US3465746A

US3465746A - Monitor for heart pump apparatus

Info

Publication number: US3465746A
Application number: US531281A
Authority: US
Inventors: Henry R Guarino
Original assignee: Avco Corp
Current assignee: KONTROL CARDIOVASCULAR Inc
Priority date: 1966-03-02
Filing date: 1966-03-02
Publication date: 1969-09-09
Anticipated expiration: 1986-09-09

Description

P 1969 H. R. GUARINO 3,465,746

MONITOR FOR HEART PUMP APPARATUS Filed March 2, 1966 2 Sheets-Sheet 29 If 7 +0 j i TRANSDUCER 27 2s- -1 7 VALVE l3 Q 22 $26 Q f 4/ Q V:

2! 28 T0 25 VALVE 24 s3 54 To +J( 1L EMITTER 1r I N FOLLOWER 42 J- TO EMITTER 43 57 55 FOLLOWER 44 I -s.ev

FROM g TRIGGER NORMALLY OPEN CIRCUIT 4s NORMALLY 64 66 CLOSED I HENRY R. GUARINO INVENTOR.

as v

I Baum p0? PM 3 n5 +5 v I ATTORNEYS 3,465,746 MONITOR FOR HEART PUMP APPARATUS Henry R. Guarino, Revere, Mass., assignor to Avco Corporation, Cincinnati, Ohio, a corporation of Delaware Filed Mar. 2, 1966, Ser. No. 531,281 Int. Cl. A61b 19/00; A61f 1/00 US. Cl. 128-1 9 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to heart pumps and more particularly to apparatus for monitoring the operation of heart pumps.

As is well known, the systemic circulation is maintained by the action of the left ventricle in pumping blood into the aorta, or main artery. A back-flow of blood into the left ventricle is prevented by the aortic valve. During its contraction (systole), the left ventricle works primarily against the elastic compliance of the aorta, raising the pressure in the aorta and distending it. As soon as contraction is complete and the ventricle relaxes, the aortic valve closes and the elastic contraction of the aorta then maintains a continuing flow of blood through the capillaries and other vessels (diastole). In addition to its function as a vessel for carrying blood to various organs, the aorta thus acts as an elastic reservoir storing some of the energy supplied by the heart. In many cases of heart insufficiency, it is found that the aorta has become relatively stiff or inelastic because of physiological processes, and thus requires excessive pressures from the heart to maintain normal cir= culation.

Heretofore, mechanical assistance to the systemic cir' culation has been attempted by veno-arterial pumping,- left-heart bypass, diastolic augmentation, postsystolic augmentation, intra-arterial balloon pumping and counterpulsation. Paracorporeal mechanical pumps and introcorporeal mechanical assistance have also been tried.

In most, if not all, of the above-noted systems, it is necessary that the ventricle, which may comprise a collapsible bulb in a rigid case, be synchronized with the patients heart. A typical electrically operated synchronized circuit for the purpose of synchronizing a ventricle with a patients heart is disclosed in US. Patent No. 3,099,260, to which reference is made. Another electrically operated synchronizing circuit is disclosed in patent application No. 355,273 filed Mar. 27, 1964, now abandoned, to which reference is also made, and which is assigned to the same assignee as this application.

Briefly stated, such synchronizing circuits are triggered by the R-wave from the patients heart or by his EKG, and control a three-way solenoid actuated valve in the pneumatic portion of the system for admitting and then United States Patent ice exhausting air or other gas from the ventricle in accordance with the demands of the patients system. As disclosed in the aforementioned patent application, the synchromzrng circuit may, for example, be comprised of a suitable 1nput amplifier wave form generator and output amplifier. As noted previously, another synchronizing cir cult sultable for control of the three-way solenoid actuated valve 1s disclosed in the above-mentioned US. patent.

However, in the aforementioned patent application, no provision 1s made in the event the synchronizing circuit fails and in the aforementioned patent, the only provision for failure is a normally open manual three-way valve coupled to the solenoid actuated three-way valve in such a way that when the manual valve is operated, the ventrlcle responds regardless of whether the electrical power supply 18 in the on position so long as air pressure or gas pressure is available. The failure of the manuallly operated three-way valve and/or failure of the solenoid operated three-way valve, singly or in combination with a failure of the synchronizing circuit which results in the contlnuous application of pressure in the ventricle will in turn result in blockage of the circulatory system.

