Catheter with controllable stiffness and method for operating a selective stiffening catheter
A method and device for treating a Chronic Total Occlusion provides a controllable stiffness catheter with a shaft having a stiffness sheath and an access lumen. The device has a stiffness device in a stiff state below a given temperature and in a soft state above the temperature, a temperature-changing device in thermal contact with the stiffness device, the temperature-changing device changing a temperature of the stiffness device below and above the temperature, and a power controller electrically connected to the stiffness device and selectively supplying power to the temperature-changing device to change a stiffness of the stiffness device between the stiff and soft states. A guidewire is moved to a treatment site and the catheter moves along the guidewire up to CTO in its soft state. The catheter stiffens without straightening and, in the stiff state, the catheter or the guidewire is projecting through the CTO.
1. A controllable stiffness catheter, comprising:
a shaft having a stiffness sheath and an access lumen;
a stiffness device having a heater and a melting binder in thermal contact with said heater, said stiffness device being disposed in said stiffness sheath, said binder having a transition temperature, being substantially solid at body temperature and softening as said heater warms said binder above said transition temperature;
a first electrical conductor electrically contacting said stiffness device;
a second electrical conductor electrically contacting said stiffness device and being electrically isolated from said first electrical conductor;
a power supply for supplying power;
a controller electrically connected to said first electrical conductor, to said second electrical conductor, and to said power supply to form an electrically resistive circuit having said stiffness device as a resistor of said circuit, said controller controlling power supplied to said stiffness device through said circuit and, thereby, controlling a temperature of said heater and said binder; and
said stiffness device changes a stiffness of said stiffness sheath between a relatively stiff state when said heater is not energized by said controller and a relatively soft state when said heater is energized by said controller.
2. The catheter according to claim 1 , wherein said stiffness sheath is of a polymer.
3. The catheter according to claim 2 , wherein said polymer is polyurethane.
4. The catheter according to claim 1 , wherein said access lumen is of a polymer.
5. The catheter according to claim 4 , wherein said polymer is PTFE.
6. The catheter according to claim 1 , wherein said access lumen is disposed inside said stiffness sheath and is substantially concentric therewith to define an annulus therebetween.
7. The catheter according to claim 6 , wherein said stiffness device is disposed in said annulus.
8. The catheter according to claim 6 , wherein:
said access lumen has an outer diameter of approximately 0.4 mm; and
said stiffness sheath has an outer diameter of between approximately 0.4 mm and approximately 1.73 mm.
9. The catheter according to claim 1 , wherein said stiffness device is disposed between said access lumen and said stiffness sheath.
10. The catheter according to claim 1 , wherein said stiffness device is a resistive heating element.
11. The catheter according to claim 10 , wherein said resistive heating element is Nickel/Chromium wire.
12. The catheter according to claim 1 , wherein said binder is a mixture of discontinuous fibers.
13. The catheter according to claim 12 , wherein said discontinuous fibers are of chopped carbon fiber or glass.
14. The catheter according to claim 1 , wherein said stiffness device is at least one carbon fiber tow impregnated with said binder.
15. The catheter according to claim 14 , wherein:
said shaft has a shaft distal end and a shaft proximal end;
said power supply and said controller are disposed at said shaft proximal end;
said at least one carbon fiber tow has a tow proximal end and a tow distal end;
said first electrical conductor has a first distal end electrically connected to said tow distal end and a first proximal end electrically connected to said controller; and
said second electrical conductor has a second distal end electrically connected to said tow proximal end and a second proximal end electrically connected to said controller.
16. The catheter according to claim 15 , wherein said controller selectively applies a voltage to said first and second electrical conductors to:
cause current to flow through said circuit and resistively heat said at least one carbon fiber tow; and
remove current flowing through said circuit and cool said at least one carbon fiber tow.
17. The catheter according to claim 16 , wherein said heated carbon fiber tow melts and softens said binder to allow individual carbon fibers of said tow to move with respect to each other and, thereby, increase flexibility of said shaft.
18. The catheter according to claim 15 , further comprising:
a third electrical conductor having a third distal end electrically connected to an intermediate point of said at least one carbon fiber tow and a third proximal end electrically connected to said controller; and
said controller selectively heating at least one portion of said at least one carbon fiber tow dependent upon current supplied to at least two of said first, second, and third conductors.
19. The catheter according to claim 1 , wherein said heater is located only at a portion of said stiffness sheath.
20. The catheter according to claim 19 , wherein said portion is a distal portion of said stiffness sheath.
21. The catheter according to claim 1 , wherein said stiffness device is present throughout an entire length of said stiffness sheath.
22. The catheter according to claim 14 , wherein:
said stiffness device is disposed between said access lumen and said stiffness sheath; and
said at least one carbon fiber tow substantially surrounds said access lumen.
23. The catheter according to claim 22 , wherein said at least one carbon fiber tow is a plurality of carbon fiber tows.
24. The catheter according to claim 23 , wherein said tows helically surround said access lumen.
25. The catheter according to claim 23 , wherein said tows are braided around said access lumen.
26. The catheter according to claim 14 , wherein said at least one carbon fiber tow is a plurality of carbon fiber tows.
27. The catheter according to claim 1 , wherein said binder is a low-melt-point wax selected from the group consisting of paraffin, microcrystalline, or blended wax.
28. The catheter according to claim 1 , wherein said first and second electrical conductors are copper wire.
29. The catheter according to claim 1 , wherein one of said first and second electrical conductors electrically contact a distal end of heater and runs from said distal end of the catheter to said proximal end of the catheter and another of said first and second electrical conductors electrically contact a proximal end of heater.
30. The catheter according to claim 1 , wherein said power supply is one of a battery and an electric mains.
31. The catheter according to claim 1 , wherein said controller limits heating of said binder by limiting current through said circuit.
32. The catheter according to claim 1 , wherein said controller limits heating of said heater by limiting current through said circuit.
33. The catheter according to claim 1 , wherein said controller includes a Proportional-Integral-Derivative current-sensing controller to limit at current supplied in said circuit.
34. The catheter according to claim 1 , wherein said controller includes a thermocouple for monitoring and regulating a temperature of said binder.
35. The catheter according to claim 1 , wherein said binder is relatively substantially solid up to approximately 105° F. and is relatively soft at or above approximately 115° F.