Gastrointestinal Motility Recording Using Balloon Insertion

Summary

This protocol outlines a method for recording gastrointestinal motor activity. It employs a condom and a plastic tube to create a system that visualizes gastrointestinal motility through balloon pressure. This method can be used in the study of diseases related to gastrointestinal motility disorders.

Abstract

Gastrointestinal motility is one of the most important physiological functions of the digestive system. The migrating motor complex (MMC) is a characteristic form of movement that occurs in the gastrointestinal tract during fasting. The MMC is present in many species, including humans. Although the physiological role of the MMC is not completely understood, its abnormalities are associated with various diseases. The measurement of gastrointestinal motility is important for the diagnosis of gastrointestinal diseases. Thus, a system was constructed using a rubber condom and polyethylene (PE) tube, with one side placed in the gastrointestinal tract of the mice and the other side connected to the pressure transducer. Gastrointestinal movements were visualized when the balloon was squeezed during gastrointestinal movements. This study work provides a detailed protocol of the system's design and operation and shows representative results demonstrating its effectiveness. By using this system device, gastrointestinal motor function can be recorded in vivo. This provides additional approaches for future studies of gastrointestinal disorders.

Introduction

The migrating motor complex (MMC) is a special pattern of circulatory movement of the gastrointestinal tract in humans and other animals, which occurs in the fasting and inter-digestive periods¹. The MMC is involved in the transport of undigested foods and helps in bacterial transport from the small intestine into the large intestine². Code and Marlett³ divided the MMC into four phases. In phase I, the smooth muscles of the gastrointestinal tract are quiescent. In phase II, gastrointestinal peristaltic activity increased. In phase III, the contractile activity is high, which is referred to as a characteristic phase of the MMC. Because the pylorus remains open, allowing undigested food to move into the small intestine, phase III has a sudden onset and ends with a burst of contractions with maximal amplitudes and durations. Phase IV is characterized by a rapid decrease in contractions, which is a short transition to the next cycle. Given the crucial role of the MMC, it has become one of the hot research topics for scientists.

Properly functioning MMC is essential for the maintenance of gastrointestinal homeostasis. MMC abnormalities are associated with various gastrointestinal disorders, such as gastroparesis, pseudo-obstruction, and bacterial overgrowth in the small intestine¹. Abnormalities in different phases of the MMC are associated with various gastrointestinal diseases. An extended phase I may result in delayed gastric emptying. This is often seen in patients with diabetes or idiopathic gastroparesis⁴. Abnormal phase II contraction can lead to slower gastric emptying, which can cause bloating, early satiety, etc. Reduced phase II activity can lead to the retention of small intestinal contents, increasing the risk of bacterial overgrowth⁵. Reduced or absent phase III activity can lead to the retention of intestinal contents, resulting in chronic intestinal obstruction^6,7. Phase IV abnormalities may be associated with gastric contents refluxing into the esophagus and worsening reflux symptoms⁸. Meanwhile, anorexia nervosa is also associated with phase IV abnormalities⁹. Overall, understanding the temporal characteristics of MMC and its relationship with the disease is valuable in the diagnosis and treatment of gastrointestinal disorders.

Therefore, we introduce a method for measuring MMC by visualizing it. We believe that this technique will provide further information on gastrointestinal dynamics.

Protocol

The study protocol was approved by the Institute of Acupuncture and Moxibustion Animal Care and Use Committee (Approval No. Y2023-03-14-02). The United States National Institutes of Health Guide for the Care and Use of Laboratory Animals was followed in this study.

1. Balloon capsule generation

1. Break the syringe needle, remove the metal side, and insert it into the polyethylene (PE) tube.
2. After step 1.1, insert the PE tube into the condom and tie it with a medical suture at 0.5 cm from the end. Make sure the suture is tight and does not leak when ligated.
3. Cut the remaining condom to ensure that the balloon is smooth.
4. Fill the capsule with pure water to empty the air in the balloon and catheter and connect the catheter to the motility pressure transducer through a medical three-way valve.

2. Surgery

1. Use 6-8-week-year-old SD male/female rats. Before the surgery, deprive the rats of food but not water for 12-18 h to ensure the stomach is empty.
2. Anesthetize the rat with isoflurane (maintained with 2% isoflurane gas), shave the abdominal area, sterilize the rat with iodaphor.
3. Place it supine (Figure 1A), and maintain the body temperature using a heating blanket.
4. Make an incision along the midline of abdominal skin at a site 1 cm below the xiphoid process, approximately 2 cm in length (Figure 1B). Separate layer by layer from the skin to the muscle to make sure other internal organs would not be cut.
5. Expose the stomach and make an incision along the duodenum approximately 2 cm away from the pylorus, with an incision length of 0.2 cm. Place the balloon capsule into the duodenum through the incision and push it upward along the duodenum, but do not place it into the gastric antrum through the pylorus (Figure 1C). Secure the surgical incision and fix the catheter.
6. Finally, use sterile gauze (moistened with saline) to cover the incision. Connect the other side of the tube to a pressure transducer.
7. At this time, a rectum recording procedure is feasible. Rectal motion recording does not require surgery. The balloon would be inserted directly through the anus 0.5-1 cm.

