Gas supply control method, gas supply control device, and gas supply control system

Abstract

[Problem] To provide a gas supply control method for quickly and accurately performing examination. [Solution] According to the present invention, a gas from a gas supply source is supplied to a lumen of a subject at a first flow rate, the pressure of the gas in the lumen is measured, and the gas is supplied to the lumen at a second flow rate lower than the first flow rate when the pressure reaches a first pressure.

Description

Gas supply control method, gas supply control device, and gas supply control system

[0001] Embodiments of the present invention relate to a method for controlling gas supply to a lumen of a subject, a gas supply control device for supplying gas to a lumen of a subject, and a gas supply control system for supplying gas to a lumen of a subject.

[0002] Gastroesophageal reflux disease (hereinafter referred to as "GERD") is a functional disorder in which, for example, the function of the gastric cardia is impaired, causing gastric juice to reflux into the esophagus. Methods for diagnosing GERD (hereinafter referred to as "GERD diagnostic methods") include 24-hour esophageal pH monitoring and 24-hour esophageal impedance pH monitoring.

[0003] As a method for diagnosing GERD, a method of observing the relaxation state of the lower esophageal sphincter (LES) in the cardiac region of the stomach using an endoscope is being adopted in order to reduce the burden on the subject.

[0004] International Publication No. 2021 / 166127 discloses an endoscopic system that supplies gas to a subject's lumen while measuring the pressure within the lumen and diagnoses GERD based on the pattern of pressure changes.

[0005] Another esophageal dysfunction is achalasia, which occurs when abnormalities occur in the function of the lower esophageal sphincter, making it difficult for food to pass from the esophagus to the stomach, which is the opposite of GERD.

[0006] International Publication No. 2021 / 166127

[0007] In order to further reduce the burden on the subject, there has been a demand for a diagnostic method and device that can be completed in a shorter time and is more accurate.

[0008] An object of embodiments of the present invention is to provide a gas supply control method that performs inspections quickly and accurately, a gas supply control device that performs inspections quickly and accurately, and a gas supply control system that performs inspections quickly and accurately.

[0009] In one embodiment of the gas supply control method, gas from a gas supply source is supplied to a lumen of a subject at a first flow rate, the pressure of the gas in the lumen is measured, and when the pressure reaches the first pressure, the gas is supplied to the lumen at a second flow rate that is lower than the first flow rate.

[0010] The gas supply control device of one embodiment comprises a first tube communicating with a lumen inside the subject's body, a pressure sensor disposed in the first tube for measuring the pressure of the gas, a second tube communicating with the lumen and supplying the gas from a gas supply source to the lumen, a valve for adjusting the flow rate of the gas supplied to the lumen via the second tube, and a controller for controlling the valve based on the pressure detected by the pressure sensor, wherein the controller controls the valve to supply the gas to the lumen at a first flow rate, and when the pressure reaches the first pressure, to supply the gas to the lumen at a second flow rate that is lower than the first flow rate.

[0011] a pressure sensor disposed in the first tube for measuring a pressure of the gas; a second tube for supplying the gas from a gas supply source to the lumen via the gas and water pipe; a valve for adjusting the flow rate of the gas supplied to the lumen via the second tube; and a controller for controlling the valve based on the pressure detected by the pressure sensor. The controller supplies the gas to the lumen at a first flow rate, and when the pressure reaches the first pressure, controls the valve to supply the gas to the lumen at a second flow rate that is lower than the first flow rate.

[0012] According to the embodiments of the present invention, it is possible to provide a gas supply control method that performs inspections quickly and accurately, a gas supply control device that performs inspections quickly and accurately, and a gas supply control system that performs inspections quickly and accurately.

