as depicted in fig1 a cardioplegia delivery system 10 is established to provide solution to the heart of a patient during open heart surgery . the principal component of the cardioplegic solution is blood delivered to the system through conduit 12 which is connected to the output of an oxygenator 14 of a heart / lung machine sustaining the patient &# 39 ; s vascular system while the heart is isolated during surgery . oxygenator 14 provides arterial blood to the main extracorporeal circuit through a return line 16 to the patient &# 39 ; s aorta . a fraction , usually about 10 %, of the heart / lung machine output is diverted into conduit 12 for processing by the cardioplegic circuit and , ultimately , forwarding to the patient &# 39 ; s heart through cardioplegia delivery line 18 . the cardioplegic solution flowing through line 18 may be delivered through antegrade line 20 to a heart &# 39 ; s aortic root , or through retrograde line 22 to a heart &# 39 ; s coronary sinus . a crystalloid solution is stored in container 24 for possible combination with blood flowing in line 12 . combination of these fluids occurs in a disposable pumping cassette 26 . in the preferred embodiment , pumping cassette 26 shall be of configuration generally consistent with that disclosed in u . s . pat . no . 5 , 588 , 816 , such disclosure being incorporated by reference here . pump cassette 26 is mounted in and subject to the operations of an electromechanical pump mechanism 28 . in the preferred embodiment , pump mechanism 28 shall be of a configuration generally consistent with that disclosed in u . s . patent application ser . no . 08 / 563 , 202 , filed nov . 27 , 1995 , such disclosure being incorporated by reference here . the output of cassette 26 is supplied through line 30 to a heat exchanger assembly 102 . in the preferred embodiment , a second pump 32 , delivering a potassium solution , and / or a third pump 34 , delivering other fluid additives , may also be supplied to heat exchanger assembly 102 . heat exchanger assembly 102 , described in detail below , serves among other functions to combine those fluids supplied thereto . preferably , pumps 32 , 34 are single chamber , positive displacement pumps of a configuration similar in structure and operation to that of pump mechanism 28 . pumps 32 , 34 are independently controlled by microprocessor control section 36 via signal paths 38 , 40 , respectively . as the solutions delivered by pumps 32 , 34 can be of a critical nature , the preferred pumps 32 , 34 allow for the accurate control and combination of potassium and / or other fluid additives with the cardioplegia fluid . pumps 32 , 34 dispense their respect fluids at flow rates less than about 10 %, and preferably less than about 5 %, of the total flow rate issuing from pump cassette 26 . although the preferred embodiment utilizes heat exchanger assembly 102 to combine the cardioplegia fluid from pump cassette 26 and the fluids of pumps 32 , 34 , one ordinarily skilled in the arts shall understand that the fluids from pumps 32 , 34 may be introduced at any point along the fluid path continuum from source to delivery site . data input to microprocessor 36 through control panel 42 may include an advantageous combination of the following parameters : 1 . desired overall volumetric flow rate through disposable pump cassette 26 ; 2 . desired blood / crystalloid ratio to be forwarded by disposable pump cassette 26 ; 5 . desired temperature of solution in cardioplegia delivery line 18 ; and 6 . safety parameters such as the pressure of the cardioplegia solution in the system or in the patient . the system includes patient monitoring of myocardial temperature along the signal path 44 and heart pressure along signal path 46 communicating to microprocessor control section 36 . in addition , the pressure and temperature of the cardioplegic solution in delivery line 18 is sensed ( via pressure sensor 130a and temperature sensor 130b ) and the corresponding data forwarded along respective signal paths 52 and 54 to control section 36 . in response to the data input through control panel 42 and the monitored conditions along signal paths 44 , 46 , 52 and 54 , control section 36 effects the control of the operation of ( i ) pump mechanism 28 via signal path 56 , ( ii ) potassium pump 32 by signal along path 38 ; and ( iii ) additives pump 34 by signal along path 40 . in addition , microprocessor control section 36 controls the heat exchanger circuit 100 along signal paths 58 , 60 , 62 , 64 , which will be discussed in greater detail below , for obtaining a desired cardioplegia delivery temperature . further , control panel 42 allows parameters such as pressure limits for a particular procedure or a particular patient to be controlled based upon input settings or based upon preset standards ( for example , one range of acceptable pressure limits for antegrade and another range for retrograde cardioplegia ). in accordance with the invention , the microprocessor controller section 36 controls pump mechanism 28 to combine crystalloid from container 24 and blood from line 12 in any selected ratio over a broad range of blood / crystalloid ratios . a preferred range for the blood / crystalloid ratio adjustment capability is from 0 to 20 : 1 . notwithstanding , an operator can direct system 10 to deliver blood with no crystalloid and , conversely , crystalloid with no blood . the rate of fluid flow from pump mechanism 28 is preferably variable from 0 to 500 milliliters per minute . pump mechanism 28 may be operated by microprocessor 36 in either a continuous or intermittent mode by instruction through control panel 42 . if selected for delivery of fluid , pumps 32 , 34 are automatically controlled to deliver at a rate such that the introduction of potassium solution ( or other fluid additive , if any ) to the cardioplegia fluid is automatically maintained at the selected concentration vis - a - vis the flow from disposable cassette 26 without regard to changes made to the flow rate from pump cassette 26 or changes in the blood / crystalloid ratio . referring to heat exchanger circuit 100 , circuit 100 includes heat exchanger assembly 102 and a circulation system to enable the responsive heating and cooling of the cardioplegia fluid . fig2 and 4 illustrate the preferred embodiment of heat exchanger assembly 102 . in addition to serving as a means for controlling the temperature of the fluid that passes therethrough , heat exchanger assembly 102 functions as a filtration means , gas separator and a vehicle to allow the measurement of various cardioplegia fluid properties . heat exchanger assembly 102 includes a rigid exterior 104 defining the various regions of said assembly . specifically , heat exchanger assembly 102 comprises three integrated regions : heat exchanger region 106 ; bubble trap 108 and exit region 110 . heat exchanger region 106 comprises cardioplegia fluid circulation chamber 112 and temperature controlled fluid circulation chamber 114 . cardioplegia fluid circulation chambers 112 is hermetically separate and distinct from temperature controlled fluid circulation chamber 114 . bellows 116 separates the two circulation chambers . bellows 116 is constructed of a material conducive to the transfer of heat energy and resistant to biological fluid attack ( for example , stainless steel ). temperature controlled fluid circulation chamber 114 includes inlet 118 and outlet 120 . cardioplegia fluid circulation chamber 112 includes multiple inlets 122a , 122b , 122c respectively coupled to the output from pumps 28 , 32 , 34 . chamber 112 opens into bubble trap 108 . bubble trap 108 is an enclosed region which permits the accumulation of air , or other gases , during the circulation of fluid through heat exchanger assembly 102 . bubble trap 108 includes a vent outlet 124 to allow the expulsion of said accumulated gases . bubble trap 108 also includes a plurality of sensor receptacles 126a , 126b , 126c formed into the lower surface of assembly 102 . the interior configuration of bubble trap 108 , which includes the specific placement of sensor receptacles 126a , 126b , 126c and / or flow guides 128 , serve to minimize fluid flow effects across sensor receptacles 126a , 126b , 126c to avoid inaccuracies and incorrect measurements of fluid properties ( see fig4 ). in the preferred embodiment , receptacles 126b , 126c are formed into the lower surface of assembly 102 and designed to complement the exterior of sensors 130b , 130c to insure accurate sensor operation . receptacle 126a , which receives pressure sensor 130a in an operational position , comprises a flexible membrane ( not shown ) to allow accurate pressure communication directly with sensor 130a . the flexible membrane , formed from pvc film or the like , is attached to assembly 102 by adhesive joint or other process well known to those having ordinary skill in the art . bubble trap 108 directs fluid flow into exit region 110 . exit region 110 includes outlet port 134 . exit region 110 may also incorporate an emboli filtration means 136 . in the preferred embodiment , exit region 110 includes a 160 micron filtration screen for removing any emboli greater than 160 microns . referring to fig5 cardioplegia delivery system 10 includes heat