3. Gastric pressure recording

1. Before recording, fill the pressure transducer with double distilled water.
2. Open the neuro amplifier, data acquisition unit, and data analysis software. Set the recording system parameters of the instrument with a sampling frequency of 1 kHz. Open the three-way valve to make sure the pressure in the bulb is connected with the air pressure. Then, turn the zero knob on the amplifier to adjust the baseline to 0 mmH₂O.
3. Inject approximately 0.5 mL of the double distilled water into the balloon and maintain the pressure at 20-40 mmH₂O by slightly adjusting the water volume in the balloon.
4. Connect the needle hub to the three-way valve and the other side to the pressure transducer, which converts the mechanical signal into an electrical signal.
5. After the wave shape is stabilized (the baseline maintained stably for >30 min), start recording the duodenum pressure.
   NOTE: The schematic diagram is presented in Figure 1D, the completed balloon insertion system is shown in Figure 1E, and the recording setup is shown in Figure 1F.
   NOTE: During the experiment, physiological status indicators such as respiration, corneal reflex, and skin color are monitored closely. A heated blanket is also needed. The experiment should be stopped immediately if any abnormalities in the rats' physiological condition are observed.

4. Data analysis

1. Use the data analysis software to analyze the signal of gastrointestinal tract movements. Obtain the frequency and amplitude of the contraction wave from the software.
2. Use the right mouse button to add the cursors in the software to obtain the duration between the two cursors. Similarly, use the right mouse button to add horizontal lines to know the amplitude.
3. Analyze gastrointestinal tract movements based on the changes in duration and amplitude. As shown in Figure 2A, a smooth horizontal line is noted as a baseline. The amplitude and duration above the baseline were measured to determine the different stages of MMC.

Results

Figure 2A shows the trajectory of MMC traced in the duodenum of normal rats. In normal rats, gastric motility is characterized by regular and rhythmic contractions, which can be observed through the waveform recorded by the balloon capsule. The sex of the experimental animals does not affect the MMC, and there are no statistically significant differences between the genders. In Figure 2A, the MMC waveform typically exhibits four phases:

Discussion

This protocol outlines a method of detecting gastrointestinal motility in vivo by visualizing the MMC process. This method is important for studying gastrointestinal dynamics. First, when making the balloon capsule, make sure that the interface is well connected and ensure that the medical suture is tight and not leaking. Before the surgery, the balloon capsule can be tested in a 50-mL beaker filled with deionized water. The whole system is placed in deionized water, and air is injected into the balloon capsule....

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Animal physiological signal data collector	Cambridge Electronic Design	Micro1401-4	For gastrointestinal motility recording (data acquisition system)
Biosignal amplifier	Digitimer-neurolog system	NL900D	For gastrointestinal motility recording (neuro amplifier)
Gastrointestinal motility transducer	Beijing Xinhangxingye Science and Trade Co., Ltd.	WS100	For gastrointestinal motility monitoring
Heating pad	Kobayashi Pharmaceutical Co., Ltd., China	03721	For maintaining the body temperature of rats; 95 mm ´ 70 mm
Hypodermic needle	Shanghai Kindly Enterprise Development Group Co., Ltd.	GB15811-2001	For the production of water balloons
Isoflurane	Lunan BETTER Pharmaceutical Co., Ltd.	H20020267	For the anesthesia of rats
Natural latex smooth surface condom	Okamoto, Japan	20172186398	For the production of water balloons
Polyethylene catheter	Beijing Tajiin Technology Co., Ltd.	PE90	For the production of water balloons; outer diameter of 0.94 mm and an inner diameter of 0.51 mm
Powerlab signal acquisition and analysis system	AD Instruments, Australia	PL3508	For gastrointestinal motility monitoring
Software Spike	Cambridge Electronic Design	Spike 2.0	For gastrointestinal motility waveform recording (data analysis software)
Sterile gauze	Hebei Kangji Medical Instrument Co., Ltd.	20232140292	For surgical operations
Three-way valve	Jiangsu Essica Healthcare Co., Ltd.	20203140477	For gastrointestinal motility monitoring