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A new self-regulating pump
A NEW EDWARD
SELF-REGULATING
PASSARO,
JR., AND
M.D.,
LOUIS
A HECENTLY developed blood pump,” significantly different from others in use, is being used by our laboratory. Its pumping action simulates that of the human heart. Because of its auto-regulation and safety features, simplicity, ease of operation, size, and the versatility of its pumping action, the pump is useful in a wide range of projects. For arterio-arterial pumping, it will synchronize automatically with the output of the heart by pressure/flow pattern. Should electrical synchronization be desirable, the pump can be synchronized with the electrocardiogram or other parameters for use in circulation support, dye injection, and cross transfusion. In addition, two or more pumps can be synchronized directly, nonelectrically or electrically for continuous flow, automatic cross transfusion, fluid metering, or perfusion.
DESCKIPTION MECHANISM
OF
The system is typically composed of the pump, its controls, and a source of pressurFrom the Surgical Service, Wadsworth Hospital, Veterans Administration Center, Los Angeles, California 90073; and the Department of Surgery, UCLA School of Medicine, Los Angeles, California 90024. Submitted for publication May 17, 1969. *Starling-Fields Pump, Bio/Systems, Inc., Santa Monica, California.
PUMP EARLE
G.
HERBERT,
B.A.,
FIELDS
ized gas (we are using oxygen). The supply pressure required by the pump is nominally 25-50 psi. The pump, approximately 6 inches in diameter and 12 inches high, contains two cylindrical chambers, an upper (pumping) chamber of autoclavable plastic, and a lower (driving) chamber of aluminum. A lightweight floating aluminum piston moves freely between these chambers suspended and supported between long-stroke rolling diaphragms. The edges of the long-stroke rolling diaphragms which separate the pumping and driving chambers are securely clamped to the edges of their respective chambers, and to the top and bottom of the piston, respectively. The diaphragms are made of surgical silicone rubber reinforced with Dacron mesh. They have a test pressure of 250 psi and may be used for up to one million cycles. The driving and pumping chambers are separated by a vented air space between the rolling diaphragms. Since the pressures in the driving and pumping chambers exceed atmospheric pressure during operation of the pump, a leak in either diaphragm will be vented to the outside. The pumping chamber contains a traumatic, hairline-seat inlet and outflow valves and a small reservoir with a vent to remove gas bubbles, aid priming and facilitate addition of liquids. The inlet valve is seated Gi9
JOURNAL
OF
SURGICAL
RESEARCH
VOL.
9
NO.
12,
DECEMBER
1969
only by floating on the surface of the blood rising in the chamber. It is incompetent in gas and the pump, therefore, cannot pump a gas, The outflow valve is a ball valve. The origin of the outflow line is at the bottom of the pumping chamber further insuring that no gas bubbles can be pumped. The lower driving chamber has an inlet line for the compressed gas and a sliding cycling valve vented to the atmosphere. The valve is regulated by a trigger-cycling mechanism. The output pressure of the pump is controlled by a pressure regulator in the con trol box. There are only two controls, the driving gas pressure regulator and the stroke volume regulator, both of which are located on the outside of the driving chamber, and both of which may be independentlv and continuously varied. The stroke volume .indicator gives an absolute direct indication of the delivered volume. The pumping or blood output pressure during the pump’s operation will equal the established gas pressure, since both the driving and the pumping diaphragms are of equal area.
OPERATION The pump operates as follows ( see Fi;;. 1) Oxygenated or venous blood enters the pumping chamber’s reservoir (A) by gravity flow through the inlet line (B); entrapped bubbles rise to the top of the reservoir and are removed by rising through the air vent ( C ); blood then passively fills the invaginating pumping chamber (E ) via the inflow check valve (D) simulating ventricular filling. The piston and attached diaphragms (F, Fi, F2) move freely within the two chambers with minimal friction. As blood enters the pumping chamber by gravity flow, the piston with its attached diaphragms is displaced downward by the weight of the blood, assuming a centered, dependent position. The inflow valve (D) floats shut on the blood beneath it. When the pre-set stroke volume is reached, a trigger cycling mechanism connected to the 680
Fig. 1. Starling-Fields filling stroke.
