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A new device for measuring esophageal variceal pressure

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A new device for measuring esophageal variceal pressure
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   Received November 23,2001.For revision January 30,2002. Accepted March 27,2002.Current affiliations:Temple University Hospital,Philadelphia Pennsylvania,and Olympus Corporation,Tokyo,Japan. Reprint requests:Larry Miller,MD,Department of Gastroenterology,8th Floor,Parkinson Pavilion,TempleUniversity Hospital,3401 Broad St.,Philadelphia,PA 19140.Copyright © 2002 by the American Society for Gastrointestinal Endoscopy0016-5107/2002/$35.00 + 0  37/69/126389 doi:10.1067/mge.2002.126389 E Miller,J Kim,J Gondehak,et al.A new device for measuring esophageal variceal pressure 284 GASTROINTESTINAL ENDOSCOPYVOLUME 56,NO.2,2002 A new device for measuring esophagealvariceal pressure Elan S.Miller, Joseph K.Kim, Jasneet Gandehok, Mak Hara,Qing Dai, MD, Aslam Malik, MD, Aaron Miller, Larry Miller, MD Background:  Esophageal varices are a frequent sourceof bleeding in patients with cirrhosis.Elevated intra-variceal pressure is associated with variceal bleeding.There is no simple,easy-to-use device for noninvasivemeasurement of intravariceal pressure.The purposes ofthis study were to develop a noninvasive method formeasuring intravariceal pressure,and to develop amodel of esophageal varices that can be used to testthis pressure measurement device. Methods:  A variceal pressure measurement device wasconstructed by placing a 20 MHz US transducer in alatex balloon catheter sheath and attaching the catheterto a pressure transducer.The pressure measurementdevice was passed though the accessory channel of alarge-channel endoscope and tested in blinded fashionby using tip deflection to compress each of 4 varicealmodels with the device.The pressure within each modelwas measured 10 times by 2 separate investigatorsblinded to the actual pressures.The mean (SD) pressurewas calculated for each model.The variceal modelswere made of nitrocellulose dialysis tubing filled withwater.Each “varix”had the same diameter but a differ-ent intraluminal pressure (5.5,10,15,21.5 mm Hg). Observations:  The correlation coefficient between theactual and measured “varix”pressures for the firstinvestigator (L.S.M.) was r  = 0.96:99% CI [0.93,0.98].Forthe varix models with pressures of 21.5,15,10,and 5.5the percent errors were,respectively,9.5,3.9,5.1,and0.7.The correlation coefficient between the actual andmeasured varix pressures for the second investigator(Q.D.) was r  = 0.97:99% CI [0.94,0.98].For the varix mod-els with pressures of 21.5,15,10,and 5.5 the percenterrors were,respectively,10.3,3.4,9.8,and 1.1.The cor-relation coefficient between the 2 investigators (L.S.M.,  Q.D.) for the varix model pressures was r  = 0.97:99% CI[0.95,0.99]. Conclusion:  The variceal pressure measuring devicedeveloped for this study measured intravariceal pres-sure in a model varix with a low percent error and highcorrelation to the actual pressures.Intraobserver andinterobserver variability was low. Esophageal varices are a frequent source of GIbleeding in patients with cirrhosis.A number of fac-tors are thought to contribute to variceal bleeding:Wall tension of a varix is a property of the vesselwall that can be conceptualized as an inwardlydirected force that opposes an outwardly directedexpanding force,proportional to transmural pres-sure and vessel radius and inversely proportional towall thickness.An increase in pressure results in anincrease in radius and a corresponding decrease inwall thickness.Hence,in vessels that are poorlysupported by connective tissue,such as esophageal varices,changes in pressure would be expected tohave a greater impact on vessel radius and therebycause the varix to approach its elastic limit. 1 Recent technologic advances have made it possi-ble to measure all of the variables that contribute to variceal wall tension.Variceal radius and wall thick-ness can be measured by high resolution endolumi-nal sonography (HRES). 2-6  Various methods can beused to determine intravariceal pressure, 7-10 thereference standard being needle puncture of the varices. 3 However,noninvasive methods have alsobeen developed to measure variceal pressure;the 2currently in use employ either a pressure gauge or aballoon attached at the tip of an endoscope. 