the device of the present invention is a modified catheter suitable for placement in the tissue of interest . there are a wide variety of steerable catheters well known to eardiologists . many of these could be modified to provide the device of the present invention . the invention can also be manufactured in the form of a probe rather than a catheter useful , for example , for examining the skin of a patient , but the general design can be understood from the following discussion . in general , the device provides a sensing apparatus for detecting a selected biochemical or physiological response . in addition , the device provides a means for delivering one or more compounds to the tissue under study . the sensing apparatus may include spectrophotometric apparatus ( illumination and detection , e . g . through fiber - optic leads ), biochemical monitors ( such as a compound - sensitive electrode ), temperature monitors , and other devices known in the art . referring to fig3 center portion 31 of a probe tip 30 can hold a detection device or connections to a detection device . in a preferred form , the probe tip 30 includes two fiber - optic leads , one to carry light to illuminate the area of interest , and the other to collect light from the area for subsequent detection and analysis . the light source and detection equipment are not shown but such apparatus are very well known to one skilled in the art . one useful configuration and apparatus is described in parsons et al ., u . s . pat . nos . 5 , 161 , 531 and 5 , 127 , 409 . the probe tip also includes micropipettes 33 , which are connected to a reservoir of material which can be delivered at a specified and controlled rate and time . apparatus for controlling delivery are well known . a simple application device is a conventional syringe connected to tubing which is connected to micropipette 33 . a simple variation of this is an iv ac or other controlled delivery device , such as those used for control of intravenous drip . an electronically controlled metering device is particularly useful . in one preferred embodiment , illustrated in fig4 a , 4b and 4c , the probe is a catheter , somewhat similar to that described in the parsons references . the central portion of the catheter includes fiber - optic elements 50 , 51 to carry illuminating light and detected light . other lumen elements 52 are included in the catheter and carry fluid to the catheter tip . end portion 53 is connected to 52 to deliver the contained fluid to the tissue of interest . end portion 53 is designed to move to open position 53 &# 39 ; to form an umbrella - like structure . in fig4 c , several alternate end portions 53 , 54 , 55 and 56 move to corresponding open positions 53 &# 39 ;, 54 &# 39 ;, 55 &# 39 ; and 56 &# 39 ;. although the figures illustrate a central fiber - optic portion and outer micropipettes , the actual order of elements can be varied . for example , one useful embodiment include a central core for delivery of fluid and two external fiber optic bundles for transmission of light . another useful embodiment uses one external fiber optic bundle to deliver illuminating light and two or more external fiber optic bundles for collecting detected light . the catheter tip is anchored firmly in place by ejecting an &# 34 ; umbrella - like device &# 34 ; with a central portion and peripheral portions . the catheter includes sensing components and fluid transmission components but the specific configuration of each component at the catheter tip can be modified . the important thing is to provide a metabolic substrate or other trigger compound in the presence of tissue which is evaluated using the sensing components . in one preferred embodiment , the probe tip includes three pods , the center of which contains the sampling probe . this will insure stability of the catheter on the moving myocardial surface . the sampling probe pierces the myocardial wall at a depth equal to one third of the total thickness for that wall . since the average left ventricle thickness is 6 to 10 mm , one third of this thickness is approximately 3 mm . the cardiologist can control the depth of penetration . the depth will be varied for certain clinical entities as well as in conditions of myocardial hypertrophy . once the probe is positioned on the tissue of interest , a baseline measurement is taken . a substrate compound is infused into the tissue as additional measurements are taken . in many instances , it is advantageous to infuse a second substance , a trigger compound , while continuing to take measurements . one preferred implementation uses a variation of the parsons et al . device to monitor activity of cytochrome a , a3 . the probe illustrated in fig4 a is positioned in an area of interest and spectrophotometric measurements are taken . in general , the measurements will be taken continuously but it may be sufficient to take measurements at selected times . a substrate is infused , preferably succinate , and additional measurements or taken . if there is any response at all , the tissue can be considered to have some potential viability . after some time , generally one to ten minutes , a second , trigger compound can be added . in a preferred implementation , the trigger compound is adp . additional measurements are taken , again looking for an increase in signal . it is relatively easy to observe a 10 % change in a spectrophotometric signal , and for many tissue samples the response upon administration of substrate , sometimes after trigger , is on the order of a 100 % increase in signal . the tissue viability monitor is used to assess viability of &# 34 ; segments &# 34 ; of the myocardial walls . the myocardial