the invention will be described with reference to an embodiment as applied to the treatment of blood for removal of ldl and vldl , but it is to be understood that the invention can be applied to various body fluid treatments . referring to fig1 which is a circuit diagram of the treatment block of a body fluid treating circuit according to the invention , the treatment block includes a couple of treating units or devices a1 and a2 each having the same treating capacity . each of the treating units a1 and a2 connected in parallel is charged with an adsorbent capable of selectively adsorbing ldl and vldl from the blood . also provided in this block are a source b for supply of a regenerating liquid adapted to regenerate the treating ability of the units a1 , a2 and a source c for supply of a washing liquid for forcing out the body fluid or regenerating liquid from each treating unit . connected to the upstream side of each of the treating units a1 and a2 are a body fluid feed line d , a regenerating liquid feed line f and a washing liquid feed line h . in this embodiment , the regenerating liquid feed line f is joined with the washing liquid feed line h at a position before reaching the treating units . similarly , connected to the downstream side of each of the treating units a1 and a2 are a body fluid return line e and a discharge line g ( i ) which serves as a regenerating liquid discharge line and a washing liquid discharge line . for each of the above lines , a plurality of lines or a line having branches can be used . branching out of the discharge line g ( i ) is a confirmation line k , through which the effluent washing liquid discharged from the treating unit a1 or a2 is guided to a salt concentration measuring means j . also , provided in this treating apparatus are a body fluid conveying pump l1 adapted to control the flow rate of body fluid and a liquid supply pump l2 adapted to control the flow rate of the regenerating liquid or washing liquid . at appropriate positions in the lines , valves m1 to m12 are provided , thereby controlling the switching of flow passages for the body fluid , regenerating liquid or washing liquid . further , in this embodiment , there are provided a plasma separator 1 to separate the plasma fraction from the blood to be treated , a plasma pressure gage 2 , a blood leak monitor 3 for alerting the operator to the entry of blood corpuscles into the plasma , a supply side drip chamber 4 to prevent entry of air bubbles , a feed plasma pressure gage 5 , liquid discontinuation sensors 6 and 7 , a feed liquid pressure gage 8 , a drip chamber 9 in the regeneration system , a filter 10 for preventing entry of the adsorbent into the plasma , a return plasma pressure gage 11 , and a return side drip chamber 12 . the plasma separator 1 includes a separation membrane to separate and extract the plasma fraction from the blood . however , the blood corpuscles are liable to adhere to the separation membrane and , once deposited , cannot be readily detached . since the corpuscles play particularly important roles , the loss thereof should be minimized in the treatment . the corpuscles remaining in the plasma separator has hitherto been recovered by passing physiological saline through the separator after completion of treatment . however , a thorough recovery of corpuscles demands the use of a large quantity of physiological saline , and when such a large quantity of saline is used , there occurs a sudden increase in the intracorporeal circulation to induce a decrease in colloid osmotic pressure , a change in blood pressure and other adverse effects due to blood dilution such as anemia . to avoid these disadvantages , the blood cell recovery technique illustrated in fig4 is beneficial . in fig4 like reference characters denote like parts in fig1 and 5 . fig4 is a view to illustrate a method for recovery of blood cells from the plasma separator 1 , where the treating units a1 and a2 are represented as a single block for convenience &# 39 ; s sake . after the treatment , the plasma fraction remaining in the treating block 40 is guided to the plasma separator 1 so as to pass in the direction reverse to the plasma separation direction , whereby the blood cells adhering to the membrane are released and recovered . to be specific , the plasma separator 1 is shut off at a suitable place s on the side where the collected blood enters into the separator , and at the same time , the body fluid pump l1 is driven in the reverse direction to send back the plasma fraction remaining in the treating unit a1 or a2 and other treating block circuit to the plasma separator 1 where it undergoes reverse osmosis to thereby recover the blood corpuscles from the membrane . since the plasma fraction which has a high affinity for the corpuscles , is utilized as a medium for recovery of corpuscles in the above method , the ability of releasing the corpuscles from the separation membrane is far higher than physiological saline and , therefore , the volume of plasma required for this purpose is small as compared with saline and there is no adverse effect on the human body . in addition , since this medium for recovery of corpuscles is the plasma fraction of the patient &# 39 ; s own blood , there is no risk of adverse influence on the blood