Hemodialysis system

A compact self-sterilizable proportioning hemodialysis system alternatively usable with either a coil type or parallel flow artificial dialyzer without material alteration comprises a hydraulic driven dialysate proportioning pump in a positive pressure flow path to provide dialysate in a controlled concentration to a dialysate receiving canister. A coil-type dialyzer within the canister receives dialysate in a recirculating flow from a circulation pump. A venturi in the recirculating flow path provides a negative pressure to pull dialysate through a suction loop, which may alternatively include a parallel flow dialyzer. A conductivity cell, temperature monitor and blood leak detector sample and monitor dialysate from the canister, and to control the dialysate and indicate fault conditions. The system may alternatively function as a recirculating plate-type dialyzer having high dialysis efficiency. In this mode a vortex degasifier recirculating loop and an air separator in the suction loop eliminate entrained gases. Parts of the system may be sterilized by internal means, because the system defines a closed path when certain connections are made. An upright resistive heating steam generator delivers sterilizing steam throughout the liquid flow path which terminates in a pressure relief valve. This increases the steam temperature above the atmospheric water vaporization temperature and maintains the steam at a uniform temperature-pressure equilibrium throughout the flow path. The system requires no central dialysate mixing, yet closely controls the concentration of dialysate utilized.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the field of hemodialysis, and, in particular, 
the invention relates to sterilizable dialysis systems using either coil 
or plate type dialyzers. 
2. Description of the Prior Art 
Hemodialysis systems are used for blood purification when a patient's 
kidneys no longer perform adequately or have been surgically removed. In 
hemodialysis, the patient's blood is circulated on one side of a large 
surface area membrane having microscopic pores through which waste 
products from the blood may pass but which are too small to permit passage 
of essential blood components. Opposite the blood side of the membrane is 
an isotonic fluid which is circulated to remove the waste products by 
dialysis. The salt or mineral concentration of the dialysate solution 
determines the rate and character of absorption of minerals from the 
blood. A pressure differential across the membrane controls water removal 
from the blood by reverse osmosis. Numerous critical parameters must be 
carefully monitored and adjusted to avoid trauma to the patient. 
One of those factors is the specific concentration of dialysate solution. 
If the solution is too weak, excess minerals as well as uremic wastes may 
be extracted from the blood and the blood cells may be damaged. If the 
concentration is too strong, the salts may become absorbed by the blood 
with a resulting toxic effect. However, the cost of the concentrate itself 
is a significant factor in the total cost of dialysis. 
Blood temperature and pressure must also be carefully maintained. Blood 
temperature maintenance requires precise monitoring of the dialysate 
temperature inasmuch as the dialysate is in heat exchange relationship to 
the blood as it passes across the membranes. Pressure is affected by the 
passage of blood through the dialyzer and depends upon the type of 
dialyzer and blood pump if used. Water removal from the blood is dependent 
on the pressure differential across the dialyzer membranes. It is vital 
that the dialyzer not become clogged, either with air or impurities which 
would prevent its functioning in transferring uremic wastes to the 
dialysate solution. 
Apparatus which is used in connection with more than one patient requires 
sterilization. One difficult problem associated with use of medical 
equipment in the past has been the elimination of microbial organisms such 
as type B hepatitis. Sterilization in the past has usually been effected 
by hot water at about 85.degree. C. or by the use of formalin or sodium 
hypochlorite solution. Neither of these sterilization techniques is 
sufficiently effective to eliminate type B viral hepatitis. Because of 
their relatively large size, most dialysis systems are impractical to 
sterilize by autoclaving techniques. 
Two main types of dialyzers are in current use. One is the so-called coil 
type artificial kidney or dialyzer which consists of a single tubular 
membrane which has been flattened considerably to provide high and 
efficient surface area for osmotic transfer between the blood and the 
dialysate solution. Since the blood must travel a considerable length 
through the elongated coil dialyzer, a blood pump is required. A 
substantial flow rate about the outside of the dialyzer kidney provides 
efficient dialysis. Proportional control of the dialysate has not been 
employed in this type of system. Typically, a number of the coil-type 
dialyzers are fed in parallel from a large central mixing station. 
Parallel plate dialyzers utilize a multiple membrane stack between the 
membranes of which blood and dialysate flow in adjacent passageways. Since 
blood travels a shorter distance across a greater total cross-sectional 
area than with a coil dialyzer, blood trauma is less likely to occur and 
the shorter distance often requires less in the way of pumping pressure 
requirements. However, when a parallel flow dialyzer is used a negative 
pressure system is required to pull dialysate through the dialyzer. 
Principally because of such factors, proportional control of dialysate has 
been employed, but recirculation has not been, in parallel flow systems. 
In the past, economic factors have strongly influenced the use of 
hemodialysis. One high cost factor is the central mixing room used for 
coil dialysis. The central mixing room typically requires 1000 square feet 
of hospital space for the mixing of dialysate solution. Two central 
processors are required for adequate reliability. Should a central 
processor become contaminated it must be completely shut down for 
sterilization. Solutions of sodium hypochlorite or formalin are then used 
to wash the system. Unfortunately, these chemicals also tend to leave 
residues which have a somewhat toxic effect on the patient. Typically 
twenty patients will be delivered dialysate solution from the same central 
mixing room unit. Extensive plumbing is required to transfer the dialysate 
solution from the central mixing room to the individual rooms of the 
patients or to the various beds of the ward. Yet each patient still 
requires an individual canister of dialysate solution. 