pump at the end of the
control box releases pressurized gas via valve (H) into the lower (driving) chamber (G) (see Fig. 2). The gas fills the lower chamber, driving the lower diaphragm and attached piston upward. The rolling diaphragm exerts equal, predetermined, uniformly distributed pressure upon the blood. The resultant pressure in the upper chamber holds closed the floating inlet valve ( D ) and opens the outflow ball valve (I). Blood is thus delivered from the pump at a pressure equal to the pre-set pressure delivered to the driving chamber. When the piston reaches the top of its stroke, an upper trigger valve vents the pres-
PASSARO
Fig. 2. Starling-Fields pump at the end of the pumping stroke. sure in the driving chamber. The floating piston falls, the nylon ball within the outflow valve-being denser than blood-falls to the closed position, the inlet valve opens, and the pumping chamber again passively fills with blood. At the bottom of the piston’s stroke, the lower trigger valve is again activated, releasing the gas into the driving chamber and the pump recycles. DATA Pertinent technical data are summarized in Table 1. In studies of hemolysis, mongrel dogs
ET
AL,:
SELF-REGULATING
PUMP
were exsanguinated by catheterization of thr femoral artery with standard intravenous tubing (Baxter I.V. Set) and the blood collected into sterile, siliconized liter glass flasks containing 10,000 units of sodium heparin. Blood from one dog was divided and used simultaneously in the two adjacent pump svstems. Five-milliliter samples were taken every hour from the line leading to the siliconized flask reservoir. Gas-sterilized 3/8inch Tygon tubing of identical length was used in each system. Plasma hemoglobin dcterminations were done calorimetrically using the benzidine, acetic acid, hydrogen peroxide color reaction, and the Coleman spectrophotometer. The amount of plasma hemoglobin produced with each passage of blood was less in ever\! instance with the Starling-Fields pump than with the roller pump, (Fig. 3). The rate of hemolysis increased more rapidly over successive hours with the roller pump than with the Starling-Field pump (Fig. 4). In operation, the hemolysis produced by this pump has been consistently less than we have observed with the use of a roller pump (Fig. 5). The extent of hemolysis has been consistently less than that previously reported [l, 2, 31. We have demonstrated that the pump will maintain viability of dog kidneys perfused in situ for 4-6 hours following death [4]. These kidneys have been successfully transplanted and have maintained good function for over a year [S].
ADVANTAGES The advantages of the pump are numerous. It is extremely simple, having only two operating controls (the gas pressure regulator which sets the blood pressure, and the strokevolume regulator). Those parts of the pump which come into contact with the blood-the upper (pumping) chamber and the diaphragm-piston unit-are easy to clean and sterilize, and in the future may be disposable. There is no mechanical crushing, negative or excessively positive pressure, or other 681
JOURNAL
OF SURGICAL
RESEARCH
VOL.
9 NO.
Table
1.
12,
DECEMBER
Pump Characferistics
Weight
30 lb.
Size
Height, 12 inches; pumping inches
Materials
AU heat-sterilizable. Pumping anodized aluminum
Output volume
O-10 liters/min.
Output pressure
O-600 mm. of mercury
Stroke volume
O-250 cc.
Stroke rate
0-200/min.
Pumping
Pulsative,
action
1969
chamber,
4 inches; driving
chamber,
plastic;
chamber,
driving
4
chamber,
liquid only, cannot pump gas.
positive displacement, output
adjustable
stroke volume
Pressure indicator
Built in. Indicates
line pressure
Pressure regulation
Desired output pressure set by knob on base of unit. Output will be maintained for required flow.
Flow regulation
Automatic flow regulation tion by simple lever.
Power requirements
Nominally 25 lb/sq. inch gas, integral absolute flow indication. Volume required approximately same as blood volume to be pumped, may use oxygen bottle, piped oxygen, air-line, or small
also available,
pressure
change from pressure regula-
compressor. No electrical power required. Explosion proof.
trauma-producing
effects
to the blood
at the
the
pumping site. As a result of the self-centering action of the piston during the pump’s operation, there can be no entrapment or crushing of blood elements between the diaphragm and
chamber
wall.
Stagnation
of
blood
T
HEMOCYSIS F,“E
PAIRED
, 1
DATA
oETERMlNnTlONS
100
,j T
I
I I,’ .,f /’ T
I
/’
’
’
,
ROLLER
/
,
/
/ ,
I PUMP
L
5. F, PUMP
Fig. 3. P-P. 682
Hemolysis
caused by equivalent
is
avoided since no matter how small the stroke volume, the “floor” of the pumping chamber, i.e., the rolling diaphragm, is constantly changing its relative position. In our ex-
passages of blood in a roller pump and in the Starling-Fields
PASSARO
MINUTES
Fig. 4. Hemolysis rate with a roller pump and in the Starling-Fields pump used over 4 hours.
