Tissue resecting systems and methods

1. A tissue resecting system, comprising:

a handle;

an elongated shaft extending from the handle, the elongated shaft including an outer tubular member and an inner tubular member configured to reciprocate within the outer tubular member;

a motor drive system positioned in the handle, the motor drive system including a motor and a motor shaft rotatably driving a rotation-to-linear motion conversion mechanism;

a controller configured to control reciprocation of the inner tubular member; and

a microswitch configured to engage an engagement feature formed in the rotation-to-linear motion conversion mechanism once each revolution of the rotation-to-linear motion conversion mechanism;

wherein the microswitch sends an electrical signal to the controller for each instance the microswitch engages the engagement feature;

wherein the inner tubular member is reciprocated through at least one full distal and proximal reciprocation stroke via 360 degree rotation of the rotation-to-linear motion conversion mechanism in a first rotational direction.

2. The tissue resecting system of claim 1 , wherein the rotation-to-linear motion conversion mechanism includes a rotatable drive collar having an arcuate slot formed therein.

3. The tissue resecting system of claim 2 , wherein the engagement feature is an indent formed in the drive collar.

4. A tissue resecting system, comprising:

a handle;

an elongated shaft extending from the handle, the elongated shaft including an outer tubular member and an inner tubular member configured to reciprocate within the outer tubular member;

a motor drive system positioned in the handle, the motor drive system including a motor and a motor shaft rotatably driving a rotation-to-linear motion conversion mechanism;

a controller configured to control reciprocation of the inner tubular member; and

a microswitch configured to engage an engagement feature formed in the rotation-to-linear motion conversion mechanism once each revolution of the rotation-to-linear motion conversion mechanism;

wherein the microswitch sends an electrical signal to the controller for each instance the microswitch engages the engagement feature;

wherein the rotation-to-linear motion conversion mechanism includes a rotatable drive collar having an arcuate slot formed therein;

wherein the arcuate slot engages a pin coupled to the inner tubular member.

5. The tissue resecting system of claim 4 , wherein the inner tubular member is non-rotatable relative to the outer tubular member.

6. A tissue resecting system, comprising:

a handle;

an elongated shaft extending from the handle, the elongated shaft including an outer tubular member and an inner tubular member configured to reciprocate within the outer tubular member;

a motor drive system positioned in the handle, the motor drive system including a motor and a motor shaft rotatably driving a rotation-to-linear motion conversion mechanism;

a controller configured to control reciprocation of the inner tubular member; and

a microswitch configured to engage an engagement feature formed in the rotation-to-linear motion conversion mechanism once each revolution of the rotation-to-linear motion conversion mechanism;

wherein the microswitch sends an electrical signal to the controller for each instance the microswitch engages the engagement feature;

wherein the controller uses the electrical signal to determine a tachometer signal.

7. The tissue resecting system of claim 6 , wherein the rotation-to-linear motion conversion mechanism includes a rotatable drive collar having an arcuate slot formed therein;

wherein the engagement feature defines a reference point corresponding to an angular rotation of the drive collar.

8. The tissue resecting system of claim 7 , wherein the reference point corresponds to a position of a distal edge of the inner tubular member relative to a window of the outer tubular member.

9. The tissue resecting system of claim 8 , further comprising a controller algorithm adapted to modulate motor voltage in response to tachometer signals (i) to drive the inner tubular member at a predetermined speed and (ii) to calculate resistance to driving the inner tubular member at the predetermined speed.

10. The tissue resecting system of claim 9 , wherein the controller algorithm is adapted to modulate voltage motor voltage at intervals of less than 50 milliseconds.

11. The tissue resecting system of claim 9 , further comprising a second controller algorithm responsive to the calculated resistance, the second controller algorithm adapted to de-energize the motor at a predetermined point to permit momentum to move the distal edge of the inner tubular member to a selected stop position relative to the window.

12. The tissue resecting system of claim 11 , wherein the second algorithm is configured to compare the calculated resistance to a look-up table of known resistances correlated with a momentum parameter related to stopping movement of the inner tubular member.

13. The tissue resecting system of claim 11 , wherein the controller is configured to stop the distal edge of the inner tubular member at the stop position for coagulating tissue.

14. The tissue resecting system of claim 13 , wherein the outer tubular member is fixed to the handle.

15. The tissue resecting system of claim 14 , wherein the inner and outer tubular members include opposing polarity electrodes for selectively resecting and coagulating tissue.

16. A method of controlling a tissue resecting system including a handle, an elongate shaft extending from the handle, a motor drive system positioned in the handle and engaged with the elongate shaft, and a controller configured to control the motor drive system, the method comprising:

moving an inner sleeve of the elongate shaft across a tissue-receiving window of an outer sleeve of the elongate shaft with the motor drive system to resect tissue extending into the tissue-receiving window;

extracting the resected tissue proximally through an extraction lumen of the inner sleeve;

evaluating a reciprocation rate of the inner sleeve within the outer sleeve using an algorithm within the controller that is responsive to tachometer signals associated with the motor drive system; and

modulating voltage supplied to the motor drive system based on the algorithm to maintain the reciprocation rate at a constant level.

17. The method of claim 16 , wherein the motor drive system includes a motor and a motor shaft rotatably driving a rotation-to-linear motion conversion mechanism for converting rotational motion of the motor to reciprocating motion of the inner sleeve relative to the outer sleeve.

18. The method of claim 17 , wherein the motor drive system includes a microswitch configured to engage an engagement feature formed in the rotation-to-linear motion conversion mechanism once each revolution of the rotation-to-linear motion conversion mechanism;

wherein the microswitch sends one tachometer signal to the controller for each instance the microswitch engages the engagement feature.

19. The method of claim 17 , wherein the rotation-to-linear motion conversion mechanism includes a rotatable drive collar attached to the motor and a pin attached to the inner sleeve, wherein the pin is positioned in an arcuate slot of the drive collar.

20. The method of claim 16 , wherein the algorithm is configured to modulate voltage supplied to the motor drive system at intervals of less than 50 milliseconds.