[0013] FIG. 1 is a diagram illustrating the overall configuration of a gas supply control system including a gas supply control device according to an embodiment. FIG. 2 is a diagram illustrating the configuration of a gas supply control system including a gas supply control device according to an embodiment. FIG. 3 is a flowchart of a pressure control method according to an embodiment. FIG. 4 is a graph illustrating pressure changes in the lumen of a GERD patient according to an embodiment. FIG. 5 is a graph illustrating pressure changes in the lumen of a healthy subject using a conventional device. FIG. 6 is a graph illustrating pressure changes in the lumen of a healthy subject using an embodiment. FIG. 7 is a graph illustrating pressure changes in the lumen of an achalasia patient according to an embodiment. FIG. 8 is a diagram illustrating the configuration of a gas supply control system including a gas supply control device according to a first modified embodiment. FIG. 9 is a graph illustrating pressure changes in the lumen of a healthy subject using a first modified embodiment. FIG. 10 is a graph illustrating pressure changes in a second modified embodiment. FIG. 11 is a graph illustrating pressure changes in a lumen of a healthy subject using a third modified embodiment.

[0014] Hereinafter, embodiments will be described with reference to the drawings. The drawings based on the embodiments are schematic. The relationship between the thickness and width of each part in the drawings, the thickness ratio of each part, etc., differ from the actual ones. The drawings also include parts with different dimensional relationships and ratios. Some components will not be shown or labeled.

[0015] <Embodiment> A gas supply control system 1 according to the embodiment shown in FIG. 1 includes an endoscope 9, a gas supply control device 10, a gas supply unit 20, a display 31, a video processor 43, and a light source 41.

[0016] The endoscope 9 includes an elongated insertion section 93 that is inserted into the subject, an operating section 94 provided at the proximal end of the insertion section 93, a universal cord 95 extending from the operating section 94, and a connector 96. The operating section 94 includes a bending operation knob and a plurality of buttons for operating the endoscopic functions. The insertion section 93 of the endoscope 9 includes, in order from the distal end, a distal end 93A, a freely bendable bending section 93B provided at the proximal end of the distal end 93A, and an elongated flexible tube 93C provided at the proximal end of the bending section 93B. Although not shown, the distal end 93A is provided with an imaging unit, an illumination optical system, and an opening for a forceps channel 91 ( FIG. 2 ). The forceps channel 91 is a tube that passes through the insertion section 93 from an insertion port 97 of the operating section 94 to the opening of the distal end 93A.

[0017] The connector 96 is connected to the optical fiber bundle 42 of the light source 41, the cable 44 of the video processor 43, and the second tube (air supply tube) 21 of the air supply unit 20. Illumination light generated by the light source 41 is guided via the optical fiber bundle 42 to the illumination optical system of the distal end 93A. In response to button operation of the operation unit 94, the air supply unit 20 ejects a fluid (gas or liquid) from an opening in the distal end 93A via the universal cord 95, the operation unit 94, and an air / water supply tube 92 ( FIG. 2 ) passing through the insertion unit 93. In other words, the air supply unit 20 is an air / water supply unit capable of supplying not only gas but also liquid, but in the description of the present invention, only gas is used as the fluid. Air / water supply can be switched by operating the button of the operation unit 94. The second tube 21 may be connected to the operation unit 94.

[0018] The video processor 43 processes the image pickup signal from the imaging unit of the distal end portion 93A and displays an endoscopic image on the display 31.

[0019] The gas supply control system 1 of this embodiment is configured by adding a gas supply control device 10 to the above-described endoscope system.

[0020] As shown in FIG. 2 , the gas supply control device 10 includes a first tube 11 , a pressure sensor 14 , and a controller 15 .

[0021] The first tube 11 is connected to an insertion port 97 of the forceps channel 91 of the endoscope 9. When the tip 93A of the insertion section 93 of the endoscope 9 is inserted into the stomach 100, which is a lumen of the subject, the first tube 11 communicates with the inside of the stomach 100 via the forceps channel 91. A pressure sensor 14 is disposed in the first tube 11. The pressure sensor 14 measures the pressure of gas inside the first tube 11. Because the first tube 11 communicates with the stomach 100, the pressure sensor 14 measures the pressure of gas inside the stomach 100.

[0022] For example, a controller 15 including a CPU controls the entire gas supply control system 1. A memory 16 stores setting conditions of the gas supply control system 1 and the like.

