外文原文-用于食管压力实时监测的高压球囊导管

High-pressure Balloon Catheter for Real-Time Pressure Monitoring in The Esophagus K. Y. Kwan, K. l ? I. S. Kaler, MP. Mintchev Department of Electrical and Computer Engineering, University of Calgary Calgary, Alberta, Canada T2N IN4 mintchevenel.ucalgary .ca ABSTRACT This paper reports the development of a new catheter for esophageal manometry, implemented by connecting a mhiature high-pressure sensing balloon to an external pressure sensor. The integration of the catheter into a signal conditioning and data acquisition system for real- time pressure monitoring is also described. In order to characterize the sensitivity of the novel self-contained air balloon design, experimental setup for simulating the esophageal motility was utilized. The results show that the self-contained air balloon catheter is suitable for measuring various waveforms typical to the ones generated in esophageal motility pathologies. 1. INTRODUCTION Esophageal disorders are among the top 50 reasons patients seek medical care I. In order to diagnose these disorders, esophageal manometry is utilized to measure the mechanical movement of the esophageal sphincters and the esophageal wall 2. By analyzing the pressure changes in these recordings, a clinician can recognize and classify various esophageal disorders (e.g. ashalasia, diffuse spasm, systemic sclerosis etc 3). Currently, there are two catheter techniques for esophageal manometry, water-perfusion and solid-state strain gauges 3. Although water-perfused catheters have been broadly used and verified for esophageal manometry, this technique is limited to stationary manometric studies and requires skilled technicians to conduct the laboratory testing 3. Moreover, due to the utilization of a constant water-flow, these catheters are not suitable for long- period or 24-hour ambulatory monitoring 2. On the other hand, solid-state catheters offer the ponability needed for 24-hour ambulatory monitoring. Yet, the solid-state catheters have lower sensitivity to aidliquid pressure compared to directly applied force/stress 2. For many years, air balloon pressure sensing catheters have been used in a variety of applications (e.g rectal manometry), but there is little research on utilizing this technique for esophageal manometry. In 1967, Pope suggested a liquid-filled balloon for measuring sphincter pressure 4. However, the results were not linear, because of the balloon diameter and material. In the present study we suggest that with the recent technological advancements, the limitations of Popes design can be overcome using accurate signal acquisition software and advanced balloon material. The aim of this research is to assemble and test a self-contained high-pressure air balloon catheter that has the sensitivity of a water-perfused catheter and the portability of a solid-state catheter. 2. MATERIALS AND SYSTEM DESIGN 2.1. Principle of Operation An external pressure transducer is connected to the outer end of a standard tube linked internally to a self- contained high-pressure sensing balloon. The pressure around the sensing balloon would compress the air inside the balloon. The pressure inside the catheter would be equal to or have the same ratio as the pressure around the sensing region. Thus, the gauge pressure inside the esophagus can be measured. Similarly to the water- perfused catheter and the solid-state catheter, monitoring the motility of the esophagus would he possible by analyzing the electrical signals generated by the pressure transducer. 2.2. Design Materials In order to test the feasibility of the self-contained air balloon design, a single channel catheter was assembled using polyethylene terephthalate (PET) high-pressure balloon and a polyvinyl chloride (PVC) tube. A 750-mm long catheter prototype was designed, with balloon dimensions of 8 mm (diameter) and 20 mm (length). The catheter prototype was produced by Advanced Polymers (Salem, NH). 2.2. I. High-pressure Balloon The advantages of using a high-pressure balloon include the thin wall, high tensile strength and relatively low elongation. Moreover, a high-pressure balloon can return to its original size and shape after the removal of the external pressure or force i.e. it does not exhibit a mechanical hysteresis 5. Among various high-pressure balloon materials, polyethylene terephthalate (PET) high- pressure balloon was used for the present design, because of the possibility of customization using varying diameters and precise shapes. The wall thickness of the balloon ranged from 0.0406 to 0.0483 mm, making it 0-7803-7596-3/02/$17.00 02002 IEEE 121 I sufficiently sensitive to circumferential forces in the esophagus. 