fig1 - 3 schematically depict an atherectomy catheter 10 embodying features of the invention . the catheter 10 includes a distal portion 11 having cutter head assembly 12 , an elongated catheter shaft 13 and a proximal portion 14 having a manifold assembly 15 and drive assembly 16 ( shown in phantom ). as shown in more detail in fig2 the cutter head assembly 12 has a cylindrical housing 17 formed of shape memory / pseudoelastic alloy with a side opening or window 18 and a cutting blade 19 which is slidably disposed within the inner chamber 20 of the housing 17 for both longitudinal and rotational movement . the cutting blade 19 movement , both longitudinal and rotational is effected by the flexible cable drive shaft 21 which is secured to the proximal end of the cutter blade . inflatable positioning balloon 22 is secured to the exterior of the housing 17 on a side opposite to the window 18 so that , upon its inflation within the stenotic region of the patient &# 39 ; s artery , the housing will be pressed against the stenotic material to cause some of it to enter into the inner chamber 20 where the cutter blade 19 can sever it from the rest of the stenotic material on the arterial wall . an inflation tube 23 is disposed within the outer tubular member 25 of the catheter shaft 13 and has a distal end spliced together with the proximal skirt 26 of the inflatable positioning balloon 22 to direct inflation fluid to the interior of the balloon . the distal skirt 27 of the balloon 22 is folded over and secured within the distal end of the housing as shown in fig2 . a torquing cable 28 , which is also disposed within the outer tubular member 25 , is secured to the proximal end of the housing 17 and is provided with a rotator 29 fixed by its distal end to the proximal end of the torquing cable to rotate the cutter head assembly 12 so that cutter head assembly may be initially positioned or repositioned within the patient &# 39 ; s artery during the atherectomy procedure . the proximal end of the rotator 29 is rotatably secured to the manifold assembly 15 so that the torquing cable 28 can be rotated by rotation of the rotator 29 without moving the manifold assembly . flexible nose cone 30 , which has an inner coil 31 and outer jacket 32 , is secured to the distal end of the housing 17 to prevent traumatic engagement with the artery wall when the catheter 10 is advanced through the patient &# 39 ; s arteries . the triple arm manifold assembly 15 on the proximal portion 14 of the catheter 10 generally includes a manifold body 33 and inflation arm 34 and a flush arm 35 . the inflation arm 34 is in fluid communication with the inner lumen of the inflation tube 23 for delivery of inflation fluid to the interior of the balloon 22 . the flush arm 35 is in fluid communication with the interior of the flexible drive shaft 21 for the cutter blade 19 and is adapted to direct irrigation or radiopaque liquid to the interior of the housing 17 . the drive assembly 16 is interconnected to the drive shaft 21 for the cutter blade 19 by means of a splined connector 36 which is adapted to be inserted into the drive spline ( not shown ) of the drive assembly . the splined connector in turn is connected to an intermediate drive shaft 37 which is fixed in a driving relationship to the proximal end of the flexible drive shaft 21 . a finger actuated lever 38 is rotatably mounted onto the intermediate drive shaft 37 but is fixed thereto to prevent longitudinal movement relative to the intermediate drive shaft so that longitudinal movement of the finger actuated lever will cause the longitudinal movement of the cutter blade 19 within the housing 17 . the operation of the drive assembly 16 is initiated by the actuation of switch 39 which will cause the rotation of the flexible drive shaft 21 and the cutter blade 19 secured thereto . further details of the drive assembly 16 can be found in u . s . pat . no . 4 , 771 , 774 which has been incorporated herein by reference . the drive assembly and atherectomy catheter of the structure described herein with a conventional cutter housing formed of stainless steel are available from the assignee of the present application devices for vascular intervention , inc . ( dvi ), located in redwood city , calif . fig4 and 5 illustrate the flexible housing 17 of the present invention which has a plurality of heat treated cylindrically shaped tubular sections 40 to provide improved housing flexibility . in one embodiment the housing 17 is formed of a shape memory alloy of nickel and titanium and typically is 50 % ni and 50 % ti . the entire housing 17 is initially in a cold worked condition by drawing through a series of dies of decreasing diameters , with intermediate anneals between working steps . the cylindrically shaped tubular sections 40 with a length of about 0 . 01 to about 0 . 2 inch ( 0 . 254 - 5 . 1 mm ) are heat treated , preferably with a laser beam ( e . g . co 2 or yag laser ) with a spot size of about 0 . 002 to about 0 . 010 inch ( 0 . 051 - 0 . 254 mm ) in diameter to stress relieve or otherwise heat treat the cylindrically shaped sections . the power output of the co 2 laser is about 1 to about 7 watts . it is difficult to determine the temperature at which the laser treated tubular sections are subjected , so it may be necessary to go through a trial and error procedure to optimize the laser treatment for a particular housing wall thickness , housing composition and thermomechanical processing . the size of the opening or window 18 in a wall portion of the housing 17 may vary . generally , the cutout angle , shown best in fig5 should range from about 80 ° to about 140 °, and preferably about 90 ° to about 130 °. it is contemplated that the atherectomy catheters will be offered with windows of various lengths to accommodate different sized stenoses . fig6 depicts an alternative cutter housing 17 wherein tubular section 41 , which is more flexible than adjacent tubular sections 42 and 43 , extends longitudinally across the window 18 . fig7 and 8 illustrate another