walls , right ventricle , interventricular septum , and left ventricle are divided into sixteen segments , each section corresponding to a region supplied by a significant coronary artery . these segments have been defined based on the images obtained by echocardiography . fig1 a - d demonstrate preferred standard views used in echocardiography and the division of the myocardial walls . each wall segment is named , indexed in the figures with a corresponding number ( 1 - 16 ). the name essentially describes the type of wall ( septum or wall &# 34 ; of ventricle &# 34 ;) and its location by one or two vectors , e . g ., inferior , inferior lateral , or apical inferior . furthermore , each segment can be pattern - coded according to the index . each pattern identifies the blood supply to that segment from a specific coronary artery . segments of the same pattern receive the blood supply from the same coronary artery . for example , segments 1 , 2 , and 11 - 14 receive the blood supply from the left anterior descending ( lad ) coronary artery . ______________________________________ wall motion segment coronary artery______________________________________1 mid ant sept lad2 mid ant lad3 ant lat lcx4 inf lat lcx5 inf rca ( fda ) 6 inf sept rca ( fda ) 7 basal ant sept lad ( prox ) 8 basal post lcx9 basal sept rca ( fda ) 10 basal lat lcx11 apical sept lad12 apical lat lad13 apical inf lad14 apical ant lad15 basal inf rca ( fda ) 16 basal ant lad ( prox ) ______________________________________ lad -- untitled ; lad ( prox )-- back slant ( lines descending right to left ); lcx -- speckled ; rca ( fda )-- forward slant ( lines descending left to right ). each segment is several centimeters long . an experienced cardiologist can easily position a catheter tip within a region of this size . in contrast , during electrophysiology - mapping the electrode catheter has to identify and be placed in alignment with electrical accessory pathways which are millimeters or fractions of a millimeter wide , requiring time - consuming positioning maneuvers and a high degree of precision . this problem is not pertinent to the tissue viability monitor . for the tissue viability monitor , the tip of the sensing catheter preferably is positioned at or near the center of one or more of these defined wall segments . such a catheter therefore will have maneuverability characteristics similar to standard catheters presently in use where gross positioning is easily achieved . positioning of the catheter on each wall segment is guided and verified by fluoroscopy comparable to the standard technology used during the positioning of catheters for catheterization of tiny orifices of the coronary arteries . each segment is sampled once or twice from the central area of each segment . normally three to four segments in the vicinity of the myocardial wall of concem is evaluated . the results can be scored in a variety of ways . for example , a simple gross quantitative value can be used to compare observations . in a preferred embodiment , a scale of 0 - 5 is used , 0 ) unable to score , 1 ) normal , 2 ) hypokinetic , 3 ) axikinetic , 4 ) dyskinetic , and 5 ) aneurysmal . one skilled in the art can devise alterative scoring systems . there is a recognized risk for the occurrence of limited , transient arrhythmia during an intracardiac catheter placement , e . g ., cardiac catheters , electrophysiology pacing wires , or biopsy devices . these arrhythmias occur , usually transiently , as the catheter touches specific sensitive , excitable focus areas in the myocardial wall . usually the arrhythmia self - terminates once the catheter is repositioned away from the excitable focus . in rare cases an arrhythmia does not self - terminate . a good cardiac catheterization laboratory and known procedures are designed to handle such arrhythmia by either activating temporary pacing wires , usually pre - positioned in the heart prior to attempting catheterization , or by intravenously infusing appropriate pharmacological agents . in either case , cardiac catheterization is performed daily and control of transient arrhythmias is well handled in the cath - lab or , rarely , in the intensive care unit , the only locations where catheterization should be attempted . the tissue viability monitor catheter and procedure are not significantly different than standard catheters in their potential to induce limited transient arrhythmias during positioning . response and stabilization of the tissue viability monitor of the activating metabolic signal should be achieved within minutes . positioning of the catheter probe on a particular myocardial wall segment should also be achieved within minutes , perhaps similar to the time required to position a myocardial biopsy catheter on a selected portion of the myocardium . in any such placement , certain locations in the myocardial wall may be less easily accessible than others . experienced physicians can position the catheter more quickly after repeated or frequent use . in general , the total time for the procedure is less than thirty minutes , significantly shorter than the time required to do percutaneous transluminal angioplasty ( ptca ). oxygen consumption may be measured by the tissue viability monitor ; however , as discussed above , because of the dynamic nature of the measurement , the oxygen consumption measurement by this technology may not be a valid indicator of viability . one useful substrate for practicing the invention is succinate . succinate is available in high purity ( chromatographic grade ) from sigma chemical co . standard procedures are available to prepare the material for intravenous administration . the amount to be administered