8-10 The purpose of this study was to develop a newmethod for noninvasive measurement of esophageal variceal pressure.The requirements for this systemwere as follows.It should (1) be reliable and accu-rate;(2) be suitable for use through an endoscopewithout alteration of the endoscope or the need toremove the endoscope after intubation;(3) permitmeasurement of pressure separately within individ-ual varices,and (4) provide all parameters for theLaplace equation for measurement of variceal walltension (wall thickness,radius,intravariceal pres-sure).The ultimate goal is a system for varicealpressure measurement that can be used to monitorand titrate pharmacotherapy for patients withesophageal varices. MATERIALS AND METHODSPressure measuring device The prototype variceal pressure measurement device isbased on a patent for a device held by L.Miller and wasmade by the Olympus Optical Co.,Ltd.(Tokyo,Japan)(Fig.1). 6 It consists of a 20 MHz US catheter probe (UM-BS20-26R,Olympus America,Inc.,Melville,N.Y.) (Fig.2),which is placed through a balloon catheter (Figs.3 and 4).The probe is attached to an US processor (EU-M20,Olympus) and the US balloon catheter to a pressuretransducer by means of a triple stopcock.A 10-mL syringeis attached to the triple stopcock so that the balloon canbe expanded with water.A second catheter sheath isplaced over the balloon catheter (Fig.5).This cathetersheath is notched at the balloon end so that when the bal-loon is filled with water only one side expands.In addi-tion,the sheath keeps the US transducer and balloon stiff (Fig.6).The entire assembly was inserted through theaccessory channel of a large channel “therapeutic”endo-scope (Olympus EG3800T) with the balloon deflated,sothat the balloon and notched part of the sheath projectedfrom the end of the endoscope (Fig.7).Based on experi-ments with various volumes of water,it was determinedthat the optimal volume in the balloon for pressure mea-surement was 1.5 mL.Air was removed from the systemby tapping bubbles to the top of the balloon and opening the balloon to flush these out. Variceal model The variceal model was constructed by using a 250-mLgraduated cylinder (representing esophageal lumen) and8-inch pieces of nitrocellulose dialysis tubing attached topolyethylene tubing of various lengths by rubber bands(representing varices).The dialysis tubing and polyethyl-ene tubes were attached to the inside of the base of thegraduated cylinder with waterproof tape and super glue(Fig.8).The dialysis tubing and graduated cylinder wereplaced in an upright position and filled with water.A manometry catheter was used to determine the pressurein both the dialysis tubing and the graduated cylinder ata point on the cylinder 8 inches from the top.The polyeth-ylene tubing was cut to different lengths so that the pres-  A new device for measuring esophageal variceal pressureE Miller,J Kim,J Gandehok,et al.VOLUME 56,NO.2,2002GASTROINTESTINAL ENDOSCOPY   285 Figure 1. Schematic drawing of variceal pressure measuringdevice. A, Stiff notched overtube that goes over ballooncatheter. B, Balloon catheter containing 20 MHz US transducer. AB  sure in the dialysis tubing minus the pressure in the grad-uated cylinder was equal to a specific pressure in each of 4models (5.5,10,15,21.5 mm Hg).A plastic funnel wasattached to the top of the polyethylene dialysis tubing sothat compression on the dialysis tubing from inside thegraduated cylinder would not change the pressure in theartificial varix.The dialysis tubing was filled with water anda milk substitute (Coffee-mate,Nestlé USA,Inc.,Glendale,Calif.),so that the tubing was visible on US imaging.The technique for measurement of “variceal”pressurewas as follows:the endoscope was hung from a stand sothat the balloon pressure measuring device extending from the tip was always located at the same distance atwhich the pressures were measured in all of the graduat-ed cylinders (8 inches from the top).As determined inprior experiments,compressing the artificial varix by 50%gave the most accurate pressure readings;less than 50%underestimated and more than 50% overestimated thepressure.The degree of compression was easily observedultrasonographically in all of the varix models.The bal-loon was filled with 1.5 mL of water and the stopcockopened to the pressure transducer,after the entire systemwas calibrated.The pressure transducer and the US probewere both attached to a workstation (Kayelemetrics Corp.,Lincoln Park,N.J.) so that simultaneous US and manom-etry images could be obtained.The US transducer probein the catheter assembly was used to locate the artificial varix,which appeared as a hyperechoic round structure(Fig.9).  