1. Field of the Invention
The present invention relates to artificial lungs (oxygenators). More precisely, the present invention relates to artificial lungs which are used during cardiopulmonary surgical operations, for example, to temporarily replace the function of a lung or lungs of a patient in order to supply blood of a patient, containing low oxygen, with oxygen. The blood containing low oxygen and blood containing high oxygen are called venous blood and arterial blood respectively hereinafter in the present specification and claims for simplicity.
Venous blood of the patient is supplied to the artificial lung of the present invention, the venous blood is oxygenated by means of the artificial lung to make arterial blood, and returned to the patient.
2. Prior Art
FIG. 4 shows a conventional artificial lung, comprising, from top to bottom, a venous blood reservoir 1, a heat exchanger 2 and a blood oxygenating element 3 comprising gas permeable membranes, which have been currently utilized for oxygenation of venous blood.
The venous blood reservoir 1 further comprises, a venous blood inlet 4 located at a top thereof, a venous blood line 5 which communicates with the venous blood inlet 4 and passes the venous blood downwards therethrough, and a cylindrical filter means 6 which receive and reserve the venous blood fed by the line 5 and filter out impurities, if any, while oozing the blood therethrough. The oozed venous blood drips downwards towards the heat exchanger 2. The filter means 6 is capable of storing venous blood a volume of from 500 to 3600 ml.
The heat exchanger 2 comprises an outer cylindrical wall 7, an inner cylindrical wall 9 coaxially disposed within the outer cylindrical wall 7, a bottom plate closing lower ends of the outer cylindrical wall 7 and the inner cylindrical wall 9, and at least one heat exchanger tube 8. A tubular space is defined between the outer and inner cylindrical walls 7,9, above the bottom plate. The tubular space is partitioned from the inner side of the cylindrical filter means 6 by walls of the filtering means 6. An outlet nozzle 10 is disposed at a lower part of the outer cylindrical wall 7 so that the tubular space communicates with the outer space through the nozzle 10. The tube 8 is made of a chemically stable material such as stainless steel or aluminum and accommodated within the tubular space to surround helically the inner cylindrical wall 9. One of the ends of the tube 8 is connected to a water supply means (not shown) which supplies the tube 8 with temperature controlled water. The other end of the tube 8 is connected to a waste water disposal line (not shown). Inside of the inner cylindrical wall 9 is a vacant space.
The blood oxygenating element 3 has a cylindrical body, a venous blood inlet 11 and an arterial, blood outlet 12 both inlet 11 and outlet 12 providing communication between the outer space and the inside space of the cylindrical body. There are no interconnections between the inner space of the heat exchanger 2 and the inner space of the oxygenating element 3 except through the outer space. The element 3 also has an oxygenous gas inlet which is connected to an oxygenating gas supply means (not shown) and a gas outlet. The inner space of the oxygenating element 3 is separated into at least two chambers, one of the chambers communicating with the venous blood inlet 11 and the arterial blood outlet 12, the other of the chambers communicating with the oxygeneous gas inlet and the gas outlet, both chambers contacting each other through gas permeable membranes (not shown).
Operation of the above-mentioned conventional artificial lung is explained as follows.
The venous blood is first supplied to the venous blood reservoir 1 through the venous blood inlet 4. The venous blood goes down through the venous blood line 5 and is reserved temporarily in the cylindrical filter means 6. The venous blood gradually oozes through the filter means 6 and proceeds into the heat exchanger 2. The impurities which may be contained in the venous blood is filtered from the blood by means of the filter means 6.
The venous blood supplied to the heat exchanger 2 goes down contacting with the heat exchanger tube 8, and is temporarily reserved in the tubular space of the heat exchanger 2. Meanwhile, water, of which the temperature is controlled by a water supply means, is supplied to the heat exchanger tube 8 to flow therethrough. The temperature of the venous blood is regulated to a prescribed temperature by means of heat exchange between itself and the water passing through the tube 8. The venous blood, of which the temperature is regulated as described above, then goes out of the heat exchanger 2 through the outlet nozzle 10.
The venous blood goes out of the heat exchanger 2, received and pumped out by a blood pump (not shown in FIG. 4), and goes into the blood oxygenating element 3 through the venous blood inlet 11. Meanwhile, an oxygenous gas flows into one of the chambers formed inside the cylindrical body of the element 3 through the oxygenous gas inlet and goes out of it through the gas outlet. The venous blood passes through the other chamber, oxygenated through the gas permeable membrane partitioning the chambers, transformed to arterial blood, and goes out of the element 3 through the arterial blood outlet 12.
FIG. 5 schematically shows the conventional artificial lung while in operation. A patient 50 is laid down on an operating table. An artificial lung is positioned on a floor 52. The venous blood is lead downwards to the artificial lung from the patient 50 by virtue of gravity. The venous blood passes through the artificial lung, is transformed to arterial blood and returns to the patient. The propulsion to pass the blood through the filter means 6 and the heat exchanger 2 is generated by the gravity force. The blood is then pushed out by means of the blood pump 51 to go through the oxygenating element 3 and to return to the patient 50.
The above-mentioned conventional artificial lung has following inconveniences.
As mentioned above, the propulsion to pass the venous blood through the filter means 6 and the heat exchanger 2 depends on gravity. In order to guarantee a sufficient flow of blood through them, it is necessary to install the artificial lung so that the surface 53 of the venous blood reserved in the venous blood reservoir 1 is at least 700 mm lower than the patient 50. On the other hand, the oxygenating element 3 is about 300 mm in height. The heat exchanger is about 150 mm in height. The level of the surface 53 is normally determined, considering various uncertainties, to be 100 mm higher from the bottom of the reservoir 1 generally. Therefore, the surface 53 of the venous blood becomes at least about 550 mm higher than the floor 52.
The level of the operating table 13 consequently becomes at least 1250 mm above the floor 52 (sum of 700 mm and 550 mm). The level of the table 13 is too high for the surgical staffs to operate on it. So, footstools are often positioned around the operating table 13 so that the staff may work thereon. But it is not convenient to work on the footstools, for the people are obliged to climb up and down the footstools and to pay attention not to fall down from them inadvertently. The footstools obstruct the layout of surgical equipments, also.