[0023] The air supply unit 20 has a second tube 21, a flow rate sensor 26, a pressure vessel 24, and a valve 25. The second tube 21 is connected to an air / water supply pipe 92 of the endoscope 9. When a tip portion 93A of an insertion section 93 of the endoscope 9 is inserted into a stomach 100, which is a lumen of the subject, the second tube 21 communicates with the inside of the stomach 100 via the air / water supply pipe 92.

[0024] Gas, for example, carbon dioxide gas, supplied from a cylinder 23 serving as a gas supply source is decompressed by a regulator (not shown) and sent to the second tube 21 via a pressure vessel 24 .

[0025] The gas supply control system 1 diagnoses GERD and achalasia by measuring the gas pressure (internal pressure) within the stomach 100 using the pressure sensor 14 while supplying gas from the gas supply unit 20 to the stomach 100 of the subject via the endoscope 9. The pressure data is displayed in chronological order on the display 31. The display 31 displays the pressure data together with the endoscopic image, but may also be a display dedicated to pressure data. The speaker 32 notifies the user by voice, for example, of the occurrence of an abnormality.

[0026] As will be described later, the controller 15 of the gas supply control system 1 of this embodiment starts supplying gas at a first flow rate F1, and when the internal pressure of the stomach 100 reaches a first pressure P1, supplies gas to the stomach 100 at a second flow rate F2 that is lower than the first flow rate F1. The first pressure P1 is a GERD diagnostic pressure that serves as a criterion for diagnosing GERD. The first flow rate F1 is set, for example, to be higher than the flow rates of conventional gas supply control systems, and the second flow rate F2 is set, for example, to be lower than the flow rates of conventional gas supply control systems. The first flow rate F1, the second flow rate F2, and the first pressure P1 are stored, for example, in the memory 16.

[0027] Therefore, the gas supply control system 1 can perform diagnosis more quickly and accurately than conventional gas supply control systems.

[0028] The configuration of the gas supply control system 1 described above is merely an example, and the present invention is not limited to the above configuration.

[0029] For example, the valve 25 may be disposed at a position closer to the endoscope 9 than the pressure vessel 24 of the second tube 21. The gas supply control system may also have a microphone that collects sounds made by the subject during the examination. Instead of detecting a pressure drop due to burping, the controller 15 may detect the sound of burping coming from the subject's mouth with the microphone and perform control to stop the gas supply. The gas supply control system may also have a video recorder and video printer that record images displayed on the display 31.

[0030] <Gas Supply Control Method> A gas supply control method performed by the gas supply control system 1 will be described with reference to the flowchart of FIG.

[0031] <Step S10> Tube Connection The first tube 11 is connected to the insertion port 97 of the forceps channel 91 of the endoscope 9. The second tube 21 is connected to the air / water supply pipe 92 of the endoscope 9.

[0032] <Step S11> Insertion The distal end portion 93A of the insertion section 93 of the endoscope 9 is inserted into the stomach 100 of the subject. Note that the cardia may be observed using an imaging unit provided at the distal end portion 93A.

[0033] <Step S12> Start of gas supply (first flow rate) The controller 15 controls the valve 25 of the gas supply unit 20 to supply gas into the stomach 100 at a first flow rate F1. The first flow rate F1 is, for example, 1.5 mL / s to 2.5 mL / s. The valve 25 is, for example, a type of solenoid valve, and has an adjustment valve using an electromagnetic coil in the drive unit. When a current is passed through the electromagnetic coil, a magnetic force is generated, which attracts the plunger, thereby opening and closing the valve. The magnitude of the current passed through the electromagnetic coil controls the opening of the valve, and the gas flow rate is adjusted to a predetermined value.

[0034] <Step S13> First time course? Figure 4 shows the change in intragastric pressure with respect to the insufflation time in a patient with GERD, whose gastric cardia function is impaired. Note that intragastric pressure reflects respiratory fluctuations and is higher during inspiration than during expiration. Therefore, the measured pressure repeatedly increases and decreases according to the respiratory cycle.