E Miller,J Kim,J Gandehok,et al.A new device for measuring esophageal variceal pressure 286 GASTROINTESTINAL ENDOSCOPYVOLUME 56,NO.2,2002 Figure 2. 20 MHz US transducer (UM-B520-26R, Olympus). Figure 3. Latex balloon catheter sheath that goes over UStransducer. Figure 4.A, 20 MHz US transducer within latex ballooncatheter. B, Balloon deflated. C, Balloon inflated. Figure 5.A, Stiff notched overtube that goes over ballooncatheter. B, Tip of stiff notched overtube. Figure 6.A, US transducer within latex balloon.The UStransducer and latex balloon are within the stiff notchedcatheter sheath.Together, these components comprise theprototype variceal pressure measuring device.The deflatedballoon, which contains the US transducer, projects from thetip of the stiff notched catheter. B, Deflated balloon contain-ing US transducer projecting from tip of stiff notchedcatheter. C, Inflated balloon. ABCABABC  The endoscope tip was deflected to compress the arti-ficial varix by 50% as determined from the US image(Fig.10).The balloon was held in position for a few sec-onds to stabilize the pressure tracing.The endoscope wasthen moved away from the artificial varix and repeatedpressure measurements were made at the zero referencepressure.Measurements were made in blinded fashion in 4 variceal models (actual pressures in varix models were5.5,10,15,and 21.5 mm Hg).The pressure in each varixwas measured 10 times.The investigator measuring thepressures was blinded to the pressure in the varix and tothe manometry tracing during the study.After the studywas complete,pressures were read from the workstationin blinded fashion by subtracting the varix pressure fromthe graduated cylinder pressure. A mean (SD) was calculated for the pressure measure-ments of each varix.The mean percent errors between themeasured varix pressures and the actual varix pressureswere calculated.A Pearson correlation coefficient was cal-culated with a 99% confidence interval. RESULTS The pressure within the varix model remainedconstant throughout the entire study.The US imageof the “varix”appeared as a round,hyperechoicstructure surrounded by the hypoechoic water in thegraduated cylinder.Measurements made by L.S.M.are shown in Table 1.and mean values for measuredpressures and mean percent errors in Table 2.Twomeasurements in the 10 mm Hg model and 2 in the5.5 mm Hg model were not used because of substan-dard imaging or because the pressure tracing wasunstable.Measurements made by investigator Q.D.are shown in Table 3 and mean values for measuredpressures and mean percent errors in Table 4.Onemeasurement in the 10 mm Hg model was not usedbecause of substandard imaging.The correlationcoefficient between the actual and measured varixpressures for L.S.M.was r = 0.96:99% CI [0.93,0.98].For the varix models with the pressures of 21.5,15,10,and 5.5 the percent errors were,respectively,9.5,3.9,5.1,and 0.7 (Table 2).The correlation coefficientbetween the actual and measured varix pressures forQ.D.was r = 0.97:99% CI [0.94,0.98].For the varixmodels with pressures of 21.5,15,10,and 5.5 the  A new device for measuring esophageal variceal pressureE Miller,J Kim,J Gandehok,et al.VOLUME 56,NO.2,2002GASTROINTESTINAL ENDOSCOPY   287 Figure 7.A, Prototype variceal pressure measuring deviceprojecting from endoscope. B, Balloon inflated. Figure 8. Varix model consisting of graduated cylinder filledwith water and containing nitrocellulose dialysis tubing filledwith water and a milk substitute (Coffee-mate).The funnel atthe top keeps the pressure within the varix model constanteven when the varix is compressed. AB  percent errors were,respectively,10.3,3.4,9.8,and1.1 (Table 3).The correlation coefficient between theinvestigators (L.S.M.,Q.D.) for the varix pressureswas r = 0.97:99% CI [0.95,0.99]. DISCUSSION Measurement by needle puncture is still consid-ered the reference standard for measurement of intravariceal pressure,but this technique can  E Miller,J Kim,J Gandehok,et al.A new device for measuring esophageal variceal pressure 288 GASTROINTESTINAL ENDOSCOPYVOLUME 56,NO.2,2002 Figure 9. US image of transducer, surrounded by balloon, within water of graduated cylinder.The hyperechoic area at the 12o’clock position is the varix model filled with water and Coffee-mate.Pressure tracing on right represents pressure within grad-uated cylinder (57.0 mm Hg). Figure 10. US image showing compression of varix model by balloon.The varix is compressed by 50%, as determined from theultrasound image, with a rise in pressure to 69.9 mm Hg during compression as shown at right.

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