Abstract:
A tissue profile wellness monitor measures a physiological parameter, generates a tissue profile, defines limits and indicates when the tissue profile exceeds the defined limits. The physiological parameter is responsive to multiple wavelengths of optical radiation after attenuation by constituents of pulsatile blood flowing within a tissue site. The tissue profile is responsive to the physiological parameter. The limits are defined for at least a portion of the tissue profile.

Description:
PRIORITY CLAIM TO RELATED PROVISIONAL APPLICATIONS 
     The present application claims priority benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 60/925,811, filed Apr. 21, 2007, entitled “TISSUE PROFILE WELLNESS MONITOR,” which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Spectroscopy is a common technique for measuring the concentration of organic and some inorganic constituents of a solution. The theoretical basis of this technique is the Beer-Lambert law, which states that the concentration c i  of an absorbent in solution can be determined by the intensity of light transmitted through the solution, knowing the pathlength d λ , the intensity of the incident light I 0,λ , and the extinction coefficient ε i,λ  at a particular wavelength λ. In generalized form, the Beer-Lambert law is expressed as: 
                     I   λ     =       I     0   ,   λ       ⁢     ⅇ       -     d   λ       ·     μ     a   ,   λ                     (   1   )                 μ     a   ,   λ       =       ∑     i   =   1     n     ⁢       ɛ     i   ,   λ       ·     c   i                 (   2   )               
where μ 0,λ  is the bulk absorption coefficient and represents the probability of absorption per unit length. The minimum number of discrete wavelengths that are required to solve EQS. 1-2 are the number of significant absorbers that are present in the solution.
 