[0035] In a GERD patient, even if gas is insufflated into the stomach 100, gas leaks from the cardia. Therefore, even after a predetermined first time T1 has elapsed since the start of gas insufflation, the pressure P does not reach, for example, the first pressure P1, which is the GERD diagnostic pressure. The first time T1 and the first pressure P1 are set appropriately. For example, the first time T1 is 5 minutes, and the first pressure P1 is greater than 16 mmHg and less than 19 mmHg.

[0036] When the time from the start of gas supply, in other words, the gas supply time at the first flow rate F1, has passed the first time T1 (S13, YES), the process proceeds to step S14.

[0037] The controller 15 may calculate the rate of increase ΔP / s of the pressure P. If the rate of increase ΔP / s is slower than a predetermined first rate of increase ΔP1 / s, the process may proceed to step S14 and end the test even before the first time T1 has elapsed, since GERD can be determined to have occurred, in order to speed up the test.

[0038] The first rate of increase ΔP1 / s is set to, for example, 50% to 75% of the rate of increase ΔP / s of a healthy subject. The first rate of increase ΔP1 / s is, for example, 0.1 mmHg / s. To prevent erroneous determination, it is preferable to use an average rate of increase over an examination time that is at least 20% or more of the first time T1 to calculate the rate of increase ΔP / s.

[0039] Furthermore, if the rate of increase ΔP / s is slower than a predetermined first rate of increase ΔP1 / s, the controller 15 may reduce the amount of gas delivered to a flow rate less than the first flow rate F1, for example, 1.0 mL / s-2.0 mL / s.

[0040] <Step S14> Stopping Air Supply Air supply from the air supply unit 20 is stopped by control of the controller 15, and the process ends.

[0041] <Step S15> Pressure drop due to burping? In patients with mild GERD, even low internal pressure can cause gas in the stomach 100 to be released through the mouth by burping, resulting in a sudden drop in internal pressure. When the controller 15 detects a sudden drop in pressure (YES), the process proceeds to step S14. A sudden drop is, for example, a drop rate of more than -5 mmHg / s. Note that to prevent a sudden decrease in flow rate when transitioning from step S13 or step S15 to S14 (stopping gas supply), the gas supply may be stopped (S14) after the gas supply amount is reduced to a predetermined flow rate (for example, the second flow rate F2).

[0042] <Step S16> Pressure>First Pressure? Air supply at the first flow rate F1 continues until the pressure reaches the first pressure P1.

[0043] <Step S17> Second Flow Rate Figure 5 is a graph showing changes in internal pressure in a healthy individual in a conventional gas supply control system. When gas is supplied to stomach 100 at a flow rate F0, the internal pressure gradually increases. When the internal pressure reaches standard pressure PM, the gas in stomach 100 is released through the mouth by burping, and the internal pressure suddenly decreases. The standard pressure PM for a healthy individual is, for example, greater than 18 mmHg and less than 25 mmHg.

[0044] However, in conventional gas supply control systems, if the flow rate F0 is low, the time TM until the internal pressure reaches the standard pressure PM becomes long, and the inspection time becomes long. On the other hand, if the flow rate F0 is high, there is a risk that the error in the time TM until the internal pressure reaches the standard pressure PM will be large, and the diagnostic accuracy will decrease.

[0045] 6, in the gas supply control system 1, when the pressure reaches the first pressure P1 (time TA), the gas flow rate is reduced from the first flow rate F1 to the second flow rate F2. The second flow rate F2 is preferably less than 75% of the first flow rate F1, and more preferably less than 50%. The second flow rate F2 is, for example, 0.5 mL / s to 1.5 mL / s.

[0046] That is, the first flow rate F1 is greater than the flow rate F0 in a conventional gas supply control system, and the second flow rate F2 is less than the flow rate F0.

[0047] Depending on the subject, the rate of increase ΔP / s of the pressure P may suddenly increase during air supply. In this case, even if the flow rate is reduced after the pressure reaches the first pressure P1, there is a risk of a large error in the time TM until the internal pressure reaches the standard pressure PM.

