(19)
(11)EP 2 096 994 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
03.10.2018 Bulletin 2018/40

(21)Application number: 07865424.1

(22)Date of filing:  07.12.2007
(51)International Patent Classification (IPC): 
A61B 5/1455(2006.01)
(86)International application number:
PCT/US2007/086879
(87)International publication number:
WO 2008/073855 (19.06.2008 Gazette  2008/25)

(54)

PLETHYSMOGRAPH VARIABILITY DETERMINATION

BESTIMMUNG DER VARIABILITÄT EINES PLETHYSMOGRAFEN

DETERMINATION DE LA VARIABILITE PLETHYSMOGRAPHIQUE


(84)Designated Contracting States:
AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU LV MC MT NL PL PT RO SE SI SK TR

(30)Priority: 09.12.2006 US 873663 P
12.10.2007 US 998782 P

(43)Date of publication of application:
09.09.2009 Bulletin 2009/37

(73)Proprietor: Masimo Corporation
Irvine, CA 92618 (US)

(72)Inventors:
  • AL-ALI, Ammar
    Tustin, CA 92782 (US)
  • WEBER, Walter
    Laguna Hills, CA 92653 (US)
  • MAJMUDAR, Anmol
    Irvine, CA 92618 (US)

(74)Representative: Vossius & Partner Patentanwälte Rechtsanwälte mbB 
Siebertstrasse 3
81675 München
81675 München (DE)


(56)References cited: : 
WO-A-2004/034898
US-A- 5 482 036
WO-A-2005/096922
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    PRIORITY APPLICATIONS



    [0001] This application claims priority to prior U.S. Provisional Patent Application No. 60/873,663 filed 12/09/2006 titled Plethysmograph Variability Index and U.S. Provisional Patent Application No. 60/998,782 filed 10/12/2007 titled Plethysmograph Variability Index.

    BACKGROUND OF THE INVENTION



    [0002] Pulse oximetry utilizes a noninvasive sensor to measure oxygen saturation (SpO2) and pulse rate of a person. 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. Pulse 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.

    [0003] Pulse 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 assigned to Masimo Corporation ("Masimo") of Irvine, California. Low noise pulse oximetry sensors are disclosed in one or more of U.S. Pat. Nos. 7,027,849, 6,985,764, 6,934,570 6,760,607 6,377,829 6,285,896 5,782,757 5,638,818, which are also assigned to Masimo. Moreover, pulse oximeters capable of reading through motion induced noise and low noise optical sensors including LNOP® disposable, reusable and/or multi-site sensors and Radical®, Rad-5™, Rad-8™, Rad-9™, PPO+™ monitors are also available from Masimo.

    [0004] Multiple parameter monitors and multiple wavelength sensors are described in US 2006226992 A entitled Noninvasive Multiple Parameter Patient Monitor filed 03/01/2006 and US 2006211924 A entitled Multiple Wavelength Sensor Emitters filed 03/01/2006.
    Moreover, multiple parameter monitors and multiple wavelength sensors including Rad-57™ and Radical-7™ monitors and Rainbow™ Rainbow™-brand adhesive and reusable sensors are available from Masimo. MS-brand processor boards incorporating SHARC® DSPs from Analog Devices, Inc. are also available from Masimo.

    [0005] WO 2005/096922 A1 discloses a physiological assessment system which comprises a sensor and first and second processors. The sensor is adapted to generate a signal responsive to a living organism. The first processor is configured to derive a measured parameter from the sensor signal. The second processor is configured to analyze nonlinear dynamics of the measured parameter so as to provide a physiological assessment of the living organism. WO 2005/096922 A1 further discloses a pulse oximeter adapted to measure a perfusion index and a variability analyzer configured to provide a statistic or statistics responsive to variability of the perfusion index.

    [0006] A method for presenting information concerning variations of perfusion is discussed in WO 2004/034898 A2 entitled "Method for the Presentation of Information Concerning Variations of the Perfusion".

