Patent Application
20120330116
Not applicable.
The present invention generally relates to a system, method and apparatus for measuring the activity of the liver in a patient. A fluorescent analyte is introduced into the circulatory system of the patient and the concentration of the analyte is measured over time. The fluorescence emissions and detection system disclosed can also be used to measure the blood concentration of a compound that is metabolized by the liver or other organs, or excreted. Thus, the activity of liver enzymes, liver circulatory capacity, and liver function, along with the function of other organs can be measured with the appropriate detection compound.
In addition to using percutaneous or invasive detection systems to monitor cardiac activity and circulation, systems are needed to rapidly, continuously and repeatedly measure the concentration of agents introduced into the blood that are indicative of the level of organ function. In particular, the ability of the liver to metabolize a detection agent has been employed to measure the level of activity of the liver in patients. Patients suffering from trauma, sepsis and hepatitis may have their liver function evaluated (i.e., the level of activity of the liver organ for metabolizing monitoring agents) to determine if the liver has been compromised. In addition, patients suffering from liver cirrhosis or patients in need of a liver transplant, or post-operative liver transplant patients require liver function assays in order to appropriately guide treatment regimes.
Similarly, the relative ability of other organs, such as the kidney, to metabolize circulating substances would be useful in planning and monitoring treatment for conditions affecting those organs.
Existing systems for tracking the movement through circulation, or the level of continued presence of a tracking agent suffer from low resolution and reproducibility in the clinical setting. For instance, a continuing difficulty with existing methods for detection of cardiac anomalies is the efficacy of using microbubbles as a circulatory tracking indicator. Several existing methods for analyzing cardiac, pulmonary and general circulation including transesophageal echocardiography, transthoracic echocardiography, and the transcranial Doppler method, suffer from barriers for routine use for screening, whether due to the need for anesthesia or expensive equipment. There is a need for more efficient circulatory tracking reagents, i.e. a reagent that can be reproducibly introduced into the circulatory system, be quantitatively detectable, and utilize relatively straightforward detection systems that are easily tolerated by patients.
In addition there's a long history of utilization of natural and labeled compounds to assay the activity of the liver by correlating the liver's capacity to remove plasma-borne compounds from circulation. See, e.g., Korman, et al., NEJM 292:1205 (1975) and Horak, et el., Gastronterology. 71: 809 (1976).
Mills, in U.S. Pat. No. 6,030,841 discloses a number of compounds, including fluorescent compounds that can be utilized for liver function assays. Mills identifies a variety of fluorescently labeled compounds, radio-labeled compounds, and colorimetric assays. A large family of substituted steroid fluorescent compounds, including bile acid derivatives are disclosed for utilization in assays of liver function. It is noteworthy that the state of the art method of assay disclosed in Mills involves repeated blood draws, plasma processing and a dedicated fluorescence spectrophotometer (e.g., Perkin Elmer LS5B Spectrometer).
Wissler noted that the elimination of an analyte such as ICG from the circulating blood by the liver behaves as a two-compartment system. The dye injected into the blood forms a decreasing reservoir in the systemic plasma, with a large percentage of the dye being removed after passage through the liver. A smaller percentage is recirculating through the hepatic vein into the systemic plasma. The liver effectively acts as a second compartment, accumulating sequestered dye, with the liver sequestered dye being excreted into the bile at a rate (consummate) with the processing capacity of a particular liver. See Wissler, E. H., E. J. Appl. Physiol. 111: 641-646 (2011). A number of liver activity factors are important during clinical evaluation of a patient. Such factors include the rate at which a patient's liver extracts dye from the systemic plasma, and the rate at which the liver excretes sequestered due into the bile.
Indocyanine green is a well-characterized dye and is widely used as a fluorescent indicator. ICG has been marketed as a lyophilized powder (Akorn, Inc. Buffalo Grove, Ill.). ICG has been used for a number of diagnostic procedures, including for angiography and ophthalmology, and also for procedures such as dye enhanced photocoagulation, and photodynamic therapy. ICG has a long history in clinical settings, is well tolerated and can be utilized at relatively high plasma concentrations without significant side effects. ICG has been approved by the U.S. FDA as an injectable drug for ophthalmic angiography, measuring cardiac output, liver blood flow and liver function.
Because of its long history and general acceptance, a number of ICG analogs have been developed. Alam, et al. discloses enhanced compositions of ICG for use in diagnostic and therapeutic procedures. Alam, et al. US Parent Application Publication US 2003/0060718 (2003). The Alam, et al., publication does not disclose or reference apparatus for performing such procedures, but does claim a method for performing angiography (see claims 52-66) or treating lesions such as tumors (see, e.g., claims 66, 81). The claims presented in the Alam, et al., application do not present any impediment to the currently projected practice of the Cardiox system or contemplated extensions. Moreover, the ICG compositions disclosed by Alam, et al., could be utilized with the Cardiox system if the composition was purchased by a licensed supplier.