[0048] The controller 15 of the gas supply control system 1 calculates the pressure rise rate ΔP / s, and when the rise rate ΔP exceeds a predetermined second rise rate ΔP2 / s, gas may be supplied at a second flow rate F2 even if the pressure is below the first pressure P1.

[0049] <Step S18> Pressure Drop Due to Burping? In a healthy person, when the internal pressure of the stomach 100 becomes higher than the standard pressure PM, the gas in the stomach 100 is released from the mouth by burping, and the pressure drops suddenly.

[0050] When the controller 15 detects that the pressure has dropped suddenly (YES), the process proceeds to step S14.

[0051] <Step S19> Pressure≧Second Pressure? Air supply continues until the pressure reaches a second pressure P2 that is greater than the first pressure P1.

[0052] 7, in an achalasia subject with an abnormality in the function of the lower esophageal sphincter, gas in the stomach 100 is not released by burping even when the pressure reaches a second pressure P2, which is an allowable pressure at which the subject feels extremely uncomfortable. The second pressure P2 is determined appropriately depending on the condition of the subject (age, sex, etc.), and is, for example, 25 mmHg or higher.

[0053] If the pressure reaches the second pressure P2 (YES), the process proceeds to step S14.

[0054] As described above, the gas supply control method supplies gas from a gas supply source to a lumen of a subject at a first flow rate F1, measures the pressure of the gas in the lumen, and when the pressure reaches a first pressure P1, supplies the gas to the lumen at a second flow rate F2 that is less than the first flow rate F1.

[0055] The gas supply control system 1 comprises a first tube 11 communicating with a lumen inside the subject's body, a pressure sensor 14 disposed in the first tube 11 for measuring the pressure of the gas, a second tube 21 communicating with the lumen and supplying the gas from a gas supply source to the lumen, a valve 25 for adjusting the flow rate of the gas supplied to the lumen via the second tube 21, and a controller 15 for controlling the valve 25 based on the pressure detected by the pressure sensor 14.

[0056] The gas supply control system 1 includes an endoscope 9 having an air / water supply pipe 92 and a forceps channel 91 through which an insertion portion 9 is inserted, the endoscope 9 having an insertion portion 93 inserted into a lumen of a subject, a first tube 11 connected to communicate with the forceps channel 91, a pressure sensor 14 disposed in the first tube 11 for measuring the pressure of the gas, a second tube 21 for supplying the gas from a gas supply source to the lumen via the air / water supply pipe 92, a valve 25 for adjusting the flow rate of the gas supplied to the lumen via the second tube 21, and a controller 15 for controlling the valve 25 based on the pressure detected by the pressure sensor 14, and the controller 15 controls the valve 25 to supply the gas to the lumen at a first flow rate F1, and when the pressure reaches the first pressure P1, to supply the gas to the lumen at a second flow rate F2 that is less than the first flow rate F1.

[0057] According to this embodiment, it is possible to provide a gas supply control method that performs inspections quickly and accurately, a gas supply control device 10 that performs inspections quickly and accurately, and a gas supply control system 1 that performs inspections quickly and accurately.

[0058] The gas supply control system 1 used to diagnose GERD and esophageal achalasia has been described above, taking the stomach 100 as an example of a lumen of a subject. However, the lumen is not limited to the stomach 100, and may be any lumen into which gas is supplied, such as the large intestine.

[0059] <Modifications> Modifications of gas supply control systems 1A-1C described below are similar to gas supply control system 1 and have the same effects as gas supply control system 1. For this reason, hereinafter, components with the same functions as gas supply control system 1 are given the same reference numerals, and descriptions thereof will be omitted.

[0060] <Modification 1> A gas supply control method of a gas supply control system 1A of this modification will be described with reference to the flowchart of FIG.

[0061] <Steps S20-S28> These steps are the same as steps S10-S18 described with reference to FIG. 3, so a description thereof will be omitted.

[0062] <Step S29> Pressure ≧ Third Pressure Air supply at the second flow rate F2 continues until the pressure reaches the third pressure P3 (NO). The third pressure P3 is greater than the first pressure P1 and less than the second pressure P2. The third pressure P3 is set appropriately, for example, to 20 mmHg.