Central delivery systems are not generally used with parallel flow 
dialyzers because this type of dialyzer requires an individual suction or 
proportioning delivery system. In the past, individual proportioning 
delivery systems have included servo controls to deliver dialysate within 
predetermined concentration limits. However, continuous uniform levels of 
concentration are difficult to achieve since the water and concentrate 
flows are pumped by separate positive flow devices. Though the long term 
average of the dialysate solution may not change, the short term 
proportion may change considerably as the pumping action proceeds. Since 
each of the separate flow devices have 100% control authority over the 
separate fluids prior to mixing, a failure of either one results in an 
immediate corresponding error. Since the delivery system is coupled almost 
directly to the parallel flow dialyzer minor variations during the cycle 
of the delivery system are seen at the membranes. These variations may be 
sufficient to alter the blood conditions to such an extent as to throw the 
patient into shock if not properly monitored. 
Thus the coil and parallel dialyzers each have separate special 
considerations which must be met for their safe utilization. Economics of 
hospital operations are such that the dialysis systems in use must be 
transferred at various times to different patients, yet different patients 
require the use of different types of dialyzers. Thus, numerous problems 
are still present in providing safe hemodialysis to patients at moderate 
costs. 
SUMMARY OF THE INVENTION 
A self-contained blood dialysis unit in accordance with this invention 
generally comprises a proportioning pump, a canister, and different 
dialysate flow paths. In one path, the proportioning pump receives an 
inlet water flow and an inlet saline concentrate flow and feeds dialysate 
solution to the interior of the canister in specific proportions of 
concentrate and water, maintained at controlled temperature. In a separate 
path, means including a recirculation pump deliver dialysate solution from 
the canister to a dialyzer to maintain a constant and effective flow that 
is returned to the canister. The canister allows time averaging of 
variations in concentrate from the proportioning pump, preventing abrupt 
changes in dialysate concentration and temperature delivered to the 
dialyzer. A third negative pressure loop is also provided, utilizing a 
venturi in operative relation to the recirculating pump to create suction 
that is balanced to the characteristics of a vortex degasifier coupled in 
the loop. A plate-type dialyzer operated in a proportioning mode may be 
coupled into this loop. A circulation pump having a positive pressure flow 
feeds dialysate solution to either a coil dialyzer in the canister or to a 
plate-type dialyzer in the suction loop at a rate independent of the feed 
rate of the proportioning pump. This provides a continuous washing of the 
dialyzer at high dialyzing efficiency. The negative pressure loop pulls 
dialysate through blood leak, conductivity and temperature monitoring 
devices, a passive air separator, and also the plate dialyzer when coupled 
to the unit. The monitoring devices are employed to control dialysate 
concentration and temperature and in the generation of alarm signals. In 
the plate-type dialyzer mode, the coil dialyzer is replaced by a vortex 
degasifier which establishes a different recirculation loop to the 
circulation pump. Thus, the system may be used with either a coil-type 
dialyzer or a parallel plate dialyzer and provide all of the functions 
desirable for each. 
To sterilize the system, liquid in the canister is drained, a pressurizing 
hood is clamped over the canister, and shunts for the dialyzer connections 
are inserted in each of the flow paths. The heater is vertically arranged 
such that a limited upward water flow is converted to steam with high 
efficiency, and the steam is fed throughout the positive and negative 
pressure flow paths toward a pressure relief valve set at a desired 
equilibrium pressure. The canister is sterilized on all exposed surfaces, 
and the circulation pump is also sterilized by redirection of the flow 
such that steam passes through the pump before entering the canister 
volume. 
Methods of sterilization in accordance with this invention initiate with 
the heating of water to generate steam that is fed into the conduit 
system. Steam is flowed through the multi-branch liquid flow path to be 
sterilized, but the maximum pressure developed within the flow path is 
controlled while maintaining pressure-temperature equilibrium. This 
provides a uniform sterilizing temperature throughout the branches of the 
liquid flow path, which includes both upwardly directed passageways and 
downwardly directed passageways. The steam rises and passes through the 
upwardly directed passageways by gravity, but pressure forces out the 
liquid in the downwardly directed passageways, to assure that the entire 
flow path is permeated by steam. Liquid retaining regions of the flow path 
which have interior dialysate contacting surfaces are sterilized by the 
steps of evacuating liquid from the region under steam pressure less than 
the equilibrium pressure prior to reaching the sterilization equilibrium 
temperature. Steam is then passed through to permeate and sterilize the 
dialysate contacting surfaces of the evacuated retaining region. 
Additional aspects of the method for sterilization of the hemodialysis 
system in accordance with this invention include the passage of steam 
along a dialyzing flow direction of the positive pressure flow path and 
the passage of steam in opposition to the dialyzing flow direction in the 
negative pressure flow path. To achieve sterilization, the interior flow 
paths are heated to 120.degree. C. and maintained under the pressure of at 
least 15 psi (1.1 bar). This may become accomplished for the typical 
system when utilizing a heating element of about 1500 watt by flowing 
water to the heater at a rate on the order of 50 milliliters per minute to 
convert approximately one-half of the water flowing therethrough into 
steam.