With respect to monitoring liver function using a circulating tracking agent, both invasive and minimally invasive systems exist, but have not been widely accepted or are ripe for improvement. Invasive systems rely on the injection of a dye, followed by withdrawing a blood sample and spectrophotometric analysis of the sample at regular intervals. Such a system is hampered by its labor-intensive nature, and the errors introduced by repeated inexact manual steps. A related transcutaneous system uses the injection of a dye, and then the dye concentration is measured by pulsed-light densitometry using a transcutaneous detector. The existing transcutaneous system requires a relatively high dye dosage (i.e., 20-50 mg ICG per test) in order to allow detection. Such high doses preclude continuous monitoring of liver function because the highest allowable daily dose of ICG (about 80-90 mg/day) is quickly exceeded. For additional background, see, “Indocyanine green elimination rate detects hepatocellular dysfunction early in septic shock and correlates with survival. Crit Care Med. 29:1159-63, 2001; and Sakka S, et al: “Prognostic Value of the Indocyanine Green Plasma Disappearance Rate in Critically III Patients.” Chest 122: 1715-20, 2002.
A number of public domain systems exist that utilize a single irradiation source, such as a fiber optic cable connected to a laser and an associated separate detector, such as a CCD camera or spectrophotometer. The laser emitter and fluorescence detector have been further associated with endoscopic devices. Even simpler densitometric systems have likewise existed for some time, with such systems relying on the absorption of ICG in the 805-810 nm range. An ear densitometer produced by the Waters Co. of Rochester, Minn. is advertised as being capable of in vivo measurement of ICG absorbance, but in the aforementioned higher doses.
In light of the marginally useful devices available for continuous monitoring of liver or other organ function using a circulating analyte, the present disclosure provides the advantages of a useful non-invasive system. Thus, in application for U.S. patent Ser. No. 12/418,866, to which priority is claimed, a generally non-invasive technique for screening for measuring the concentration of a circulating analyte is disclosed. The present disclosure provides advantages that will be apparent. This results in one or more intensity versus time curves, representing an analyte concentration resulting from metabolism of the indicator through the circulatory system, i.e. by the lungs, brain, kidney or other organs.
Implementation of the transcutaneous detection system for accurate detection of a circulating indicator allows monitoring of the decay of a circulating indicator in the blood, and thus allows for monitoring of organ function with relatively low doses of indicator.
The present system discloses using a transcutaneous detection system to measure the quantity of a circulating detection agent in the blood, and thereby measure the decay of concentration due to liver function. The present system utilizes a variation of the previously disclosed system, method and apparatus for detecting and quantifying right-to-left pulmonary shunts. The preferred indicator, which is employed, is indocyanine green (ICG) dye, which will fluoresce when exposed to an appropriate wavelength of higher energy light, for example, a laser in the near infrared region. The procedure is under the control of a monitor/controller having a visual display and capable of providing a cue to the operator. A vein access catheter is employed in connection with a peripheral vein such as the antecubital vein in an arm. Sensing of the indicator concentration takes place at an arterial vasculature of the animal body, preferably at the pinna or scaphoid fossa of the human ear or the finger of the hand.
The system is embodied preferably to perform assays using fluorescence sensor arrays each with three indicator fluorescing lasers, which are directed to a blood vessel under the skin surface at a location where relatively thin tissue contains a blood vessel network. These sensors are configured for transmission mode measurement wherein three lasers are combined with aspheric collimating lenses positioned opposite a photon collimating orifice and an optical band pass filter, selected to enhance selective passage of fluorescing photons to a photodetector while greatly limiting the incidence of the excitation photons at the photodetector. The two branches of these fluorescence sensor array configurations are preferably spring biased, adjustable or have fixed size gap opening (“throat”) to be held in proper and stable positions on accessible tissue.
The monitor/controller may be configured to calculate the concentration of a blood-borne indicator relative to baseline (e.g., in units of millivolts of measured fluorescence signal level), and as the indicator is metabolized the liver function can be determined by measuring the relative rate of disappearance of the indicator from the blood stream. Similarly the system can be used to calculate indicator/analyte sequestration or elimination at a steady state.
Using the data collected by the system, the monitor/controller publishes the relative indicator concentration decay as a function of time curves and the derived exponential decay coefficient, plasma disappearance rate, and residual relative concentration at 15 minutes after injection of the indicator.
In a further embodiment, the system implements comprises a sensor array with transmission mode sensing in which the sensor array comprises two or more pairs of emitters of excitation photons and fluorescence detectors of the fluorescent analyte of liver activity. The several emitters of excitation photons and fluorescence detectors are optionally energizable in a sequence of such emitter detector pairs or energizable simultaneously, wherein the monitor/controller is responsive to elect one or more of that pair exhibiting an average detection signal output of highest intensity.
A further embodiment is a sensor array apparatus in which the light path of excitation photons is arranged with an aspheric collimating lens, and the light path of emitted fluorescent photons to the photodetector is arranged with a collimator plate and an interference filter. A preferred embodiment is where the excitation source emits photons in a wavelength range of from about 750 to 820 nanometers, or even more preferably at a wavelength of from about 780 to 790 nanometers. The sensor array apparatus may be optionally positioned at paired distal locations by providing two fluorescence sensing array fixtures with sensing array arms, removeably attached to a headband.
