Webinar Q&A Report - InsideScientific

Webinar Q&A Report: Continuous Glucose Monitoring for Diabetes, Obesity and Metabolism Research in Rodents

Q: What's the maximum glucose level that this implantable device can detect? Usually glucometer can detect up to 600 mg/dl. Can it detect above 600 mg/dl? We have compared against an YSI Stat 2300 up to 900 mg/dl and shown linearity.

Q: Can the transmitter be turned off while inside the rat? Yes; however, DSI strongly recommends against turning it off. The reason is that whether the device is on or off the glucose oxidase enzyme is reacting. When it is reacting and the device is turned off it can damage the sensor and make the device fail sooner than it would if it were left on continuously.

Q: Why is there a 28 day warranty if Christian’s data shows that the sensor can last 2 to 3 months? The 28 day warranty reflects DSI’s expectation that at least 95% of sensors/devices will function acceptably for 28 days after implantation. In practice there will be a small number (less than 5%) that do not last 28 days and then as time progresses beyond 28 days more implants will stop functioning acceptably. Depending upon the application it is possible that most devices last 6 to 8 weeks but this cannot be guaranteed.

Q: can you explain the calibration process for the implant both before implantation and then during use? Prior to implantation, the HD-XG does not require user calibration. Following implantation (and a 4 to 7 day surgical recovery period) in vivo calibration is required. Initially a linear calibration is performed by collecting two reference measures at low and high glucose levels relative to your experiment. Following that linear calibration, DSI recommends twice weekly single point reference values be collected so that adjustments can be made if sensitivity loss occurs. Some customers choose to do this only once per week.

For more detail on the steps involved in performing a calibration DSI recommends viewing the calibration videos available at http://www.datasci.com/glucose/resources/videos

Q: how many calibrations are required or is the sensor factory calibrated? DSI recommends a multipoint calibration about 1 week after surgery (to obtain at least two points which will be used for a linear regression). After that, we recommend a single point reference be collected every 3-4 days to allow for determination of whether drift is occurring and to correct for that.

Q: what is the experience with the device in smaller rodents like mice? Can mice deal with the size of the transponder? What is the approved application of the implant (smallest and largest subject)? The device size is very well tolerated in mice and juvenile rats. In fact, the same transmitter body is used by other mouse transmitters, such as the HD-X11 and HD-X10, which have been available for some time. Our minimum recommended animal size for an HD-X based product varies between 17 and 23 grams depending on the specific model and whether subcutaneous or intraperitoneal transmitter body placement is used. For rat sized devices the minimum recommended size is 175 grams.

Q: How long does it take for the surgery? Can the presenters share their best-practices and tips for success? Once a surgeon is adept the surgery will typically take 30-45 minutes from first incision to final suture/staple. Additional time for pre-operative and post-operative activities is also required. Regarding best practices and tips, DSI offers customers a surgical manual, surgical video, and free consultation with its surgical group.

Q: Is there a video instruction/protocol on how to implant the device in rats/mice? Yes. A surgical manual and video are available from DSI to those considering purchasing HD-XG implants.

Q: What is your suggestion about the aorta block time? DSI recommends that temporary occlusion of the descending aorta during vessel cannulation be kept as short as possible. If it is too long, hind limb lameness or other side effects could occur.

Q: Could the implant be placed in venous instead of arterial blood? The HD-XG will measure glucose in venous or arterial blood. We recommend that arterial branches be used as our experience with pressure catheters suggests placing them on the venous compromises performance over time.

Q: how does the transmitter measure activity? Locomotor Activity is obtained from the system by monitoring changes in the received signal strength which occur upon the movement of the animal. Changes in signal strength of more than a predetermined threshold generated a digital pulse which is counted by the acquisition system. It is important to note that for the detection of activity, the transmitter has to move. For example, with the transmitter implanted in the peritoneal cavity, slight head movements during grooming or eating would not register as activity.

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