DETAILED DESCRIPTION 
With particular reference to FIG. 1, an example of a hemodialysis unit 10 
in accordance with the invention generally comprises a proportioning pump 
12 coupled to provide a dialysate solution at a regulated concentration to 
a canister 14 disposed on the superior surface of the instrument. The 
proportioning pump 12 may be of any suitable type such as that normally 
used with parallel plate dialyzers, but an advantageous system is provided 
by a unit constructed in accordance with a concurrently filed application 
of Robert L. Anderson entitled "Proportioning Pumping System For Dialysis 
Machines". The criticality of short term concentration variations is 
reduced considerably by the use of the canister 14 allowing time averaging 
in the mixed dialysate path of variations of dialysate provided by the 
proportioning pump 12. The hemodialysis unit 10 may separately use either 
a plate or a coil-type dialyzer, both being disposable items, but 
maintains proportioning in each mode. When a coil dialyzer 16 is used, it 
is situated within the canister 14 but receives its flow in an independent 
power loop from a rotating, impeller type, circulation pump 18 driven by a 
motor 19. The circulation pump 18 removes dialysate from the canister 14 
and pumps it under positive pressure so that the dialysate flows across 
and washes the outer surfaces of the coil dialyzer 16 disposed within the 
canister 14. Dialysate passing upwardly about the outer dialyzer surfaces 
spills over into the canister 14 to be recirculated, so that the principal 
portion of the dialysate is kept in the power loop by a conduit 17 return 
to the pump 18. The proportioning pump 12 supplies fresh dialysate at a 
volumetric replenishing rate to the canister 14. Simultaneously, a portion 
of the continuously replenished dialysate is drained through the upper end 
of an upright drain pipe 20 in the canister 14, the dialysate in the 
canister 14 being replenished by the fresh dialysate at the volumetric 
replenishing rate. 
A third, negative pressure, flow loop is independent both of the positive 
pressure recirculating flow and of the feed flow from the proportioning 
pump 12 to the canister 14. In this suction loop, dialysate is serially 
drawn from an orifice in the bottom of the canister 14 through a 
conductivity cell 21 and temperature monitor 22, an adjustable flow 
control 24, a negative pressure gauge 26, a plate-type or parallel flow 
dialyzer 28 (when connected to the unit), an air separator 29, a blood 
leak detector 30, and a variable orifice 31. Because it is used with 
minimal blood pressure in the dialyzer, the parallel flow dialyzer 28 
requires maintenance of a negative pressure on the solution to prevent 
accidental passage of potentially toxic dialysate solution into the 
patient's blood. Negative pressure on the solution also provides a 
sufficient pressure differential so that adequate water is removed from 
the blood. 
Negative pressure is established at the blood leak detector 30 and the air 
separator 29 by couplings to a venturi restriction 32 in the conduit 
between the circulation pump 18 and the canister 14. The one end of the 
negative pressure loop that is coupled to the outlet in the canister 14 
thus receives dialysate, while the other end of the negative pressure loop 
is coupled to the venturi restriction 32 to draw dialysate through the 
loop under negative pressure. 
In the feed flow path, a water heater 34, comprising an elongated casing 36 
of high temperature metal such as Incoloy or stainless steel having an 
internal resistive heating element is disposed at the inlet end of the 
positive pressure flow path. The resistive heating element provides an 
active region for heating water surrounding the casing 36. The water 
heater 34 is vertically disposed, with a water inlet adjacent its lower 
end and an outlet adjacent its upper end, both of these being open to a 
cylindrical region between the casing 36 and an encompassing stainless 
steel sleeve 38 so that water travels vertically upward through the 
cylindrical region. This insures that water always surrounds the heated 
region of the casing 36 (depicted by broken lines) and the unheated end 
regions to prevent burnout of the internal resistive heating element. In 
this particular example, the heater generates 1500 watts of power to 
provide sufficient steam to sterilize the system by techniques in 
accordance with the invention over a relatively fast period of time (e.g. 
20 minutes) while staying within the capacity of conventional household 
and hospital electrical systems. In response to the temperature level 
sensed by the temperature monitor 22, temperature servo circuits 37 
control the heater 34 so as to maintain the dialysate temperature in a 
selected range. The water heater 34 thus both supplies steam to the flow 
path for operation in the sterilization mode, and heats the dialysate to a 
controlled temperature. 
The proportioning pump 12 supplies water to the inlet of the heater 34 at a 
flow rate proportioned to the concentrate flow rate. A conduit 40 from the 
heater outlet directs water flow and concentrate received from the 
proportioning pump 12 through a one-way valve 41 to the canister 14. The 
proportioning pump 12 is adjustable to give selected water/concentrate 
ratios, through proportioning servo circuits 39 which generate corrective 
signals in accordance with the reading of the conductivity cell 21. 
A tap water inlet 42 to the hemodialysis unit 10 is coupled by a conduit to 
a pressure reducer 43, which lowers the pressure to a selected range, such 
as on the order of 20 psi (1.4 bar). The outlet of the pressure reducer 43 
is coupled to a solenoid actuated slide valve 44 having two outlet 
positions, one for the dialyzing mode and the other for the sterilizing 
mode. An adjustable flow meter and valve 46 couple the dialyzing mode 
outlet of the solenoid actuated slide valve 44 to the proportioning pump 
12. The flow meter portion provides a visual readout of water flow rate, 
and flow rate may then be adjusted by a control knob 47 on the flow meter 
valve 46. 
The proportioning pump 12 has a concentrate inlet which is coupled to a 
concentrate line 48 on the unit 10, and receives water for mixing with a 
concentrate via the flow meter valve 46. An additional conduit 49 couples 
the dialyzing mode outlet of the slide valve 44 to a water power inlet to 
the proportioning pump 12, to provide power for its operation. When the 
solenoid is actuated to place the slide valve 44 in the sterilization 
mode, water is directed by a conduit including a flow restriction 45 to 
the inlet to the heater 34. 
