Non-linear control systems and methods for heating and ablating body tissue

An apparatus for supplying energy to an electrode for ablating tissue comprising

• a generator adapted to be electrically coupled to an electrode to supply energy to the electrode for ablating tissue, and
• a controller coupled to the generator to adjust power to the generator and thereby adjust energy supplied to the electrode, the controller comprising
• sampling means for monitoring operating conditions resulting from supplying energy to the electrode,
• a first processing element coupled to the sampling means to derive a power control signal S.sub.DERIVED based upon a first operation condition monitored by the sampling means,
• a second processing element coupled to the sampling means to compare a second operating condition monitored by the sampling means with preselected criteria for the second operating condition and to generate an error signal (E) when the second operating condition fails to meet the preselected criteria, and
• an output element coupled to the first and second processing elements to issue a command signal S.sub.COMMAND to set power supplied to the generator,
• wherein, absent the error signal E, S.sub.COMMAND sets the power according to S.sub.DERIVED, and
• wherein, when the error signal E is generated, S.sub.COMMAND sets the power at a prescribed low power condition (P.sub.LOW), regardless of S.sub.COMMAND, P.sub.LOW being a value above zero.

An apparatus for supplying energy to an electrode for ablating tissue comprising

• a generator adapted to be electrically coupled to an electrode to supply energy to the electrode for ablating tissue, and
• a controller coupled to the generator to adjust power to the generator and thereby adjust energy supplied to the electrode, the controller comprising
• first sampling means for monitoring operating conditions resulting from supplying energy to the electrode,
• second sampling means for deriving impedance resulting from supplying energy to the electrode,
• a first processing element coupled to the first sampling means to derive a power control signal S.sub.DERIVED based upon a first operation condition monitored by the first sampling means,
• a second processing element coupled to the first processing element to compare a second operating condition monitored by the first sampling means with preselected criteria for the second operating condition and to generate an error signal (E) when the second operating condition fails to meet the preselected criteria, and
• an output element coupled to the first and second processing elements to issue a command signal S.sub.COMMAND to set power supplied to the generator,
• wherein, absent the error signal E, S.sub.COMMAND sets the power according to S.sub.DERIVED, and
• wherein, when the error signal E is generated, S.sub.COMMAND sets the power at a prescribed low power condition (P.sub.LOW), regardless of S.sub.COMMAND, P.sub.LOW being a value above zero to permit derivation of impedance by the second sensing means.

A method for ablating body tissue comprising the steps of

• applying ablating energy to an electrode,
• monitoring a selected operating condition of the electrode and derive from it an operating value (V.sub.D),
• comparing the derived operating value V.sub.D to a preselected set value (V.sub.S) for the operating condition to establish an error signal (.DELTA.), where:
• .DELTA.=V.sub.S -V.sub.D
• issuing a command signal S.sub.COMMAND to adjust power to the electrode above a zero value, thereby maintaining power to the electrode without interruption, where:
• S.sub.COMMAND =f(S.sub.SCALE X.DELTA.)
• where S.sub.SCALE is a nonlinear scaling factor that equals a first value (X) when .DELTA.>Z and equals a second value (Y), different than X, when .DELTA.<Z, and Z is a desired .DELTA..

A method for ablating body tissue comprising the steps of

• applying ablating energy to an electrode,
• monitoring first and second operating conditions for the electrode, each operating condition resulting from applying ablating energy, the first operating condition being different than the second operating condition,
• deriving a power control signal S.sub.DERIVED based upon the first monitored operation condition,
• comparing the second monitored operating condition with preselected criteria for the second operating condition to generate an error signal (E) when the second operating condition fails to meet the preselected criteria,
• issuing a command signal S.sub.COMMAND to set power supplied to the electrode,
• wherein, absent the error signal E, S.sub.COMMAND sets the power according to S.sub.DERIVED, and
• wherein, when the error signal E is generated, S.sub.COMMAND sets the power at a prescribed low power condition (P.sub.LOW), regardless of S.sub.COMMAND, P.sub.LOW being a value above zero.

A method for ablating body tissue comprising the steps of

• applying ablating energy to an electrode,
• monitoring first and second operating conditions for the electrode, each operating condition resulting from applying ablating energy, the first operating condition being different than the second operating condition,
• measuring impedance resulting from applying ablating energy to the electrode, deriving a power control signal S.sub.DERIVED based upon the first monitored operation condition,
• comparing the second monitored operating condition with preselected criteria for the second operating condition to generate an error signal (E) when the second operating condition fails to meet the preselected criteria,
• issuing a command signal S.sub.COMMAND to set power supplied to the electrode,
• wherein, absent the error signal E, S.sub.COMMAND sets the power according to S.sub.DERIVED, and
• wherein, when the error signal E is generated, S.sub.COMMAND sets the power at a prescribed low power condition (P.sub.LOW), regardless of S.sub.COMMAND, P.sub.LOW being a value above zero so that measurement of impedance can continue.