     A practical application of this technique is pulse oximetry, which utilizes a noninvasive sensor to measure oxygen saturation (SpO 2 ) and pulse rate. The sensor has light emitting diodes (LEDs) that transmit optical radiation of red and infrared wavelengths into a tissue site and a detector that responds to the intensity of the optical radiation after attenuation by pulsatile arterial blood flowing within the tissue site. Based on this response, a processor determines measurements for SPO 2  and pulse rate, and outputs representative plethysmographic waveforms. Thus, “pulse oximetry” as used herein encompasses its broad ordinary meaning known to one of skill in the art, which includes at least those noninvasive procedures for measuring parameters of circulating blood through spectroscopy. Moreover, “plethysmograph” as used herein encompasses its broad ordinary meaning known to one of skill in the art, which includes at least data representative of a change in the absorption of particular wavelengths of light as a function of the changes in body tissue resulting from pulsing blood. 
     Pulse oximeters capable of reading through motion induced noise are available from Masimo Corporation (“Masimo”) of Irvine, Calif. Moreover, portable and other oximeters capable of reading through motion induced noise are disclosed in at least U.S. Pat. Nos. 6,770,028, 6,658,276, 6,584,336, 6,263,222, 6,157,850, 5,769,785, and 5,632,272, which are owned by Masimo, and are incorporated by reference herein. Such reading through motion oximeters have gained rapid acceptance in a wide variety of medical applications, including surgical wards, intensive care and neonatal units, general wards, home care, physical training, and virtually all type of monitoring scenarios. 
       FIG. 1  illustrates an absorption graph  100  having a dimensionless vertical axis  101  of relative light absorption and a horizontal axis  102  of transmitted wavelength in nm. Shown is a plot of HbO 2  absorption  110  and Hb absorption  120  versus wavelength, both normalized to the absorption at 800 nm. At red and near IR wavelengths below 970 nm, where water has a significant peak, Hb and HbO 2  are the only significant absorbers normally present in the blood. Thus, typically only two wavelengths are needed to resolve the concentrations of Hb and HbO 2 , e.g. a red (RD) wavelength at 660 nm and an infrared (IR) wavelength at 940 nm. In particular, SPO 2  is computed based upon a red ratio Red AC /Red DC  and an IR ratio IR AC /IR DC , which are the AC detector response magnitude at a particular wavelength normalized by the DC detector response at that wavelength. The normalization by the DC detector response reduces measurement sensitivity to variations in tissue thickness, emitter intensity and detector sensitivity, for example. The AC detector response is a plethysmograph, as described above. Thus, the red and IR ratios can be denoted as NP RD  and NP IR  respectively, where NP stands for “normalized plethysmograph.” In pulse oximetry, oxygen saturation is calculated from the ratio NP RD /NP IR . 
     SUMMARY OF THE INVENTION 
     Oxygen saturation is a very useful physiological parameter for indicating the cardiovascular status of a patient, but allows healthcare providers only a few minutes warning that a patient is potentially having a medical crisis. A wellness indicator advantageously monitors changes in a patient&#39;s “tissue profile” so as to provide an advance warning of a deteriorating medical condition. This tissue profile is provided by a multiple wavelength sensor and a noninvasive multi-parameter patient monitor, which make blood absorption measurements at more than a red wavelength and an IR wavelength of conventional pulse oximetry. In one embodiment, described below, blood absorption measurements are made at eight wavelengths. Advantageously, this rich wavelength data characterizes a tissue site over a wavelength spectrum. 
       FIG. 2  illustrates an example of a tissue profile. In this example, the sensor emits eight wavelengths (610, 620, 630, 655, 700, 720, 800 and 905 nm). A tissue profile graph  200  has a NP ratio axis  201  and a wavelength axis  202 , where the NP ratios are of the form NP λ1 /NP λ2 . This is a generalization to multiple wavelengths of the ratio NP RD /NP IR  described above for two (red and IR) wavelengths. In order to provide a common scale for these NP ratios, the ratios are calculated with respect to a reference wavelength, λr, which may be any of the available wavelengths. Thus, the plotted NP ratios  210  are denoted NP λn /NP λr . Note that the NP ratio at the reference wavelength is NP λr /NP λr =1, which is 700 nm in this example. In this example, a tissue profile  210  is plotted for SPO 2 =97%. 
     Not surprisingly, the tissue profile  210  has the same general shape as the absorption curves  110 ,  120  of  FIG. 1 . In particular, the AC component of the detector signal relative to the DC component (NP) for a specific wavelength is proportional to the light absorption at that wavelength. Thus, the NP ratio magnitudes and hence the points along a tissue profile curve are proportional to absorption. Assuming negligible abnormal Hb species, if SPO 2  is close to 100%, most of the absorption is due to HbO 2  and, accordingly, the tissue profile is shaped closely to the HbO 2  absorption curve. As SpO 2  decreases from 100%, the tissue profile shape is increasing influenced by the shape of the Hb absorption curve. 
     In one embodiment, the tissue profile  210  consists solely of the measured NP ratios at the sensor wavelengths, i.e. a finite set of discrete values. In another embodiment, the tissue profile  210  consists of the measured NP ratios and defined NP ratio values between the sensor wavelengths, which are based upon tissue absorption characteristics. That is, the tissue profile  210  is a curve defined over a continuous range of wavelengths, including the sensor wavelengths. Although described above with respect to NP ratios derived from the AC component of the detector signal, a DC tissue profile may also be defined and applied to patient monitoring, as described below. 