    Summary of the Invention



    [0007] The invention is defined by the features of the independent claims. Further preferred embodiments of the invention are defined in the dependent claims.

    [0008] An aspect of a plethysmograph variability processor inputs a plethysmograph waveform, derives perfusion values, determines variability values, and calculates a plethysmograph (pleth) variability index. The plethysmograph waveform has pulses corresponding to pulsatile blood flow within a tissue site. The perfusion values correspond to the pulses. The variability values are each indicative of the variability of a series of the perfusion values. The plethysmograph variability index is representative of the variability values. The plethysmograph variability index is displayed.

    [0009] The perfusion values are derived by identifying peaks and valleys for the pulses, calculating AC values for the pulses from the peaks and the valleys, calculating DC values for the pulses, and normalizing the AC values with the DC values. Variability values are determined by accumulating the perfusion values in buffers and calculating one of the variability values for each of the buffers. As an example, variability values are determined by sorting the perfusion values within each of the buffers from the largest of the perfusion values to the smallest of the perfusion values and trimming at least one of the largest perfusion values and at least one of the smallest perfusion values from each of the buffers.

    [0010] Plethysmograph variability indexes (PVIs) are determined from a percentage difference between a maximum perfusion value and a minimum perfusion value for each of the buffers. A median value of the PVIs is calculated. Preferably, physiologically acceptable pulses are identified and a minimum amount of time's worth of acceptable data for each buffer is determined. An IR channel is input for the plethysmograph waveform and a red channel is used to verify acceptable pulses.

    [0011] An aspect of a plethysmograph variability processing system is an optical sensor that transmits multiple wavelengths of optical radiation into a tissue site, detects the optical radiation after attenuation by pulsatile blood flowing within the tissue site, and generates a sensor signal responsive to the detected optical radiation. A patient monitor demodulates the sensor signal so as to generate a plethysmograph channels. A digital signal processor (DSP) within the patient monitor inputs at least one of the plethysmograph channels and outputs a plethysmograph variability (PV) parameter accordingly. A PV process executes on the DSP so as to process the plethysmograph channel and derive the PV parameter. A patient monitor output is responsive to the PV parameter.

    [0012] The PV process has a plethysmograph input corresponding to the at least one plethysmograph channel. The pleth has pleth features. A measure pleth process extracts the pleth values from the plethysmograph according to the pleth features. A pleth value input corresponds to the pleth values. A pleth variability process generates a plurality of variability values from the pleth values. A pleth variability input corresponds to the variability values. A variability parameter process generates a pleth variability (PV) parameter from the variability values. Physiological acceptability criteria are applied to the plethysmograph input. A reduce data dispersion process trims outlying ones of the pleth values according to dispersion criteria. Post processing applies at least one of a smoothing or slew rate limit to the PV parameter. Pre-processing applies a bandpass filter to the plethysmograph input so as to remove a cyclical baseline shift or oscillation from the plethysmograph. The patient monitor output generates a graph of the PV parameter versus time so as to indicate a trend in plethysmograph variability.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0013] 

    FIG. 1 is a general block diagram of a plethysmograph variability processing system;

    FIG. 2 is a graph of an exemplar plethysmograph;

    FIG. 3 is a detailed flow chart of a plethysmograph variability index process; and

    FIG. 4 is a general functional flow diagram of a plethysmograph variability process.


    DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS


    PV Monitor



    [0014] FIG. 1 illustrates a plethysmograph variability processing system 100, which calculates one or more measures of plethysmograph variability (PV). The plethysmograph variability processing system 100 advantageously provides at least some of displays, alarms or controls responsive to PV so as to indicate, and affect the treatment of, a patient condition. The PV processing system 100 may further generate SpO2, pulse rate (PR), perfusion index (PI),signal quality and in multiple wavelength configurations additional blood parameter measurements such as HbCO and HbMet.