[0063] 9, when the third pressure P3 is reached (YES in S29), gas is supplied at a third flow rate F3 that is lower than the second flow rate F2. The third flow rate F3 is, for example, 0.1 mL / s to 1.0 mL / s.

[0064] For accurate diagnosis, the third flow rate F3 is preferably less than 75% of the second flow rate F2, and particularly preferably less than 50%.

[0065] <Steps S31-S32> These steps are the same as steps S18-S19 described with reference to FIG. 3, and therefore a description thereof will be omitted.

[0066] The gas supply control system 1A can perform a more accurate diagnosis than the gas supply control system 1.

[0067] As already explained, the pressure thresholds (first pressure P1, second pressure P2, and third pressure P3) are set appropriately. The pressure thresholds may be set by the user for each test, or a set of multiple pressure thresholds may be stored in advance in memory 16 and the user may be able to select one.

[0068] <Modification 2> As already explained, intragastric pressure reflects respiratory fluctuations and rises during inspiration compared to expiration. Therefore, the measured pressure includes biological vibrations that repeatedly increase and decrease according to the respiratory cycle.

[0069] In the gas supply control system 1B of this modified example, the flow rate is controlled using an average pressure that cancels out the increase and decrease in pressure (broken line) that increases and decreases at a substantially constant cycle, as shown by the solid line in FIG.

[0070] For example, by using a low-pass filter, the gas supply control system 1B cancels short-term periodic increases and decreases in pressure.

[0071] Furthermore, the controller 15 may cancel out increases or decreases by performing calculations using a moving average or the least squares method. For example, the controller 15 may calculate an approximation formula using acquired pressure data for a predetermined time range, and predict and control pressure changes based on the approximation formula. When the approximation formula is a linear formula, the constants a and b of (pressure P = a × time T + b) are calculated. The constant a corresponds to the slope of the line (rate of increase).

[0072] In control based on an approximation formula, the controller 15 performs a predetermined control before the pressure detected by the pressure sensor 14 reaches the threshold pressure, or does not perform the predetermined control even if the pressure detected by the pressure sensor 14 reaches the threshold pressure.

[0073] In order to reduce errors, it is preferable to use pressure data within a range of at least two cycles of increase and decrease for the calculation of the approximate expression.

[0074] In addition, data on the pattern of pressure changes (amount of increase or decrease, period) due to the subject's breathing may be acquired before the start of the diagnosis, and the increase or decrease in pressure may be canceled out by subtracting the change pattern data from the acquired pressure data.

[0075] The gas supply control system 1B can perform a more accurate diagnosis by canceling the influence of biological vibrations.

[0076] 11, in the gas supply control system, the rate of increase of the internal pressure is slow immediately after the start of gas supply, and then the internal pressure may temporarily increase significantly. The reason for this is not clear.

[0077] In the gas supply control system 1C of this modified example, the supply of gas at the first flow rate F1 continues until the time for which the gas is supplied at the first flow rate F1 reaches the second time T2. Note that the controller 15 may start pressure-based control and display of the pressure change on the display 31 after the rate of increase of the internal pressure becomes less than a predetermined rate and stabilizes.

[0078] The gas supply control system 1C can prevent malfunctions caused by temporary increases in internal pressure.

[0079] The present invention is not limited to the above-described embodiments, and various modifications, combinations, and applications are possible within the scope of the invention.

[0080] DESCRIPTION OF SYMBOLS 1, 1A-1C...Gas supply control system 10...Gas supply control device 11...First tube 14...Pressure sensor 15...Controller 16...Memory 20...Air supply unit 21...Second tube 23...Cylinder 24...Pressure vessel 25...Valve 26...Flow rate sensor 31...Display 32...Speaker 41...Light source 42...Optical fiber bundle 43...Video processor 44...Cable 91...Forceps channel 92...Air supply and water supply tube 93...Insertion section 93A...Tip 93B...Bending section 93C...Flexible tube 94...Operation section 95...Universal cord 96...Connector 97...Insertion port 100...Stomach

Claims

1. Supply gas from a gas supply source to the lumen of a subject at a first flow rate, measure the pressure of the gas in the lumen, and when the pressure reaches a first pressure, supply the gas to the lumen at a second flow rate that is less than the first flow rate. A gas supply control method characterized by the above.

