Blood pumps

1. An apparatus comprising:

a catheter;

first and second impellers configured to be inserted into a subject's body via the catheter, the first and second impellers being disposed in series with each other;

a first impeller cage configured to be disposed around the first impeller;

a second impeller cage configured to be disposed around the second impeller;

a sleeve configured to extend longitudinally along more than 50 percent of a distance between the first and second impellers wherein the sleeve is separate from the first and second impeller cages.

2. The apparatus according to claim 1 , wherein the first and second impellers are configured to rotate in opposite directions from each other.

3. The apparatus according to claim 1 , wherein the first and second impellers are configured to rotate in the same direction as each other.

4. The apparatus according to claim 1 , wherein the first and second impellers are configured to rotate at different rates of rotation from each other.

5. The apparatus according to claim 1 , wherein the first and second impellers are configured to rotate at the same rate of rotation as each other.

6. The apparatus according to claim 1 , wherein the first and second impellers are configured to pump blood in opposite directions from each other.

7. The apparatus according to claim 1 , wherein the first and second impellers are configured to pump blood in the same direction as each other.

8. The apparatus according to claim 1 , wherein the first and second impellers are configured to be inserted into a blood vessel within the subject's body and are configured to generate a region within the blood vessel that is of lower blood pressure than elsewhere within the blood vessel by pumping blood away from a region of the blood vessel between the first and second impellers.

9. The apparatus according to claim 1 , wherein at least one end of the sleeve is open so that the first impeller cage and the first impeller are able to pass through the open end of the support sleeve even when the first impeller cage and the first impeller are in radially non-constrained configurations thereof.

10. The apparatus according to claim 1 , wherein the first impeller cage and the sleeve are cut from a single piece of a shape memory alloy.

11. The apparatus according to claim 1 , wherein the sleeve is configured to extend at least from a longitudinal center of the first impeller to a longitudinal center of the second impeller.

12. The apparatus according to claim 1 , wherein the first and second impeller cages are integrally formed with the sleeve.

13. The apparatus according to claim 1 , wherein the first and second impeller cages are separately formed from the sleeve.

14. The apparatus according to claim 1 , further comprising:

one or more motors configured to generate rotational motion; and

one or more rotation shafts configured to extend from the one or more motors to the first and second impellers and configured to impart rotational motion from the one or more motors to the first and second impellers.

15. The apparatus according to claim 14 , where:

the one or more motors comprise first and second motors; and

the one or more rotation shafts comprise a first rotation shaft configured to extend from the first motor to the first impeller and to impart rotational motion from the first motor to the first impeller, and a second rotation shaft that is coaxial with the first rotation shaft, the second rotation shaft being configured to extend from the second motor to the second impeller and to impart rotational motion from the second motor to the second impeller.