Automatic locking and unlocking vacuum syringes, and associated systems and methods

A syringe, comprising:

• a barrel;
• and
• a plunger assembly slidably positioned within the barrel, wherein the plunger assembly comprises—
• a handle assembly including a shaft having a distal portion and a locking recess formed at the distal portion;
• and
• a seal assembly including a shield member, wherein the seal assembly is movable relative to the handle assembly between (a) a first position in which the shield member radially shields the locking recess and (b) a second position in which the shield member is axially spaced apart from the locking recess.

A plunger assembly, comprising:

• a handle assembly including a first shaft having a distal portion;
• a seal assembly including a second shaft and a seal head coupled to the second shaft;
• and
• a biasing member operably coupling the first shaft to the second shaft, wherein the biasing member has a biasing force, and wherein—
• the biasing force is configured to bias the seal assembly to a first position that is axially toward the distal portion of the first shaft;
• and
• a force on the seal assembly greater than the biasing force is configured to move the seal head to a second position that is axially away from the distal portion of the first shaft.

A clot treatment system, comprising:

• an aspiration catheter defining a lumen;
• a tubing assembly fluidly coupled to the lumen of the catheter, wherein the tubing assembly includes a valve that is movable between (a) a first position permitting fluid flow through the tubing assembly from the lumen and (b) a second position inhibiting fluid flow through the tubing assembly from the lumen;
• and
• a syringe including a barrel, a plunger assembly slidably positioned within the barrel and movable between a first position and a second position, and a locking assembly coupled to the barrel, wherein—
• the barrel is configured to be fluidly coupled to the tubing assembly,
• with the valve in the first position,
• the plunger assembly is configured to be withdrawn through the barrel to generate vacuum pressure in the barrel,
• the plunger assembly is configured to move from the first position to the second position in response to the vacuum pressure, and
• the plunger assembly is configured to lock to the locking assembly in the second position such that the locking assembly inhibits movement of the plunger assembly through the barrel, and
• upon subsequent movement of the valve from the first position to the second position,
• the plunger assembly is configured to move from the second position to the first position in response to the vacuum pressure being released, and
• the plunger assembly is configured to unlock from the locking assembly in the first position such that the locking assembly permits movement of the plunger assembly through the barrel.