A preferred embodiment of the system and apparatus configured for measuring a relative organ activity in a patient, comprises of providing an indicator analyte delivery system having an outlet located in a vein of the patient in blood flow communication with the right side of the heart; said indicator analyte delivery system being actuateable to cue the injection of a fluorescing biocompatible dye excitable by tissue penetrating excitation radiation to derive fluorescence emission corresponding with the indicator analyte concentration; the indicator delivery system includes a flow sensor responsive to derive signals corresponding with the commencement and termination of fluid flow through the system; providing an indicator analyte that is fluorescently labeled and the concentration of said indicator analyte is responsive to the metabolic status of said organ; a sensor array comprising a excitation photon emitter energizable to generate light at the excitation radiation wavelength and a photodetector which is filtered for response substantially only to the fluorescence emission, further providing a transmissive sensor positionable to sense the presence of at least a portion of the indicator at the vasculature of one or of symmetrically paired distal locations of the patient and having one or more outputs corresponding with the instantaneous concentration of indicator at such vasculature in which the sensor array further two or more paired excitation photons emitters and photodetectors and energizable in a sequence of such pairs or simultaneously; even further providing a sensor array further comprising the excitation photon emitters and photodetectors arranged with filtering system comprising an aspheric collimating lens, a collimator plate and an interference filter in the transmission path to the photodetector, and then providing a monitor/controller having a display and responsive to said actuation of the indicator analyte delivery system to commence timing the time following first detection of indicator analyte, responsive to a sensor output; and finally providing an associated monitor/controller responsive to publish one or more of a decay curves or to display one or more indicator analyte decay curves to determine relative activity of the organ, whereby the injection of the indicator analyte commences activation of the excitation photon emitters, and detection of any data signal by the associated photodetectors, with the monitor controller collecting said data signal and calculating a organ function metric.
The disclosure is further embodied in a kit supplying consumable materials necessary for quantifying liver function comprising an indicator delivery tubing system providing a valve, syringe connectors, a flow sensor and sterile intravenous injector, one or more doses of liver activity indicator reagent as a shelf stable material, a diluent for preparing the dose of liver activity indicator reagent for injection or for delivering an indicator bolus and a dose of nonreactive blood compatible clearing reagent for completing the injection. The kit may further be embodied in a flow initiation sensor that further comprises an initiation sensor with a circuit that in communication with a monitor-controller responds to a query determining the number of injections a flow initiation sensor has cued and that is disabled for repeated use after a testing procedure time period. The kit further comprises a sealed tray containing the kit contents maintained in a sterile condition until opened.
Yet another embodiment of the disclosure is a method for measuring the relative concentration over time of a liver activity indicator in the circulating blood stream, comprising the steps a) selecting a liver activity indicator analyte that is predominantly removed from circulating blood by the liver said analyte further comprising a fluorescent moiety that can be excited to emit fluorescence through irradiation by excitation photons in wavelength range known to induce fluorescence in said analyte; b) positioning about the skin of a human subject one or more emitter/detector arrays for emitting excitation photons in a given wavelength range known to induce fluorescence in said fluorescent moiety of the liver activity indicator analyte, said emitter in alignment with one or more detectors configured to measure the intensity of emitted fluorescence photons from the liver activity indicator analyte; c) injecting said liver activity indicator analyte into the blood stream of a human subject; d) recording the relative concentration over time of the liver activity indicator analyte by recording time-varying fluorescence signal level; and e) calculating a liver activity metric according to Formula 1, whereby the relative liver activity of the patient is displayed in a report.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter. The various embodiments of the invention, accordingly, comprises the method, apparatus and system possessing the construction, combination of elements, arrangement of parts and steps which are exemplified in the following detailed description.
For a full understanding of the nature and objects of the various embodiments of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:
A generally applicable non-invasive technique for screening for and measuring the concentration of a circulating blood analyte indicating organ function is disclosed. With the system and method, the analyte is preferably an injectable fluorescing indicator (such as indocyanine green dye). A resultant dilution curve is detected at the vasculature at the scaphoid fossa of the ear, or other chosen location. In general, a near infrared wavelength region laser beam is applied at the ear surface in alternatively a reflection operational mode or a transmissive mode, the transmitted photons are filtered and the fluorescence photons measured for intensity. This results in a curve which is characterized by the exponential decay of the indicator concentration in the blood stream measured during the period beginning about two to three minutes after the time of indicator injection until about 10 to 20 minutes after the time of indicator injection. The starting time for indicator concentration level is delayed to ensure that the injected ICG dye is uniformly mixed throughout the circulating blood volume.
Implementation of the transcutaneous detection system for accurate detection of a circulating indicator allows for monitoring of the decay of a circulating indicator in the blood, and thus allows for monitoring of liver function with relatively low doses of indicator.
The discourse to follow tracks further animal and initial human testing and presents a review of published research, resulting in a diagnostic approach which permits a practical survey for the phenomena over a large patient population.