The circulation pump 18 comprises a pumping chamber 50 having an inlet 
coupled to the conduit 17 return from the canister 14, and communicates 
through the venturi 32 with an outlet fitting 52 (not shown in detail) at 
the canister 14 for connecting to the coil dialyzer 16. A separate drain 
conduit 51 is used during sterilization. 
The canister 14 is an elongated upright uncovered clear cylindrical 
container, which may be of polycarbonate "LEXAN" or another suitable 
transparent material. The upright pipe 20 in the canister 14 is coupled to 
a drainage outlet 62 via a drain pipe 64 including an upwardly extending 
portion which receives the upright pipe 20 which is movable between two 
positions therein. The upright pipe 20 has an aperture 66 adjacent its 
lower end for draining liquid from the canister 14 when it is moved to an 
upward position for the sterilization mode. Canister drainage occurs when 
the aperture 66 is exposed within the canister 14, allowing dialysate to 
flow through the aperture 66 and down into the drain pipe 64. When the 
upright pipe 20 is in a downward position, the aperture 66 is closed and 
excess dialysate is allowed only to overflow into the top of the upright 
pipe 20 and into the drain pipe 64. In the dialysis mode, the drain line 
64 is held open at a shut off valve 65, but this valve 65 is closed for 
the sterilization mode. 
When sterilizing also, a hood 68 is mounted over the canister 14 after it 
is drained. The hood 68 is of sterilizable material such as stainless 
steel, preferably cylindrical in shape and has an outer circular lip to 
engage a conforming surface (not shown in detail) on the upper portion of 
the unit 10. Holding means 70, shown symbolically as screws but preferably 
comprising wedging clamps that may be engaged with a partial turn, are 
disposed on the sides of the hood 68 for locking the hood 68 into position 
over the canister 14 to pressure seal the system during the sterilization 
mode. The hood 68 has a height somewhat greater than that of the canister 
14 to prevent canister interference and to allow steam to contact both the 
interior and exterior exposed surfaces of the canister 14 during the 
sterilization mode. The hood 68 also includes a safety valve 71 to allow 
for the release of steam at a design pressure of for example 25 psi which 
is in excess of the equilibrium pressure used during sterilization. 
A steam pressure activated relief valve 72 having a release pressure on the 
order of 15 psi at sea level is coupled to the drainage outlet 62 in shunt 
with the shut off valve 65. Normally the relief valve 72 is bypassed by 
the open shut off valve 65 in the dialysis mode. However when sterilizing, 
the shut off valve is closed and relief valve 72 allows pressure to 
develop to 15 psi. The steam being under pressure causes the temperature 
to rise to a sterilization temperature of about 120.degree., at which 
sterilization equilibrium is achieved throughout the entire system. 
A 10 psi drain relief valve 74 couples the drain conduit 51 to the lower 
end of the pumping chamber 50 with the drain pipe 64 for drainage of any 
liquid dialysate solution remaining therein prior to achieving 
pressure-temperature equilibrium in the sterilization mode. The relief 
valve 74 has a design pressure lower than that of the pressure relief 
valve 72, such that as pressure is developed the valve 74 opens at 10 psi 
and the steam pressure forces liquid remaining in the lower portion of the 
pumping chamber 50 and through the drain outlet 64. Relief valves of the 
same or similar pressure may also be utilized at other branches in the 
system to eliminate liquid from lower liquid retaining regions of the 
system, where steam would otherwise not penetrate. 
The conductivity cell 21 and temperature monitor 22 provide indications of 
the salinity or concentration and the current temperature respectively of 
the dialysate solution. Conventional devices and circuits may be used in 
each. For example, a thermistor (not shown) in the flow path may be 
coupled to an ordinary bridge circuit including a meter for monitoring 
temperature. In the temperature servo circuits 37 the bridge may be 
coupled to a zero crossing detector which controls a relay for turning the 
heater 34 on and off to maintain temperature control. High and low 
temperature conditions in the dialysate solution affect the rate of 
transfer of uremic waste. In addition, temperature also affects the blood 
condition so that inappropriate temperatures can induce blood trauma. The 
use of a canister further permits the employment of a switching approach 
because temperature changes are time averaged in the canister 14 bath. 
Similarly, the concentration of the dialysate must be carefully controlled 
to maintain isotonicity assuring one way osmotic transfer across the 
membranes. The conductivity cell 21 may be of any suitable type currently 
in use in hemodialysis systems, but preferably is of the type described in 
co-pending application Ser. No. 599,691, filed July 28, 1975, entitled 
"Conductivity Cell", Robert L. Anderson, and assigned to the inventor 
herein. Whatever type of conductivity cell is employed, the signal derived 
is used in the proportioning servo circuits 39 to generate an appropriate 
corrective signal so as to tend to maintain the concentration at a 
reference level selectable at the operator's option. Conventional controls 
and panel indicators for the temperature and concentration functions have 
not been shown for simplicity. 
The adjustable flow control 24 includes a threaded adjustment knob coupled 
to an adjustable shaft 73 having a tapered tip. A flow path normally 
established between the inlet and the outlet of a flow chamber 76 in the 
negative pressure control device is selectively restricted by the end of 
the shaft in the flow path. In addition, a bypass restriction 75 shunting 
the inlet and outlet of the flow control 24 establishes a lower limit on 
the minimum pressure available so that a certain minimum flow is always 
maintained. The flow path from the negative pressure control 24 is 
connected to the negative pressure sensor and gauge 26. This provides a 
visual indication of the pressure passing through the negative pressure 
loop so that the flow control may be manually adjusted. The sensor and 
gauge 26 may include a diaphragm separated from the indicator mechanism so 
that dialysate contacting surfaces of the negative pressure gauge 26 may 
be fully sterilized in isolation from the indicator mechanism. Although 
the maximum suction available is dependent upon the recirculation flow of 
the circulation pump 18, the suction pressure is independently adjustable 
by means of the flow control 24. 