T
T
0.16 -
w” 0.12 s2 0.08 -
0
60
120
180
240
MINUTES
Fig. 5. Hemolysis index with a roller pump and in the Starling-Fields pump used over 4 hours.
ET
AL.:
SELF-REGULATING
PUMP
periments, the amount of hemolysis after pumping five hours with whole blood has been grossly reduced when compared with pumps currently used. Stroke volume is continuously and positively variable and can be preset on a calibrated scale. Pumping pressure can also be preset and positively varied. Final pumping pressure is indicated on an included gauge. The absolute flow rate is indicated by counting strokes/ unit time. No additional ilow instruments are required. The flow rate of the pump is determined by the filling time of the upper chamber, the preset pressure, and the total hydraulic resistance. The actuating time of the control mechanism is insignificant being less than a hundredth of a second. Since the pressure within the pump is preset, if the pressure in the subject (or the lines leading to the subject) exceeds this driving pressure, whether due to internal or external causes, the pump will stop. If this subjectpressure falls, or if the driving pressure is raised to exceed it, the pump automatically restarts. Clamping or kinking of the arterial flow line will, therefore, automatically and instantly stop the pump without the increase in the delivered blood pressure or the severe blood trauma which is commonlv found in non-self-regulating pumps. Similarly, if the resistance within the perfused organ (kidney, brain, heart) increases due to vasoconstriction or other causes, the flow-rate of the pump will automatically decrease. The preset blood pressure is the limiting factor, not the flowrate as is the case in other, non-self-regulating, cannot be pumps. The organ, therefore, harmed by blood being forced through it at ever increasing pressure. This pressure-safety mechanism is a totally reliable, inherent part of the pump. No additional safety devices are needed. Although the pump is driven by pressurized gas, this gas cannot escape into the pumping chamber as the two diaphragms are separated by a vented area, open to the atmosphere. Any leaks will result in a small loss of blood rather than a small influx of gas, since positive pressure is alwavs maintained within the
JOURNAL
OF SURGICAL
RESEARCH
VOL.
9 NO.
chamber. Extraneous bubbles are vented from the blood in the system through the airvent in the top of the reservoir. Since the inflow valve between the reservoir and the pumping chamber is denser than gas, the inflow valve will only be competent when floating in a full chamber of blood. The dependent position of the pumping chamber’s outflow valve in relation to the inflow valve, makes it impossible for a gross amount of gas to be pumped into the subject. Should the venous input supply to the pump fail, the pump will pause since pumping is initiated only-when the pumping-chamber is filled to the preset volume. This makes it unnecessary to constantly adjust the level of the oxygenator in order to regulate the volume of the blood reservoir. In turn, this reliable inherent safety feature reduces the standby fresh blood requirements presently needed with other types of pumps, Even if gas is forced into the pumping chamber, and the pump is forced to cycle, the blood inflow valve will remain away from its seat. The trapped gas will be vented out of the inflow valve with no possibility of a quantity of gas sufficient to overload a bubble trap being pumped to the subject. It is anticipated that the usual filter-bubble trap will be used in the arterial-outflow line to trap microbubbles.
684
12,
DECEMBER
1969
The light weight and small size of the pump plus the fact that it can be operated by a small tank of compressed gas (generally already needed for blood oxygenation), makes the system exceptionally portable and economic. It requires no electrical power. The volume of gas used to drive the pump is equal to the delivered blood volume, and is usually far less than the volume necessary for oxygenation. We have used it in over 30 renal perfusion experiments employing a wide range of pressure and flow rates. The full potential of the Dump is yet to be explored.
REFERENCES Bernstein, E., Blackshear, P., and Keller, K. Factors influencing erythrocyte destruction in artificial organs. Amer. J. Surg. 114:126, 1967. Bernstein, E., Castaneda, A., Blackshear, P., and Varco, R. Prolonged mechanical circulatory support: Analysis of certain physical and physiologic considerations. Surgery 57: 103, 1965. Bernstein, E., and Gleason, L. Factors influencing hemolysis \vith roller pumps. Surgery 61:432, 1967.
Wilson, S,, Gordon, H., and Passaro, E.
Short term in situ perfusion of the canine kidney following death. Arch. Surg. 99:413, 1969. Wilson, S., and Passaro, E. Transplantation of in yitu perfused kidneys. Ann. Surg., in press.