In general, the preferred embodiments of the present disclosure observe that an indicator such as an externally detectable indicator dye material will traverse through the arterio-venous system from an injection point in a vein, toward the heart. Venous blood containing such an indicator will pass through the heart and the indicator is then carried through the pulmonary circulatory system (i.e., through the lungs) back through the heart and through the various arteries to the tissues of the body. The organs of the body will interact with a circulating indicator, and so long as the presence of the indicator or the metabolic products of the indicator remain in the circulatory system, those indicators and metabolites are detectable by an external or minimally invasive sensor system. The present system is especially adapted to the use of labeled indicators, particularly fluorescently labeled indicators, whose concentration is affected by the metabolic activity of one or more organ. Thus, as organs interact with circulating blood, a blood-borne indicator is subject to degradation, metabolism, excretion, sequestration and other processes to alter the concentration of a measurable indicator in the blood. Because the “indicator” may be modified by organ systems and thus change the detectability of the indicator, as used herein, the indicator is recognized to be the indicator as injected and further modified or metabolized. As described herein an “analyte” is the native indicator dye, and the detectable metabolic products of the indicator, as differentiated from undetectable metabolic products. Thus, an analyte includes a moiety that is measured by the system, directly or indirectly, including products that are analyzed to determine organ activity.
A number of organ systems are subject to analysis by a circulating analyte. In particular, the liver is known to exclusively extract indocyanine green. Thus, the health, vitality, or relative activity of the human liver can be monitored by the liver's capacity to extract indocyanine green from the circulating blood and other tissues of the human body. As noted by Mandell, the ICG dye is rapidly extracted from the blood only by the liver and is excreted in the bile. Mandell Anesth. Analg. 95: 1182-1184 (2002). Analytes that can be used to assist in monitoring other organ systems are known, or could be determined by using the testing systems disclosed herein. Other indicator analytes may be metabolized by the patient body, i.e., modified, excreted, or sequestered. Thus, metabolism may function to remove a detectable form, or to generate a detectable form of an analyte that can be used to monitor various metabolic activities and organ function. Organs adapted for monitoring by the present system include also the kidneys, pancreas, lungs, colon, the immune system, and the brain. Monitoring of organs is primarily limited by the identification of appropriate analytes for use with the system.
A number of fluorescent labeling systems are available for utilizing metabolites as analytes with the present system, including, e.g., labeled alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase, 5′ nucleotidase and gamma-glutamyl transpeptidase (GGT). With respect to liver function testing, the system disclosed is useful for liver function testing including indications where said testing may be performed in a hospital, outpatient or office-based setting depending on the indication and the condition of the patient. Examples include critically ill patients, especially those with sepsis, acute liver or multi-organ failure, and after multiple trauma; patients with chronically reduced hepatic function (hepatitis, liver cirrhosis); for the evaluation of liver function in organ donors and projected recipients; for monitoring of liver function during liver or abdominal surgery (resection, porto-caval shunt); for diagnosis and monitoring of congenital liver failure in children and neonates; and for the assessment of new drugs and their potential for adverse effect(s) on the liver. Similar parameters are envisioned for using the system with analytes that monitor other organ systems.
As an initial illustration of the system disclosed, a preferred embodiment is the use of indocyanine green (ICG) as a liver activity analyte. Injection of ICG in a vein will lead to the transit of the dye analyte through the circulating blood including to the hepatic artery. As the indicator passes through the liver, a liver extractable indicator such as ICG will be reduced in concentration by the activity of liver enzymes, for instance. Thus, the level of liver activity can be measured by the rate at which the liver activity indicator dye is decreased over time. A variety of metrics can be tested using the present system, including analyte retention rate or residual analyte concentration, R15 at 15.0 minutes after ICG injection (as a percentage); exponential decay coefficient associated with the rate of extraction of the ICG by the liver, K (in reciprocal minutes) and the plasma disappearance rate of ICG in percent per minute.
Turning to
As shown in
Following injection of a quantity of analyte, (e.g., 5 to 10 mg of the liver activity dye, ICG), a dwell period of about 2 to 3 minutes is allowed to pass. During this dwell period, the indicator is being distributed throughout the circulating blood of the patient, by successive passages through the heart and aorta. After about 2 to 3 minutes, monitoring of the concentration of the liver activity indicator dye can yield a useful signal. It is anticipated that monitoring can be continuous, or can be taken at regular intervals, such as at five-minute intervals. In a preferred embodiment, after injection of the dye, the first measurement is taken at about two minutes post-injection, and then followed by successive measurements at 5 second intervals, for a testing period of about 10 to 20 minutes.
The monitor 154 is configured to calculate the detected relative blood concentration of liver activity indicator analyte (i.e., the detected fluorescence signal level relative to baseline), and provide a semi-logarithmic graph of relative ICG concentration as a function of a linear abscissa, time, as well as the aforementioned metrics exponential decay coefficient, plasma disappearance rate and residual level of ICG at 15 minutes. The slope of the liver activity semi-logarithmic graph indicates the level of enzymatic activity of the liver for a given period of time. For certain patients, the initial monitoring period will confirm adequate liver activity. Other patients may need nearly continuous monitoring, utilizing repeated injections of indicator dye or alternatively, a low continuous dose supplied through an intravenous drip. In addition, certain patients may be subjected to daily monitoring, for instance, and the relative liver activity can be compared over a period of time, including months or weeks.