     A tissue profile or tissue characterization is described in U.S. patent application Ser. No. 11/367,034, filed Mar. 1, 2006 entitled Physiological Parameter Confidence Measure; a multiple wavelength sensor is disclosed in U.S. patent application Ser. No. 11/367,013, filed Mar. 1, 2006 entitled Multiple Wavelength Sensor Emitters; and a multi-parameter patient monitor is disclosed in U.S. patent application Ser. No. 11/367,033, filed Mar. 1, 2006 entitled Noninvasive Multi-Parameter Patient Monitor, all of the aforementioned applications are assigned to Masimo Laboratories, Inc., Irvine, Calif. and all are incorporated by reference herein. 
     One aspect of a tissue profile wellness monitor comprises generating a tissue profile, predetermining rules and applying the rules to the tissue profile. The tissue profile is responsive to absorption of emitted wavelengths of optical radiation by pulsatile blood flowing within a tissue site. The rules are used to evaluate at least a portion of the tissue profile. A patient condition is indicated according to the applied rules. 
     Another aspect of a tissue profile wellness monitor comprises measuring a normalized plethysmograph (NP) to generate a tissue profile, testing the tissue profile and outputting the test results. The NP is measured at each of multiple wavelengths of optical radiation, and the NP is responsive to attenuation of the optical radiation by constituents of pulsatile blood flowing within a tissue site illuminated by the optical radiation. The tissue profile is tested against predetermined rules. The test results are output as at least one of a display, alarm, diagnostic and control. 
     A further aspect of a tissue profile wellness monitor comprises measuring a physiological parameter, generating a tissue profile, defining limits and indicating when the tissue profile exceeds the defined limits. The physiological parameter is responsive to multiple wavelengths of optical radiation after attenuation by constituents of pulsatile blood flowing within a tissue site. The tissue profile is responsive to the physiological parameter. The limits are defined for at least a portion of the tissue profile. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a graph of oxyhemoglobin and reduced hemoglobin light absorption versus wavelength across portions of the red and IR spectrum; 
         FIG. 2  is a graph of normalized plethysmograph (NP) ratios versus wavelength illustrating a tissue profile for 97% oxygen saturation; 
         FIG. 3  is a general block diagram of a patient monitoring system embodiment that implements a tissue profile wellness monitor; 
         FIG. 4  is a graph of tissue profiles for high saturation, low saturation, high carboxyhemoglobin (HbCO) and high methemoglobin (MetHb); 
         FIG. 5  is a graph illustrating tissue profile changes indicative of patient wellness; and 
         FIG. 6  is a block diagram of a tissue profile wellness monitor embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 3  illustrates a patient monitoring system  300 , which generates NP ratios and blood parameter measurements, such SPO 2 , HbCO and HbMet, accordingly. The patient monitoring system is advantageously adapted as a tissue profile wellness monitor, as described below. The patient monitoring system  300  has a patient monitor  302  and a sensor  306 . The sensor  306  attaches to a tissue site  320  and includes a plurality of emitters  322  capable of irradiating the tissue site  320  with differing wavelengths of light, perhaps including the red and infrared wavelengths utilized in pulse oximeters. The sensor  306  also includes one or more detectors  324  capable of detecting the light after attenuation by the tissue site  320 . A multiple wavelength sensor is disclosed in U.S. App. No. 11,367,013, filed on Mar. 1, 2006, titled Multiple Wavelength Sensor Emitters, cited above. Multiple wavelength sensors, such as Rainbow™-brand adhesive and reusable sensors are available from Masimo Corporation, Irvine, Calif. 
     As shown in  FIG. 3 , the patient monitor  302  communicates with the sensor  306  to receive one or more intensity signals indicative of one or more physiological parameters. Drivers  310  convert digital control signals into analog drive signals capable of driving the sensor emitters  322 . A front-end  312  converts composite analog intensity signal(s) from light sensitive detector(s)  324  into digital data  342  input to the DSP  340 . The DSP  340  may comprise a wide variety of data and/or signal processors capable of executing programs for determining physiological parameters from input data. In an embodiment, the DSP  340  executes the processors  610 ,  620 ,  630  ( FIG. 6 ), described below. 
     The instrument manager  360  may comprise one or more microcontrollers providing system management, such as monitoring the activity of the DSP  340 . The instrument manager  360  also has an input/output (I/O) port  368  that provides a user and/or device interface for communicating with the monitor  302 . In an embodiment, the I/O port  368  provides threshold settings via a user keypad, network, computer or similar device, as described below. 
     Also shown in  FIG. 3  are one or more user I/O devices  380  including displays  382 , audible indicators  384  and user inputs  388 . The displays  382  are capable of displaying indicia representative of calculated physiological parameters such as one or more of a pulse rate (PR), plethysmograph (pleth), perfusion index (PI), signal quality and values of blood constituents in body tissue, including for example, oxygen saturation (SpO 2 ), carboxyhemoglobin (HbCO) and methemoglobin (HbMet). The monitor  302  may also be capable of storing or displaying historical or trending data related to one or more of the measured parameters or combinations of the measured parameters. The monitor  302  may also provide a trigger for the audible indictors  384 , which operate beeps, tones and alarms, for example. Displays  382  include for example readouts, colored lights or graphics generated by LEDs, LCDs or CRTs to name a few. Audible indicators  384  include speakers or other audio transducers. User input devices  388  may include, for example, keypads, touch screens, pointing devices, voice recognition devices, or the like. 