SELF-REGULATING
PASSARO,
JR., AND
M.D.,
LOUIS
A HECENTLY developed blood pump,” significantly different from others in use, is being used by our laboratory. Its pumping action simulates that of the human heart. Because of its auto-regulation and safety features, simplicity, ease of operation, size, and the versatility of its pumping action, the pump is useful in a wide range of projects. For arterio-arterial pumping, it will synchronize automatically with the output of the heart by pressure/flow pattern. Should electrical synchronization be desirable, the pump can be synchronized with the electrocardiogram or other parameters for use in circulation support, dye injection, and cross transfusion. In addition, two or more pumps can be synchronized directly, nonelectrically or electrically for continuous flow, automatic cross transfusion, fluid metering, or perfusion.
DESCKIPTION MECHANISM
OF
The system is typically composed of the pump, its controls, and a source of pressurFrom the Surgical Service, Wadsworth Hospital, Veterans Administration Center, Los Angeles, California 90073; and the Department of Surgery, UCLA School of Medicine, Los Angeles, California 90024. Submitted for publication May 17, 1969. *Starling-Fields Pump, Bio/Systems, Inc., Santa Monica, California.
PUMP EARLE
G.
HERBERT,
B.A.,
FIELDS
ized gas (we are using oxygen). The supply pressure required by the pump is nominally 25-50 psi. The pump, approximately 6 inches in diameter and 12 inches high, contains two cylindrical chambers, an upper (pumping) chamber of autoclavable plastic, and a lower (driving) chamber of aluminum. A lightweight floating aluminum piston moves freely between these chambers suspended and supported between long-stroke rolling diaphragms. The edges of the long-stroke rolling diaphragms which separate the pumping and driving chambers are securely clamped to the edges of their respective chambers, and to the top and bottom of the piston, respectively. The diaphragms are made of surgical silicone rubber reinforced with Dacron mesh. They have a test pressure of 250 psi and may be used for up to one million cycles. The driving and pumping chambers are separated by a vented air space between the rolling diaphragms. Since the pressures in the driving and pumping chambers exceed atmospheric pressure during operation of the pump, a leak in either diaphragm will be vented to the outside. The pumping chamber contains a traumatic, hairline-seat inlet and outflow valves and a small reservoir with a vent to remove gas bubbles, aid priming and facilitate addition of liquids. The inlet valve is seated Gi9
JOURNAL
OF
SURGICAL
RESEARCH
VOL.
9
NO.
12,
DECEMBER
1969
only by floating on the surface of the blood rising in the chamber. It is incompetent in gas and the pump, therefore, cannot pump a gas, The outflow valve is a ball valve. The origin of the outflow line is at the bottom of the pumping chamber further insuring that no gas bubbles can be pumped. The lower driving chamber has an inlet line for the compressed gas and a sliding cycling valve vented to the atmosphere. The valve is regulated by a trigger-cycling mechanism. The output pressure of the pump is controlled by a pressure regulator in the con trol box. There are only two controls, the driving gas pressure regulator and the stroke volume regulator, both of which are located on the outside of the driving chamber, and both of which may be independentlv and continuously varied. The stroke volume .indicator gives an absolute direct indication of the delivered volume. The pumping or blood output pressure during the pump’s operation will equal the established gas pressure, since both the driving and the pumping diaphragms are of equal area.
OPERATION The pump operates as follows ( see Fi;;. 1) Oxygenated or venous blood enters the pumping chamber’s reservoir (A) by gravity flow through the inlet line (B); entrapped bubbles rise to the top of the reservoir and are removed by rising through the air vent ( C ); blood then passively fills the invaginating pumping chamber (E ) via the inflow check valve (D) simulating ventricular filling. The piston and attached diaphragms (F, Fi, F2) move freely within the two chambers with minimal friction. As blood enters the pumping chamber by gravity flow, the piston with its attached diaphragms is displaced downward by the weight of the blood, assuming a centered, dependent position. The inflow valve (D) floats shut on the blood beneath it. When the pre-set stroke volume is reached, a trigger cycling mechanism connected to the 680
Fig. 1. Starling-Fields filling stroke.
