Measurements of blood pressure (BP) by radio-telemetry have been described for many animals but not for mice. We describe the use of a commercially available telemetry and data acquisition system to record the systolic, diastolic and mean BP as well as heart rate (HR) and respiratory rate (RR) of freely moving mice. By using implantable telemetry, measurements from freely moving animals are more efficient, reliable and less labor-intensive than the measurement techniques described in the literature thus far.

Experiences with the use of a new BP implant for monitoring mice will be presented, including a surgical procedure which has been found to be successful for implantation of the device as well as special considerations and necessary precautions, like using an operation room with an operation microscope and using completely sterilized equipment for performing surgery on mice. Three mice were successfully operated upon. After surgery, recovery of the animals was indicated by an increase in weight after an initial decrease and by changes in their behavior such as building a nest of the available paper towels. Animals appeared lively throughout the study and no behavioral changes were observed compared to the mice without transmitters. Two days after the operation the daily recording was started and the lowest values in HR (300-400 beats/mean), diastolic (70-80 mmHg), systolic (102-112 mmHg) and mean BP (86-96 mmHg) were found while the mice were in sleep in their home cages. Stressful situations such as hand restraint of the animals or placement of the mice in other cages increased the HR to a maximum of 750-800 beats per mean (bpm), the diastolic pressure to 105-120 mmHg, the systolic pressure to 140-155 mmHg and the mean BP to 123-138 mmHg, respectively. Circadian rhythms in HR and BP (low during the light period: 07:00 to 19:00 h, and high during the dark period: 19:00 to 07:00 h) could be established in the same mice, however no circadian rhythms in RR could be found.

In conclusion, it appears to be possible to implant a transmitter to monitor BP, HR, RR and activity by telemetry in freely moving mice. The most important advantage is the possibility for the direct and accurate measurement of chronic effects of cardioactive compounds, without the added stress which results from conventional measurement techniques.