2. The gas supply control method according to claim 1, characterized in that when the air supply time of the first flow rate has elapsed for a first time, the supply of the gas to the lumen is stopped.

3. The gas supply control method according to claim 1, characterized in that when the pressure reaches a second pressure exceeding the first pressure, the supply of the gas to the lumen is stopped.

4. The gas supply control method according to claim 3, characterized in that when the pressure reaches a third pressure that exceeds the first pressure and is less than the second pressure, the gas is supplied to the lumen at a third flow rate that is less than the second flow rate.

5. The gas supply control method according to claim 1, characterized in that the second flow rate is less than 75% of the first flow rate.

6. The gas supply control method according to claim 3, characterized in that the first pressure is the GERD diagnostic pressure and the second pressure is the allowable pressure.

7. The gas supply control method according to claim 4, characterized in that the third flow rate is less than 75% of the second flow rate.

8. Calculate the rate of increase in the pressure, and when the rate of increase reaches a first rate of increase, supply the gas to the lumen at the second flow rate even if the pressure is below the first pressure. A gas supply control method characterized by the above.

9. The gas supply control method according to claim 1, characterized in that control is performed using an average pressure obtained by canceling the increase and decrease of the pressure that increases and decreases at a substantially constant period.

10. The gas supply control method according to claim 1, characterized in that the supply of the gas at the first flow rate is continued until the supply time of the gas at the first flow rate reaches a second time.

11. A gas supply control device comprising: a first tube communicating with a lumen in a subject; a pressure sensor disposed in the first tube for measuring the pressure of a gas; a second tube communicating with the lumen for supplying the gas from a gas supply source to the lumen; a valve for adjusting the flow rate of the gas supplied to the lumen via the second tube; and a controller for controlling the valve based on the pressure detected by the pressure sensor, wherein the controller supplies the gas to the lumen at a first flow rate, and when the pressure reaches a first pressure, controls the valve to supply the gas to the lumen at a second flow rate less than the first flow rate.

12. The gas supply control device according to claim 11, wherein the controller controls the valve so as to stop the supply of the gas to the lumen when the air supply time at the first flow rate has elapsed for a first time.

13. The gas supply control device according to claim 11, wherein the controller controls the valve so as to stop the supply of the gas to the lumen when the pressure reaches a second pressure exceeding the first pressure.

14. The gas supply control device according to claim 13, wherein the controller controls the valve so as to supply the gas to the lumen at a third flow rate less than the second flow rate when the pressure reaches a third pressure exceeding the first pressure and less than the second pressure.

15. A gas supply control system comprising: an endoscope having an air / water supply tube and a forceps channel through which an insertion portion is inserted, the insertion portion being inserted into a lumen of a subject; a first tube connected to communicate with the forceps channel; a pressure sensor disposed in the first tube for measuring the pressure of a gas; a second tube for supplying the gas from a gas supply source to the lumen via the air / water supply tube; a valve for adjusting the flow rate of the gas supplied to the lumen via the second tube; and a controller for controlling the valve based on the pressure detected by the pressure sensor, wherein the controller supplies the gas to the lumen at a first flow rate, and when the pressure reaches a first pressure, controls the valve to supply the gas to the lumen at a second flow rate less than the first flow rate.

16. The controller controls the valve so as to stop the supply of the gas to the lumen when the air supply time of the first flow rate has elapsed for a first time, in the gas supply control system according to claim 15.

17. The controller controls the valve so as to stop the supply of the gas to the lumen when the pressure becomes a second pressure exceeding the first pressure, in the gas supply control system according to claim 15.

18. The controller controls the valve so as to supply the gas to the lumen at a third flow rate less than the second flow rate when the pressure becomes a third pressure exceeding the first pressure and less than the second pressure, in the gas supply control system according to claim 17.

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