is very low in terms of whole body exposure , while local concentrations are generally close to normal physiological ranges . glucose uptake is a property of viable tissue . the glucose uptake process obtains its energy from the chemical gradient present across the cell membrane . this chemical gradient is established by active pumping of sodium to the outside and potassium to the inside of the wall by the atp - dependent sodium - potassium pump . this gradient has a potential of - 90 mv ( millivolts ). to establish and maintain this gradient , the cell membrane has to be intact and atp - dependent pumps must be viable . cell viability requires maintenance of the potential across the cell membrane . dead cells , irreversibly damaged cells and non - salvageable cells do not have this capacity and therefore cannot transport glucose across the cell membrane in an active fashion , particularly when a stimulus such as insulin introduced . similarly the electron transport chain within the mitochondria requires for its proper functioning the presence of a strong chemical / ionic gradient across the mitochondrial membrane ( the chemiosmotic hypothesis ). failure of this gradient , or failure of the cellular gradient which in turn affects the mitochondrial gradient , will compromise function of the electron transport chain . electron transport chain activity in isolated mitochondria is different than corresponding activity in intact cells and tissue . this activity , then , can be used as an indicator of whether or not the cells are intact and capable of functioning . in conclusion , therefore , many , if not all , ionic gradient - dependent dynamic measurements ( e . g ., electron transport , cytochrome activity , or glucose uptake ) are significantly affected by cell viability . a cell may be compromised to varying degrees depending on the trauma that initiated cell injury and the time since the trauma . since one or more intermediate states of so - called &# 34 ; reversible damage &# 34 ; may exist , the tissue viability monitor can be used to quantify grades of viability . the tissue viability monitor of this invention incorporates backscatter technology . therefore , development of the probe will contribute to the development of backscatter technology . furthermore , any advances in backscatter technology over the next few years can be incorporated within the viability probe . however , it should be clear that information obtained by backscatter technology either transthoracic or on a catheter does not represent an objective measurement of ischemia or viability . in contrast , measurements of metabolic alterations represented by glucose transport or the electron transport chain provides solid objective information regarding viability . the main users of the tissue viability monitor initially will be cardiologists in the cardiac catheterization lab and surgeons intraoperatively . the general teachings of this invention can be utilized to monitor the viability of other organs and the device and method can be used by other sub - specialists , including gastroenterologists and interventional radiologists . organs and areas of particular interest include large and small intestines , kidney , liver , brain , and extremities . intestinal infaret can be life threatening . after transplant of any organ , it would be helpful to use the new device to examine tissue in the transplanted organ and possibly in other host tissues as well . liver or kidney can become fibrotic , leading to loss of function in the organ . using the new invention , a catheter can be directed though the renal artery to probe selected portions of the renal cortex . a probe also might be inserted through an incision in the abdomen to examine either the liver or kidney . the new invention may be particularly helpful in examining these organs . at present , about the only way to effectively probe the liver and kidney is during autopsy after the patient has died . the new invention could be used earlier in order to ascertain whether any medical intervention might have a reasonable chance of success and keep the patient alive . the new invention may be useful in examining muscle and other tissue in various body parts . one significant application is in examining skin after a grafting procedure . the probe can be applied eternally . another significant application is in examining gangrenous or necrotic tissue , such as muscle or connective tissue , in extremities . these conditions often arise in severe or late stage diabetes , atherosclerosis or after a clot , bum or trauma affecting the region of interest . a general description of the device and method of the present invention as well as preferred embodiments of the present invention have been set forth above . one skilled in the art will recognize and be able to practice many changes in many aspects of the device and method described above , including variations which fall within the teachings of the invention . the spirit and scope of the invention should be limited only as set forth in the claims which follow .
a method and apparatus for evaluating the viability of a tissue of interest , particularly that presents as dead but may be merely stunned or hibernating with reduced or no contractility . dynamic measurement of oxidative metabolism permits distinguishing between different stages of compromised myocardium . measurements can be made using near - infrared illumination and detection coupled with infusion of one or more metabolic substrates to the region of interest to evaluate whether a metabolic pathway cascade or a trans - membrane ionic potential are intact and thereby provide an indication of the viability of the cell .