       FIG. 4  illustrates tissue profile curves  400 , which are responsive to Hb constituents. In this example, the sensor emits eight wavelengths (610, 620, 630, 660, 700, 720, 805, 905 nm), which are normalized at 700 nm. Shown is a high saturation profile curve  420 , e.g. SPO 2 =100% (⋄); a low saturation profile curve  440 , e.g. SpO 2 =70% (□); a high HbCO profile curve  460 , e.g. HbCO=30% (Δ); and a high HbMet profile curve  480 , e.g. HbMet=6% (X). The profile curves  420 - 480  each has a head portion  401  at wavelengths less than 700 nm and a corresponding tail portion  402  at wavelengths of greater than 700 nm. As shown in  FIG. 4 , a tissue profile head portion  401  has higher values when HbCO (Δ) or HbMet (X) has a higher percentage value. The head portion  401  has lower values when HbCO or HbMet has a lower percentage value. Also, both the head portion  401  and the tail portion  402  have higher values when SPO 2  is a high percentage (⋄) and lower values when SPO 2  is a low percentage (□). 
       FIG. 5  illustrates an example tissue profile  500  utilized as a wellness indicator. As described with respect to  FIG. 4  above, the position or shape of the tissue profile or changes in the position or shape of the tissue profile provide an indication of patient wellness. In particular, position, shape or relative movements of the curve “head”  510  or the curve “tail”  520  or both indicate potentially detrimental values or changes in values of hemoglobin constituents. For example, a drop in the tissue profile head  510  or tail  520  below a predefined boundary  530 ,  540  may indicate reduced oxygen saturation. As another example, a rise in the tissue profile head  510  above a predefined boundary  550  may indicate increased concentrations of abnormal hemoglobin species, such as carboxyhemoglobin (HbCO) and methemoglobin (HbMet). Further, relative movements  570 ,  580  of the tissue profile  500  faster than a predefined rate may indicate potentially serious trends in the concentrations of normal or abnormal hemoglobin species. 
       FIG. 6  illustrates a tissue profile wellness monitor  600  having a NP processor  610 , a tissue profile processor  620  and an output processor  630 . In an embodiment, these processors  610 - 630  execute in the DSP  340  ( FIG. 3 ) to monitor tissue profile changes. The NP processor  610  has digitized sensor signal input  601  from one or more sensor channels, such as described with respect to  FIG. 3 , above, and generates normalized plethysmograph (NP) calculations  612  as described with respect to  FIG. 1 , above. 
     As shown in  FIG. 6 , the tissue profile processor  620  is configured to compare tissue profile changes  612  with respect to predetermined rules  603  and communicate the test results  622  to the output processor  630 . As an example, the tissue profile processor  620  may communicate to the output processor  630  when a tissue profile portion changes faster than a predetermined rate. 
     Also shown in  FIG. 6 , the output processor  630  inputs the tissue profile processor results  622  and generates outputs  602  based upon predetermined output definitions  605 . For example, if a test profile result is “true”, it might trigger an audible alarm. Rules and corresponding outputs are described in further detail with respect to TABLE 1, below. 
     In an embodiment, the tissue profile wellness monitor  600  provides outputs  602  according to TABLE 1, below. The terms listed in TABLE 1 are described with respect to  FIG. 6 , above. Various other indicators, alarms, controls and diagnostics in response to various combinations of rules and output definitions can be substituted for, or added to, the rule-based outputs illustrated in TABLE 1. 
     In an embodiment, the tissue profile wellness monitor  600  grades a patient with respect to wellness utilizing green, yellow and red indicators. For example, a green panel light signals that the tissue profile is indicative of normal blood hemoglobin. A yellow panel light signals that changes in the tissue profile shape or position are indicative of potentially problematic changes in blood hemoglobin. A red panel light signals that the tissue profile is indicative of blood hemoglobin outside of normal ranges. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Tissue Profile Rules and Outputs 
               
             
          
           
               
                 TISSUE PROFILE RULES 
                 OUTPUTS 
               
               
                   
               
               
                 If all portions of tissue profile are within 
                 Then illuminate 
               
               
                 boundaries and relatively unchanging over time 
                 green indicator. 
               
               
                 If tail drops faster than tail trend limit; or 
                 Then illuminate 
               
               
                 head rises faster than head trend limit 
                 yellow indicator 
               
               
                 If tail or head are outside of boundaries 
                 Then illuminate 
               
               
                   
                 red indicator 
               
               
                   
               
             
          
         
       
     
     A tissue profile wellness monitor has been disclosed in detail in connection with various embodiments. These embodiments are disclosed by way of examples only and are not to limit the scope of the claims that follow. One of ordinary skill in art will appreciate many variations and modifications.