In the succeeding figures,
Turning now to
Array body 332 is formed of two parts, main body 342 and body cap 344. Cap 344 is retained by press fit, adhesive, or by lug 346 capturing pin 347. Inside the body 332 are found connector board 354, detector board 355, and emitter board 356. A three-laser array and collimating aspheric lenses 346A-C are mounted within a protrusion/emitter head 350 extending outwardly from support body 332. That protrusion is seen, particularly, at
Looking to
Referring to
In a preferred embodiment, the sensor arrays are utilized at paired locations on the patient body, e.g., preferably on both ears, fingers of both hands, or both great toes. In order to connect the sensor array apparatus to the monitor controller, a reusable connection cable 420 is provided as seen in
As shown in conjunction with
Thus returning briefly to
A general flow chart of the operation of the system is described in
If the voltage output levels are within the acceptable ranges, arrow 1020 is followed to block 1022, where the physician identification number, the patient identification number, age, sex and intended injectate dose(s) are entered via the monitor touchscreen, or associated keyboard. Following arrow 1024 to block 1026, the maximum number of tests, i.e. dye injections is entered. This number, N, is dependent on the particular analyte being utilized, and for ICG, the maximum number of tests is calculated by determining the maximum daily dose (typically as mg/kg body weight) for the patient, and dividing the maximum daily dose by the injectate dose, i.e. 5 or 10 mg), and then rounding the result to the next lowest whole number.
Next, as represented at arrow 1028 to block 1030 the test count variable is set to testcount=1 and, as represented at arrow 1032 to block 1038, where the injectate (indicator solution for injection) is prepared, for example by mixing a known weight of indocyanine green dye with a predetermined volume of sterile water. A predetermined volume of that mixed indicator is withdrawn into a first syringe. That syringe is shown as 292 in
Block 1058 of
Arrow 1068 extends to block 1070, which will prompt the operator to inject indicator. In the event that the operator is not ready, the system waits for an operator ready cue or prompt. Then at block 1170 the waits for a positive response to the query posed as to whether the time for instructing injection is present. When the time to inject is present, the practitioner is instructed, first to be ready, immediately followed by instructions to commence the injection of the first syringe, which forces the indicator solution into the vein, followed by the second syringe isotonic saline flush solution. The practitioner may be provided with a visual cue via, for example, an illuminated LED light affixed on or near the flow sensor, so that the cue may be conveyed without difficulty. The flow sensor will detect the flow of indicator, as represented by arrow 1072 to block 1074. The flow sensor will make such a detection within a predetermined time after the injection cue is made to the practitioner at block 1070. For example, at block 1074, the flow sensor attempts to detect the presence of indicator solution for a six second period following its issuance of the cue to indicate the start of the injection. If no detection is made within this time, as at arrow 1076 to block 1078, the procedure is deemed invalid and the test is ended. When such a flow is detected, as represented by arrow 1080 to block 1082, time clock t1 is set to zero at the moment the flow sensor detects the start of the injection of indicator. At block 1086 t1, post-injection elapsed time clock is set to t1=0. Following arrow 1084 to block 1086, time t1 then begins counting up, to be used to determine first query time t2, and end query time t3.
Arrow 1088 reappears in
Then, as represented at arrow 1092 to block 1094, a query is made as to whether the measured signal for at least one channel is equal to or greater than a minimum designated signal. Where it is not, then as represented at arrow 1096 to block 1098, the practitioner is alerted with an audible/visual error message that there is insufficient coupling between the sensor and blood-borne indicator in the tissue.
When the S(N) for at least one of the channels is greater than the minimum value, next, as represented at arrow 1100 to block 1102, an inquiry is made to whether the delay flag is now zero, i.e. whether the first query time t2 has been reached. Where t1<t2, the query is repeated. When t1>t2, the system invokes the actions of block 1108, querying those sensor array channels, N for which S(N) is greater than the minimum value and measuring and recording analyte fluorescence for those channels. If the delay flag=0, then the liver function metrics are calculated and displayed and the semi-logarithmic graph is optionally displayed. For monitoring liver activity, the calculated best fit of the log concentration versus time decay line may be displayed as data is collected.
The measuring and recording function continues until the end time t3 has been reached. Thus, following arrow 1110 to block 1112, the end time query is posed as to whether t1>t3. When it is not, then as represented at arrow 1114 back to block 1108, measuring continues. When the query at block 1112 is answered in the affirmative, following arrow 1116 to block 1118, active measurements are discontinued, and liver metrics are determined and optionally displayed on the monitor.
During or after completion of the calculation steps in block 1118, following arrow 1120 to block 1122, a determination is made as to whether the number of tests performed is equal to the preset test limit. If the test count equals the test limit, arrow 1124 is followed to symbol 1126, and the test is ended. The monitor controller will terminate the access key to the flow sensor apparatus, preventing reuse or an excess number of re-tests.