exchanger mounting block 138 . heat exchanger mounting block incorporates sensor plate 132 ; temperature controlled fluid circulation ports 140a , 140b ; vent valve means 142 and locking means 144 . sensor plate 132 maintains pressure sensor 130a , infrared temperature sensor 130b and ultrasonic level sensor 130c . the specific sensors identified herein are merely an example of the preferred embodiment , one ordinarily skilled in the art shall appreciate that other types of sensors or the like may be used to effect the intended purpose of the present invention . heat exchanger assembly 102 is positioned on mounting block 138 and locked into place with locking means 144 . as discussed above , sensor receptacles 126a , 126b , 126c receive sensors 130a , 130b , 130c , respectively , when assembly 102 is locked into position . likewise , inlet 118 and outlet 120 engage circulation ports 140a , 140b , respectively . inlet 122a of heat exchanger assembly 102 is coupled to line 30 , inlet 122b is coupled to the outlet of second pump 34 , and inlet 122c is coupled to the outlet of third pump 32 . vent line 146 is coupled to vent outlet 124 and passes through vent valve means 142 . line 18 is coupled to outlet port 134 . operationally , cardioplegia fluid is circulated across the exterior surface of bellows 116 while a temperature controlled fluid is circulated across the interior surface of bellows 116 to effect temperature control of the cardioplegia fluid . pump 148 circulates temperature controlled fluid through heat exchanger assembly 102 either by push or pull . fig2 depicts a &# 34 ; push through &# 34 ; coolant system in which pump 148 circulates the temperature controlled fluid through heat exchanger assembly 102 and then to two - way valve 150 . valve 150 directs , subject to the direction of microprocessor 36 , the circulating fluid either to hypothermic reservoir 152 or warm water reservoir 15 . hypothermic reservoir 152 may consist of a reservoir containing a water - ice solution . warm water reservoir 154 may consist of an internal reservoir having one or more sensors 156 and one or more heaters 160 . microprocessor 36 controls heaters 160 in accordance with that specified by control panel 42 and the measured data received from sensors 156 . as described above , sensors 130a , 130b , 130c provide information to the central microprocessor control section 36 . control section 36 utilizes said information for making adjustments , for example , adjusting the delivery flow rate to attain a particular pressure , adjusting valve 150 to select between heating and cooling the cardioplegia fluid , or , as immediately described above , the process for maintaining the temperature of the warm water reservoir 154 . likewise , control section 36 uses that information provided by sensor 130c , via signal path 48 , to automatically open and close vent valve means 142 to expel any accumulated gases . for some applications , where the fluid delivery system disclosed here does not require a heat exchanger stage , heat exchanger assembly 102 may comprise merely the bubble trap stage 108 . an example of such application is the fluid delivery system 10 serving as a cardiopulmonary bypass machine . while the invention has been described herein relative to a number of particularized embodiments , it is understood that modifications of , and alternatives to , these embodiments , such modifications and alternatives realizing the advantages and benefits of this invention , will be apparent to those of ordinary skill in the art having reference to this specification and its drawings . it is contemplated that such modifications and alternatives are within the scope of this invention as subsequently claimed herein , and it is intended that the scope of this invention claimed herein be limited only by the broadest interpretation of the appended claims to which the inventors are legally entitled .
a cardioplegia system for delivering cardioplegic solution to the heart during open heart surgery in cooperation with an extracorporeal blood circuit employing a heart / lung machine , includes a conduit diverting a portion of the blood flow from the heart / lung machine to a cardioplegia delivery line . a heat exchanger assembly including a heat exchanger for controlling fluid temperature is provided in the cardioplegia delivery line . in addition to a heat exchanger , the heat exchanger assembly includes an integral bubble trap , filtration means and means to enable the measurement of certain physical characteristics of the circulating cardioplegia fluid and / or certain events occurring within the heat exchanger assembly .