Electrical means to normalize ablational energy transmission to a luminal tissue surface of varying size
Methods and devices for measuring the size of a body lumen and a method for ablating tissue that uses the measurement to normalize delivery of ablational energy from an expandable operative element to a luminal target of varying circumference are provided. The method includes inserting into the lumen an expandable operative element having circuitry with resistivity or inductance that varies with circumference of the operative element, varying the expansion of the operative element with an expansion medium, measuring the resistivity of the circuitry, and relating the resistivity or inductance to a value for the circumference of the operative element. In some embodiments the sizing circuit includes a conductive elastomer wrapped around the operative element. Other embodiments apply to operative elements that include an overlapping energy delivery element support in which the overlap varies inversely with respect to the state of expansion, and electrodes that sense the amount of the overlap.
1. A device for treating a body lumen comprising: an expandable operative element including an inflatable balloon and an ablation energy delivery element support arranged on an exterior of the inflatable balloon; and a sensing circuitry mounted to the support, wherein a resistivity of the sensing circuitry varies according to an amount of expansion of the inflatable balloon.
2. The device of claim 1 , wherein the operative element further includes an ablative energy delivery element.
3. The device of claim 2 , wherein the ablative energy delivery element includes any of a radiofrequency electrode, a radio frequency electrode array, or solid-state circuitry.
4. The device of claim 1 , wherein the sensing circuitry comprises a portion of a band of conductive elastomer wrapped around the operative element such that when the inflatable balloon is contracted a length of the conductive elastomer band is also contracted, and when the inflatable balloon is expanded, the length of the conductive elastomeric band is stretched.
5. The device of claim 1 , wherein the ablation energy delivery element support comprises a longitudinal first edge and a second longitudinal edge that overlap each other to form an area of mutual overlap.
6. The device of claim 5 , wherein the support is circumferentially expandable by the balloon such that the area of mutual overlap is inversely related to the amount of expansion of the balloon.
7. The device of claim 5 , wherein the sensing circuitry comprises sensing elements on both longitudinal edges of the ablational energy delivery element support in the area of mutual overlap, such elements configured to connect across the area of mutual overlap to form a circuit with a particular resistivity, the elements further configured such that the connection formed between sensing elements varies according to an amount of mutual overlap of the two longitudinal edges.
8. The device of claim 7 , wherein the first edge includes a single sensing element and the second edge includes a plurality of spaced-apart sensing elements, the particular element among the plurality of elements on the second edge that connects to the element on the first edge varying according to an amount of mutual overlap of the two edges, the resistivity of the circuit formed varying according to the particular element on the second edge that is included in the circuit.
9. The device of claim 7 , wherein the first edge includes a single sensing element and the second edge includes a plurality of closely-spaced sensing elements, the elements configured such that the element on the first edge connects with one of the plurality of the elements on the second edge or with a pair of adjacent elements on the second edge, the resistivity of the circuit formed varying according to which of the one or which adjacent pair of the elements on the second edge is included in the circuit.
10. The device of claim 7 , wherein the first edge includes a single sensing element and the second edge includes an elongated sensing element, the elements configured such that the single element on the first edge forms a circuit by connecting with the elongated element on the second edge at a point that varies along the length of the elongated element thereby creating a circuit of varying length, the resistivity of the circuit formed varying according to the length of the element on the second edge that is included in the circuit.
11. The device of claim 1 , wherein the ablation energy delivery element support is furled around the inflatable balloon in a deployable configuration.
12. The device of claim 1 , wherein the operative element is configured for delivery of energy to tissue at a target tissue area.