with reference to fig7 , 1 denotes in its entirety a machine for extracorporeal blood treatment , which can be used in particular for treatment of renal insufficiency , and / or for therapeutic replacement of plasma , and / or for hemoperfusion . the machine 1 comprises a blood pump 2 for blood circulation in an extracorporeal circuit . the extracorporeal circuit , of known type and not illustrated , comprises an arterial line which removes blood from a vascular access of a patient and takes it to a blood treatment unit ( for example a dialysis filter ), and a venous line which returns the blood to the patient after it has been treated and is outflowing from the treatment unit . the machine 1 further comprises other pumps , in the illustrated case four pumps 3 , for the circulation of various liquids used in treatment , such as for example a fresh treatment liquid which is supplied to an inlet of the blood treatment unit , a used liquid discharged from an outlet of the blood treatment unit , one or more infusion liquids which are infused into the extracorporeal blood circuit . the machine 1 comprises other known - type elements , in particular various actuators and sensors ( pressure sensors , blood leakage sensor , air bubble sensor , venous check valve , etc .) which are not described herein in detail . the machine 1 to which reference is made in this description is a machine for intensive extracorporeal blood treatment , sold under the name of prismaflex ®. the machine 1 comprises a syringe pump 4 for infusion of a liquid into the extracorporeal blood circuit . in particular the syringe pump 4 is used for infusion of an anticoagulant , for example heparin , or another infusion liquid , for example a calcium solution that can be used together with a separate infusion of a citrate - based anticoagulant . the syringe pump 4 , which is described in greater detail in figures from 1 to 6 , comprises a support 5 for receiving and removably holding a syringe , a linear pusher 6 for moving a mobile part 7 ( plunger ) of the syringe , a sensor for emitting a signal indicating the push force exerted by the plunger 6 , and a control unit 8 for receiving the force signal and for guiding the linear pusher 6 according to the signal received . the force sensor is an element of known type and not described in detail : it can comprise an analog force transducer ( for example a load cell ). the syringe pump can be further provided with a front end - run transducer ( upper ) and a back end - run sensor ( lower ), of known type and not illustrated . a syringe pump having the characteristics as described is already used in the prismaflex ® machine , at present available commercially . the syringe pump described herein has a vertical - axis operating configuration and the following description makes reference to this configuration ; however the invention is applicable to syringe pumps in which the operating position of the syringe can be of any type . in the present invention the support 5 of the syringe pump comprises a series of interchangeable gripping elements 9 and a base , fixed to the machine frame , having a seating 10 for receiving the gripping elements 9 in a predetermined position . the seating 10 for receiving the gripping elements 9 comprises a linear sliding guide which is parallel to the longitudinal axis of the housing of the fixed part of the syringe . in the example the sliding guide comprises a pair of parallel sliding guides , for example of the dovetail type . each gripping element 9 can be mounted on the seating 10 by sliding on the linear guide up to reaching an endrun position , at a predetermined operating position in which the gripping element 9 is fixed to the seating 10 using removable blocking means ( for example a fastening of the screw type inserted internally of an eye in the gripping element 9 ). each gripping element 9 comprises two gripping arms 11 , arranged one by the side of another , which are elastically deformable in order to embrace the diameter of a fixed part 12 ( cylinder ) of the syringe . a frontal opening is afforded between the two arms 11 for introducing the diameter of the fixed part of the syringe . the arms 11 are further elastically extendable in order to be able to introduce the syringe by force and to hold the syringe in position . the two arms 11 each exhibit a fixed end part 11 a , rigidly constrained to a plate - shaped base body , and a curved intermediate part 11 b which defines , together with the curved intermediate part 11 b of the other arm , a contact surface with the fixed part 12 of the syringe . the contact surface is counter - shaped with respect to the external surface of the fixed part 12 of the syringe and is , in the illustrated example , cylindrical in shape . each arm 11 further exhibits a free end part 11 c which , together with the free end part 11 c of the other arm , delimits the frontal opening for introduction of the syringe . the free end part 11 c exhibits a curvature towards the outside of the frontal opening so as to define , together with the curvature of the other arm , an entry zone for facilitated introduction of the syringe diameter . each gripping element 9 of the series of elements 9 is conformed such as to define a housing for the fixed part 12 ( cylinder ) of the syringe . the housing defined by each gripping element 9 of the series has a different diameter with respect to another gripping element in the same series and also has a longitudinal axis x which coincides with a longitudinal axis of the fixed part 12 of the syringe . the difference in the housings is evident from fig6 , in which four different gripping elements 9 of a same series are shown : in each gripping element of a series a first portion , which is predisposed to couple with the seating fixed to the machine , is identical for all ( in the preferred embodiment it comprises the plate - shaped