As will now be obvious, failure of a component of prior art heart pump apparatus can result in the ventricle being held in the closed or pressure position-a condition which if not fatal is to say the least unsatisfactory.

Briefly, in accordance with the present invention, there is provided in heart pump apparatus including a movable diaphragm for sequentially inducing positive pressure around a collapsible bulb comprising a ventricle; means for deriving a direct current signal proportional to the volumetric displacement of the diaphragm, a solenoid actuated valve having a first position for supplying to the bulb positive pressure generated by the volumetric displacement of the diaphragm and a second position for venting the environment surrounding the bulb to the atmosphere, and means actuated by the direct current signal for actuating the valve to its second position when the direct current signal drops below a predetermined level representative of the desired minimum permissible volumetric displacement of the diaphragm during normal operation of the heart pump apparatus.

The principal object of the present inventionis to provide a practical stable and dependable monitoring circuit for heart pump apparatus.

It is another object of the present invention to provide a monitoring circuit for heart pump apparatus that will fail-safe, i.e., should any component fail, the effect will not introduce any danger or risk.

It is a further object of the present invention to provide a monitoring circuit for heart pump apparatus that will cause the heart pump apparatus to fail safe for substantially any change in volumetric displacement from a selectable amount which the apparatus is set to provide.

The novel features that are considered characteristic of the present invention are set forth in the appended claims; the invention itself, however, both as to its organization and method of operation together with'additional objects and advantages thereof, will best be understood from the description of a specific embodiment when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a block diagram of a heart pump incorporating the present invention;

FIGURE 2 is a diagrammatic representation of the pumping unit;

FIGURE 3 is a block diagram of the electrical circuit comprising the present invention;

FIGURE 4 is a schematic diagram Of the AC to DC conversion circuit of FIGURE 3 and includes means for varying the magnitude of the direct current signal supplied to the trigger circuit; and

FIGURE 5 is a schematic diagram of the solenoid driver of FIGURE 3. V

Directing attention now to FIGURE 1, there is shown a block diagram of heart pumping apparatus intended to provide intercorporeal mechanical assistance and incorporating the present invention. As shown in this figure, a suitable pressurized source of gas 11 feeds into a low pressure regulator 12. Large oxygen bottles which are readily available and are a satisfactory source of oxygen are generally pressurized to a pressure of several thousand pounds and generally have a pressure regulator which, While not particularly sensitive, is satisfactory to provide a reduction in pressure approaching that required for the actuation of a ventricle. A satisfactory ventricle pressure has been found to be approximately 3 pounds per square inch; hence, pressure regulator 12, while of conventional design, should permit small adjustments in the pressure range of about to 3 pounds per square inch. The output of the low pressure regulator 12 is fed to a three-way solenoid actuated valve 13. The valve 13, which is normally open to the atmosphere, is adapted to be operated by the syncronizing circuit 14 and allows compressed gas to be supplied to an actuating or pumping unit 15. Thus, only when the valve .13 is actuated by the synchronizing circuit 14 does the valve 13 supply compressed gas to the pumping unit which in turn controls the action of the ventricle 16. Broadly, the action of both the pumping unit and the ventricle must be capable of being synchronized with the patients heart. The pumping unit must be capable of being phased with the patients heart while the duration of the systole and diastole strokes should be adjustable. The synchronizing circuit 14 performs the function of properly synchronizing the operation of the solenoid in valve 13 for admitting the pressurized gas into the pumping unit in accordance with the demands of the patient. Typically, the synchronizing circuit is actuated by the patients electrocardiogram or the R-wave taken directly from his heart. By way of example, the output of an EKG unit may be fed into an amplifier and synchronizer pulse circuit that is adapted to amplify the sync pulse or electrical signal used for synchronizing purposes. The amplifier and synchronizing pulse shaper if provided may be designed not only to limit the magnitude of the sync pulse but also to shape it. Since the pumping unit is designed to be synchronized with the R-Wave of the sync pulse, all other portions of the wave may be either reduced or removed, thereby leaving only the R-wave. Since the hydraulic events in the patients heart are not simultaneous with the EKG unit or the R-wave and, furthermore, since the hydraulic events in the patients arterial system are delayed behind the systolic pulse of the heart by varying amounts depending on the distance of the artery from the left ventricle of the heart, it is desirable to provide means for phasing the systolic pulse of the pumping unit with the systolic pulse of the heart in order to accommodate these time delays and provide the desired time delay. For this purpose, a systole delay network triggered by the R-wave may be provided to create a sync pulse delayed behind the R-wave by a controlled amount to enable the systolic pulse of the pumping unit to be delayed behind the systolic pulse of the patients heart by an appropriate time interval. By providing this time delay interval, the pumping unit may be adjusted so that the pressure reflections from the systolic pulse of the pump will be properly phased with the pressure reflections from the systolic pulse of the patients heart and in such a Way as to physiologically aid the patients heart.

