Long-term Blood Pressure Measurement in Freely Moving Mice Using Telemetry

The goal of this protocol is to assess systemic blood pressure in conscious freely moving mice using implantable radiotelemetry devices. This method can help answer key question in the field of vascular diseases and allows the evaluation of many factors involved in the blood pressure regulation. The main advantage of this technique is that it allows collection of a wide variety of physiological parameters from freely moving animals without the artifacts associated with use of restraint, human interaction, or anesthesia that are required by other techniques.

House the animals for this study at 21 degrees Celsius with 60%relative humidity under a 12 hour light dark cycle, and with free access to food and water. Weigh a selected mouse, handling it gently and calmly. Because the body must fit a telemetry probe the mouse must weigh at least 20 grams.

To induce anesthesia use an induction chamber with four to five percent isoflurane blowing at 0.45 liters per minute. Transfer the unconscious mouse to a warming plate, and provide two percent isoflurane to it via a nose cone. Then confirm the anesthetized state with a toe pinch.

If the mouse is non-reactive proceed with depilating the ventral side of it's neck using hair cream. Then wipe away the hair and excess cream and scrub the skin clean with three alternating applications of betadine and 70%isopropyl alcohol. The telemeters for this experiment can be reused if they are sterilized according to the manufacturer instructions and the tips of their catheters are refilled with the manufacturers gel.

Now with the mouse in a supine position make a one centimeter midline incision below the neck of the mouse with a scalpel. In the left side of the cut create a subcutaneous space by carefully separating the skin from the underlying connective tissue. Then flip the mouse over and use a scalpel to make a 1.5 centimeter incision in the dorsal left side behind the scapula.

Therein create a subcutaneous pocket large enough to accommodate the device. Now insert the transmitter into the pocket. Then insert a small hemostat clamp in the back incision and maneuver it subcutaneously towards the anterior neck opening.

Using the clamp gently grasp a four centimeter long plastic tube and pull the hemostat back through the tunnel and out the lateral incision in the back. Unclamp the tube once it protrudes from both the abdominal and dorsal incisions. Now from the back insert the catheter sensor into the tube to tunnel the tip of the pressure sensing catheter through the neck.

Then from the neck anterior pull and remove the polyethylene tube and close the dorsal incision using metal clips. Next carefully separate the mandibular glands using cotton applicators. Then retract the left mandibular gland using and elastic stay hook.

Now with fine tipped curved forceps locate the carotid artery along the left side of the trachea and carefully isolate the vessel from the surrounding tissue. Then gently separate the vagus nerve from the carotid artery being careful not to cut or damage either the nerve or artery. Once separated pass three pieces of non-absorbable 7-0 suture underneath the isolated carotid artery and tie the cranial suture to close off blood flow.

Pull the suture that is closest to the sternum to temporarily occlude blood flow from the aorta. Now make a loose knot using the middle suture to secure the catheter. Then make a small incision in the artery between the sutures using micro-scissors.

Using special vessel cannulation forceps gently secure the catheter so the probe is not squeezed out. Then use tweezer forceps to gently grasp the artery. Now retrieve the catheter and insert it into the vessel through the small incision.

The most critical step in this protocol is inserting the probe in the vessel. So make sure you are relaxed and sitting comfortably when you are performing it because good hand coordination is critical for this step. Next tighten the middle suture node around the artery and gently advance the catheter.

Then gently release the suture proximal to the sternum and continue to advance the catheter towards the transverse aorta. When advancing the catheter into the carotid artery it is important to look at the mic end of the probe. Going too far will occlude the aorta and the mouse will die.

Once the catheter has been inserted to the correct mark gently tighten both the lower and the upper suture around the catheter to secure it to the carotid artery. Finally close the skin incision with non-absorbable 5-0 suture and seal the incision with tissue adhesive. Postoperatively monitor the mouse until it shows normal postures and behaviors.

During the first 24 hours administer analgesia as directed by the staff veterinarian. Once the animals have recovered five to seven days post surgery house them individually in a regular mouse cage placed on top of the telemetry receiver plate. To collect data place the mouse's cage over a telemetry receiver plate and turn on the transmitter using the manufacturer's magnetic device.

After the described procedure data can be acquired remotely by a receiver. Traces are visualized on a computer screen for quality control. Details such as animal ID, diastolic and systolic blood pressure, and date of acquisition are also shown.

Arterial blood pressure can be recorded continuously or for short programmed intervals. One easily apparent finding from continuous recordings of murine blood pressure is that they follow a circadian rhythm. After watching this video you should have a good understanding of how to implant telemetry probes for black basal monitoring.

Once mastered this technique can be done in 30 minutes if it is performed properly.