2.2.2. Extprnal Pressure Transducers Piezoresistive integrated semiconductor air pressure transducer SXOSG2 (Semsys, Austin, TX) was utilized for the self-contained air balloon catheter. It is capable of measuring a gauge pressure range from 0 to 600 mmHg. The sensing tip of the transducer is connected to the air balloon catheter, and is located outside the human body. The voltage output of this transducer was conditioned and digitized for processing and visualization. The offset of the transducer was compensated by the manufacturer at atmospheric pressure of 101 kPa and room temperature of 22 “C. 2.3. System Design A multichannel computer-based measurement system (DAQCard 1200, National Instruments, Austin, TX) using custom-made data acquisition and monitoring software Gastrointestinal signal Acquisition System v.3 (GAS3) (Low Frequency Instrumentation Laboratoly, University of Calgary, Calgary, AB) was utilized for this application. GAS3 is a software graphical user interface (GUI) package developed using LabWindowsiCVL (National Instruments, Austin, TX) for signal monitoring and processing. The GAS3 package was utilized for scaning the inputs and displaying time vs. pressure plots on the computer screen in real time, while recording the samples into an ASCII file. The output voltage produced by the catheter required preliminary analog signal condjtioning. The signal was amplified so that the maximal possible voltage range of the conditioned signal was equal to the analog range of the analog-to-digital converter (ADC) of the computer- based measurement system (Figure 1). 1 CGLh 1 Figure 1. Block diagram ofthe system. 2.3.1. Experimental Model of the Esophagus In order to assess the performance of the air-contained balloon, externally applied pressures were compared to the internally recorded pressure by the catheter using an experimental model of the esophagus. An experiment compared externally applied pressure detected by a second air pressure transducer SXOSG2 to the internal pressure in the self-contained air balloon catheter. Figure 2 illustrates a 5-mL syringe simulating the esophagus. Using a pump, the pressure in the 5-mL syringe was changed to mimic esophageal motility. Using a two- channel measurement setup, the externally applied pressure (Channel 1) was compared to the measurement of the internal pressure (Channel 2). Sensor SX05G2 APPb P.W.“.C SP- SXmGz Figure 2. Erperimental model o f the esophagusfor testing the feasibilil ofthe se(/-confained design. 2.3.2. Analog Voltage Amplrfication The Semsys SXOSG2 senses extremely small changes in resistances, which are converted into voltages in the range of milivolts. Therefore, a voltage amplifier was required for reliable measurements. This amplification also brought the voltage within the input range of the ADC. A low-power instrumentation amplifier AD620 (Analog Device, Norwood, MA) is utilized to amplify the SX05G2 differential signal. This 8-pin IC is equivalent to the routinely used three-opamp configuration. There is an external resistor Rg controlling the voltage gain. The gain of the circuit is defined as: 49.9*1000 G = l + (0 where G is the gain and Rg is the external resistor. Since the outputs of SX05G2 are in the range of 0 to 300 mV, the output signal was amplified IO times and the external resistor, Rg, was calculated to be 5.55 kn . 2.3.3. Analog-to-Digital Conversion After the transducer signal was amplified, analog-to- digital conversion was performed in order to digitize the signal and prepare it for further digital conditioning. Since the voltage output of the SXO5G2 should always be considered positive, the voltage input range was set to be unipolar0-IO V. The DAQCard-1200 board performs multiplexed A/D conversions of up to 8 channels. The two-channel analog outputs from the voltage amplifiers connected to the DAQCard-1200 using a custom-made inpurhtput connector. The 12-bit A/D procedure controlled by the GAS3 software digitized the signals at a sampling rate of IO Hz. The analog signals were converted with a resolution of 2.44 mV, and after appropriate data buffering were fed into a laptop computer in a real-time stream 161. 1212 3. RESULTS 3.1. Linearity of lnternal and Applied Pressures Air pressye changes were simulated to test the sensitivity of the new design. A set of external pressures was applied to the experimental model. Two voltmeters measured the output of the two transducers in order to examine the linearity of both the internal and the applied pressures. The externally applied pressure ranged between 0 to 150 mmHg and was increased by about IO to 25 mmHg to simulate esophageal motility. Ten independent measurements were obtained from the catheter prototype. There was ahout 1 or 2 seconds pause to let the voltmeter reading settle between each recording. Figure 3 depicts the relationship of applied pressures vs. internal pressures in the self-contained air balloon catheter prototype. 110 110 r“ loo f 90 3 80 6 70 so - 4 3 10 10 - 10 0 8 6 0 0 10 20 30 40 50 60 70 80 90 100110110130140150160 Applied pressure (rnmHgl Figure 3. Appliedpressure vs internal pressure in the experimental model. 3 . 2 . Real-Time Monitoring Three kinds of waveforms are routinely seen in the esophagus: the upper esophageal sphincter (UES) wave, the esophageal body wave, and the lower esophageal sphincter (LES) wave 3. Each of these waveforms was simulated by applying similar pressure amplitude, pattern, and duration to the ones occurring during esophageal motility. 