    [0015] As shown in FIG. 1, the PV processing system 100 has a patient monitor 102 and a sensor 106. The sensor 106 attaches to a tissue site 1 and includes a plurality of emitters 122 capable of irradiating the tissue site 1 with at least two wavelengths of light, such as the red and infrared (IR) wavelengths utilized in pulse oximeters and in some configurations multiple wavelengths different than or in addition to those red and IR wavelengths. The sensor 106 also includes one or more detectors 124 capable of detecting the light after attenuation by the tissue 1.

    [0016] Also shown in FIG. 1, the patient monitor 102 communicates with the sensor 106 to receive one or more intensity signals indicative of one or more physiological parameters and displays the parameter values. Drivers 110 convert digital control signals into analog drive signals capable of driving sensor emitters 122. A front-end 112 converts composite analog intensity signal(s) from light sensitive detector(s) 124 into digital data 142 input to the DSP 140. The input digital data 142 is referred to herein as a plethysmograph waveform, plethysmograph or pleth for short. The digital data 142 has plethysmograph channels corresponding to each emitter wavelength, such as a red channel and an IR channel. The digital data 142 is 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. The DSP 140 may comprise a wide variety of data and/or signal processors capable of executing programs for determining physiological parameters from input data. The DSP executes one or more pleth variability (PV) processes 130, such as described with respect to FIGS. 3-4, below. The PV processes 130 may be implemented in software, firmware or other form of code or instructions, or logic or other hardware, or a combination of the above.

    [0017] Further shown in FIG. 1, the instrument manager 160 may comprise one or more microcontrollers controlling system management, such as monitoring the activity of the DSP 140. One or more output devices 180 include displays 182, alarms 184 and controls 186. Displays 182 may be numerical, such as readouts, or graphical, such as trends and bar graphs, generated by LEDs, LCDs or CRTs to name a few. Displays 182 may also be indicators, such as LEDs of various colors that signify variability magnitude. Alarms 184 may be visual or audible indications that variability is, say, above a predetermined threshold. Controls 186 may be inputs to medical equipment, such as drug administration devices, ventilators and fluid IVs, so as to control the amount of administered drugs, ventilator settings or the amount of infused fluids based up pleth variability. The instrument manager 160 also has an input/output (I/O) port 168 that provides a user and/or device interface for communicating with the monitor 102. User input devices 188 may include a keypad, touch screen, pointing device, voice recognition device, network and computer, to name a few. In an example, the I/O port 168 provides initialization settings for PV processes, as described below. The monitor 102 may also be capable of storing or displaying historical or trending data related to PV and other measured parameters or combinations of measured parameters.

    Pleth Waveform



    [0018] FIG. 2 illustrates a plethysmograph 200 plotted on an intensity axis 201 versus a time axis 202. The plethysmograph 200 has multiple pulses 210 each with a peak 212 and a valley 214 and extending over a time period 216. A perfusion index (PI) value can be defined for each pulse 210:

    "AC" 220 designates a peak amplitude 212 minus a valley amplitude 214 for a particular pulse. "DC" 230 designates a peak amplitude 212 for a particular pulse. A plethysmograph variability measure is calculated that is responsive to the magnitude of pleth variations, such as depicted by envelope 250. One variability measure is a plethysmograph variability index (PVI), described with respect to FIG. 3, below. Other plethysmograph variability (PV) measures are described with respect to FIG. 4, below. Advantageously, PV measures may provide a numerical indication of a person's physical condition or health.

    Pleth Variability Index (PVI)



    [0019] FIG. 3 illustrates a PVI process 300, which derives and displays a plethysmograph variability index (PVI). Initially, a first buffer is filled with calculated perfusion index (PI) values 310-330. In an embodiment, these values are based upon the IR channel, as described above. If a sufficient amount of physiologically acceptable data is in the first buffer 335, then a second buffer is filled with calculated plethysmograph variability index (PVI) values 340-360. The median PVI in the second buffer is calculated and displayed 370-380. If the amount of acceptable data in the first buffer is insufficient, then the display is frozen with the last calculated median PVI 390.