When the test limit has not been reached, as at arrow 1128, the test count is changed to be test count=J+1 at block 1130. The program then continues as represented at arrow 1132 to Node A 1134 in preparation for a subsequent liver function test, if desired (e.g., the liver function test may be repeated two or more times after a time interval of 60 minutes after the start of the preceding test). Node A reappears in
The course of the procedures is summarized in a Chart 1200 shown in
In a preferred embodiment, the liver function metrics just described are calculated as described in the following steps. The first step, after digital filtering of the raw data for each of the six channels of ICG concentration vs. time data, is to use an off-the-shelf exponential curve fit software algorithm to determine the exponential coefficient of the equation listed below:
C[t2]=C[t1]*Exp{−K*t2} (Equation 1)
Where:
C[t2]=concentration of ICG relative to Baseline ICG concentration at elapsed time, t2 with time, t2 expressed in units of minutes and concentration expressed in units of millivolts
C[t1]=concentration of ICG relative to Baseline ICG concentration at elapsed time, t1 with time, t1 expressed in units of minutes and concentration expressed in units of millivolts; t1 would be starting time for exponential curve fitting (e.g., 2.00 minutes)
K=ICG exponential decay clearance coefficient expressed in units of reciprocal minutes
The ICG Exponential Decay coefficient, K is computed for each of the six channels for a range of starting and ending times. The matrix will include 2.0 and 3.0 minutes as the starting time and ending time of 10.0 to 20.0 minutes. The “goodness of fit” parameter computed using the selected exponential curve-fitting algorithm may be used to select the best channel of the six available data channels.
In this curve fitting step, the curve fitting involves dividing C[t2]/C[t1] for a range of C[t2] and a constant C[t1] value (i.e., the relative ICG concentration value at 2.00 minutes). Once the K value is derived, then solve Equation 1 for elapsed time, t2=0.0 minutes and setting C[t1]=100%. Re-plot semi-logarithmic graph (e.g., originally plotted using relative ratios of C[t2]/C[t1] for t1=2.00 minutes and t2 ranging from 2.5 to 10.0 minutes) with the maximum ordinate value set equal to 100%.
Once the exponential decay coefficient, K (in units of reciprocal minutes) is derived as described above, the Plasma Disappearance Rate, PDR (in units of % per minute) is determined by multiplying the exponential decay coefficient by 100.
PDR(%/minute)=K*100 (Equation 2)
The residual fractional ICG concentration at 15 minutes after ICG bolus injection, R15 is given by the following equation:
R15(%)=100%*Exp(−K*15.0 minutes) (Equation 3)
An advantage of the enhanced sensitivity of the disclosed system is that it allows regular testing of liver activity, without exceeding the daily allowable dose of liver analyte indicator. Present systems may require using the full available dose for a single test, while the present system may allow ten or more tests over a given 24 hour period. When utilizing a rapidly metabolized indicator delivered at low concentrations, frequent determinations of liver function metrics is practical (e.g., at an interval of 30 to 90 minutes between each test). It is a substantial advantage of the present system to allow near real-time monitoring of the activity of organs. By displaying the present activity of an organ such as the liver or kidney, a drop in organ activity due to insult, trauma, or disease can be identified prior to the patient entering a critical phase when liver or kidney failure is already advanced.
The present system is applicable to non-human patients, as well as human patients. In general the system is operable with a variety of mammalian patients, including working animals, such as dog and horse, and laboratory animals such as pig, sheep, and rabbit. In particular, certain very valuable animals, such as pets, companion animals, race horses, and show horses may at times be afflicted with disease. As such, the disclosed monitoring system can be readily utilized in conjunction with essentially any large mammal of interest, and adapted to use with small laboratory animals such as rat and hamster.
As is clear from the forgoing disclosure, identification of an efficacious analyte is of particular importance, and specifically looking to the liver activity indicator, a circulating tracking reagent is called for. Studies at the outset of the research leading to the present invention indicated that a preferred embodiment was to employ fluorescing dyes, certain of which had been approved for use in humans. Two such exemplary dyes include fluorescein and indocyanine green dye (ICG). As disclosed above, ICG as an analyte indicator of liver activity is a preferred embodiment. By no means, however, is the present disclosure restricted to ICG as an analyte indicator.
A number of additional analyte indicator reagents are available for use with the system at hand including such indicators as follows: U.S. Pat. No. 3,412,728 describes the method and apparatus for monitoring blood pressure, utilizing an ear oximeter clamped to the ear to measure blood oxygen saturation using photocells which respond to red and infrared light; U.S. Pat. No. 3,628,525 describes an apparatus for transmitting light through body tissue for purposes of measuring blood oxygen level; U.S. Pat. No. 4,006,015 describes a method and apparatus for measuring oxygen saturation by transmission of light through tissue of the ear or forehead; and U.S. Pat. No. 4,417,588 describes a method and apparatus for measuring cardiac output using injection of indicator at a known volume and temperature and monitoring temperature of blood downstream. This and several similar systems in the art suffer from an inability to effectively quantify the magnitude, i.e., functional conductance of shunts, as opposed to the presently disclosed embodiments.
