Intestinal transport function examination mainly involves putting markers into the gastrointestinal tract, and by observing the metabolism, operation and distribution of the markers in the gastrointestinal tract, the operation rate of the gastrointestinal tract contents can be inferred, thereby judging the transit function of the gastrointestinal tract.
There are three main types of markers commonly used, namely.
① Catabolic class (e.g. lactose, salicyl dipyridamole, etc.);
(ii) X-ray impermeable.
③ Radionuclides (such as technetium 99, sulfur 131, indium 111, etc.). The catabolic and radiopaque X-ray markers are mainly used to detect small intestinal and colonic transport functions, respectively, while the radionuclide markers can be used to examine small intestinal and colonic transport functions.
The usual reference to the intestinal transport function test refers mainly to the colonic transport function test. In this test, the application is somewhat limited because the nuclide marker test method requires special equipment and the patient is exposed to nuclides. The impermeable X-ray marker test method, on the other hand, is widely used because of its simplicity, convenience, patient painlessness, no need for special equipment, and low price.
1.Small intestine transport test
(1)Mechanism
There are various methods to determine the transport function of the small intestine, and the more commonly used method is the exhaled gas hydrogen concentration measurement. The mechanism is: after the subject takes lactose orally, it is transported to the colon through the small intestine, and the lactobacillus in the colon can decompose lactose to produce hydrogen gas, which is excreted from the lungs through blood circulation, and the small intestine transport function is judged by measuring the duration of the increase of hydrogen concentration in the exhaled gas after taking lactose orally.
This method is simple, non-invasive and easily accepted by patients. However, there are many influencing factors, such as abnormal gastric emptying, diarrhea, dysbiosis of intestinal flora and certain drugs, which can affect the accuracy of the results and give rise to false positives or false negatives.
(2) Method
No high-fiber diet for 1 month before the test, fasting for 15 h. At the beginning of the test, 12 g of lactulose (dissolved in 120 ml of water) was administered orally. End-expiratory lung gas was collected at 15-min intervals before and 3 h after the administration of lactulose, and the hydrogen content was measured. The patient was placed in a sitting position during the examination, and fasted from food, water and smoking. Hydrogen solubility was measured with a hydrogen chromatography analyzer, and a gas with a hydrogen concentration in the megaratio ratio (ppm, or 10-6) was used as a standard. The subject was considered to have exhaled hydrogen when the exhaled hydrogen exceeded 20 ppm. When the second consecutive exhaled hydrogen exceeds 5 ppm at this baseline of 20 ppm, it is considered as an indicator of the concentration of exhaled hydrogen in the fasted state. This time is the oral-blind transport time.
(3)Normal reference value 48min±13min.
(4)Clinical significance of small intestine transport test
Some patients with colonic slow-transport constipation have a combination of small intestinal transport retardation. It is thought that constipation is a problem of total intestinal involvement. However, it is not clear whether this slow small bowel motor space is the cause of constipation itself or the result of an inhibitory reflex to partial dysfunction of the distal part of the intestine (colon). It is also believed that the slow transport constipation function of the colon is examined to exclude the presence of small bowel transport dysfunction, otherwise the procedure is not effective.
Constipation is a symptom that accompanies many diseases, and in the identification of the causes of constipation, the small intestine and colon transport test is only an important method of examining the state of the intestinal transit function itself, and should be used in conjunction with other functional tests in clinical applications to evaluate constipated patients comprehensively. Small intestine transport test can also be used to diagnose small intestine motor dysfunction diseases, such as pseudo small intestine obstruction, vagotomy diarrhea, etc.
2.Colonic transport test
The main methods to determine the transport function of the colon are: opaque marker tracking method and radionuclide scintillation scanning method. The former is widely used in clinical practice because of its simplicity, safety, non-invasiveness and no need for special equipment. In contrast, radionuclide scintigraphy is limited by the need for special equipment and exposure of patients to nuclides. The opaque marker tracking method is described here.
(1) Mechanism
The normal adult colonic prograde propulsion speed is about 8 cm/h retrograde propulsion speed is about 3 cm/h net propulsion distance of about 5 cm per hour. colonic propulsion speed can be affected by many factors. For example, after a meal, the prograde velocity may increase to 14 cm/h, but the retrograde velocity may remain unchanged; after intramuscular injection of certain parasympathetic drugs, the net propulsion velocity may increase to 20 cm/h. In some patients with constipation, the net propulsion velocity may be as slow as 1 cm/h. The opaque marker tracing method involves the oral administration of an x-ray-opaque marker, which is mixed with the intestinal contents and is closer to physiological. The movement of the colon is observed by radiography.
Although the colonic transport time reflects the functional state of the neuromuscles of the colonic wall, after a single oral dose of 20 radiopaque markers, not all 20 reach the cecum at the same time, and the movement of the markers in the colon does not advance in a group. This is due to the fact that the running time of the marker from the mouth to the cecum is influenced by the meal time, food composition, gastric emptying function and small intestine transport function. Therefore, this method can only understand the general outline of colonic motility and cannot fully reflect the functional status of each segment of the colon.
To ensure accurate and reliable results, the marker should not be too heavy and should be similar to the specific gravity of chyme or feces, and show clear, non-absorbable, non-toxic and non-irritating. At present, commercial markers are available at home and abroad.
(2) Method
From 3 d before the examination, stop using all drugs that may affect the function of the digestive tract and give a diet according to certain standards (containing about 14 g of fiber per day), and maintain normal habits without special changes. Since laxatives and enemas cannot be used during the examination, for those who have not been able to defecate for many days and are expected to have difficulty in continuing to complete the examination, they will be prepared as required after defecation.
The luteal phase should be avoided for women of childbearing age because the intestinal transit becomes slower during the luteal phase. After breakfast on the day of the examination, 20 capsules containing an opaque X-ray marker are swallowed. One abdominal plain film was taken on the 5th and 7th day after taking the marker. The method of reading the film: a line was made from the spinous process of the thoracic vertebra to the spinous process of the 5th lumbar vertebra and then a tangent line was made from the spinous process of the 5th lumbar vertebra to both sides of the pelvic outlet, and the large intestine was divided into 3 regions: the right colonic region, the left colonic region, and the rectosigmoid region. The marker location was described by these 3 regions. The marker shadow is easy to overlap with the spine and iliac bone and must be searched carefully. Sometimes the colon, liver and spleen curves are located higher and not all of them are shown on the X-ray, which should be noted.
(3) Normal reference value
In normal adults, after oral administration of the marker, all the marker can enter the right hemicolectum within 8 h. Then the marker can be stored in the right hemicolectum for 38 h, the left hemicolectum for 37 h and the rectosigmoid colon for 34 h. The normal reference value of the colonic transport test is: at least 80% of the marker (16 grains) is excreted in the 5th day after oral administration of the marker, and all of it is excreted in the 7th day.
(4) Clinical significance
It is an important test for the diagnosis of colonic incompetence type constipation at present. It can distinguish slow transport type of colon from outlet obstruction type of constipation.
In addition to the prolonged intestinal passage time of markers, constipation can be divided into four types according to the characteristics of marker distribution.
(1) Colonic slow transport type: the marker is diffusely distributed throughout the colon.
② Exit obstruction type: the marker accumulates at the junction of the rectosigmoid colon. This type is more common in patients with megacolon, decreased rectal sensory function and pelvic floor dyslaxation syndrome.
(3) Left-sided slow colon type: the markers are collected in the left colon and rectosigmoid area, which may be due to weakness of left colon propulsion or secondary to outlet obstruction.
④Sluggish right colon type: the markers are mainly concentrated in the right colon, which is rare.