pump at the end of the
control box releases pressurized gas via valve (H) into the lower (driving) chamber (G) (see Fig. 2). The gas fills the lower chamber, driving the lower diaphragm and attached piston upward. The rolling diaphragm exerts equal, predetermined, uniformly distributed pressure upon the blood. The resultant pressure in the upper chamber holds closed the floating inlet valve ( D ) and opens the outflow ball valve (I). Blood is thus delivered from the pump at a pressure equal to the pre-set pressure delivered to the driving chamber. When the piston reaches the top of its stroke, an upper trigger valve vents the pres-
PASSARO
Fig. 2. Starling-Fields pump at the end of the pumping stroke. sure in the driving chamber. The floating piston falls, the nylon ball within the outflow valve-being denser than blood-falls to the closed position, the inlet valve opens, and the pumping chamber again passively fills with blood. At the bottom of the piston’s stroke, the lower trigger valve is again activated, releasing the gas into the driving chamber and the pump recycles. DATA Pertinent technical data are summarized in Table 1. In studies of hemolysis, mongrel dogs
ET
AL,:
SELF-REGULATING
PUMP
were exsanguinated by catheterization of thr femoral artery with standard intravenous tubing (Baxter I.V. Set) and the blood collected into sterile, siliconized liter glass flasks containing 10,000 units of sodium heparin. Blood from one dog was divided and used simultaneously in the two adjacent pump svstems. Five-milliliter samples were taken every hour from the line leading to the siliconized flask reservoir. Gas-sterilized 3/8inch Tygon tubing of identical length was used in each system. Plasma hemoglobin dcterminations were done calorimetrically using the benzidine, acetic acid, hydrogen peroxide color reaction, and the Coleman spectrophotometer. The amount of plasma hemoglobin produced with each passage of blood was less in ever\! instance with the Starling-Fields pump than with the roller pump, (Fig. 3). The rate of hemolysis increased more rapidly over successive hours with the roller pump than with the Starling-Field pump (Fig. 4). In operation, the hemolysis produced by this pump has been consistently less than we have observed with the use of a roller pump (Fig. 5). The extent of hemolysis has been consistently less than that previously reported [l, 2, 31. We have demonstrated that the pump will maintain viability of dog kidneys perfused in situ for 4-6 hours following death [4]. These kidneys have been successfully transplanted and have maintained good function for over a year [S].
ADVANTAGES The advantages of the pump are numerous. It is extremely simple, having only two operating controls (the gas pressure regulator which sets the blood pressure, and the strokevolume regulator). Those parts of the pump which come into contact with the blood-the upper (pumping) chamber and the diaphragm-piston unit-are easy to clean and sterilize, and in the future may be disposable. There is no mechanical crushing, negative or excessively positive pressure, or other 681
JOURNAL
OF SURGICAL
RESEARCH
VOL.
9 NO.
Table
1.
12,
DECEMBER
Pump Characferistics
Weight
30 lb.
Size
Height, 12 inches; pumping inches
Materials
AU heat-sterilizable. Pumping anodized aluminum
Output volume
O-10 liters/min.
Output pressure
O-600 mm. of mercury
Stroke volume
O-250 cc.
Stroke rate
0-200/min.
Pumping
Pulsative,
action
1969
chamber,
4 inches; driving
chamber,
plastic;
chamber,
driving
4
chamber,
liquid only, cannot pump gas.
positive displacement, output
adjustable
stroke volume
Pressure indicator
Built in. Indicates
line pressure
Pressure regulation
Desired output pressure set by knob on base of unit. Output will be maintained for required flow.
Flow regulation
Automatic flow regulation tion by simple lever.
Power requirements
Nominally 25 lb/sq. inch gas, integral absolute flow indication. Volume required approximately same as blood volume to be pumped, may use oxygen bottle, piped oxygen, air-line, or small
also available,
pressure
change from pressure regula-
compressor. No electrical power required. Explosion proof.
trauma-producing
effects
to the blood
at the
the
pumping site. As a result of the self-centering action of the piston during the pump’s operation, there can be no entrapment or crushing of blood elements between the diaphragm and
chamber
wall.
Stagnation
of
blood
T
HEMOCYSIS F,“E
PAIRED
, 1
DATA
oETERMlNnTlONS
100
,j T
I
I I,’ .,f /’ T
I
/’
’
’
,
ROLLER
/
,
/
/ ,
I PUMP
L
5. F, PUMP
Fig. 3. P-P. 682
Hemolysis
caused by equivalent
is
avoided since no matter how small the stroke volume, the “floor” of the pumping chamber, i.e., the rolling diaphragm, is constantly changing its relative position. In our ex-
passages of blood in a roller pump and in the Starling-Fields
PASSARO
MINUTES
Fig. 4. Hemolysis rate with a roller pump and in the Starling-Fields pump used over 4 hours.
