Surgical generator for ultrasonic and electrosurgical devices

1. A method for controlling power provided to tissue via a surgical device, the method comprising:

providing a pulsed drive signal, wherein a power of the drive signal is proportional to a power provided to the tissue via the surgical device;

periodically receiving indications of an impedance of the tissue;

applying a first composite load curve to the tissue, wherein applying the first composite load curve to the tissue comprises:

modulating a first predetermined number of first composite load curve pulses on the drive signal; and

for each of the first composite load curve pulses, determining a pulse power and a pulse width of the first composite load curve pulses modulated on the drive signal according to a first function of the impedance of the tissue, wherein the modulating comprises modulating the first predetermined number of first composite load curve pulses according to the determined pulse powers and pulse widths; and

applying a second composite load curve to the tissue, wherein applying the second composite load curve to the tissue comprises:

modulating at least one second composite load curve pulse on the drive signal; and

for each of the at least one second composite load curve pulses, determining a pulse power and a pulse width according to a second function of the impedance of the tissue.

2. The method of claim 1 , further comprising:

conditioned upon the impedance of the tissue rising above a predetermined impedance threshold, interrupting the applying of the second composite load curve.

3. The method of claim 2 , further comprising:

conditioned upon the impedance of the tissue rising above the predetermined impedance threshold, modulating at least one cut-region power curve pulse on the drive signal; and

determining a pulse power for the at least one cut-region pulse according to the second function of the impedance of the tissue.

4. The method of claim 3 , wherein a pulse width for the at least one cut region pulse is constant.

5. The method of claim 3 , further comprising:

receiving an indication that a cut is complete; and

upon receiving the indication that the cut is complete, modulating a predetermined number of completion pulses on the drive signal.

6. The method of claim 5 , further comprising determining a power of the predetermined number of completion pulses according to the second function of the impedance of the tissue.

7. The method of claim 1 , further comprising terminating the drive signal when a total time of the drive signal exceeds a timeout time.

8. The method of claim 1 , wherein determining a pulse power and a pulse width of a first composite load curve pulse comprises accessing a look-up table comprising indications of potential values for the impedance of the tissue and corresponding values for pulse power and pulse width.

9. The method of claim 1 , wherein modulating the at least

one second composite load curve pulse on the drive signal comprises modulating a second predetermined number of second composite load curve pulses on the drive signal, and wherein the method further comprises:

applying a third composite load curve to the tissue, wherein applying the third composite load curve to the tissue comprises modulating at least one third composite load curve pulse on the drive signal, wherein each of the at least one third composite load curve pulses comprises a pulse power and a pulse width selected according to a third function of the impedance of the tissue.

10. The method of claim 1 , wherein providing the drive signal comprises providing the drive signal to a harmonic transducer in mechanical communication with a harmonic end effector.

11. The method of claim 1 , wherein providing the drive signal comprises providing the drive signal to first and second electrodes in electrical communication with the tissue.

12. A surgical generator for providing a drive signal to a surgical device, the generator comprising at least one processor and operatively associated memory, wherein the memory comprises instructions that, when executed by the at least one processor, cause the generator to:

generate a pulsed drive signal, wherein a power of the drive signal is proportional to a power provided to tissue via the surgical device;

periodically receive indications of an impedance of the tissue;

apply a first composite load curve to the tissue, wherein applying the first composite load curve to the tissue comprises:

modulating a first predetermined number of first composite load curve pulses on the drive signal; and

for each of the first composite load curve pulses, determine a pulse power and a pulse width of the first composite load curve pulses modulated on the drive signal according to a first function of the impedance of the tissue, wherein the modulating comprises modulating the first predetermined number of first composite load curve pulses according to the determined pulse powers and pulse widths; and

apply a second composite load curve to the tissue, wherein applying the second composite load curve to the tissue comprises:

modulating at least one second composite load curve pulse on the drive signal; and

for each of the at least one second composite load curve pulses, determining a pulse power and a pulse width according to a second function of the impedance of the tissue.

13. The surgical generator of claim 12 , wherein the memory

comprises instructions that, when executed by the at least one processor, cause the generator to:

conditioned upon the impedance of the tissue rising above a predetermined impedance threshold, interrupt the applying of the second composite load curve.

14. The surgical generator of claim 13 , wherein the memory comprises instructions that, when executed by the at least one processor, cause the generator to:

conditioned upon the impedance of the tissue rising above the predetermined impedance threshold, modulate at least one cut-region power curve pulse on the drive signal; and

determine a pulse power for the at least one cut-region pulse according to the second function of the impedance of the tissue.

15. The surgical generator of claim 14 , wherein a pulse width for the at least one cut region pulse is constant.

16. The surgical generator of claim 14 , wherein the memory comprises instructions that, when executed by the at least one processor, cause the generator to:

receive an indication that a cut is complete; and

upon receiving the indication that the cut is complete, modulate a predetermined number of completion pulses on the drive signal.

17. The surgical generator of claim 16 , wherein the memory comprises instructions that, when executed by the at least one processor, cause the generator to determine a power of the predetermined number of completion pulses according to the second function of the impedance of the tissue.

18. The surgical generator of claim 12 , wherein the memory comprises instructions that, when executed by the at least one processor, cause the generator to terminate the drive signal when a total time of the drive signal exceeds a timeout time.

19. The surgical generator of claim 12 , wherein determining a pulse power and a pulse width of a first composite load curve pulse comprises accessing a look-up table comprising indications of potential values for the impedance of the tissue and corresponding values for pulse power and pulse width.

20. The surgical generator of claim 12 , wherein modulating the at least one second composite load curve pulse on the drive signal comprises modulating a second predetermined number of second composite load curve pulses on the drive signal, and wherein the memory comprises instructions that, when executed by the at least one processor, cause the generator to:

apply a third composite load curve to the tissue, wherein applying the third composite load curve to the tissue comprises modulating at least one third composite load curve pulse on the drive signal, wherein each of the at least one third composite load curve pulses comprises a pulse power and a pulse width selected according to a third function of the impedance of the tissue.

21. The surgical generator of claim 12 , wherein providing the drive signal comprises providing the drive signal to a harmonic transducer in mechanical communication with a harmonic end effector.

22. The surgical generator of claim 12 , wherein providing the drive signal comprises providing the drive signal to first and second electrodes in electrical communication with the tissue.