the disclosure of my parent application , ser . no . 06 / 599 , 883 , filed apr . 13 , 1984 , now abandoned is hereby incorporated by reference . in the figure an embodiment of a unipuncture or single - needle apparatus 100 is shown with which a single - needle method can be carried out . accordingly , a y - shaped needle 14 as usually employed in the single - needle dialysis leads from the patient 12 . the one end of the y - piece is connected to a discharge line 16 whilst the other end of the y - piece is connected to a supply line 18 . the arrows indicated in the drawings show the direction of flow of the blood from and to the patient . the two lines 16 and 18 unite at 20 and merge into a flexible tube connection 102 which is inserted into a flow meter 104 . as further apparent from the figure in the vicinity of the branch point 20 a first clip 132 is inserted into the outgoing line 16 and is connected via an electrical line 133 to a control unit 118 . furthermore , also in the vicinity of the branch point 20 a second clip 34 is inserted in the supply line 18 and is connected via a further electrical line 136 to the control unit 118 . the two clips 132 and 134 are controlled in push - pull relationship by the control unit 118 , i . e . when the clip 132 is open the clip 134 is closed and vice versa . as the figure also shows , the tube section 102 is restricted substantially only to the region of the flow meter 104 , i . e . downstream of the flow meter 104 the tube section branches at 106 , and in known manner a tube 108 leading to the dialyzer 24 and a tube 110 leading away from the dialyzer 24 are provided . the tube section 108 may advantageously comprise a peristaltic blood pump 112 which pumps the blood from the patient through the flow meter 104 and the line 108 to the dialyzer 24 in pumping operation . the tube 110 is closed by a tube clip 114 disposed in the vicinity of the branch point 106 . to have available adequate blood volume , for example about 30 - 35 ml for the dialysis treatment , downstream of the pump 112 there is inserted into the tube section 108 a resilient reservoir 116 in which the blood in pumping operation is buffered and which after stopping of the pump due to the resilient forces acting on the stored blood presses the blood to the dialyzer 24 and into the discharge line 110 . the hosepump 112 or 126 acts like a throttle . as further apparent from the drawing in the discharge line 110 a second peristaltic pump 126 is inserted which is connected via an electrical line 124 to the control unit 118 . furthermore , the control unit 118 is connected via an electrical line 122 to the first blood pump 112 . both pumps are connected in push - pull operation , the clips 114 and 134 and the blood pump 126 being connected synchronously , as are the clip 132 and the blood pump 112 . the control unit 118 is further connected via an electrical line 119 to a pressure sensor 120 which is connected to the supply line 108 downstream of the pump 112 and upstream of the dialyzer . the control unit 118 is connected via a line 121 to an input means 123 with which preselectable data , for example a definable ultrafiltration rate and / or a definable excess pressure , can be entered into the control unit 118 . the dialyzer 24 further comprises a dialysis solution path , the inlet of the dialyzer being connected to a supply line 42 and the outlet of the dialyzer to a discharge line 52 . the supply line 42 is connected to a dialysis solution source 40 whilst the discharge line 52 comprises a delivery pump 50 which pumps the dialysis solution through the dialyzer 24 . according to a preferred embodiment described below said dialysis solution pump 50 may also be used to generate a partial vacuum in the dialysis solution path . for this purpose the pump 50 is connected via a line 62 to an ultrafiltrate controller 60 which is connected via a line 59 to the flow meter 104 and via a line 130 to the control unit 118 . according to a first preferred embodiment the blood side is controlled via a predetermined pressure whilst the ultrafiltration on the dialysis solution side is set with the reduced pressure generated by the pump 50 . accordingly , the control unit 118 sets the first pump 112 in operation and at the same time opens the clip 132 until the pressure value indicated at the pressure centre 120 coincides with the entered excess pressure value . then the clip 132 is closed and the pump 112 stoped whilst the clip 114 is opened and the pump 126 is set in operation . the pump 126 continues to operate until a predetermined lower pressure value is achieved or the pump 126 is operated with a predetermined number of revolutions . thereafter , the clip 114 is closed again and the pump 126 stopped . likewise , the clip 134 , which was open during this half cycle , is closed again . on the dialysis solution side the pump 150 generates a predetermined partial vacuum or reduced pressure which in turn effects a predetermined