The air separator 29, referring now to FIG. 2, comprises a cylindrical 
housing 77 having a bottom central inlet 78 for receiving dialysate having 
entrained bubbles. Concentric with the housing 77, but to a lesser height, 
the inlet 78 is encompassed by an internal tubular flow guide 79. A small 
suction outlet 80 in the top wall of the housing 77 opposite from the 
inlet 78 is coupled to the suction line to remove dialysate solution rich 
in dissolved gases in the form of large bubbles. A protective screen 81 is 
disposed across the suction outlet 80 to provide isolation from steel wool 
82 filling the chamber interior. The internal tubular flow guide 79 is 
typically stainless steel and first carries the dialysate up, before it 
flows down outside the flow guide 79 to an outlet aperture 83 adjacent the 
housing 77 bottom. The stainless steel wool 82 between the flow guide 79 
and the lower outlet 83 traps bubbles traveling through its volume. As the 
dialysate flows upwardly in the center region some bubbles rise to the 
suction outlet 80, particularly the larger bubbles having adequate 
buoyancy. The downward flow of dialysate outside the flow guide 79 occurs 
within a larger volume which slows down the flow velocity so that it is 
less than the terminal upward velocity, due to buoyancy, of a substantial 
proportion of the bubbles. Moreover, under these conditions the more 
minute bubbles tend to be captured on the steel wool 82, coalescing as 
more bubbles are captured, and ultimately acquiring sufficient buoyancy to 
escape. The size of the suction hole 80 is chosen such that air plus about 
10% of the total flow follows this path. Adjustable orifice sizes may be 
utilized if desired. The dialysate solution containing large bubbles is 
passed by the conduit system back into the negative pressure flow path 
through the venturi restriction 32 and back into the canister 14, in which 
the large bubbles rise to the surface and are released to atmosphere. 
The air separator 29 is a passive device which functions adequately by 
itself for the coil dialyzer mode, and variations in system design and 
operating conditions can be accommodated by varying the relative diameters 
of the internal flow guide 79 and the external flow guide defined by the 
housing 77. For higher dialysate flow rates in the suction loop, such as 
are used when a plate-type dialyzer is employed, more energetic air 
separation must be achieved, and this is described below in conjunction 
with FIG. 3. 
It should be noted that the suction loop comprises an important part of the 
system but utilizes only negative pressure from the venturi for flow 
maintenance. Because of the number of elements in this loop, varying 
operating conditions can tend to introduce changes in suction, which in 
most systems is troublesome because flow falls off at higher suction. In 
the present system, however, suction flow is automatically regulated, for 
a given setting, by a variable orifice device 31, also shown in FIG. 2. 
The variable orifice 31 comprises a thin flexible diaphragm 85 having a 
flow aperture 86 of fixed size, and mounted to span a flow chamber 87 
having an inlet orifice 88 on one side and a central outlet orifice 89 on 
the other. The outlet orifice 89 is in the form of a boss facing an 
opposed seal 92 mounted on the diaphragm 85, with the diaphragm 85 being 
biased against closure by an encompassing spring 93. 
When suction is drawn on the outlet orifice 89, a small differential 
pressure exists across the diaphragm 85 because of the flow restriction 
introduced by the fixed orifice 86. The pressure difference tends to close 
the variable orifice defined by the end surface of the outlet orifice 89 
and the facing seal 92. The greater the suction, the greater the 
deflection of the diaphragm 85, and the smaller the size of the variable 
orifice. Thus because the variable orifice is inversely related to the 
suction level, the flow rate is automatically compensated. At high suction 
the orifice is small and the flow rate which would tend to be high is 
reduced to a selected nominal level; in contrast if suction goes low the 
variable orifice opens to permit more ready flow and equalize at the 
nominal level. 
The blood leak detector 30 is coupled to the parallel flow kidney to detect 
any leakage of blood through the membranes of the parallel flow kidney, 
and activates conventional alarms (not shown). The blood leak detector may 
be of any suitable type or the type described in a co-pending application 
of the invention herein, entitled "Blood Leak Detector", filed July 18, 
1975, Ser. No. 597,243. For safety purposes, it is also conventional to 
use a concentrate monitor 95 at the concentrate line 48 to insure that the 
concentrate supply is present during operation. 
The presence of a substantial proportion of minute bubbles in the dialysate 
during operation with a plate-type dialyzer is detrimental to system 
operation in a number of respects. Foremost of these is the inaccuracy 
which results in the readings of the conductivity sensor, arising from 
collection of bubbles on the inner walls of the device. The passive air 
separation device described in conjunction with FIG. 2 is not effective 
for purposes of elimination of the minute bubbles under high flow rate 
conditions, when the presence of minute bubbles is visibly evidenced as an 
increased opacity or cloudiness of the solution. Larger bubbles which can 
readily be perceived by the unaided eye are not the problem, because these 
have sufficient buoyancy to rise to the top of the dialysate bath. 
However, the minute bubbles do not have sufficient volume and therefore 
buoyancy to overcome the fluid viscosity, particularly in the presence of 
currents. Thus the minute bubbles move through the system, including the 
air separation device, and gradually accumulate on the inner surfaces of 
the conductivity sensor, there being insufficient fluid velocity to keep 
these surfaces wiped clean. 