As disclosed herein, preferred indicator analytes are capable of circulating in the blood or perfusing other tissues and/or fluids, and the indicator analyte is associated with a fluorescent moiety that can be excited to emit fluorescence through irradiation by excitation photons in wavelength range known to induce fluorescence in said fluorescent moiety. In certain cases, the metabolism of the patient body may activate the moiety, or otherwise result in the moiety losing its fluorescent capacity. The correlation of the action of an organ of interest may be established with the relative availability of the fluorescent moiety or fluorescence capacity therein.
A number of patents describe potential reagent systems that if adapted could be utilized with the present system method and apparatus. U.S. Pat. No. 4,804,623 describes a spectral photometric method used for quantitatively determining concentration of a dilute component in an environment (e.g., blood) containing the dilute component where the dilute component is selected from a group including corporeal tissue, tissue components, enzymes, metabolites, substrates, waste products, poisons, glucose, hemoglobin, oxy-hemoglobin, and cytochrome. The corporeal environment described includes the head, fingers, hands, toes, feet and ear lobes. Electromagnetic radiation is utilized including infrared radiation have a wavelength in the range of 700-1400 nanometers. U.S. Pat. No. 6,526,309 describes an optical method and system for transcranial in vivo examination of brain tissue (e.g., for purposes of detecting bleeding in the brain and changes in intracranial pressure), including the use of a contrast agent to create image data of the examined brain tissue.
Looking to the indocyanine green dye (ICG), excitation curves have been illustrated as having a peak excitation wavelength at about 785 nanometers. Correspondingly, for the fluorescent emission of the two fluorescent dyes, a peak wavelength of fluorescing photons resides at about 830 nanometers.
The transmission mode of sensing as described in connection with
The system outlined in
Referring to
In general, the controller circuitry used with the system will compute the exponential decay shown as solid line region 1262. As stated above as related to Equations 1, 2 and 3, the measured ICG fluorescence signal levels relative to baseline (following digital filtering to remove heart beat artifact and other sources of higher frequency noise) are recorded in this example over the period from about 2 to 15 minutes. Decay curve 1262, which is preferably a straight line when plotted on a semi-logarithmic graph can be displayed on the system monitor, with or without the representation of data points, as shown in
The recorded values are then analyzed using an exponential curve fitting algorithm to derive the exponential decay coefficient, K that provides the best fit (i.e., least error) to the measured data. Once the exponential decay coefficient, K is derived then the Plasma Disappearance Rate, PDR value can be derived as specified in Equation 2 above. The residual ICG relative concentration level at 15 minutes, R15 can be calculated as specified in Equation 3 above and/or can be derived based on the actual measured relative ICG signal level at an elapsed time of 15.0 minutes. A normal liver is generally characterized by a Plasma Disappearance Rate 15% per minute or greater. A Plasma Disappearance Rate 4% to 10% per minute is generally associated with a diseased or otherwise compromised liver.
It is also contemplated that rather than having discreet injections of an analyte, a continuous delivery of analyte could be produced by use of an IV drip, or measured perfusion pump to deliver the analyte. In such a situation, the monitor could display a second order calculation showing the change in organ activity over time. Thus, a curve 1460 shows the instantaneous liver activity, while a curve from continuous perfusion could display a measure of sustained the liver processing capacity.
A further embodiment of the system is a kit supplying consumable materials necessary for quantifying a circulatory anomaly.
The following examples are provided to more fully explain the system and apparatus. However, they should not be viewed as limiting.
Objectives of prospective indicator dosing trials and comparative analysis tests include optimization of the injection protocol to further increase the system sensitivity for monitoring liver function. Another objective is to determine test procedure parameters in preparation for subsequent trials. Further objectives include providing additional data for developing the disclosed method for the calculation and display of the functional flow conductance of a patient's liver. The following protocol demonstrates a testing procedure for determining the ability of different analyte indicators to assay organ function. In particular, the following protocol is designed for demonstrating efficacy of liver targeted analytes. Similar protocols can be readily implemented for demonstrating the efficacy of analytes suitable for assaying other organs. Undue experimentation is not necessary to demonstrate the efficacy of any analyte for use with the minimally invasive organ assay systems disclosed herein.
A kit, similar to that disclosed in relation to
Two reusable Fluorescence Sensor Array units, of the type disclosed in
A single-use, sterile catheter set is connected to an AngioCath catheter similar to that illustrated in
A 20 gauge Angiocath AutoGuard catheter (Becton, Dickinson and Company, Franklin Lakes, N.J.) is first placed in a vein in the antecubital fossa and is subsequently used in the method for assaying liver function.
The supplied, single-use Catheter Set (see
The patient is next instructed by the display on the Monitor/Controller unit to remain still for the next 15 to 20 minutes while the ICG signal levels are continuously measured and recorded. Within about one minute after the end of the test period (nominally two minutes after dye injection), the monitor displays a graph showing the recorded ICG concentration levels from the six fluorescence sensors over the 15-minute period of the test.