The sync pulse produced by the aforementioned systolic delay network may be utilized to actuate a trigger circuit which may include a systole duration control circuit which is provided for controlling the duration of the tripped condition of the trigger circuit. The output of the trigger circuit may be fed directly into an amplifier, the function of which is to create a signal for firing a thyratron switching circuit or the like which controls the operation of the three-way solenoid valve 13. For a further discussion of suitable synchronizing circuits for different applications, reference is made to the aforementioned US. Patent No. 3,099,260, and patent application Ser. No. 355,273.

Directing attention now to the pumping unit 15, diagrammatically represented in FIGURE 2, it may be of the type disclosed in the aforementioned patent for extracorporeal systems but is preferably of the type comprising, as shown in FIGURE 2, a low inertial diaphragm 21 separating the unit into an input compartment 22 and an output compartment 23, the pressurized gas from valve 13 being admitted into the input compartment 22 and the gas in the output compartment 23 being in communication with the ventricle 16 through a second threeway solenoid valve 24. The pumping unit preferably is provided with stops 25-26 to prevent the diaphragm 21 from providing a volumetric displacement substantially greater than about 60 cc. which is in the range of the average volumetric displacement of the left ventricle of the human heart. Further, the pumping unit should have a low resistance to maintain the load on the heart as low as possible since the heart must move the diaphragm 21 unless the input compartment 22 is coupled at the appropriate time to a partial vacuum through valve 13 during diastole.

Mounted or affixed to the pumping unit is a transducer 27 (see FIGURE 1) actuated by the movement of the diaphragm 21 in the pumping unit. This may be accomplished in conventional fashion for example as shown in FIGURE 2 by providing a mechanical connection such as a rod 28 between the transducer 27 and the diaphragm 21. While the particular type of transducer used is not essential to the invention, it should preferably provide a direct current signal, the magnitude of which is proportional to the movement of the diaphragm. Thus, if the diaphragm 21 is moving, the output signal of the transducer 27 will be a varying signal and if the diaphragm stops in any particular place, the output signal will be a direct current voltage.

While a transducer utilizing a variable resistance or variable capacitance, for example, may in theory be used, a transducer utilizing the principle of frequency modulation is preferable because of its linearity, the absence of moving parts which may wear out and the fact that it has essentially zero inertia.

By way of example, as diagrammatically represented in FIGURE 2, the rod 28 actuated by the diaphragm 21 may be movable into and out of a coil 29 to vary the output frequency of an oscillator (not shown) which is rectified to provide either a constant direct current signal or a varying direct current signal, depending on the movement of the diaphragm.

Since the zero position of a low inertia diaphragm can move or be made to move because, for example, of a slow leak, changes in pressure and the like, a centering valve 31 (see FIGURE 1) coupling the input compartment 22 and the output compartment 23 of the pumping unit is provided for centering and/or recentering of the diaphragm.

The output compartment 23 of the pumping unit is coupled to the ventricle 16 through the second solenoid actuated three-way valve 24 which is identical to valve 13. The output signal of the transducer 27 is fed to failsafe circuitry 32 (more fully disclosed hereinafter in connection with FIGURES 3-5) which controls the second three-way valve 24. The second three-way valve 24 is normally open, i.e., if the diaphragm is not moving, the environment surrounding the collapsible bulb of the ventricle is vented to the atmosphere. A typical ventricle comprises a rigid container containing a collapsible bulb, the outer surface of which is in communication with a pressurized gas (the output compartment of the pumping unit and the inner surface of which is in communication with the circulatory system of the body. A typical extracorporeal ventricle is disclosed in the aforementioned U.S. Patent No. 3,099,260, and a typical intercorporeal ventricle is disclosed in the aforementioned patent application Ser. No. 355,273.