In accordance with the invention, the recirculation loop for the dialysate 
bath is employed for degasification during usage of a plate-type dialyzer, 
by simply replacing the coil-type dialyzer of FIG. 1 with a vortex flow 
degasifier 100, as seen in FIG. 3. The vortex unit comprises a housing 102 
which may advantageously be of a transparent material to view the 
degasification process, and which may be sectioned (not shown) for easy 
fabrication. Within the housing a central chamber 104 of circular cross 
section is disposed about a central axis that is substantially parallel to 
the plane of the base of the canister 14 in this example. The circular 
cross section need not be uniform, although a cylindrical chamber is shown 
in FIG. 3, and in fact conical chambers may be employed as described 
hereafter. The vortex degasifier includes conduit couplings to several of 
the apertures in the canister 14, and for ready insertion and removal may 
be mounted with O-ring fittings (not shown), as may be the coil dialyzers 
that are attached. One coupling 106 is made to the conduit from the 
venturi 32 and circulation pump (not shown), and terminates in a dialysate 
injection port 108. The injection port 108 is directed approximately 
tangential to the peripheral margin of the chamber 104, and approximately 
normal to the central axis. Thus dialysate is injected into the chamber 
104 with a circular motion about the central axis. 
Adjacent the opposite end of the chamber 104, an outlet port 110 is 
disposed tangential to the peripheral margin of the chamber 104, but 
positioned so as to receive the circular flow axially. The outlet flow is 
passed through a coupling 112 into the system conduit that returns to the 
circulation pump. In a central region of the end surface of the chamber 
104 that is closest the outlet port 110 is disposed a gas port 114 facing 
the direction of the central axis. The gas port 114 leads to an enlarged 
ejection conduit 116 containing stainless steel wool 117 through which 
bubble laden dialysate comprising a small part (of the order of 10%) of 
the dialysate is delivered from the vortex flow degasifier. Additionally a 
small inlet port 118 angled to be tangential to the inner circular flow is 
disposed adjacent the same end as the injection port 108 and is in 
communication with a coupling 120 to the heater and proportioning pump 
(not shown), whereby fresh dialysate is fed into the system. 
In operating in the plate dialyzer mode, therefore, the vortex flow 
degasifier 100 is used as a direct replacement for the coil dialyzer of 
FIG. 1 (and a plate dialyzer is attached at its appropriate connections). 
As operation begins, fresh dialysate enters the degasifier 100 through the 
inlet port 118 and carries with it substantial amounts of dissolved gas, 
essentially air. The chamber 104 fills quickly, and as it does some of the 
dialysate is extracted from the outlet port 110 and returned to the 
circulation pump, from which it passes through the venturi 32 into the 
injection port 108, and thus back into the chamber 104 at high velocity. 
Recirculation then takes place continuously. The injected flow quickly 
establishes a vortex flow approximately about the central axis of the 
chamber 104, with the dialysate following an at least approximately 
helical path as shown, and establishing a high angular velocity at the 
periphery. Immediately about the central axis, however, the angular 
velocity is even greater. Two effects act to bring the bubbles toward the 
center of the chamber. Centrifugal separation forces the heavier 
constituents (i.e. dialysate) outwardly relative to the lighter 
constituents (i.e. gas), and a narrow rotating bubble stream is defined 
from approximately the inlet port 118 to the gas port 114. The bubble 
stream, as shown in FIG. 3, tends to overshoot the central axis before 
becoming aligned approximately with the central axis just before the gas 
outlet port 114, and moves quite rapidly from one end of the chamber 104 
to the other. The visible and spinning bubble flow represents the 
accumulation of small bubbles at the center region into large bubbles 
which readily float up through the dialysate. The turbulence of the flow, 
and within the bath, and the content of minute bubbles, are reduced 
substantially by the inclusion of stainless steel wool 117 in the enlarged 
outlet conduit. Large bubbles pass freely through the conduit 116 while 
small bubbles coalesce into larger ones and then float to the surface. The 
additional effect to be observed is that the bubble stream is stabilized 
despite the turbulent flow, because shear forces created by the different 
angular velocities at different radii limit the ability of bubbles to 
escape outwardly. After the vortex flow degasifier 100 has been in 
operation for a short time this degassing recirculation flow perceptibly 
clarifies an opaque dialysate, and continues the clarification with 
constant diminution of the gas level. The dialysate, viewed through a 
clear canister under strong illumination, is in the steady state seen to 
have a minimal amount of contained gases present, even as minute bubbles. 
Experimental measurements have also been taken to the accuracy of the 
conductivity sensor, and these measurements confirm reduction of contained 
gases to a level at which there exists no discernible drift or other 
effect on conductivity readings. 
Thus the system is arranged such that the suction loop fulfills unique and 
different functions when operated with a parallel or plate-type dialyzer 
in contrast to a coil-type unit. In the coil mode, the suction loop needs 
only relatively low flow rates sufficient for the various sensing 
functions to be performed. Consequently the air separator 29 can function 
as a passive device having sufficient capability for removing bubbles from 
the dialysate. With a plate-type dialyzer connected and the coil unit 
removed, however, the flow rate in the suction loop is adjusted to be high 
enough to permit adequate interchange at the membrane surfaces. 
