Method of managing energy delivered by a shockwave through dwell time compensation
A method of delivering shock waves to treat calcified lesions includes advancing an angioplasty balloon mounted on a carrier, to reach the calcified lesion. A pair of electrodes is located within the balloon. The balloon is filled with a conductive fluid. A series of high voltage pulses are supplied to the electrodes. Each voltage pulse has sufficient energy to generate an arc in the fluid and allows current to flow across the pair of electrodes to produce a shock wave. During each pulse, the current flowing across the pair of electrodes is monitored. When the sensed current reaches a predetermined value, that voltage pulse is terminated. The predetermined value is selected to be high enough to ensure the creation of the arc while compensating for the variable dwell time between initial application of a given voltage pulse and creation of the arc.
1. A method for controlling delivery of shock waves to treat calcified lesions in the wall of a blood vessel of a patient, the method comprising:
positioning an angioplasty catheter device within the blood vessel of the patient, the catheter device comprising an angioplasty balloon surrounding an arc generator, the angioplasty catheter including a central guide wire sheath for receiving a guide wire therein;
inflating the angioplasty balloon of the catheter device within the vessel with a conductive liquid; and
delivering, via a power source, a plurality of voltage pulses to the arc generator disposed within the angioplasty balloon, wherein
the arc generator comprises a first electrode and a second electrode, and
delivering the plurality of voltage pulses comprises, for each pulse of the plurality of voltage pulses,
applying a voltage to the arc generator,
monitoring signals representing values of a current flow between the first electrode and the second electrode caused by the voltage, wherein the signals are generated by a current sensor, and
terminating the voltage to the arc generator to complete the respective pulse, wherein terminating comprises
i) receiving a respective signal from the current sensor indicative of a current of at least a predetermined value, and
ii) causing switching of a switch to disconnect the power source from the arc generator;
wherein each pulse of the plurality of voltage pulses is sufficient to ensure creation of a respective plasma arc by the arc generator, creating a respective expansion shock wave conducted through the conductive liquid and through the angioplasty balloon to the vessel, thereby delivering energy to the calcified lesions within the wall of the vessel to break apart the lesions, wherein
a respective dwell time between initial application of each pulse and creation of the respective plasma arc varies from pulse to pulse, and
the predetermined value is selected to compensate for the variable dwell times and minimize excess energy delivered to the arc generator.
2. The method of claim 1 , wherein the switch is a solid state switch.
3. The method of claim 1 , further comprising adding a contrast medium to the conductive liquid for imaging the catheter device during treatment.
4. The method of claim 1 , wherein:
applying the voltage to the arc generator comprises applying the voltage via output terminals of the power source; and
monitoring the signals representing the values of the current flow comprises monitoring a voltage drop across a resistor connected to one of the output terminals.
5. The method of claim 1 , wherein terminating the voltage to the arc generator comprises
beginning a delay timer responsive to receiving the respective signal, and
terminating the voltage upon completion of a predetermined period according to the delay timer.
6. The method of claim 1 , wherein the voltage of each pulse of the plurality of voltage pulses is between 500 volts and 10,000 volts.
7. The method of claim 1 , wherein the voltage of each pulse of the plurality of voltage pulses is between 1000 volts and 10,000 volts.
8. The method of claim 1 , wherein the predetermined current value is selected to ensure the creation of the expansion shock wave associated with the expansion of a steam bubble and minimize energy available for a trailing shock wave associated with the subsequent collapse of the steam bubble.
9. A method of delivering shock waves to treat calcified lesions comprising:
advancing an elongated carrier through a body lumen to reach the calcified lesion, said carrier having a flexible member mounted near the distal end of the elongated carrier, said flexible member having a pair of electrodes disposed therein;
filling the flexible member with a conductive liquid;
delivering a series of voltage pulses from a power source to the electrodes through a switch, each voltage pulse having a voltage between 500 volts and 10,000 volts, each voltage pulse having sufficient energy to generate an arc in the liquid within the flexible member and allowing current to flow across the pair of electrodes to produce a shock wave associated with the expansion of a steam bubble, wherein a dwell time between initial application of a given voltage pulse and creation of the arc is variable from pulse to pulse;
sensing the current flowing across the pair of electrodes during each voltage pulse; and
for each given voltage pulse, initiating the termination of the given voltage pulse when the sensed current reaches a predetermined value, wherein the termination includes switching the switch, the predetermined value being high enough to ensure the creation of the arc while compensating for the variable dwell time thereby minimizing excess energy delivered to the pair of electrodes.
10. The method of claim 9 , wherein the initiating the termination of the given voltage pulse includes activating a delay timer in response to the sensing of the current reaching the predetermined value prior to the switch being switched.
11. The method of claim 9 , wherein the switch is a solid state switch.
12. The method of claim 9 , further comprising adding a contrast medium to the conductive liquid for imaging the carrier during treatment.
13. The method of claim 9 , wherein sensing the current comprises sensing the current using a current sensor including a resistor and wherein the voltage drop across the resistor is monitored to determine the current flowing between the pair of electrodes.
14. The method of claim 9 , wherein the voltage of each pulse of the plurality of voltage pulses is between 1000 volts and 10,000 volts.
15. The method of claim 9 , wherein the predetermined value is selected to ensure the creation of the shock wave associated with the expansion of a steam bubble and minimize energy available for a trailing shock wave associated with the subsequent collapse of the steam bubble.
16. A method of delivering shock waves to treat calcified lesions in the wall of a blood vessel comprising:
advancing an elongated angioplasty carrier through a blood vessel to reach the calcified lesion, said angioplasty carrier having an angioplasty balloon mounted near the distal end of the angioplasty carrier, said balloon having a pair of electrodes disposed therein;
filling the balloon with a conductive liquid;
delivering a series of voltage pulses from a power source to the electrodes through a switch, each voltage pulse having a voltage between 500 volts and 10,000 volts, each voltage pulse having sufficient energy to generate an arc in the liquid within the balloon and allowing current to flow across the pair of electrodes to produce a shock wave in the conductive liquid, wherein a dwell time between initial application of a given voltage pulse and creation of the arc is variable from pulse to pulse;
monitoring a current sensor to sense the current flowing across the pair of electrodes during each voltage pulse; and
for each given voltage pulse, initiating a delay period when the sensed current reaches a predetermined value,
once the delay period is over, initiating the termination of the given voltage pulse,
wherein the termination includes switching the switch, and
wherein the predetermined value and the delay period are selected to ensure the creation of the arc while compensating for the variable dwell time thereby minimizing excess energy delivered to the pair of electrodes.
17. The method of claim 16 , wherein the switch is a solid state switch.
18. The method of claim 16 , further comprising adding a contrast medium to the conductive liquid for imaging the carrier during treatment.
19. The method of claim 16 wherein the current sensor includes a resistor and wherein the voltage drop across the resistor is monitored to determine the current flowing between the pair of electrodes.
20. The method of claim 16 , wherein the predetermined current value and the delay period are selected to ensure the creation of an expansion edge shock wave associated with the expansion of a steam bubble and minimize energy available for a trailing shock wave associated with the subsequent collapse of the steam bubble.