components . the total capacity of the above - mentioned treating units a1 and a2 may be less than one - half of the capacity of a single treating unit conventionally used . the reason is that although the capacity of removing ldl and vldl from the plasma depends on the total amount of adsorbent used , the regeneration and reuse of the treating units enables to reduce the amount of adsorbent required because of increase in the total amount of adsorbent utilized for the treatment . the regenerating liquid is selected according to the adsorbent used . in case of an adsorbent composed of a water - insoluble support and a polyanion compound , immobilized thereto , capable of adsorbing harmful substances in the blood such as ldl and vldl , aqueous solutions of electrolytes in high concentrations are used as the regenerating liquid . examples of the electrolytes are , for instance , sodium chloride , potassium chloride , calcium chloride , sodium phosphate , potassium phosphate , sodium carbonate , potassium carbonate , and the like . for instance , when the adsorbent is a dextrane - immobilized cellulose gel , an aqueous solution of sodium chloride having a concentration of 0 . 18 to 6 moles / liter , especially 0 . 3 to 1 mole / liter , is preferably used . physiologically harmless liquids , e . g . ringer solution and physiological saline ( salt concentration : about 0 . 15 mole / liter ), can be used as the washing liquid in the present invention . it is necessary that the washing liquids are physiologically harmless , because they may come into contact with the body fluids or may flow into the human body . the salt concentration measuring means j is intended to confirm that the salt concentration of the effluent from the treating unit is equal to the physiological salt concentration , and may for example be a conductivity meter , although this is not an exclusive choice . any devices or means which can attain this purpose can be used . the plasma separator 1 may be any of the known types , e . g . a membrane separator using a semi - permeable membrane for blood filtration or a centrifugal plasma separator which utilizes a difference in sedimentation constant . the valves m1 to m12 may each be a clamp , a pinch cock or the like . a solenoid pinch cock is preferred in that it is simple in construction and control . when the solenoid pinch cock is such that it is open when current flows and closed when current does not flows , accidents in emergencies such as an interruption of current can be prevented . further , accident due to an erratic operation can be prevented when the action of the pinch cock is detected by an appropriate sensor . a method for treating a body fluid using the above - mentioned treating circuit will be explained with reference to fig2 ( a ) to 2 ( j ). in the drawings , the open condition of any of valves m1 to m12 is indicated by white dot and the closed condition by black dot •. further , any circuit line in which a liquid such as a body fluid is flowing is indicated by a solid line , while any circuit line in which no liquid is flowing is indicated by a broken line . as to the order of use of the treating units , a1 is the pre - stage unit and a2 is the post - stage unit . first , the blood withdrawn from the human body is guided to plasma separator 1 where the plasma fraction is separated from the blood . the plasma so separated is fed to pre - stage treating unit a1 through body fluid feed line d . since , as stated above , the treating units a1 and a2 are filled with a washing liquid such as physiological saline used in a washing step prior to the treating step , the introduction of the plasma drives out this washing liquid from the treating unit a1 . the volume of the treating unit used in the invention is far smaller than that of a conventional treating unit and , therefore , the infusion of the washing liquid in a volume corresponding to the volume of one treating unit into the human body does not cause any trouble . thus , only at the start of the treatment procedure , the washing liquid is guided to the body fluid return line e and joined with the concentrated blood immediately following separation of the plasma . since the return of the concentrated blood as it is to the human body may cause a trouble to the body , it is rather preferred to infuse this effluent washing liquid from the treating unit a1 into the body . however , the washing liquid forced out by the introduction of plasma into the unit a1 may be guided to the withdrawal line g ( i ) for discharge from the circuit , as occasion demands . after the treating unit a1 has been filled with the plasma , a further amount of plasma is subsequently fed into the treating unit a1 for treatment . the treated plasma is joined with the blood which had passed through the plasma separator 1 and returned to the human body . when the amount of the body fluid treated in the treating unit a1 has reached a predetermined level , the supply of plasma is switched to post - stage treating unit a2 and the passage on the downstream side of the treating unit a2 is connected to the discharge line g ( i ). simultaneously , the washing liquid is fed to the prestage treating unit a1 from washing liquid feed source c through line h , whereby the plasma in the unit a1 is forced