Cryosurgical device

Claim 1

Cryosurgical instrument with a probe for cooling limited zones of biological tissues, including a thermally conductive probe tip having a hollow inner chamber, into which a supply duct leads through a constricted exit gap, through which duct a gas is suppliable for cooling the tip, on the basis of the Joule-Thomson effect resulting from gas flow through the exit gap, a discharge duct having first and second ends, said first end communicating with said inner chamber and said second end being open to the atmosphere, said discharge duct extending within and coaxial with respect to said supply duct, said instrument having also a valve adjustable from the outside for control of the operating temperature of the probe tip, and further comprising the improvement which consists in that said discharge duct (4) is displaceable in the axial direction relative to the supply duct (3) surrounding it, said first end of said axially movable discharge duct has a conical member arranged symmetrically around the axis of said discharge duct, with the base of said conical member facing in the direction of said inner chamber, the end of said supply duct adjoining said inner chamber having a conically tapered inner wall arranged symmetrically around the axis of the supply duct, said tapered inner wall being narrowed in the direction away from said inner chamber and said gap being formed between the edge of the base of said conical member and said inner wall of said supply duct, the size of said gap being adjustable by moving said discharge duct axially with respect to said supply duct, said conical member and said tapered inner wall being sized and positioned such that when said duct is moved axially in the direction away from said inner chamber, the edge of the base of said conical member will ultimately come in contact with the tapered inner wall of said supply duct, and said tapered inner wall narrows more strongly than the taper of said conical member.