Syringe with stops for maintaining intermediate piston level - esp. to sustain suction of plasma sample chamber

摘要

Syringe for use in pulling and maintaining a vacuum in a closed vessel fitted with a rubber cap is provided with means for locking the syringe piston at one or more intermediate positions in the syringe barrel. Used esp. for establishment of a vacuum in a side chamber bounded by a semi-permeable membrane to isolate samples of plasma from blood recirculating through e.g. an artificial kidney, to monitor the purification level. A specific form of the syringe has the piston carried on a rod with radial ribs extending almost to the barrel walls. The barrel wall has 1 or more internal lugs which can be engaged by slots in the piston rod ribs to prevent the piston from shifting unless it is rotated to disengage the lug. Pref. the piston can be arrested at 1 or more levels in a barrel graduated the swept vol. by which the sample chamber has been increased. The lugs may have a tapered end .