    [0020] As shown in FIG. 3, a plethysmograph is first identified 310. In particular, only physiologically acceptable pulses are used for calculating PI. Physiological plethysmograph identification is disclosed in U.S. Pat. No. 7,044,918 entitled Plethysmograph Pulse Recognition Processor, which is assigned to Masimo.

    [0021] In an embodiment, the red channel plethysmograph is utilized to verify acceptable pulses in the IR channel. The PI of each acceptable plethysmograph is then calculated 320 according to EQ. 1 and as described with respect to FIG. 2, above. The calculated Pis are stored in a first buffer 330, and the buffer criteria are tested 335. The buffer criteria require both a minimum number of acceptable pulses and a minimum amount of time of acceptable data in the first buffer.

    [0022] In an example, a plethysmograph 200 (FIG. 2) has a 62.5 Hz sample rate, i.e. a sample interval of 16 msec. The first buffer holds 15 sec. of data at that sample rate. Accordingly, a sliding 15 sec. window of plethysmograph data is stored in the first buffer, and the window is moved in 1.2 sec. increments. The minimum number of acceptable pulses in the first buffer is 6, and the minimum amount of acceptable data in the first buffer is 7.5 sec. The 15 sec. window size allows one respiration cycle, assuming a worse case respiration rate of 4 breaths per min. This window size also allows 6 PIs assuming a worse case pulse rate of 25 bpm. Partial plethysmograph cycles cutoff by a particular window are ignored by that window, but are taken into account in the next window.

    [0023] Also shown in FIG. 3, if the buffer criteria are met 335, then the first buffer is sorted and trimmed 340. The sort orders the PI values from the minimum PI at one end of the buffer to the maximum PI at the other end of the buffer. Then a predetermined number of PIs are dropped from each end of the buffer, i.e. both the maximum PIs and the minimum PIs are deleted. In an example, 12% of the PIs are trimmed from each end of the buffer. For example, if the buffer holds 10 Pis, a 12% trim = floor(10•12/100) = floor(1.2) = 1, where the floor operator truncates digits to the right of the decimal point. Hence, in this example, one max PI and one min PI are dropped from the first buffer. A plethysmograph variability index (PVI) is then calculated 350 from the trimmed first buffer. PVI is calculated as:

    That is, PVI is the PI variation, expressed as a percentage of the maximum PI, reflected by the PI values remaining in the first buffer.

    [0024] Further shown in FIG. 3, calculated PVIs are stored in a second buffer 360. In an embodiment, the second buffer holds 11 PVIs, where one PVI is derived for every 1.2 sec shift in the sliding 15 sec. window described above. Next, the median PVI is calculated from the second buffer. This median PVI value is communicated to a display 380. If the buffer criteria 335, described above, are not met, then the last calculated median PVI value is displayed 390. That is, the display is frozen with that last calculated median PVI value until the buffer criteria are satisfied.

    [0025] In an example, the median PVI value is displayed as a two-digit numerical value on a monitor screen along with other parameters, such as SpO2 and pulse rate. In an example, the median PVI value is displayed on a monitor screen as vertical or horizontal bar graph. In an example, the median PVI value is displayed on a monitor screen as trend graph versus time. In an example, the median PVI value is compared to a predetermined maximum PVI threshold. If the median PVI value crosses the predetermined threshold, one or more visual or audible alarms are triggered. In an example, a visual PVI alarm is one or more colored indicators, such as green, yellow and red, indicating levels of patient health or physiological condition.

