System and method for control of tissue welding

A control method for welding of biological tissue comprising:

• (a) applying an increasing RF voltage to the electrodes of a tissue welding tool during a first stage;
• (b) measuring the values of the RF voltage and electric current passing through the tissue, and the duration of the first stage;
• (c) calculating tissue impedance values by dividing the RF voltage values by the electric current values;
• (d) determining a minimum tissue impedance value;
• (e) storing the minimum tissue impedance value;
• (f) calculating relative tissue impedance values by dividing of the tissue impedance values by the minimum tissue impedance value;
• (g) stopping the first stage when the relative tissue impedance reaches an endpoint relative tissue impedance value calculated as a function of the relative tissue impedance;
• (h) storing the duration of the first stage and a value of the RF voltage at the end of the first stage;
• (i) calculating an RF voltage level for a second stage as a function of the value of the RF voltage at the end of the first stage;
• (j) calculating the duration of the second stage as a function of the duration of the first stage;
• and
• (k) applying an RF voltage during the second stage at the RF voltage level calculated in step (i).

A control method for welding of biological tissue comprising:

• (a) applying an increasing RF voltage to the electrodes of a tissue welding tool during a first stage;
• (b) measuring the values of the RF voltage and electric current passing through the tissue, and the duration of the first stage;
• (c) calculating tissue impedance values by dividing the RF voltage values by the electric current values;
• (d) determining a minimum tissue impedance value;
• (e) storing the minimum tissue impedance value;
• (f) calculating relative tissue impedance values by dividing the tissue impedance values by the minimum tissue impedance value;
• (g) stopping the RF voltage increase when the relative tissue impedance reaches an endpoint relative tissue impedance value calculated as a function of the relative tissue impedance;
• (h) storing the duration of the first stage and the RF voltage at the end of the first stage;
• (i) calculating an RF voltage level for a second stage as a function of the value of the RF voltage at the end of the first stage;
• (j) calculating the duration of the second stage as a function of the duration of the first stage;
• (k) calculating a modulation frequency as a function of the duration of the first stage;
• and
• (l) applying an RF voltage at the RF voltage level calculated in step (i) for the duration of the second stage calculated in step (j), and modulating the RF voltage by pulses at the modulation frequency calculated in step (k).

A control method for welding of biological tissue comprising:

• (a) applying an increasing RF voltage to the electrodes of a tissue welding tool during a first stage;
• (b) measuring the values of the RF voltage and electric current passing through the tissue, and the duration of the first stage;
• (c) calculating tissue impedance values by dividing the RF voltage values by the electric current values;
• (d) determining a minimum tissue impedance value;
• (e) storing the minimum tissue impedance value;
• (f) calculating relative tissue impedance values by dividing the tissue impedance values by the minimum tissue impedance value;
• (g) stopping the first stage when the relative tissue impedance reaches an endpoint relative tissue impedance value calculated as a function of the relative tissue impedance;
• (h) storing the duration of the first stage and value of the RF voltage at the end of the first stage;
• (i) calculating the duration of the second stage as a function of the duration of the first stage;
• and
• (j) applying the RF voltage during the second stage, wherein the RF voltage is varied as a function of the relative tissue impedance during the second stage.

A control method for welding of biological tissue comprising:

• (a) applying an increasing RF voltage to the electrodes of a tissue welding tool during a first stage;
• (b) measuring the values of the RF voltage and electric current passing through the tissue, and the duration of the first stage;
• (c) calculating tissue impedance values by dividing the RF voltage values by the electric current values;
• (d) determining a minimum tissue impedance value;
• (e) storing the minimum tissue impedance value;
• (f) calculating relative tissue impedance values by dividing the tissue impedance values by the minimum tissue impedance value;
• (g) stopping the first stage when the relative tissue impedance reaches an endpoint relative tissue impedance value calculated as a function of the relative tissue impedance;
• (h) storing the duration of the first stage and a value of the RF voltage at the end of the first stage;
• (i) calculating an initial RF voltage level for a second stage as a function of the value of the RF voltage at the end of the first stage;
• (j) calculating the duration of the second stage as a function of the duration of the first stage;
• (k) calculating a modulation frequency as a function of the duration of the first stage;
• and
• (l) applying an RF voltage for the duration of the second stage calculated in step (j), initially setting the amplitude of the RF voltage to the initial RF voltage level calculated in step (i), modulating the RF voltage by pulses at the modulation frequency calculated in step (k), and varying the amplitude of the RF voltage as a function of the relative tissue impedance.

An apparatus for tissue welding comprising:

• a surgical instrument having electrodes adapted to engage tissue to be welded;
• a power source coupled to the electrodes for providing RF voltage, the power source including one or more sensors for sensing the RF voltage and current between the electrodes;
• and
• a control device coupled to the power source;
• wherein the control device:
• controls the power source to provide an RF voltage to the electrodes during a first stage;
• monitors tissue impedance;
• determines a minimum tissue impedance value;
• determines relative tissue impedance as a ratio of the measured tissue impedance and the minimum tissue impedance value;
• detects when the relative tissue impedance reaches a predetermined relative tissue impedance value;
• and controls the power source to provide an RF voltage during a second stage, the duration of the second stage being calculated by the control device as a function of the duration of the first stage.

An apparatus for welding of biological tissue comprising:

• (a) means for applying an RF voltage during a first stage to electrodes of a tissue welding tool;
• (b) means for monitoring tissue impedance, and determining a minimum tissue impedance value during the first stage;
• (c) means for determining relative tissue impedance, the relative tissue impedance being equal to the ratio of tissue impedance to the minimum tissue impedance value;
• (d) means for detecting when the relative tissue impedance reaches a predetermined relative tissue impedance value;
• (e) means for starting a second stage when the relative tissue impedance reaches the predetermined relative tissue impedance value;
• (f) means for calculating the duration of the second stage as a function of the duration of the first stage;
• and
• (g) means for applying the RF voltage during the second stage to the electrodes of the tissue welding tool.