Incidence of loss of patency was 2.3% (N = 44). This system has a demonstrated ability to obtain accurate continuous chronic measurements of arterial pressure free of the stressors associated with conventional systems.

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This paper describes for the first time the possibility for recording the systolic pressure (SP), diastolic pressure (DP), and the mean arterial pressure (MAP) as well as the heart rate (HR) and locomotor activity (LA) in freely moving mice, using a commercially available telemetry and data acquisition system. The system comprises a new, small radio-telemetry transmitter implanted in the peritoneal cavity, a receiver board placed underneath the home cage, a multiplexer and a computer-based data acquisition system. The signals from the receiver were consolidated by the multiplexer and were stored and analysed by the computer. The telemetered pressure signals (absolute pressure) were corrected automatically for changes in atmospheric pressure measured by an ambient pressure monitor. The effects of implantation on animal behaviour, and, after the animals had recovered, the effects of handling on the SP, DP, MAP and HR were examined. The radio-telemetry system for recording the SP, DP, MAP and HR provides an accurate and reliable method for monitoring the direct effects of handling on SP, DP, MAP and HR. In addition, by using this new blood pressure (BP) transmitter, we maintain that BP measurements in freely moving mice are more efficient, reliable, and less labour-intensive than the measurement techniques described in the literature thus far.