Catheter pressure transducer

Claim 2

A pressure sensing assembly comprising: a catheter; a miniature pressure transducer carried by the catheter adjacent one end thereof, said transducer comprising a substantially rigid-walled capillary tube which is open at at least one end and which contains a liquid column extending along part of the length of the tube from said one end and a gas column extending along the remainder of the length of the tube, and a reservoir filled with liquid which communicates with the liquid column at said one end of the tube, the reservoir having a wall at least a portion of which is deformable by external pressure so as to cause a variation of the position of the gas-liquid interface in the tube; and communication means carried by the catheter for enabling the position of said interface to be sensed at the other end of the catheter.

Claim 3

A pressure sensing assembly according to claim 1 in which the liquid is a dielectric and said communication means comprises a pair of spaced electrodes the capacitance between which is dependent upon the position of the gas-liquid interface, and a pair of conducting leads respectively connected to said electrodes and extending to said other end of the catheter.

Claim 4

A pressure sensing assembly according to claim 2 in which said spaced electrodes are in overlapping co-axial relationship.

Claim 5

A pressure sensing assembly according to claim 1 in which said deformable wall portion extends substantially parallel to the longitudinal axis of the catheter.

Claim 6

A pressure sensing assembly according to claim 4 in which said deformable wall portion is in the form of a tubular member closed at one end by a rigid sealing member and sealed at the other End to said one end of the catheter.

Claim 7

A pressure sensing assembly comprising: a catheter having a first end and a second end; a miniature electrical pressure transducer including a chamber filled with liquid and having a wall at least a portion of which is deformable, an impedance-sensing element comprising a pair of elongated electrodes extending parallel to each other, and impedance-varying means whereby variations in the pressure of the liquid in said chamber are effective to cause variations in the electrical impedance measurable between said electrodes; means mechanically connecting said transducer to said catheter adjacent said first end thereof with said deformable part of said wall exposed for contact with an external medium whose pressure is to be sensed; and a pair of electrical conductors respectively electrically connected to said electrodes and extending therefrom along the length of said catheter to said second end thereof wherein the improvement comprises the incorporation in said impedance-varying means of: a substantially rigid-walled capillary tube having its length extending parallel to said electrodes and having adjacent a first end thereof an opening through which the interior of said tube communicates with the interior of said chamber; a column of liquid contained by said tube and in contact with the liquid in said chamber, said liquid column extending along only part of the length of said tube from said first end thereof; and a column of gas contained by said tube and extending along the remainder of the length of said tube, said gas column meeting said liquid column at an interface at least part of which is disposed between said pair of electrodes.

Claim 8

A pressure sensing assembly comprising: a catheter having a first end and a second end; a miniature electrical pressure transducer including a chamber filled with liquid and having a wall at least a portion of which is deformable, an impedance-sensing element comprising a pair of elongated electrodes extending parallel to each other, and impedance-varying means whereby variations in the pressure of the liquid in said chamber are effective to cause variations in the electrical impedance measurable between said electrodes; means mechanically connecting said transducer to said catheter adjacent said first end thereof with said deformable part of said wall exposed for contact with an external medium whose pressure is to be sensed; and a pair of electrical conductors respectively electrically connected to said electrodes and extending therefrom along the length of said catheter to said second end thereof wherein the improvement comprises the incorporation in said impedance-varying means of: a substantially rigid-walled capillary tube having its length extending parallel to said electrodes and having adjacent a first end thereof an opening through which the interior of said tube communicates with the interior of said chamber; a column of liquid contained by said tube and in contact with the liquid in said chamber, said liquid column extending along only part of the length of said tube from said first end thereof; and a column of gas contained by said tube and extending along the remainder of the length of said tube, said gas column meeting said liquid column at an interface at least part of which is disposed between said pair of electrodes.

Claim 9

A pressure sensing assembly according to claim 6, in which one of said electrodes is constituted by said tube and the other of said electrodes extends along the interior of said tube.

Claim 10

A pressure sensing assembly according to claim 6, in which said liquid column is electrically insulating.

Claim 11

A pressure sensing assembly according to claim 6, in which said liquid column is electrically conducting and is in direct contact with both of said electrodes.

Claim 12

A pressure sensing assembly according to claim 1 in which the liquid is a conductor and said communication means comprises a pair of spaced electrodes the resistance between which is dependent upon the position of the gas-liquid interface, and a pair of conducting leads respectively connected to said electrodes and extending to said other end of the catheter.

Claim 13

A pressure sensing assembly according to claim 1 in which the said deformable wall portion extends substantially perpendicularly to the longitudinal axis of the catheter and has a surface area considerably greater than the cross-sectional area of said capillary tube.