Device for measuring negative pressures in an extracorporeal blood circuit

Device for measuring the pressure of blood in a pipe (44) of an extracorporeal blood circuit (42), comprising a pressure measurement section (46) having a compartment (58) which is delimited especially by a main wall (64) and by a secondary wall (65) facing the main wall (64), the two walls (64, 65) being substantially rigid and parallel, the main wall (64) having a hole (66) which is sealed by a main closure element (68) having an internal face (70) which is in contact with the blood and an external face (72) which is in contact with the ambient air, the entire main closure element (68) being elastically deformable or displaceable along a deformation or displacement axis (A—A), which is substantially orthogonal to its general plane, under the effect of the blood pressure, the main closure element (68) being designed to engage with a load sensor (56) so that a portion of the external face (72) of the main closure element (68), in its rest state, is in direct or indirect contact with the load sensor (56) which can measure the force applied axially to the internal face (70) of the main closure element (68) by the blood pressure, in order to calculate therefrom the value of this pressure, characterized in that the pressure measurement section (46) comprises:

• in its secondary wall (65), facing the hole (66) of the main wall (64), a secondary hole (84) which is sealed by a secondary closure element (86) having a deformation or displacement axis (A—A) which is substantially coincident with that of the main closure element (68), the area of the internal face (92) of the secondary closure element (86) being greater than the area of the internal face (70) of the main closure element (68), such that when the pressure of the blood is less than the pressure of the ambient air, the axial displacement of the secondary closure element (86) towards the main closure element (68) is greater than the axial displacement of the main closure element (68) towards the secondary closure element (86);
• and comprising, in the compartment (58), a transmission spacer (94) which, when the pressure of the blood and the pressure of the ambient air are substantially equal, occupies a rest position in which the transmission spacer (94) is in contact by a first axial end (96) with the internal face (70) of the main closure element (68) and, by a second axial end (98), with the internal face (92) of the secondary closure element (86);
• such that when the blood pressure is less than the ambient air pressure, the spacer (94) transmits the axial displacement, in the direction of the load sensor (56), from the secondary closure element (86) to the main closure element (68), so that the load sensor (56) can measure the resultant axial force in order to calculate therefrom the value of the blood pressure.