    Plethysmograph Variability (PV)



    [0026] FIG. 4 illustrates a plethysmograph variability (PV) processor 400 having process steps 401 and initializations 402. The initializations 402 determine the specific characteristics of the process steps 401. The PV processor 400 inputs one or more plethysmograph (pleth) channels 405 and generates PV outputs 407. The pleth channels 405 each correspond to a different optical sensor wavelength, such as a red wavelength channel and an IR wavelength channel corresponding to red and IR emitters of a pulse oximeter sensor. There may be more than two channels when using a multiple wavelength sensor, such as described in US 2006211924 A, cited above. For example, there may be eight channels varying in wavelength from about 630 nm to about 905 nm. In an example, two or more pleth channels 405 are processed in parallel or combined as a composite pleth for increased accuracy or robustness in PV calculations. Input 410 determines which pleth channel 405 is used as the pleth input 414 for PV calculations, according to a select channel initialization 412. Input 410 may select any single channel 405 or some combination of channels 405. Pre-process 415 modifies the pleth input 414 according to a predetermined formula 417. In an example, pre-process 415 filters the pleth input 414 so as to remove any slow variation or low frequency oscillation in the plethysmograph baseline or average value, such as a respiration-induced variation that shifts the entire plethysmograph up and down with inhalation and exhalation. In an example, pre-process 415 is a bandpass filter having a 30 to 550 beats per minute passband. Identify acceptable pulses 420 applies pulse criteria 422 to pass only physiologically acceptable pulses 424, such as disclosed in U.S. Pat. No. 7,044,918 cited above.

    [0027] As shown in FIG. 4, measure pleth 440 extracts pleth values 444 from the remaining pulses 424 according to pleth features 442. The pleth features 434 may be a pulse peak 212 (FIG. 2) and pulse valley 214 (FIG. 2) and the pleth values 444 may relate to perfusion, such as PI described with respect to EQ. 1 above. In another example, the "DC" value in EQ. 1 may be other than a pulse peak, such as a pulse valley or an average of pulse peak and pulse valley, to name a few. In other examples, pleth features 442 may include more that two values per pulse and pleth values 444 may be other than perfusion related. Also, measure pleth 440 may be performed over more than one pulse per pleth value 444.

    [0028] As shown in FIGS. 2 and 4, in an example, pleth features 442 define a pleth envelope 250 interpolated from pulse peaks 212 and pulse valleys 214. Measure pleth 440 defines a series of adjacent slices 260 of envelope height and Δ width, where Δ may vary from one pleth sample to many samples. Accordingly, pleth values 444 are the areas of each slice. In another example, measure pleth 440 calculates the area under each absorption pleth pulse 270, the absorption pleth being the inverse of the intensity pleth 200. In an example, the slices 260 or areas 270 are normalized with respect to a pleth value, such as a DC value or an average value, to name a few.

    [0029] Also shown in FIG. 4, accumulate pleth values 445 identifies those pleth values 444 within a specified window 446. Accept window 450 determines whether there are a sufficient number of pleth values within the window 446. If not, the remaining steps 460-490 are bypassed and a default PV output 407 is generated. If so, the remaining steps 460-490 are performed. Reduce data dispersion 460 eliminates outlying data, leaving trimmed pleth values 464, according to a dispersion criteria 462. Calculate pleth variability 470 determines a variability value 474 from the trimmed pleth values 464 according to a variability formula 472. In an example, the variability formula is the percentage variability in a window compared with a maximum value in the window, such as described with respect to EQ. 2, above. Accumulate variability values 475 identifies those variability values 474 within a specified window 476. Windows 446, 476 are sliding time intervals or segments having predetermined sizes according to an initialization 402. Adjacent windows may be spaced apart, abutting or overlapping in time.

    [0030] Further shown in FIG. 4, calculate variability parameter 480 determines a pleth variability (PV) parameter 407 from the accumulated variability values 478 according to a reduction criteria 482. In an example, PV 407 is a median of the variability values 478 in the window 476. In other examples, PV 407 is any of average, mode, geometric mean or weighted mean of the windowed variability values, to name a few. Post processing on the PV parameter 407 data may be performed including smoothing and a slew rate filter. In an example, an exponential smoothing is used. The slew rate filter limits the positive or negative slope of the PV parameter 407 to a predetermined maximum.

