Fig 1.
Schematic presentation of sensor placement and sites for intraperitoneal fluid sampling.
Blue stars indicate sites for IP fluid sampling. SC = subcutaneous, IP = intraperitoneal, CRAN = cranial, CAUD = caudal, L = left, R = right, IA = intra-arterial, IV = intravenous.
Fig 2.
Sketch of retainer for sensor and reading device.
The FreeStyle Libre was held in place on the inside of the abdominal wall, while the reading device (LimiTTer) was held tightly to the outside of the abdominal wall [25]. 1 = FreeStyle Libre sensor, 2 = LimiTTer, 3 = Retainer, 4 = IP fluid sampling tube, 5 = Guide wire with guide tube, 6 = Abdominal wall, a = Near-field communication, b = Bluetooth low energy.
Table 1.
Order of glucose infusions for all pigs.
Fig 3.
Example of raw data and Kalman smoothed data.
The figure shows data from the entire experiment from the cranial left IP sensor in pig 12. The blue points represent raw data read by the LimiTTer, the red solid line represents the Kalman smoothed data and the dashed line represents ± 1 standard deviation of the Kalman smoothed curve. The black stars (*) represent the IA glucose samples and the green stars (*) represent the IP glucose samples of the cranial left IP location. The glucose infusions are seen as solid lines at the bottom part of the graphics.
Table 2.
Settings and tuning parameters used for Kalman smoothing of FreeStyle Libre data [26].
Fig 4.
Scheme of included and excluded IP sensor recordings.
Fig 5.
Examples of excluded (top panels) and included (bottom panels) sensor recordings.
The red curves represent the intra-arterial blood glucose values, the solid blue lines represent the Kalman smoothed sensor signals and the dashed dark blue lines represent the sensor signals predicted by the model. The percentage of model fit is displayed in the top right corner of each panel. BGA = blood glucose analysis, Gsens = sensor glucose concentration.
Fig 6.
Point estimates and 95% confidence intervals for time delay (A), time constant (B), time to 50% max (C) and time to 50% decline to baseline level (D) for all IP sensors. Sensor location is set as fixed effect in the lmerTest-model. * indicates a significant difference (p <0.01).
Fig 7.
Point estimates and 95% confidence intervals for time delay (A), time constant (B), time to 50% max (C) and time to 50% decline to baseline level (D) for IP and SC sensors. The mean parameter values for the IP sensors compared to those for the SC sensors with sensor location (SC or IP) as fixed effect in the lmerTest-model. * indicates a significant difference (p <0.01).
Fig 8.
Distribution of sensor recordings from the included IP and SC sensors during IV-meals.
The blue curve represents the mean of the normalized IP sensor signals, and the green curve represents the mean of the normalized SC sensor signals. The sensor values were not calibrated and thus do not necessarily show the real glucose values. We therefore compare the normalized glucose deviation from the baseline. The mean was calculated by averaging at each sample over all IP and SC sensors, respectively. The average deviation was then scaled to the range [0, 1]. The same scaling factor was used to normalize all sensor readings from the sensing site under consideration before the standard deviation was determined.
Table 3.
Summary of results for the four IP sensor locations and mean of the IP and SC sensors.
Fig 9.
Boxplots of time delay (A), time constant (B), time to 50% max (C) and time to 50% decline to baseline level (D) for IP sensors with different positioning of sensor element. Mean values are presented as a red *.
Fig 10.
Distribution of included sensor recordings from the four different IP sensor locations compared to corresponding IP fluid samples during IV-meals.
The blue curves represent the mean of the normalized sensor signals, and the red curves represent the mean of the normalized IP fluid samples. The hatched areas indicate ± 1 SD of the included data. Data was normalized by means of offset correction and scaling to the range [0, 1]. arb.unit = arbitrary unit.
Fig 11.
Boxplots of time delay (A), time constant (B), time to 50% max (C) and time to 50% decline to baseline level (D) for IP sensors with the different IV fluid regimens for both IP and SC sensors. Mean values are presented as red *.