out by the washing liquid and returned to the human body , while the washing liquid in the post - stage treating unit a2 is forced out and discharged from the circuit by the plasma introduction . in order that the blood collection rate and the blood return rate are kept constant , it is preferable to ensure that the plasma feed rate is equal to the washing liquid feed rate . after the plasma has been forced out from the pre - stage treating unit a1 , the passage on the downstream side of the unit a1 is switched into communication with the discharge line g ( i ). on the other hand , after the washing liquid is forced out from the post - stage treating unit a2 , the passage on the downstream side of the post - stage unit a2 is switched into communication with the body fluid return line e , thus the treatment by the post - stage treating unit a2 is conducted . simultaneously with the treatment operation by the post - stage treating unit a2 , a predetermined amount of a regenerating liquid is fed to the pre - stage treating unit a1 from regenerating liquid feed source b through line f . when the adsorbent is a cellulose gel carrying dextran sulfate as immobilized thereto and the regenerating liquid is a 0 . 7 mole / liter aqueous sodium chloride solution , the optimum volume of the regenerating liquid for recovery of treating ability is approximately 70 % of the volume of the treating unit . the washing liquid forced out from the unit a1 by the regenerating liquid is discharged from the circuit via discharge line g ( i ). in this step , ldl and vldl are eluted from the adsorbent , whereby the treating ability of the adsorbent is restored . upon completion of feed of a predetermined amount of regenerating liquid , the passage on the upstream side of the treating unit a1 is switched into communication with the washing liquid feed line h , thus the regenerating liquid in the unit a1 is forced out by the introduction of the washing liquid and is discharged from the circuit through the line g ( i ). after withdrawal of the regenerating liquid from the treating unit a1 , the unit a1 is washed with a further supply of the washing liquid to lower the salt concentration to the physiological concentration . when the regenerating liquid is the above - mentioned 0 . 7 mole / l aqueous solution of sodium chloride and the washing liquid is a physiological saline , it is preferable to pass the washing liquid in an amount of 1 . 5 to 2 times the volume of the treating unit . after feeding the predetermined amount of the washing liquid to the unit 1 , the passage on the downstream side of the treating unit a1 is switched into communication with the confirmation line k so as to guide the effluent washing liquid from the treating unit a1 to salt concentration measuring means j , while continuing the supply of washing liquid . the regenerating liquid flowing out of the treating unit and the washing liquid discharged just after withdrawal of the regenerating liquid from the unit contain protein components such as ldl and vldl which were eluted from the adsorbent . if such liquids containing the proteins are fed to the salt concentration measuring means j , which may for example be a conductivity meter , its sensor part will be contaminated to detract from the accuracy and reliability of the measuring means . therefore , to the salt concentration measuring means j is supplied the washing liquid discharged from the unit after the completion of the washing procedure , which is substantially free of proteins , as stated above . when the amount of the body fluid treated by the post - stage treating unit a2 has reached the predetermined level , the supply of the plasma is switched to the pre - stage treating unit a1 with confirmation that the salt concentration of the effluent washing liquid from the unit a1 is equal to the physiological concentration , and simultaneously the route of feed of the washing liquid is switched to the post - stage treating unit a2 . the salt concentration in the treating unit a1 decreases gradually as the prior washing step proceeds , and reaches the physiological concentration level by the end of the washing step . however , if it is found that the salt concentration has not dropped to the physiological level , the switching of the plasma feed line d is not performed in order to further continue the washing of the unit a1 , or the treatment of the body fluid is discontinued . by the above switching operation , the plasma in the post - stage treating unit a2 is forced out by the washing liquid and returned to the human body . the washing liquid in the pre - stage treating unit a1 is forced out by the plasma and discharged out from the circuit . the plasma feed rate is preferably kept equal to the washing liquid feed rate . when the washing liquid has been discharged from the treating unit a1 by replacement with the plasma , the passage on its downstream side is switched into communication with the body fluid return line e to conduct the treatment by the treating unit a1 again . at the same time , when the body fluid is sent out of the treating unit a2 and the unit a2 has been filled with the washing liquid , the passage on the downstream side of the unit a2 is switched into communication with the discharge line g ( i ). ( 11 ) when the pre - stage unit a1 and the post - stage unit a2 are used alternately and repeatedly , the regeneration of the post - stage unit a2 is carried out simultaneously with the execution of the above treatment by the unit a1 in preparation for the next treating operation by the unit a2 . according to the present invention , as stated above , treating devices or units can be reused and , moreover , line switching can be effected safely without entry of the regenerating liquid into the human body or without contact between the regenerating liquid and the body fluid . the alternating and repeated use of the treating units a1 and a2 not only enables to drastically decrease the amount of the adsorbent to be used , but also helps to reduce the volume of the treating device and minimize the extracorporeal circulation volume of the blood . the above embodiment employs two treating units but it is , of course , possible to provide three or more treating units within the treating block . as an example , an embodiment comprising three treating units , namely first unit a3 , second unit a4 and third unit a5 , is shown in fig3 . in this embodiment , the treating units a3 , a4 and a5 are used for the treatment in succession and repetition in the order of the first , second and third units , provided that the following steps ( a ) and ( b ) are added to the above - mentioned steps . ( a ) when the amount of the body fluid treated by the first unit a3 has reached a predetermined level , the supply of the body fluid is switched to the second unit a4 . the regeneration of the first unit a3 is performed simultaneously with the treatment of body fluid by the second unit a4 . ( b ) when the amount of the body fluid treated by the second unit a4 has reached a predetermined level , the supply of the body fluid is switched to the third unit a5 . the regeneration of the second unit a4 is performed simultaneously with the treatment of the body fluid by the third unit a5 . the regeneration and washing of the first unit a3 are to be completed only by the time when the treatment of the body fluid by the third unit a5 is completed . while the invention has been described with reference to preferred embodiments thereof , it is to be understood that the invention is not limited thereto but various changes and modifications may be made without departing from the scope of the invention . it is also possible to apply the invention to various other body fluids , of course . ( 1 ) since the treating units can be reused , it is possible to make the volume of the treating unit smaller than that of a conventional treating unit so as to decrease the volume of the body fluid to be extracorporeally circulated . therefore , with the body fluid treating apparatus according to the present invention , even underweight or hypotensive patients can be successfully treated . ( 2 ) with the use of a smaller amount of adsorbent , a comparable or even a greater body fluid treating capacity can be realized in comparison with the prior art , thus contributing to a reduced cost of health care . ( 3 ) when the regenerated treating unit is reused , line switching is made after confirming that the regenerating liquid has been thoroughly discharged and the salt concentration in the treating unit has returned to the physiological level . therefore , there is no risk of entry of the regenerating liquid into the human body , nor does it happen that the body fluid contacts the regenerating liquid to raise the salt concentration of the body fluid . that is , a safe switching of circuit lines is assured . ( 4 ) the present invention includes a highly reliable safety confirmation means when the line switching is automatically carried out in accordance with a computer program . when computer control is adopted , line switching is generally carried out automatically on the basis of the flow rate of body fluids or time data of passing body fluids . in that case , the safety can be further raised by confirming the validity or invalidity of any switching action again at a predetermined switching time . thus , the present invention provides a body fluid treating circuit and method which reduces the burden on the patients and is safe to the patients .
a body fluid treating circuit comprising a block for collecting a body fluid from a human body , a body fluid treating block and a block for returning the treated body fluid to the human body , said body fluid treating block comprising a plurality of treating units for treating the body fluid by passing therethrough , the units being arranged in parallel flow relationship , body fluid feed and return lines connected to each of the treating units so as to selectively feed to and return from the units through line switching means , regenerating liquid feed lines connected to each of the units so as to selectively feed the regenerating liquid to the units through line switching means , washing liquid feed lines connected to each of the units so as to selectively feed the washing liquid to the units , discharge lines for discharging the regenerating liquid or washing liquid connected to each of the units so as to selectively discharge from the units through line switching means , and a means for measuring the salt concentration of the washing liquid effluent from the units .