    PV Applications



    [0031] Many clinicians currently observe a pulse oximeter plethysmograph waveform for changes in patient physiology. Unfortunately, there is no consistency among pulse oximeter manufacturers in the way a plethysmograph waveform is displayed. Further, smoothing, autoscaling and other display data processing mask changes in the raw plethysmograph waveform. Thus, some patient physiology cannot be readily predicted from mere observation of a bedside monitor plethysmograph display. Pleth variability (PV) parameters, such as PVI, advantageously quantify plethysmograph waveform variations, which are displayed in a numerical format that can also be trended as needed. Accordingly, even slight changes in physiology may be reliably observed.

    [0032] PV can be advantageously used for noninvasive functional hemodynamic monitoring. A plethysmograph waveform is responsive to beat-to-beat changes in peripheral blood volume and perfusion. Thus, plethysmograph variability reflects changes in the intravascular volume status of patients. PV parameters, as described above, are clinically useful hemodynamic measurements that respond to changes in, for example, volemia, fluid responsiveness and ventricular preload. Volemia relates to the volume of blood circulating throughout the body, which is difficult to estimate in a clinical setting. Hypovolemia, for example, is an abnormally low blood volume. Fluid responsiveness is the percent increase in ventricular stroke volume after fluid volume expansion. Ventricular preload is the degree of tension in the cardiac muscle when it begins to contract.

    [0033] Advantageously, a PV parameter is monitored during patient treatments. As an example, a downward trend in PV monitored during the addition of fluids to a suspected hypovolemic patient indicates the efficacy of that treatment. Likewise, a downward trend in PV monitored during administration of drugs for asthma indicates the efficacy of the administered drug and the likelihood that the asthma can be controlled.

    [0034] PVI or other pulse variability (PV) measure may be a significant parameter in a variety of critical conditions, for example those conditions shown in Table 1, below.
    Table 1: Conditions Associated with Increased PV
    Cardiac CausesNon-Cardiac Causes
    Cardiogenic Shock Hypovolemia
    Cardiac Tamponade Septic Shock
    Pericardial Effusion Anaphylactic Shock
    Constrictive Pericarditis Superior Vena Cava Obstruction
    Restrictive Cardiomyopathy Asthma
    Acute myocardial infarction  



    Claims

    1. A plethysmograph variability processing method comprising:

    inputting a plethysmograph waveform having a plurality of pulses corresponding to pulsatile blood flow within a tissue site to a digital signal processor (DSP), said plethysmograph waveform being digital 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;

    deriving a plurality of perfusion indexes (Pis) corresponding to the plurality of pulses;

    storing said plurality of perfusion indexes in a first buffer;

    sorting the plurality of perfusion indexes from the minimum perfusion index at one end of the first buffer to the maximum perfusion index at the other end of said first buffer;

    trimming at least one of the largest perfusion indexes and at least one of the smallest perfusion indexes from the first buffer;

    calculating a plethysmograph variability index (PVI) as follows:

    wherein PIMax is the maximum perfusion index remaining in said first buffer and PIMin is the minimum perfusion index remaining in said first buffer; and

    displaying the plethysmograph variability index (PVI).


     
    2. The plethysmograph variability processing method according to claim 1 wherein deriving a plurality of perfusion indexes (PIs) comprises:

    identifying peaks and valleys for the plurality of pulses;

    calculating AC values for the plurality of pulses from the peaks and the valleys;

    calculating DC values for the plurality of pulses; and

    normalizing the AC values with the DC values.


     
    3. The plethysmograph variability processing method according to claim 2 wherein calculating a plethysmograph variability index (PVI) further comprises:

    accumulating the PIs in a plurality of buffers; and

    calculating a PVI for each of the plurality of buffers.


