Neuromodulation cryotherapeutic devices and associated systems and methods

1. A cryotherapeutic device, comprising:

an elongated shaft having a distal portion, the shaft being configured to locate the distal portion intravascularly at a treatment site within or otherwise proximate a renal artery;

a cooling assembly at the distal portion of the shaft, the cooling assembly having a low-profile delivery state and an expanded deployed state, the cooling assembly including an applicator having

a first balloon that defines a chamber, and

a second balloon adjacent to the first balloon and configured to thermally insulate a region of tissue at the treatment site from the first balloon when the cooling assembly is in the deployed state;

a supply tube configured to carry liquid refrigerant distally to the chamber along at least a portion of the shaft; and

an exhaust tube configured to carry gaseous refrigerant proximally from the chamber along at least a portion of the shaft,

wherein the second balloon is more complaint than the first balloon.

2. The cryotherapeutic device of claim 1 , wherein the first balloon is non-compliant and the second balloon is compliant.

3. The cryotherapeutic device of claim 2 , wherein:

the first balloon has a D shaped transverse cross-sectional area; and

the second balloon has a C-shaped transverse cross-sectional area.

4. The cryotherapeutic device of claim 1 , wherein the applicator is configured to completely occlude renal arteries having different cross-sectional dimensions.

5. The cryotherapeutic device of claim 1 , wherein the applicator includes a non-compliant partition between the first balloon and the second balloon.

6. The cryotherapeutic device of claim 1 , wherein;

the chamber is a firs chamber;

the second balloon defines a second chamber that is fluidly separate from the first chamber; and

the cryotherapeutic device further comprising a filler lumen extending along at least a portion of the shaft; and configured to carry filler material to the second chamber.

7. The cryotherapeutic device of claim 1 , wherein:

the cooling assembly has a first length;

the first balloon is elongated and has a second length; and

the second balloon is elongated and has a third length; and

the first, second, and third lengths are parallel when the cooling assembly is in the deployed state.

8. A method for treating a patient, comprising:

locating an applicator of a cooling assembly of a cryotherapeutic device intravascularly at a treatment site within or otherwise proximate a renal artery, the applicator being at a distal portion of an elongated shaft;

deploying the cooling assembly from a delivery state to a deployed state, deploying the cooling assembly including non-compliantly expanding a first balloon of applicator and compliantly expanding a second balloon of the applicator;

transitioning liquid refrigerant into gaseous refrigerant to cool a first region of tissue at the treatment site through a heat-transfer portion of the first balloon at a heat-transfer rate sufficient to cause therapeutically-effective, cryogenic renal-nerve modulation; and

thermally insulating a second region of tissue at the treatment site with the second balloon while transitioning liquid refrigerant into gaseous refrigerant to cool the first region of tissue.

9. The method of claim 8 , wherein deploying the cooling assembly includes expanding the applicator to span a cross-sectional dimension of the renal artery.

10. The method of claim 8 , further comprising introducing filler material into the second balloon through a filler lumen extending toward the second balloon along at least a portion of the shaft.

11. The cryotherapeutic device of claim 1 , wherein:

the chamber is a first chamber; and

the second balloon defines a second chamber that is fluidly connected to the first chamber and configured to receive refrigerant from the first chamber.

12. The cryotherapeutic device of claim 1 , wherein the first and second balloons are helical and at least partially interwined.

13. The cryotherapeutic device of claim 12 , wherein the first and second balloons wrap around the exhaust tube.

14. The cryotherapeutic device of claim 12 , wherein:

the chamber is a first chamber;

the second balloon defines a second chamber that is fluidly separate from the first chamber; and

the cryotherapeutic device further comprises a filler lumen extending along at least a portion of the shaft and configured to carry filler material to the second chamber.

15. The cryotherapeutic device of claim 12 , wherein:

the chamber is a first chamber; and

the second balloon defines a second chamber that is fluidly connected to the first chamber and configured to receive refrigerant from the first chamber.

16. The cryotherapeutic device of claim 12 , wherein the applicator includes a third balloon at least partially intertwined with the first and second balloons.

17. The cryotherapeutic device of claim 16 , wherein:

the cooling assembly has a length;

the first balloon has a first curved portion;

the second balloon has a second curved portion;

the third balloon has a third curved portion; and

the second and third curved portions are at opposite sides of the first curved portion along the length of the cooling assembly.

18. The method of claim 8 , further comprising:

exhausting gaseous refrigerant from the first balloon; and

supplying the exhausted gaseous refrigerant from the first balloon to the second balloon.

19. The method of claim 18 , wherein supplying the exhausted gaseous refrigerant from the first balloon to the second balloon includes passively inflating the second balloon with the exhausted gaseous refrigerant.