Referring to
Turning to
As shown in
The flow sensor as shown can be utilized to monitor and record the injection of analytes for assaying organ function. Thus, a single injection at a given time may be recorded by the monitor controller by way of the flow sensor, in order to initiate measurement with the sensor arrays. Alternatively, if an analyte/indicator dye is being continuously delivered to the patient, for instance through an IV bag, the flow sensor can monitor and allow recording of the amount of indicator delivered and allow the indication of dye delivery to be integrated by the monitor/controller.
The construction of the monitor/controller is shown generally in the applications to which priority is claimed. Schematics for the fluorescence sensor arrays described in connection with
Following experimentation, including using animal models, it was determined that sensitivity of the sensor array could be improved by the implementation of multiple emitters and detectors in a sensor array. In order to utilize low concentrations of analyte, such as ICG, sensitivity is highly preferred for assaying organ function. Once a multiple emitter/detector sensor array was implemented, it was recognized that the overall system sensitivity was being hampered by the efficacy of the bandpass filter and collimating plates that were limited by cross talk between related channels in the sensor array. It should also be noted that such cross talk may be even more pronounced when utilizing reflectance mode excitations and detection. The interference filter is necessary in order to reduce incident light arising from the excitation lasers, with the detectors being tuned to detect light emitted as a result of fluorescence. When the interference (i.e. bandpass) filter is ineffective, the excitation light may overwhelm the detection system. As shown by way of example in
Interference filter 282 is designed to pass essentially only the photons resulting from fluorescence to impinge upon photodetectors 284 and 284′. However, when emitted laser light interacts with tissue 274, a portion of such light is scattered, as shown in part by dashed lines 286 and 286′. Such scattered light would be prevented from entering the detector when a single emitter is present, by the first collimating plate 280. When multiple emitters are present, the scattered light may strike the interference filter 282 at an angle less than perpendicular. Since the filter is most efficient when the angle of incidence is 90 degrees, as the angle of incidence is reduced, scattered light (such as excitation laser light) as at 286 and 286′ can pass unimpeded through the filter, and substantially increase the noise detected by the photodetectors 284 and 284′. Recognizing this phenomenon, a preferred embodiment of the array system provides an additional second collimating plate as at 283, thereby maximizing the efficiency of the interference filter, and reducing the light of low angle of incidence that can pass through the interference filter.
As is known, the performance of interference filter 282 is dependent upon the angle of incidence of photons reaching it. Performance degrades as the angle of incidence increases.
A bench top, ex vivo, or animal model system is useful for testing a variety of parameters useful for optimizing the system and apparatus. Although ICG is the presently preferred indicator dye for assaying liver activity, other dyes may be even better adapted, and proof of concept of the system, using tissue phantoms, actual tissue and other factors can be readily screened with the apparatus shown in the referenced patent applications, including co-pending U.S. patent application Ser. No. 12/754,888, filed Apr. 6, 2010, which is incorporated herein by reference. Additional dyes useful for assaying other organs or organ systems may be tested using the referenced system. Moreover, improvements to the detection system itself are amenable to bench top testing for system optimization.
The present application herewith provides reference to U.S. application for patent Ser. No. 12/418,866, filed Apr. 6, 2009 and entitled “Hemodynamic Detection of Circulatory Anomalies” which, in turn, makes reference to U.S. Provisional application Ser. No. 61/156,723, filed Mar. 2, 2009, and to U.S. Provisional application Ser. No. 61/080,724, filed Jul. 15, 2008, the disclosures of which are incorporated by reference. Also, all citations referred herein are expressly incorporated herein by reference. All terms not specifically defined herein are considered to be defined according to Dorland's Medical Dictionary, and if not defined therein according to Webster's New Twentieth Century Dictionary Unabridged, Second Edition.
Since certain changes may be made in the above-described system, apparatus and method without departing from the scope of the invention herein involved, it is intended that all matter contained in the description thereof or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. The disclosed invention advances the state of the art and its many advantages include those described and claimed.
This application claims priority to pending U.S. Provisional Patent Application Ser. No. 61/528,562, filed Aug. 29, 2011, entitled “System for Non-Invasive Quantification of Liver Function” and claims priority to pending U.S. patent application Ser. No. 12/754,888, filed Apr. 6, 2010, entitled “Hemodynamic Detection of Circulatory Anomalies,” which is a continuation in part of and also claims priority to U.S. patent application Ser. No. 12/418,866, filed Apr. 6, 2009 and entitled “Hemodynamic Detection of Circulatory Anomalies,” the disclosures of which are incorporated by reference. The application also qualifies as an application under 35 U.S.C. §371 and claims the benefit of to pending PCT application No. PCT/US11/31433, filed Apr. 6, 2011 and published in English under PCT Article 21(2) the disclosure of which is also incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61528562 | Aug 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12754888 | Apr 2010 | US |
| Child | 13597999 | US | |
| Parent | 12418866 | Apr 2009 | US |
| Child | 12754888 | US |