Attention is now directed to FIGURE 3 which is a block diagram of the fail-safe circuit 32 shown in FIG- URE 1. As shown in FIGURE 3, the output signal of the transducer 27, which Signal may not exceed one volt, is coupled to a stable essentially low frequency amplifier 41. The output of the amplifier 41 is coupled to a first emitter follower 42 (or alternately a cathode follower) to provide a relatively high current signal because suitable amplifiers may have a low output impedance but generally will deliver only a minor amount of current. The emitter follower 42 is coupled to an AC to DC conversion circuit 43. During normal operation of the heart pump apparatus, the output signal of the emitter follower 42 will be an AC or varying DC signal proportional to the volumetric displacement of the diaphragm in the pumping unit. While in theory a varying signal may be used throughout the fail-safe circuit, it was found convenient to operate with a direct current signal.

The transducer 27 provides a peak-to-peak voltage proportional to the peak-to-peak travel (volumetric displacement) of the diaphragm. Accordingly, the AC to DC conversion circuit converts the peak-to-peak voltage generated during normal operation of the transducer to a direct current voltage whose magnitude is proportional to the aforementioned peak-to-peak voltage. As more fully described hereinafter, the AC to DC conversion circuit 43 may include means to prevent actuation of thesecond solenoid actuated valve 24 until a predetermined number of heart beats have elapsed and means to permit the second solenoid actuated valve to be actuated for any given change in volumetric displacement of the diaphragm from a preselected amount.

The output signal of the AC to DC conversion circuit 43 is coupled to a second emitter follower 44, amplified by a stable DC amplifier 45 and supplied to a trigger circuit 46 of the Schmitt variety which may comprise first and second regenerating transistors wherein the second transistor is conducting only when the magnitude of the output signal of the AC to DC conversion circuit 43 is greater than a predetermined amount.

The trigger circuit 46 controls a solenoid driver 47 which, for the case of a transistorized Schmitt trigger circuit, follows the second transistor. The solenoid driver more fully described hereinafter functions as a switch in series with the solenoid 48 of valve 24 whereby when the diaphragm of the pumping unit is delivering a predetermined volumetric displacement, the output compartment of the pumping unit is coupled to the ventricle through valve 24 and when the volumetric displacement decreases by more than a given amount, the current to the solenoid circuit of valve 24 is interrupted and the valve vents the ventricle to atmosphere.

FIGURE 4 shows details of the AC to DC conversion circuit 43 shown in FIGURE 3. As shown by way of example in FIGURE 4, the AC to DC conversion circuit 43 may comprise an input capacitor 53 for receiving the output signal from the emitter follower 42. As previously pointed out, the output signal from emitter follower 42 is derived from and proportional to the output signal of transducer 27, the output signal of transducer 27 being proportional to the volumetric displacement of the diaphragm 21. A rectifier S4 is connected between capacitor 53 and an RC discharge circuit comprising capacitor 55 and resistor 56. One terminal of clamping circuit 57 comprising a diode is connected to ground and the other terminal is connected between the input capacitor 53 and rectifier 54.

The clamping circuit clamps the output signal of emitter follower 42 to a reference point. In this case, the signal supplied to rectifier 54 is clamped to ground and thereby forced to go from ground to a more negative potential. The rectifier 54, capacitor 55, and resistor 56 provide a DC output signal whose magnitude is proportional to the peak-to-peak value of the output signal from transducer 27. Because a direct current signal is supplied to the trigger circuit 46, the clamping circuit is necessary in order that this DC signal be proportional to the peak-to-peak value of the output signal of the transducer. The values of capacitor 55 and resistor 56 are selected to provide an RC discharge circuit having a time constant such that the magnitude of the signal supplied to the trigger circuit 46 (which is representative of the volumetric displacement of the diaphragm) does not decrease below a preselected level (representative of a decrease in volumetric displacement of the diaphragm) for a predetermined time interval. While the time constant may be varied within wide limits, a practical minimum value is two seconds and a practical maximum value is eight seconds, being equivalent respectively to approximately two and eight heart beats. A time constant of eight seconds has been found to be satisfactory. The provision of a potentiometer comprising at least part of resistor 56 provides a convenient and simple means for permitting the second three-way valve to be actuated for any given change in volumetric displacement of the diaphragm from a preselected amount.