Consequently, passive air separation does not make available sufficient 
separation energy to eliminate the deleterious minute bubbles (except if 
the passive device is made unacceptably large). However, at the higher 
flow rates the vortex degasifier 100 uses the dynamic flow itself to 
achieve an adequate level of degasification. 
Note that although the vortex degasifier is interchangeable with the coil 
unit, a substantially different flow path is established in the plate 
dialyzer mode. Instead of directing dialysate into the canister 14 bath 
through the coil unit, and then withdrawing dialysate back into the pump 
from a different point in the bath, the major dialysate flow is directly 
returned to the pump. Only a small proportion is transferred into the 
bath, but because the gas concentration has been formed into large 
bubbles, these float immediately to the top of the bath and are vented. 
Further in accordance with the invention, certain interrelationships should 
advantageously be observed in the vortex degasifier configuration. In 
order to achieve adequate separation, the angular velocity of the dialyzer 
should be of the order of 1000 radians/sec, and in general between 500 and 
1500 radians/sec. While the capacity of the pump and the size of the 
venturi establish the flow rate, the flow impedances in the system must 
not react upon the venturi. For example, some coil dialyzers have small 
entry orifices which would create back pressure on a venturi of comparable 
size, reducing the effectiveness of the venturi action. In addition, two 
primary considerations should be observed to maintain a proper 
degasification action. For the desired concentric flow pattern, the 
diameter of the circular chamber should be from approximately 3 to 5 times 
the diameter of the injection orifice. In the practical example shown the 
ratio was slightly greater than 3. Also, to control the entrained bubble 
stream to the exit, the length of the chamber, between injection and 
outlet port centers, should be from 3 to 5 times the injection port 
diameter. A value of 5 was employed in the example shown. 
There are, however, other variables which can be employed to enhance or 
stabilize the degasification function. The circular chamber may expand 
outwardly in diameter in the direction toward the exit end; alternatively 
or concurrently the outlet port may be shifted in position so that it is 
not directly in line to receive the revolving liquid (i.e. it may be moved 
to the same side, relative to the central axis, as the injection port). 
Each of these expedients has the effect of slowing down the outer liquid 
flow near the exit end while not appreciably affecting the angular 
velocity directly adjacent the bubble stream, because the former increases 
the cross-sectional flow area and the latter acts as a brake on flow at 
the outer periphery. Each expedient therefore contributes to establishment 
of a shear barrier arising from the differential angular velocities in the 
region approaching the exit end, and this shear barrier aids in 
confinement of the axial bubble stream. 
The significance of the establishment of a recirculating flow path for a 
plate-type dialyzer should also be appreciated. In prior art systems 
without recirculation a constant flow of fresh dialysate is employed 
(typically about 300-500 ml/minute). In the present system, in contrast, a 
substantially higher flow rate of dialysate can be employed at the 
membrane. The recirculating suction loop feed rate which passes through 
the dialyzer is independent of the fresh feed flow rate, and is typically 
held in the range of 800 ml to 1 liter/minute. A high flow rate at the 
membrane reduces surface layer boundary effects and markedly improves 
osmotic transfer at the membrane. The resultant improvement in dialysis 
efficiency more than overcomes loss factors arising from the fact that 
there is a partially spent constituent in the dialysate. It must be 
recognized, however, that there are differences between the clearance of 
large molecules and small molecules, and that improvements in the 
transport efficiency involve complex relationships. Substances of 
relatively lower molecular weight, such as urea and creatinine, are 
transferred with relatively high efficiency, so that these quickly appear 
in the recirculating solution and efficiency decreases somewhat as to 
these constituents. Larger molecules, and particularly constituents such 
as vitamin B.sub.12 and inulin (which have molecular weights of 
approximately 1,000 and 5,000 respectively) are cleared with a higher 
efficiency rate than with existing systems. Clinical testing has shown, 
for example, a decrease in clearance efficiency of approximately 25% for 
urea and creatinine, in contrast to an increase of approximately 12% for 
vitamin B.sub.12 and 15% for inulin. While the susceptability of patients 
to different toxic wastes may vary, the constituents of smaller molecular 
wastes are generally less troublesome and investigations seeking an 
enhanced ability to clear constituents of higher molecular weight have 
been undertaken independently. In any event, the option of being able to 
utilize a substantially higher permeation rate enables the urologist to 
take advantage of machine characteristics for specific patients in 
accordance with their individual requirements. 
The structure in accordance with the invention can, moreover, be utilized 
without substantial modification in a non-recirculating mode. For this 
purpose, dialysate would be degasified using a pumping degasifier of the 
type disclosed in a pending patent application entitled "Liquid Degasifier 
System And Method", Ser. No. 653,229, filed Jan. 29, 1976, Robert L. 
Anderson, and the flow would then be directed from the heater 34 to the 
conductivity cell 21 and the outlet from the suction device such as a 
venturi would be sent directly to the drain. If a venturi is used, some 
proportion of the flow is typically employed to establish the venturi 
effect, but other types of suction devices might alternatively be used. It 
is evident, however, that only a few connections are required to operate 
in a non-recirculating mode, and that the system may be internally 
sterilized as described hereinafter. 
The provision of a proportional type of coil dialyzer also affords unique 
advantages in comparison to previously known systems. Conditions of system 
operation may be varied so as to conform to the needs of an individual 
patient, unlike conventional central delivery systems. If a substantial 
number of patients are to be placed on coil dialyzers, adequate 
reliability is assured merely by having one or two extra machines. The 
cost of each is comparable to the individual coil dialyzer stations and at 
a small fraction of the cost of a single central delivery system, without 
regard to the redundant central system which must be kept on hand for 
safety purposes. 