embodiment of the invention wherein the housing 17 is provided with an elongated strip 50 in the martensite phase which is transformable to an austenite phase with a straight memory by the application of heat to raise the temperature of the strip to above the a f temperature . the rest of the housing is in a cold worked state . fig9 and 10 illustrate yet another embodiment of the invention where the area 60 surrounding the opening 18 of the housing 17 is heat treated above the a f , which preferably is above body temperature , to develop an austenite phase with a straight memory . should the housing become deformed during use , it may be heated above the a f to cause the formation of the austenite phase which returns to the shape remembered , which in this case is straight . in fig4 and 6 - 10 the area immediately adjacent to the area which has been heat treated may have properties intermediate the cold worked and heat treated properties thereby providing additional variations in properties which may be found helpful in designing a housing with multiple locations with various properties . fig1 is a graphical representation of the relationship between the a f of a niti alloy and the temperature at which the alloy is subjected to after cold working in the thermomechanical processing described herein . as shown , the a f decreases as the temperature of thermal treatment increases to a temperature of about 550 ° c . thereafter , the a f increases until the temperature rises to the recrystallization temperature of the alloy . as previously indicated , the general shape of the graphical representation of the relationship remains essentially the same even though the composition of the alloy and the amount of cold work varies . fig1 is a graphical representation of the stress - strain relationship of a pseudoelastic niti alloy . as indicated the strain is proportional to stress up to a strain of about 2 %. at about 2 % strain the austenite phase begins to transform to martensite and continues the transformation to completion over a constant stress region to a strain of about 5 %. beyond a strain of about 8 % the deformation is elastic to about 15 % when it becomes plastic . upon reduction of the stress level the material first returns to a constant stress plateau where the martensite phase transforms back to the austenite . upon completion of the transformation at about a 2 % strain the strain returns to zero if no permanent deformation has occurred . an atherectomy catheter or other intracorporeal catheter with a flexible housing in accordance with the invention may be used in essentially the same manner of prior catheters , except for the notable difference that the characteristics of the housing can be changed within the patient &# 39 ; s body by changing the temperature of the housing therein . if the housing is in the martensite phase at body temperature and the housing has been provided with a desired &# 34 ; remembered shape &# 34 ; at an austenite transformation temperature above body temperature , the housing may be heated within the body to a temperature at or above the a 50 of the shape memory alloy so that the housing will transform to essentially the shape remembered . if the housing is in the austenite phase at body temperature and it is desired to transform the austenite phase to the lower strength martensite , e . g . when it is desired to have a more flexible housing such as when moving the housing through tortuous passageways , the temperature of the housing can be reduced to a temperature at or less than the m 50 of the shape memory alloy . by allowing the housing to return to body temperature , the martensite transforms back to austenite and the shape of the housing returns to the remembered shape suitable for the procedure , e . g . straight . the temperature of the housing can be changed when the catheter is within the patient &# 39 ; s body by a variety of suitable means . for example , the temperature of the housing can be raised by resistance / inductance heating with electrical conductors in contact with or formed integral with the housing . one convenient method of heating the housing with atherectomy catheters which have cutting elements within the housing which fictionally engage the housing is to move the cutting element within the inner chamber with sufficient velocity to raise the temperature of the housing to the desired level above body temperature . other means of heating the housing within the patient &# 39 ; s body include directing a fluid at elevated temperature through an inner lumen of the catheter which is in fluid communication with the interior of the housing . rf heating may also be employed as will be recognized by those skilled in the art . if it is desired to lower the temperature of the housing , a fluid at a temperature less than body temperature may be directed through an inner lumen within the catheter to the interior of the housing . while the housing of the present invention has been described herein in terms of certain presently preferred embodiments directed to atherectomy catheters , those skilled in the art will recognize that it may be used in a wide variety of intracorporeal devices for performing diagnostic or therapeutic procedures within a patient &# 39 ; s body lumen or body cavity . various modifications and improvements can also be made to the invention without departing from the scope thereof .
an elongated flexible housing for an atherectomy or other intracorporeal catheter which is formed of a shape memory alloy such as an alloy formed predominantly of niti intermetallic compound . the housing preferably has an inner chamber with a tissue cutter or other diagnostic or therapeutic system provided within the chamber to sever stenotic material which is urged into the chamber through a opening or window in the housing . in one embodiment the housing has at least one section which is relatively flexible with adjacent sections which are relatively stiff to provide an increase in the overall flexibility of the housing .