The ability to vary the magnitude of the signal supplied to the trigger circuit 46 is an important feature of the invention. It will be apparent that by varying the pressure supplied to the input compartment of the pumping unit, substantially any desired volumetric displacement of the diaphragm may be provided. Now, for purposes of explanation, assume that the trigger circuit is a conventional Schmitt circuit comprising first and second regenerating transistors requiring an input signal below a predetermined value to keep the second transistor conducting. Thus, if the input signal to the trigger circuit is above this predetermined or threshold value, the second transistor will be cut off and as previously described, the ventricle will be vented to atmosphere. However, because of the design requirement of the trigger circuit, i.e., it requires an input signal below a predetermined value to keep the second transistor conducting, a voltage is derived from the direct current output signal of the AC to DC conversion circuit 43 and this voltage is of course proportional to this direct current signal and as shown in FIGURE 4 may be only a portion thereof. Due to amplifier 45, the derived voltage is out of phase with the aforementioned direct current output signal. Thus, if the direct current output signal decreases in magnitude, the derived voltage supplied to the trigger circuit will increase in magnitude. Therefore, it will now be seen that if the derived voltage becomes greater than the threshold level of the trigger circuit, which increase is representative of a decrease in volumetric displacement of the diaphragm, the second transistor will be cut off as will the solenoid driver 47.

Accordingly, it will now be seen that if only a portion of the direct current output signal is supplied to the trigger circuit, then the amount of change in volumetric displacement of the diaphragm required to actuate the trigger circuit is reduced over that required if the entire direct current output signal is supplied to the trigger circuit. Thus, the provision to the trigger circuit on only a portion of the direct current signal permits the second three-way valve 24 to be actuated for any given decrease in volumetric displacement of the diaphragm from a preselected amount.

FIGURE shows details of the solenoid driver circuit 47. As shown in this figure, the base 61 of transistor 62 is coupled to the trigger circuit 46. Relay 63 and the solenoid 48 of three-way valve 24 are connected in parallel between the collector 64 and a plus 6.8 volt supply, the emitter 65 is connected to a minus 6.8 volt supply, and a normally open restart switch 66 is connected between the aforementioned emitter 65 and collector 64. Relay 63 actuates the normally closed switch 67 connected between the base 61 and collector 64 and, which, by shorting the base 61 and collector 64 during normal operation, prevents the solenoid driver 47 from conducting once it is cut off and switch 67 thereby caused to open.

When the restart switch 66 is closed, this energizes relay 63, thereby closing switch 67 and permitting the solenoid driver 47 to return to the conducting state if the second transistor of the trigger circuit 46 is conducting. It will now be obvious that when the solenoid driver is conducting, current is supplied to the solenoid 48 of the three-way valve 24, thereby allowing pressure to be supplied to the ventricle. As previously described, when the current to the solenoid 48 is cut oif, the environment surrounding the collapsible bulb in the ventricle is vented to atmosphere.

The various features and advantages of the invention are thought to be clear from the foregoing description. Various other features and advatnages not specifically enumerated will undoubtedly occur to those versed in the art, as likewise will many variations and modifications of the preferred embodiment illustrated, all of which may be achieved without departing from the spirit and scope of the invention as defined by the following claims:

I claim:

1. In a system for augmenting blood flow within a living body wherein said system has means for sequentially actuating a pumping unit including a movable diaphragm for sequentially applying positive pressure to a colla sible bulb and transducer means for providing a varying electrical signal proportional to the movement of said diaphragm, the combination comprising:

(a) first means actuated by said varying electrical signal for providing an output signal substantially proportional to the amplitude of said varying signal whereby when the amplitude of said varying signal approaches zero said output signal approaches zero, said first means comprising an input capacitor for receiving said varying signal, a clamping circuit, a rectifier, and an output R-C discharge circuit for supplying said output signal to said second means, said rectifier being connected between said input capacitor and said output R-C discharge circuit, the input terminal of said clamping circuit being connected between said capacitor and said rectifier whereby said output signal is proportional to substantially only the peak-to-peak value of said varying signal;

(b) a solenoid actuated valve having a first position for supplying said positive pressure to said bulb and a second position for venting said bulb to the atmosphere; and

(c) second means actuated by said first means for actuating said valve to its second position when said output signal of said first means drops below a predetermined level.