When the system is operated in a sterilizing mode referring again to FIG. 
1, a steam shunt 124 is coupled across fittings (not shown in detail) at 
the inside of the canister 14 to direct steam flow from the heater 34 
directly to the circulation pump 18. A separate steam shunt 126 is applied 
across the plate dialyzer fitting (or across the ends of connector tubes, 
if used, to insure their sterilization), and the outlet fitting 52 
coupling the circulation pump 18 to the canister 14 is blocked by a seal 
128 so that steam is forced through the circulation pump 18 rather than 
back into the canister 14. The shunts 124, 126, and the blocking seal 128 
are used to force the steam through a uniquely defined flow path since 
steam, being lighter than air travels upward but will not travel downward 
as certain of the flow paths are positioned, unless forced to do so. In 
FIG. 1, it will be noted that an arrow with an "S" indicates the direction 
of flow in the sterilization mode, to distinguish from the dialysis mode, 
designated by an arrow with a "D". 
To initiate sterilization, the circulation pump 18 is turned off. The 
upright pipe 20 is raised to allow drainage of dialysate from the canister 
14. The manually operated shut off valve 65 is held open to allow flow of 
solution to the drain. Then the steam shunt 124, the plate dialyzer shunt 
126 and the blocking seal 128 for the coil kidney fitting are secured. The 
circulation pump 18 is then turned on. In order for water to bypass the 
proportioning pump 12, the solenoid valve 44 is activated to the 
"sterilize" position. Tap water flows through the valve 44 and through 
both the positive pressure and negative pressure flow paths. This 
pre-rinses and flushes the system with water. 
The hood 68 is placed on the unit 10 and clamped in place and the safety 
valve 71 is positioned on the hood 68. The heater 34 is turned on and the 
recirculation pump 18 is turned off. The shut off valve 65 is then closed 
so that escaping fluid, whether steam or dialysate, must pass through the 
15 psi relief valve. 
Tap water continues to be passed through the pressure reducer 43, reducing 
the pressure to 20 psi, and then the solenoid actuated slide valve 44 
directs water flow through the conduit restriction 45 and then to the 
water heater 34. Water flows through the heater 34, and approximately 50% 
of the water is converted into steam, which is entrained with the water 
entering the flow path. 
The system is designed to convert to steam only a portion of the water 
entering the heater, to provide sufficient latitude both to maintain 
pressure-temperature equilibrium, requiring the presence of both steam and 
vapor phases in the system and also to avoid the possibility of 
overheating the heater casing 36. 
Water completely surrounds the heater casing 36 and travels vertically 
upward. The heater 34 is upright to prevent formation of stagnant gas 
pockets which would burn out the heater. The steam bubbles enclosed by 
water travels through the flow path and upward to the canister 14. Upon 
reaching the canister 14 it is immediately shunted by the steam shunt 124 
to the circulation pump pumping chamber 50. As pressure is built up within 
the pumping chamber 50, liquid that is physically above the entry level of 
steam is sputtered through the negative flow path. Liquid beneath the 
level of the entry to the pumping chamber 50 is forced downward through 
the pressure responsive drain valve 74 after its design pressure is 
exceeded, and out through the drain 62. Since the venturi restriction 32 
opening to the canister 14 is blocked by the seal 128, the steam is forced 
to travel through the negative pressure flow path in the opposite 
direction of dialysate solution flow. As shown by the flow arrows, the 
steam generally travels in the same direction as the dialysate solution in 
the positive pressure flow path. Dialysate solution traveling downward 
through the negative pressure flow path travels first through the variable 
orifice 31 and the blood leak detector 30. The shunt 126 applied across 
the parallel flow dialyzer fitting directs steam through the principal 
flow path of the air separator 29, thence through the dialysate contacting 
surfaces including the diaphragm of the negative pressure gauge 26 and 
through the negative pressure control 24. The steam then flows through the 
temperature monitor 22 and conductivity cell 21 and is directed upward 
into the canister 14. Since the hood 68 is latched in place, the entire 
inside and outside exposed dialysate contacting surfaces of the canister 
14 are permeated with steam. Should excess pressure be present within the 
canister 14, the safety release valve 71 opens allowing steam to escape. 
As steam is generated in the multi-branch flow path, pressure begins to 
build. As the pressure reaches 15 psi, the relief valve 72 adjacent the 
drain opens, and conversely when pressure drops below 15 psi the pressure 
relief valve 72 closes. The opening and closing of the valve 72 at this 
pressure maintains the temperature within the entire flow path at 
approximately 120.degree. C., although it should be borne in mind that 
pressure/temperature conditions are affected by the altitude in which the 
hemodialysis unit is used. A pressure/temperature equilibrium is assured 
by converting only a part (here about 50%) of the water passing through 
the heater into steam while the rest of the water remains liquid. 
Sterilization is a simple procedure which may be performed by a medical 
technician. A temperature of 120.degree. C., maintained at equilibrium for 
about 20 minutes, has been found sufficient to destroy all known forms of 
microbial organisms thereby allowing the transfer of the hemodialysis unit 
from patient to patient. Since the unit is relatively compact, expensive 
hospital space may be saved with resultant cost savings. The hemodialysis 
unit is versatile in that it allows use with either a coil-type dialyzer 
or a plate dialyzer. 
While the invention has been particularly shown and described with 
reference to preferred embodiments thereof, it will be understood by those 
skilled in the art that the foregoing and other changes in form and 
details may be made therein without departing from the spirit and scope of 
the invention.