the best mode and preferred embodiment of the invention is illustrated in fig4 . the proximal end of the balloon catheter 1 is attached to the inflation syringe 3 . the syringe is of standard type but modified for reasons which will be apparent below . a plunger 10 moves through the barrel of the syringe 3 displacing liquid , such as diluted contrast media , into the balloon catheter 1 . the plunger shaft 7 is finely threaded all along its length so that when turned , the shaft moves longitudinally through an oppositely threaded annular member 8 . the annular member 8 is attached to the syringe 3 . in this way , slow and even displacement of liquid into the balloon catheter is produced by rotating the shaft 7 . the more fine the threads , of course , the slower will be the fluid displacement . a hand crank 4 has been added to facilitate the balloon inflation process . interposed between the balloon catheter 1 and inflation syringe 3 is an electronic pressure transducer 2 of conventional type . an electronic signal proportional to the fluid pressure existing within the catheter is then fed to an oscilloscope 9 for real - time display . any type of electronic recording device could also be used . a linear displacement transducer 6 , which produces an electronic signal proportional to its length at any given time also feeds into the oscilloscope 9 . the ends of the linear displacement transducer 6 are connected by means of coupling bars 5a and 5b to the plunger shaft 7 and inflation syringe 3 respectively . in this way the signal produced by the linear displacement transducer 6 is proportional to the volume of fluid displaced from the syringe 3 and hence residing in the balloon catheter 1 . thus , there are two electronic signals fed to the oscilloscope 9 which represent the volume and pressure of the fluid contained by the balloon at any given time . by displaying the pressure and volume inputs simultaneously a curve is generated by the oscilloscope wherein one axis corresponds to pressure and the other axis corresponds to volume . the information contained in this curve enables one to draw certain conclusions regarding the physical process taking place during the dilation process as will now be explained . fig1 - 3 depict expansion curves generated by dilating models of arterial lesions with three different types of behavior . superimposed on all three figures is the expansion curve 10 of the balloon expanded by itself . this represents the compliance of the balloon alone and will be used as the reference curve . referring first to fig1 expansion curve 12 shows that as the pressure is raised initially , there is little change in the volume of the balloon as compared with the reference curve 10 . this indicates that the atherosclerotic plaque which surrounds the balloon is preventing the balloon from expanding . as the pressure is increased further , however , the pressure within the balloon becomes great enough to overcome the resistance of the plaque material . at this point the occluded artery begins to dilate as the balloon expands . it is not clear whether the plaque material is actually compressed so as to occupy less volume or is deformed so as to be redistributed along the length of the artery , but what is important is that the expansion takes place at relatively constant pressure . at any given point along the curve , the pressure of the fluid within the balloon is exactly balanced by the pressure exerted by the surrounding plaque . a region of constant pressure , or isobaric , expansion indicates that the plaque material is exerting the same force irrespective of the extent of the plaque &# 39 ; s deformation . the theory of the properties of materials would predict that the stress exerted on the plaque had exceeded the yield point of the plaque material . this would mean that the plaque material is being deformed plastically rather than elastically . this is consistent with a young or at least still malleable atheroma which can be expected to retain the deformation produced by the expanded balloon . thus , when an expansion curve like that of fig1 is obtained , the operator may infer that the angioplasty procedure has been relatively successful and no further inflation cycles are necessary , especially if a repeat inflation yields a curve superimposed on curve 10 . furthermore , the knowledge that the atheroma responded to the procedure in this way is useful in the subsequent management of the patient &# 39 ; s atherosclerotic disease . next , in fig2 is an expansion curve 14 which indicates that as the balloon expands against the occluded artery , the artery exerts increasing force against the balloon . this would lead one to conclude that the occluded artery is acting like a spring and storing the work of expansion only to return to its former occluded shape when the balloon is deflated . this has been found experimentally to be the case although with repeated inflations the curve sometimes moves closer to the reference curve indicating that the artery is becoming more compliant . unlike the case in fig1 the atheroma in this example has probably been deformed very little by the expanding balloon . since plaque is known not to be composed of elastic , or energy storing , material the likely source of the elasticity is the medial layer of the arterial wall itself . in any case , an expansion curve like that in fig2 indicates a less desirable result for the patient than that in the first example above . the increased compliance of the arterial wall following repeated inflations may also indicate plastic changes such as thinning and microscopic tearing , such that it would be hazardous to try another inflation cycle . finally , fig3 shows an expansion curve 16 exhibiting sharp drops in pressure as the balloon expands . a sudden decrease in the pressure exerted against the balloon by the occluded artery can only mean that a stress relieving fracture of some kind has occurred . one can then infer that the plaque was hard and brittle , presumably due to calcification , and was fractured by the expanding balloon . not only does this indicate that angioplasty is not likely to be successful in dilating the artery , but remedial steps may need to be taken to prevent the plaque fragments from separating from the rest of the plaque causing complications at some point downstream . one such remedial step might be to inflate the balloon a second time , although at a lower pressure , in order to &# 34 ; tack &# 34 ; the plaque fragments down and prevent their dislodgment . anticoagulant therapy may also be indicated . in generating the expansion curves discussed above , the particular instrumentation used must be able to respond to the extremely small changes in volume involved when the balloon expands as well as pressures reaching twelve atmospheres . the inflation syringe described in the preferred embodiment was also constructed with a shaft possessing screw - type threads fine enough so that many rotations are necessary to move the shaft through the oppositely threaded annular member . a slow and even displacement of fluid into the balloon is necessary to avoid introducing artifacts into the pressure signal and obscuring the information contained therein . that is , a properly constructed expansion curve only contains pressure values which have been obtained after any transient pressure waves in the fluid have died out . it should be understood that the embodiment disclosed hereinabove is not meant to limit the invention in any manner . on the contrary , it is intended to cover all modifications , alternatives , and equivalents as may be included within the spirit and scope of the invention as defined by the following claims .
a novel method and device for performing percutaneous transluminal angioplasty to treat occlusive artery disease is disclosed . the method involves simultaneous measurement and display of the fluid pressure and volume existing within the balloon catheter as the procedure is performed . information is produced which is useful in determining the efficacy of the procedure as it is performed which obviates the need for arbitrary repeated inflations . the information is also useful in the subsequent management of the patient &# 39 ; s disease .