     
    4. The plethysmograph variability processing method according to claim 3 further comprising:

    sorting PIs within each of the plurality of buffers from the largest of the perfusion indexes (Pis) to the smallest of the PIs; and

    trimming at least one of the largest PIs and at least one of the smallest PIs from each of the plurality of buffers.


     
    5. The plethysmograph variability processing method according to claim 4 wherein calculating a PVI further comprises calculating a median value of the PVIs.
     
    6. The plethysmograph variability processing method according to claim 5 further comprising:

    identifying physiologically acceptable ones of the plurality of pulses; and

    determining a minimum amount of time of acceptable data in each of the plurality of buffers.


     
    7. The plethysmograph variability processing method according to claim 6 wherein inputting comprises using an IR channel for the plethysmograph waveform; and identifying comprises using a red channel to verify the acceptable ones of the plurality of pulses.
     
    8. A plethysmograph variability processing system comprising:

    an optical sensor (106) configured to transmit multiple wavelengths of optical radiation into a tissue site, detect the optical radiation after attenuation by pulsatile blood flowing within the tissue site, and generate a sensor signal responsive to the detected optical radiation;

    a patient monitor (102) configured to demodulate the sensor signal so as to generate a plethysmograph waveform having a plurality of pulses corresponding to pulsatile blood flow within a tissue site;

    a digital signal processor (140) within the patient monitor that is configured to input the plethysmograph waveform and output a plethysmograph variability index (PVI) according the following process:

    deriving a plurality of perfusion indexes (Pis) corresponding to the plurality of pulses in the plethysmograph waveform;

    storing said plurality of perfusion indexes in a first buffer;

    sorting the plurality of perfusion indexes from the minimum perfusion index at one end of the first buffer to the maximum perfusion index at the other end of said first buffer;

    trimming at least one of the largest perfusion indexes and at least one of the smallest perfusion indexes from the first buffer;

    calculating a plethysmograph variability index (PVI) as follows:

    wherein PIMax is the maximum perfusion index remaining in said first buffer and PIMin is the minimum perfusion index remaining in said first buffer; and

    a patient monitor output (180) that is configured to display the plethysmograph variability index (PVI).


     
    9. The system according to claim 8 wherein deriving a plurality of perfusion indexes (PIs) comprises:

    identifying peaks and valleys for the plurality of pulses;

    calculating AC values for the plurality of pulses from the peaks and the valleys;

    calculating DC values for the plurality of pulses; and

    normalizing the AC values with the DC values.


     
    10. The system according to claim 9 wherein calculating the plethysmograph variability index (PVI) further comprises:

    accumulating the PIs in a plurality of buffers; and

    calculating PVI for each of the plurality of buffers.


     
    11. The system according to claim 10 wherein the digital signal processor is further configured to perform the following steps:

    sorting PIs within each of the plurality of buffers from the largest of the PIs to the smallest of the PIs; and

    trimming at least one of the largest PIs and at least one of the smallest PIs from each of the plurality of buffers.


     
    12. The system according to claim 11 wherein calculating a PVI further comprises calculating a median value of the PVIs.
     
    13. The system according to claim 12 wherein the digital signal processor is further configured to perform the following steps:

    identifying physiologically acceptable ones of the plurality of pulses; and

    determining a minimum amount of time of acceptable data in each of the plurality of buffers.


     
    14. The system according to claim 13 wherein the digital signal processor is further configured to input the plethysmograph waveform using an IR channel; and identifying comprises using a red channel to verify the acceptable ones of the plurality of pulses.
     