ultrafiltration rate through the dialyzer . this ultrafiltation rate can be measured with the aid of a single flow meter 104 which is connected to the flow controller 60 . since by the ultrafiltration water is withdrawn from the blood , the flow rate of the blood changes . during the first half cycle , unpurified blood flows through the flow meter 104 ; during the second half cycle , purified blood flows through the flow meter 104 . this results in different measurement parameters which are transmitted by the flow meter to the ultrafiltrate controller 60 . on the basis of the difference in parameters , the ultrafiltration rate may be determined . the desired ultrafiltration rate can be entered with the input device 123 into the control unit 118 . as a result , via the line 130 the measured actual value can be compared with the entered desired value and thus a control of the pump effected . by increasing or decreasing the number of revolutions of the pump the reduced pressure in the dialysis solution path and thus the ultrafiltration can be controlled . according to a second embodiment , however , on the blood side as well an excess pressure can be exerted on the blood volume included between the pump 112 and the pump 126 . for this purpose the peristaltic blood pump 126 blocks the line 110 . with the aid of the blood pump 112 blood is pumped into the resilient reservoir 116 and into the blood chamber of the dialyzer , the pressure sensor 120 passing the pressure value arising onto the control unit 118 . at a predetermined excess pressure the pump 112 , as explained below , is then switched off and the pump 126 switched on so that the excess pressure generated is diminished . the excess pressure value at which the changeover occurred with the aid of the control unit 118 is associated with a predetermined ultrafiltration rate . this correlation is made by the ultrafiltrate controller 60 which receives the corresponding signal from the control unit 118 via the line 130 . previously , a predetermined ultrafiltration rate or a program with which the time sequence of the ultrafiltration rate can be controlled has been entered via the input device 123 into the control unit 118 . as explained above , the ultrafiltration rate is determined with the aid of the flow meter 104 in the time intervals indicated , the ultrafiltrate controller 60 storing the particular actual value of the ultrafiltration . this actual value is correlated with a predetermined excess pressure value at which the switchover of the operating elements of the blood circuit takes place . this correlation is stored in the control unit 118 , a desired value / actual value comparison being made with the result that when a deviation of the values occurs the excess pressure value is regulated . if for example the ultrafiltration rate is too high , following the ultrafiltration rate signal the changeover signal occurring at the pressure sensor is reduced , i . e . the control unit 118 switches the pump 112 off at a lower excess pressure and switches the pump 126 on simultaneously . if however the ultrafiltration rate is too low the control unit 118 increases the excess pressure , i . e . the pump 112 pumps for a longer time than in the previous cycle , that is until the desired excess pressure is reached . in the above case of course the pump 50 does not serve to generate a reduced pressure in the dialysis solution path but instead solely to pump the dialysis solution through the dialyzer 24 . with the embodiment shown in the figure hemofiltration and hemodiafiltration may also be carried out , a drip chamber 30 then being connected into the discharge line 110 , said chamber being connected via a line section 138 shown in dashed line to a substitution fluid reservoir 138 &# 39 ;. a substitution pump 140 is connected into the line 138 . with this hemodiafiltration apparatus a relatively large ultrafiltrate amount is replaced by almost the same amount of a substitution fluid . accordingly , the pump 50 during the entire treatment pumps off 10 ∝ 20 liters filtrate which minus the ultrafiltrate amount actually to be removed must be replaced by a substitution fluid which is added directly to the blood circulation downstream of the dialyzer 24 . conveniently , this substitution fluid is introduced into the drip chamber 30 from the reservoir 138 &# 39 ; via the tubing 138 with the aid of the pump 140 . advantageously , the pump 140 can be regulated so that the rate with which the substitution fluid is supplied to the venous drip chamber 30 can be adjusted . for this purpose the pump 140 is connected via an electrical line 141 to the control unit 118 which with the aid of ultrafiltrate controller 60 coordinates the pumping rates of the two pumps 50 and 140 . advantageously , one of the two pumps may be set to a predetermined pumping rate whilst the other pump is regulated in its pumping rate with the aid of the flow meter 104 and ultrafiltrate controller 60 to obtain the