base body ), while a second portion , predisposed for removable coupling with the syringe , is different for the various elements , defining housings of various conformation but all having a longitudinal axis x ( perpendicular to the sheet in fig6 ) having a same relative position with respect to the first portion and thus with respect to the fixed seating and the pusher 6 . each gripping element 9 of the series is thus conformed and arranged in such a way that , when it is received in the seating in the predetermined operating position , the longitudinal axis x of the syringe housing is in a predetermined position with respect to the linear pusher 6 . the predetermined relative position is the same for all the interchangeable gripping elements 9 in the series . the first portion of each gripping element 9 has a counter - guide for sliding coupling with the linear guide of the fixed seating 10 of the support . the counter - guide comprises , in particular , two dove - tailed elements which are parallel for sliding coupling with the corresponding guide elements . the gripping arms 9 exhibit an predetermined axial length so that they do not obstruct the zone of the syringe which is full of liquid , or , in other words , the zone of the syringe which is interested by the run of the mobile element ( plunger ) of the syringe directly operating on the liquid . the mobile part 7 of the syringe has a mobile element ( plunger ) which operates directly on the liquid . the mobile element exhibits a front surface which is in direct contact with the liquid to be infused . even when the syringe is full of liquid , the front surface is situated at a certain distance from the end of the fixed part 12 of the syringe bearing the radial projection 14 . the fixed part 12 ( cylinder ) of the syringe exhibits an axially - extended tract which is not involved with the liquid and which is comprised between the radial projection 14 and the front surface in the configuration in which the syringe if completely full . the gripping arms 11 are conformed and arranged in such a way as to embrace and hold the axial tract of the syringe i . e . the axial tract which is not involved in the run of the plunger acting directly on the liquid . thanks to this the pushing force generating the infusion liquid flow rate ( anticoagulant ) is not significantly influenced by any obstruction caused by the gripping force of the support element holding the syringe tight . each gripping element 9 further comprises a first striker element 13 for limiting the axial movement of the fixed part of the syringe in a first direction thereof ( in the illustrated embodiment in a downwards direction ). the first striker element 13 , which in the preferred embodiment comprises a pair of forwards - projecting fins , side by side and defining a striker plane , is positioned at a predetermined axial distance from the gripping arms 11 in order to define , together with the deformable gripping arms , a cavity for receiving a radial projection 14 of the fixed part 12 of the syringe . the radial projection comprises a ribbing normally present in known - type syringes . the deformable gripping arms 11 inferiorly define a second striker element for the radial projection , for limiting the axial movement of the fixed part of the syringe in a second direction ( in the illustrated embodiment in an upwards direction ) opposite the first . the deformable gripping arms 11 in effect collaborate with the first striker element 13 to hold the fixed part 12 of the syringe in position with reference to axial displacements , i . e . parallel to the longitudinal axis of the syringe pump . the gripping arms 11 collaborate with each other to immobilize the fixed part 12 of the syringe with reference to transversal displacements . the machine 1 further comprises a sensor , not illustrated , for recognising a means for identification , also not illustrated , borne by each interchangeable gripping element 9 , for sending a recognition signal of the gripping element 9 to the control unit 8 . the identification device comprising the sensor and the means for identifying can be any identifying device of known type ( for example mechanical and / or electronic ) for recognising an interchangeable element : the identification device can comprise , for example , a sensor detecting the presence or position of a reference element , an optical sensor of a code , a sensor of an electromagnetic signal , and so on . the linear pusher 6 is powered by a step motor , of known type and not illustrated . the pusher 6 is provided with a gripping element 15 for removably anchoring the mobile part 7 of the pump to the pusher 6 . the gripping element 15 comprises a hook which is rotatable between a hooking position in which it holds in position a flanged body borne at an end of the mobile part 7 of the syringe , and a rest position ( not illustrated ) in which the flanged body is free . the syringe pump , which in the described example is applied to a dialysis machine , can be applied to another type of machine for extracorporeal blood treatment , or to another type of medical apparatus ( for example an infusion device ).
in a machine for extracorporeal blood treatment , a syringe pump for infusion of an anticoagulant comprises a support for the syringe , a pusher , a sensor of the pushing force of the pusher , and a control unit for guiding the pusher in accordance with the force measured by the sensor . the support comprises a series of interchangeable gripping elements , each of which defines a housing for a syringe having a different diameter , the housing having a longitudinal axis which , for all of the interchangeable gripping elements in the series , is always in the same position in relation to the pusher . the invention provides a dialysis machine with a pump that is easily and rapidly adaptable for syringes over a wide range of sizes .