T
T
0.16 -
w” 0.12 s2 0.08 -
0
60
120
180
240
MINUTES
Fig. 5. Hemolysis index with a roller pump and in the Starling-Fields pump used over 4 hours.
ET
AL.:
SELF-REGULATING
PUMP
periments, the amount of hemolysis after pumping five hours with whole blood has been grossly reduced when compared with pumps currently used. Stroke volume is continuously and positively variable and can be preset on a calibrated scale. Pumping pressure can also be preset and positively varied. Final pumping pressure is indicated on an included gauge. The absolute flow rate is indicated by counting strokes/ unit time. No additional ilow instruments are required. The flow rate of the pump is determined by the filling time of the upper chamber, the preset pressure, and the total hydraulic resistance. The actuating time of the control mechanism is insignificant being less than a hundredth of a second. Since the pressure within the pump is preset, if the pressure in the subject (or the lines leading to the subject) exceeds this driving pressure, whether due to internal or external causes, the pump will stop. If this subjectpressure falls, or if the driving pressure is raised to exceed it, the pump automatically restarts. Clamping or kinking of the arterial flow line will, therefore, automatically and instantly stop the pump without the increase in the delivered blood pressure or the severe blood trauma which is commonlv found in non-self-regulating pumps. Similarly, if the resistance within the perfused organ (kidney, brain, heart) increases due to vasoconstriction or other causes, the flow-rate of the pump will automatically decrease. The preset blood pressure is the limiting factor, not the flowrate as is the case in other, non-self-regulating, cannot be pumps. The organ, therefore, harmed by blood being forced through it at ever increasing pressure. This pressure-safety mechanism is a totally reliable, inherent part of the pump. No additional safety devices are needed. Although the pump is driven by pressurized gas, this gas cannot escape into the pumping chamber as the two diaphragms are separated by a vented area, open to the atmosphere. Any leaks will result in a small loss of blood rather than a small influx of gas, since positive pressure is alwavs maintained within the
JOURNAL
OF SURGICAL
RESEARCH
VOL.
9 NO.
chamber. Extraneous bubbles are vented from the blood in the system through the airvent in the top of the reservoir. Since the inflow valve between the reservoir and the pumping chamber is denser than gas, the inflow valve will only be competent when floating in a full chamber of blood. The dependent position of the pumping chamber’s outflow valve in relation to the inflow valve, makes it impossible for a gross amount of gas to be pumped into the subject. Should the venous input supply to the pump fail, the pump will pause since pumping is initiated only-when the pumping-chamber is filled to the preset volume. This makes it unnecessary to constantly adjust the level of the oxygenator in order to regulate the volume of the blood reservoir. In turn, this reliable inherent safety feature reduces the standby fresh blood requirements presently needed with other types of pumps, Even if gas is forced into the pumping chamber, and the pump is forced to cycle, the blood inflow valve will remain away from its seat. The trapped gas will be vented out of the inflow valve with no possibility of a quantity of gas sufficient to overload a bubble trap being pumped to the subject. It is anticipated that the usual filter-bubble trap will be used in the arterial-outflow line to trap microbubbles.
684
12,
DECEMBER
1969
The light weight and small size of the pump plus the fact that it can be operated by a small tank of compressed gas (generally already needed for blood oxygenation), makes the system exceptionally portable and economic. It requires no electrical power. The volume of gas used to drive the pump is equal to the delivered blood volume, and is usually far less than the volume necessary for oxygenation. We have used it in over 30 renal perfusion experiments employing a wide range of pressure and flow rates. The full potential of the Dump is yet to be explored.
REFERENCES Bernstein, E., Blackshear, P., and Keller, K. Factors influencing erythrocyte destruction in artificial organs. Amer. J. Surg. 114:126, 1967. Bernstein, E., Castaneda, A., Blackshear, P., and Varco, R. Prolonged mechanical circulatory support: Analysis of certain physical and physiologic considerations. Surgery 57: 103, 1965. Bernstein, E., and Gleason, L. Factors influencing hemolysis \vith roller pumps. Surgery 61:432, 1967.
Wilson, S,, Gordon, H., and Passaro, E.
Short term in situ perfusion of the canine kidney following death. Arch. Surg. 99:413, 1969. Wilson, S., and Passaro, E. Transplantation of in yitu perfused kidneys. Ann. Surg., in press.