Wireless insufflation of the gastrointestinal tract

Abstract

Despite clear patient experience advantages, low specificity rates have thus far prevented swallowable capsule endoscopes from replacing traditional endoscopy for diagnosis of colon disease. One explanation for this is that capsule endoscopes lack the ability to provide insufflation, which traditional endoscopes use to distend the intestine for a clear view of the internal wall. To provide a means of insufflation from a wireless capsule platform, in this paper we use biocompatible effervescent chemical reactions to convert liquids and powders carried onboard a capsule into gas. We experimentally evaluate the quantity of gas needed to enhance capsule visualization and locomotion, and determine how much gas can be generated from a given volume of reactants. These experiments motivate the design of a wireless insufflation capsule, which is evaluated in ex vivo experiments. These experiments illustrate the feasibility of enhancing visualization and locomotion of endoscopic capsules through wireless insufflation.

Fig. 1

(a) Image from a colonoscope of the colon prior to insufflation. (b) Image after insufflation illustrating the ability to view a larger portion of the intestinal surface. Also pictured is a capsule robot with legs [10]. (c) Magnetically actuated capsule [11] whose motion is impeded by the collapsed intestinal folds.

Fig. 2

Experimental setup for determining how much insufflation is required to improve visualization in the large intestine. Ex vivo porcine intestine was arranged in a phantom model to simulate the shape of the human colon within the abdomen.

Fig. 3

Results of the colon inflation experiment pictured in Fig. 2. (a) Intestine in its deflated state with no markers visible. (b) With just 50 mL of insufflation, four of the nine markers became visible. (c) At 200 mL, all nine markers first came into the field of view. (d) Threshold above which all nine markers were consistently visible was 450 mL. (e) Intestine in its fully inflated state at 1500 mL of insufflation.

Fig. 4

Results of the locomotion experiment at different inflation increments. (a) Intestine in its deflated state, where no capsule motion was possible. (b) With just 50 mL of insufflation, the capsule moved an average distance of 67 mm. (c) At 100 mL, the capsule moved an average distance of 150 mm. (d) At 150 mL, the capsule moved an average distance of 188 mm. (e) At 200 mL, the capsule moved an average distance of 243 mm. (f) At 250 mL, the capsule was able to move the entire length of the colon (300 mm), with an average distance of 295 mm.

Fig. 5

Experimental setup for reacting known volumes of the base, the acid, and water to measure carbon dioxide production. The powdered acid and base were placed into the flask, and water was added through a syringe to start the reaction. The gas generated displaced water in the holding flask which was measured in a graduated cylinder.

Fig. 6

Carbon dioxide generated by the four combinations of potassium bicarbonate (PB), sodium bicarbonate (SB), acetic acid (AA), and citric acid (CA). The average output is presented as a line, and the minimum and maximum values are presented with error bars. From this, we observe that the PB+CA reaction generated the most gaseous output.

Fig. 7

Carbon dioxide generated by varying ratios of water to reactants for potassium bicarbonate and citric acid. The average output is presented as a line, and the maximum and minimum values are presented with error bars. From this, we observe that the 1:2 water:reactant ratio produced the most gaseous output.

Fig. 8

Carbon dioxide produced by varying total initial volumes of reactants (potassium bicarbonate, citric acid, and water). The average output is presented as a line, and the maximum and minimum values are presented with error bars. From this, we observe that a larger initial volume produces a larger gaseous output, following a linear relationship.

Fig. 9

Cross section views of the capsule in its closed (top) and opened (bottom) state.

Fig. 10

Capsule prototype and its components. The upper chamber is designed to hold the acid solution, while the lower chamber holds the powdered base. In the presence of an external magnetic field, the two magnetic ball valves move toward the top of the upper chamber, and the citric acid solution mixes with the potassium bicarbonate. The CO₂ produced is vented through small perforated holes just under the midline of the capsule.

Fig. 11

Experimental setup for ex vivo insufflation capsule experiments, consisting of a heated water bath, an endoscope, and an external magnet attached to a robotic arm.

Fig. 12

Endoscopic view (left) and external view (right) demonstrating the level of insufflation provided by a single internal reaction capsule approximately 4 min after activation, at which point six of the nine markers were visible.

Fig. 13

Endoscopic view (left) and external view (right) demonstrating the level of insufflation provided by three internal reaction capsules approximately 4 min after the initial activation. At this point, eight of the nine markers were visible on the intestinal wall.