2. In a system for augmenting blood flow within a living body wherein said system has means for sequentially actuating a pumping unit including a movable diaphragm for sequentially applying positive pressure to a collapsible bulb and transducer means for providing a varying electrical signal proportional to the movement of said diaphragm, the combination comprising:

(a) first means actuated by said varying electrical signal for providing a DC voltage substantially continuously proportional to the amplitude of said varying signal whereby when the amplitude of said varying signal approaches zero the magnitude of said DC voltage approaches zero;

(c) second means actuated by said first means for actuating said valve to its second position when the magnitude of said DC voltage drops below a pretermined level, said second means including trigger circuit means controlled by DC voltage level, for impressing said DC voltage on said trigger circuit means, and a switching circuit controlled by said trigger circuit means for permitting current to flow through said solenoid only when said DC voltage exceeds said predetermined level.

3. The combination as defined in claim 2 wherein said means for impressing said DC voltage on said trigger circuit includes means for varying the magnitude of said DC voltage impressed on said trigger circuit.

4. The combination as defined in claim 2 wherein said second means includes a trigger circuit, means for impressing at least a portion of said DC voltage on said trigger circuit, and a switching circuit controlled by said trigger circuit for permitting current to flow through said solenoid only when the magnitude of the portion of said DC voltage impressed on said trigger circuit does not pass through the magnitude of the voltage required to change the state of operation of said trigger circuit.

5. In a system for augmenting blood flow within a living body wherein said system has means for sequentially actuating a pumping unit including a movable diaphragm for sequentially applying positive pressure to a collapsible bulb, the combination comprising:

(a) first means for deriving a direct current signal proportional to the movement of said diaphragm;

(b) a trigger circuit including first and second regenerating transistors wherein the second transistor is conducting only when said direct current signal is greater than a predetermined amount;

(0) second means for impressing said direct current signal on the input of said first transistor;

(d) a solenoid actuated valve having a first position for supplying said positive pressure to said bulb and a second position for venting said bulb to the atmosphere; and

(e) solenoid control means in the solenoid circuit of said valve and in driven connection with said second transducer for actuating said valve to its second position when said direct current signal is less than said predetermined amount.

6. The combination as defined in claim 5 wherein said second means includes means for varying the magnitude of said direct current signal impressed on said first transducer.

7. The combination as defined in claim 5 wherein the movement of said diaphragm is selectably controllable from a maximum to a minimum volumetric displacement and said second means includes third means for independently varying the magnitude of said direct current signal impressed on said first transducer whereby said valve may be actuated to its second position for substantially any change in volumetric displacement of said diaphragm from substantially any selected volumetric displacement of said diaphragm.

8. The combination as defined in claim 7 wherein said first means additionally includes fourth means for rendering said direct current signal substantially insensitive to changes in the selected volumetric displacement of said diaphragm for not less than two seconds and not more than about ten seconds.

9. The combination as defined in claim 8 wherein said fourth means comprises an input capacitor, a clamping circuit, a rectifier, and an output RC discharge circuit for supplying said direct current signal to said third means,

9 10 said rectifier being serially connected between said capaci- OTHER REFERENCES tor and said discharge circuit, and the input terminal of Amen Electronics JulSLSePt' 1963 pp said clamping circuit being connected between said capaci- 221 (Hiner et tor and 531d rectlfier' Chestnut et al., IEEE Trans. on Bio-Medical Engr.

References Cited 5 July-Oct. 1965, vol. 12, No. 34, pp. 173-186.

UNITED STATES PATENTS DALTON L. TRULUCK, Primary Examiner 3,099,260 7/1963 Birtwell 128-1 3,266,487 8/1966 Watkins et a1. 12s 1 US 3,337,878 8/1967 Bolie 31 10 31 m 0 n y I W 1" A W I CEPL'HJSECATZL UP CQRRECTZQN Patent No. 3,465, 7&6 D d Sepiumbc1 j, 196) Tmmn r014?) Henrv R. Guarino It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Colunm 2, line 17, for "manuallly" read---1nanually---; C0lun1n 7, line 2?, for "advatnages" read---advantages Cohunn 8, line 11, after "level, read---rneans--.

SIGNED AND SEALED JUL141970 (SEAL) Anest:

Edward M. Fletcher, Ii.

WILLIAM E. 'SGHUYLER, JR. Anesnng Officer Commissioner of Patents