3.2.1. UES Simulation Constant pressure (about 58 mmHg) was applied for 2 seconds to the 5-mL syringe to simulate the resting pressure of the UES. Then, the pressure was reduced to around zero to simulate a relaxation of the UES. Since the relaxation of the UES lasts about 2 seconds 3, the pressure was elevated up to 70 mmHg to simulate a contraction of the UES. After the simulation of a relaxation, the pressure was once again brought to 58 mmHg. Figure 4 shows the output of the two transducers measuring the applied (Channel 1) and the internal (Channel 2) pressures for the tested catheter. 3.2.2. Esophageal Body Simulation Similar simulation was performed to mimic the waveforms in the esophageal body. Pressure was kept at 0 mmHg to simulate the esophageal body at relaxation. 1 Then, external pressure of 75 mmHg with I-second duration was applied to the experimental setup. Figure 5 shows a typical example of the contraction of the simulated esophageal body with the externally applied pressure (Channel 1) and the resulting internal pressure (Channel 2) of the sensing system. L + $ + z50-r k z i i i i z +/ Channel 2 is the resulting internal pressure jChlmn.lI YreIPUle (Mnrll) Figure 5. Manometric representation o f the esophageal body in the experimental model. 3.2.3. LES Simulation The simulation of LES relaxations and contractions was performed using the same methodology. Resting LES pressure varies among individuals from 10 to 45 mmHg 3. Therefore, 30 mmHg was chosen for the resting pressure of the LES. This pressure was kept constant before the simulated relaxation. Then, the pressure was reduced to 0 mmHg for 5 m n d to simulate LES relaxation. After that, the pressure was brought up to 70 mmHg to simulate the closing of the LES. Figure 6 compares the two pressure channels. Tlmc (8) Figure 6 Manometric representation ofthe LES in the experimental model. 213 3.2.4. Random Waveform The esophageal peristaltic wave does not exhibit solely the three waveforms simulated above. In individuals with esophageal motility disorders, a variety of different kinds of pressure waveforms could occur in the esophagus. These various waveforms have different amplitudes, propagation patterns and durations. In order to test the sensitivity of the self-contained air balloon catheter system to various pressure patterns, series of random pressure waveforms were simulated. Figure 7 demonstrates some of these waveforms. The simulation period was I8 seconds. Three different amplitudes of esophageal body contractions were simulated. Then, the pressure was kept constant at 50 mmHg for 3 seconds. Subsequently, the pressure dropped to simulate about 80 percent of relaxation (20 mmHg). Following that, a double-peak waveform was simulated. Finally, a sharp contraction of less than I second was also simulated. Tim (5) - Figure 7 Manomefric representafton ofseries o f random waveforms in the experimental model 4. DISCUSSION Testing the self-contained air balloon catheter with controlled externally applied pressures from 0 to 150 mmHg in a simulated model of the esophagus showed a strong correlation between the applied and the measured internal pressures. A practically linear response was observed from the catheter prototype. The experimentally obtained linear equation derived for the catheter prototype is. P; = Pa * 0.777 - 2.86 (2) where Pa is the externally applied pressure and Pt is the resulting internal pressure. Although the externally applied pressures and the resulting internal pressures in the self-contained air balloon catheter were not at one-to-one ratio, the experiments showed good linear relationship. The internal pressures demonstrated lower values than the applied pressures by a ratio of 0.777. This could he related to possible air leaking from the syringe-based model of the esophagus during testing. This limitation could possibly be overcome with a better sealing material for the experimental setup. Zero offset of 2.86 mmHg was also noted. Due to this offset, the catheter could not measure small pressures lower than this offset value. The computer-based data acquisition system GAS3 successfully displayed two channels in real time. The self-contained air balloon catheter accurately responded to externally applied pressure. Experiments demonstrated that the UES, the esophageal body and the LES pressure dynamics could be successfully monitored by the experimental setup. Moreover, this new design system was sensitive to random dynamic pressure changes as well. Thus, the self-contained air balloon catheter was found to be suitable for measuring different kinds of waveforms generated in esophageal motility pathologies. 5. CONCLUSION The present study demonstrated that the self-contained air balloon catheter system is capable of measuring simulated esophageal motility. Quantitative testing methods performed on the transducer showed an adequate linear response. Zero offsets of the internal pressure signals were noted, which could be overcome by applying initial pressure in the air balloon. T