desired amount of ultrafiltrate . the control can take place according to one of the two above methods , i . e . either on the reduced pressure side with the aid of the pump 50 or on the excess pressure side with the aid of the pump 112 . furthermore , a heating means 80 may advantageously be connected into the tubing 138 . the heating means 80 heats the substitution fluid , taken sterilely from the reservoir 138 &# 39 ;, to the body temperature . as already mentioned above , one of the two pumps is set to a predetermined pumping rate whilst the other pump is regulated . advantageously , the pump 140 is set to the desired exchange rate . the ultrafiltrate controller 60 then sets the desired liquid withdrawal or ultrafiltration rate at the pump 50 and 112 respectively . this hemodiafiltration apparatus can of course also be used as pure hemofiltration apparatus or plasma filtration apparatus . for this purpose , it is only necessary to clamp off the tubing section 42 or seal the dialysis solution inlet of the dialyzer 24 . a further hemodiafiltration apparatus in a further improved embodiment is shown in the figure , the parts represented also being drawn in dashed line . in this embodiment the substitution fluid used according to the embodiment described above is a sterilely filtered dialysis solution . this has the advantage that the usually expensive substitution fluid which because of its sterile and pyrogen - free properties had to be prepared by the manufacturer , is replaced by a usual dialysis solution which is filtered sterile and pyrogen - free at the bedside . accordingly , the dialysis solution is again provided in the dialysis solution reservoir 40 and can be withdrawn therefrom via the line 42 . connected into said line is a throttle 84 as flow resistance which can also be used to adjust the pressure between the pump 50 and the throttle 84 . moreover , the closure of the throttle 84 changes the apparatus from a hemodiafiltration apparatus to a hemofiltration apparatus . upstream of the throttle 84 from the tubing 42 a tubing 88 branches off which is connected to the input of a filter 90 . also connected into said tubing 88 is a pump 92 which pumps dialysis solution from the reservoir 40 to the filter 90 in which the purification of the dialysis solution takes place which is thus sterile and pyrogen - free downstream of the filter 90 . this purified dialysis or substitution solution leaves the filter 90 via a tubing 94 which is again connected to the drip chamber 30 . in the figure this line 94 is connected for clarity to the line 138 but this need not necessariy be the case . advantageously , the heating means 80 is again however provided in the line 94 . the pump 92 is again connected via the line 141 to the control unit 118 , i . e . is operated corresponding to the pump 140 so that the latter can be referred to . moreover , the mode of operation of this apparatus also corresponds to the mode of operation described above of the first hemodiafiltration apparatus so that reference can be made thereto . filter 90 may comprise a conventional hemodialysis filter in which only two connections are employed so that the other connections are sealed . of course , this embodiment can also be employed as hemofiltration and plasma filtration apparatus . in this case the throttle 84 shuts off the tubing 42 or alternatively the dialysis solution inlet of the dialyzer 24 is closed . as flow meters , fundamentaly all known flow meters are possible . since however a blood flow is to be measured flow meters operating practically contactless are to be preferred , i . e . ultrasonic flow meters , electromagnetic flow meters and thermal flow meters . particularly preferred are electromagnetic flow meters . such a flow meter should operate so accurately that during the treatment time substantially no changes of its measurement behavior occur . only then is it ensured that the difference formation can be considered exact . according to a further preferred embodiment the line section 102 consists of a substantially rigid plastic material , for example hard pvc or polycarbonate , and thus does not have any yielding properties , i . e . compliance . such a plastic tube can either be inserted into a flow meter or it is equipped with elements , for example electrodes , which are implemented in the tube and form the flow meter .
an apparatus for controlling the ultrafiltration rate in machines for the extracorporeal purification of blood in which the difference obtained in the blood circuit by an electromagnetic flow meter is used for controlling the ultrafiltration rate . the ultrafiltration rate is controlled by controlling the transmembrane pressure across the membrane separating the blood chamber from the dialysis fluid chamber in a dialyzer . in one embodiment , the pressure in the blood circuit is varied to change the transmembrane pressure . in a second embodiment , the pressure in the dialysis solution circuit is varied .