SPARC: Wireless, Continuous Monitoring of Bowel State and Function

Abstract

Introduction and ObjectiveThe neural control of bowel function during content storage, motility, and defecation is not well understood. A more complete understanding may be possible with electrophysiology or pharmacology studies that include functional measures of the bowel in conscious subjects. To overcome this, we developed a wireless colonic pressure and volume monitoring sensor for use anaesthetized pigs. This study validated sensor function and physiologic outcomes in 2 acute animal studies.MethodsThe device measured 80 mm long and 7 mm wide and consisted of a flexible printed circuit board housed in a silicone‐gel filled, thin‐walled silicone tube to maintain flexibility when implanted in the colon. The fully packaged device contained 5 sensors: two pressure sensors to measure circumferential and longitudinal bowel contractions, and three ring electrodes to measure conductance and conductivity of bowel contents near the device. An additional ring electrode was used as a common return for the 3 ring electrodes. The device transmitted radio data at 10 Hz and included an inductive energy interface antenna for battery recharging.Accuracy and precision of sensors were first characterized through benchtop testing in a benchtop colon phantom against a reference pressure sensor, and with artificial stools of varying water content. The functionality of the sensors was further evaluated in 2 preliminary acute in vivo experiments with the device powered through a power source.Yorkshire pigs, approximately 4–5 months old, weighing 40–60 kg were used for the in vivo experiment. Each pig was anaesthetized and the sensor was affixed to the rectum first and then to the colon using a mucosal clip. Recording was done for 5 hours and data was transmitted wirelessly to the recording device. Artificial stool of different saline concentration was inserted into the rectum to simulate different conductivity and conductance of the stool. Artificial stool was also mixed with radio contrast to take CT images of the stool location.ResultsPower consumed by the device was 140 μA when on and 2 μA when off, with an expected battery lifetime between charges of 40 hours. Benchtop results showed that the pressure sensors detected controlled pressure changes with a root mean square error (RMSE) of 3.7 cmH20. Regression analysis for the conductivity measurements showed a maximum error of 19% and a RMSE of 675 μS/cm. For volume estimation, there was a maximum error of 26% and a RMSE of 4.5 mm for the diameter of a stool. In vivo conductivity measurements were qualitatively sensitive to stools with different conductivities, and to increasing stool volume. The pressure sensors recorded changes in bowel pressure in response to abdominal compressions and slow‐wave bowel contractions.ConclusionSmall wireless, bowel sensors can help us understand the physiologic functions of the bowel and its connection with the nervous system. Initial testing indicated the feasibility of this device in pigs in measuring pressure and volume inside the bowel.Support or Funding InformationThis work was funded by the NIH Stimulating Peripheral Activity to Relieve Conditions (SPARC) program, NIH grant number OT2OD023873.