    Ansprüche

    1. Plethysmograph-Variabilitätsverarbeitungsverfahren aufweisend:

    Eingeben einer Plethysmograph-Wellenform, deren mehrere Pulse einem pulsierenden Blutstrom in einem Gewebeort entsprechen, in einen digitalen Signalprozessor (DSP), wobei die Plethysmograph-Wellenform digitale Daten sind, die eine Änderung in der Absorption von bestimmten Wellenlängen von Licht als eine Funktion der Änderungen im Körpergewebe, die aus pulsierendem Blut resultieren, repräsentieren;

    Ableiten mehrerer Perfusionsindizes (PIs) entsprechend den mehreren Pulsen;

    Speichern der mehreren Perfusionsindizes in einem ersten Speicher;

    Sortieren der mehreren Perfusionsindizes von dem minimalen Perfusionsindex an dem einen Ende des ersten Speichers zu dem maximalen Perfusionsindex an dem anderen Ende des ersten Speichers;

    Aussortieren mindestens eines der größten Perfusionsindizes und mindestens eines der kleinsten Perfusionsindizes aus dem ersten Speicher;

    Berechnen eines Plethysmograph-Variabilitätsindexes (PVI) wie folgt:

    wobei PIMax der in dem ersten Speicher verbleibende maximale Perfusionsindex ist und PIMin der in dem ersten Speicher verbleibende minimale Perfusionsindex ist; und

    Anzeigen des Plethysmograph-Variabilitätsindexes (PVI).


     
    2. Plethysmograph-Variabilitätsverarbeitungsverfahren nach Anspruch 1, wobei Ableiten mehrerer Perfusionsindizes (PIs) aufweist:

    Identifizieren von Spitzen und Tälern für die mehreren Pulse;

    Berechnen von AC-Werten für die mehreren Pulse aus den Spitzen und Tälern;

    Berechnen von DC-Werten für die mehreren Pulse; und

    Normalisieren der AC-Werte mit den DC-Werten.


     
    3. Plethysmograph-Variabilitätsverarbeitungsverfahren nach Anspruch 2, wobei Berechnen eines Plethysmograph-Variabilitätsindexes (PVI) ferner aufweist:

    Speichern der PIs in mehreren Speichern; und

    Berechnen eines PVI für jeden der mehreren Speicher.


     
    4. Plethysmograph-Variabilitätsverarbeitungsverfahren nach Anspruch 3, ferner aufweisend:

    Sortieren von PIs in jedem der mehreren Speicher von dem größten der Perfusionsindizes (PIs) zu dem kleinsten der PIs; und

    Aussortieren mindestens eines der größten PIs und mindestens eines der kleinsten PIs aus jedem der mehreren Speicher.


     
    5. Plethysmograph-Variabilitätsverarbeitungsverfahren nach Anspruch 4, wobei Berechnen eines PVI ferner aufweist: Berechnen eines Medianwerts der PVIs.
     
    6. Plethysmograph-Variabilitätsverarbeitungsverfahren nach Anspruch 5, ferner aufweisend:

    Identifizieren von physiologisch akzeptablen der mehreren Pulse; und

    Bestimmen einer minimalen Zeitdauer von akzeptablen Daten in jedem der mehreren Speicher.


     
    7. Plethysmograph-Variabilitätsverarbeitungsverfahren nach Anspruch 6, wobei Eingeben aufweist: Verwenden eines IR-Kanals für die Plethysmograph-Wellenform; und Identifizieren aufweist: Verwenden eines roten Kanals, um die akzeptablen der mehreren Pulse zu verifizieren.
     
    8. Plethysmograph-Variabilitätsverarbeitungssystem aufweisend:

    einen optischen Sensor (106), der konfiguriert ist, um mehrfache Wellenlängen einer optischen Strahlung zu einem Gewebeort zu übertragen, die optische Strahlung nach Abschwächung durch in dem Gewebeort strömendes pulsierendes Blut zu detektieren und ein Sensorsignal als Antwort auf die detektierte optische Strahlung zu erzeugen;

    einen Patientenmonitor (102), der konfiguriert ist, um das Sensorsignal zu demodulieren, um eine Plethysmograph-Wellenform zu generieren, deren mehrere Pulse dem pulsierenden Blutstrom in einem Gewebeort entsprechen;

    einen digitalen Signalprozessor (140) in dem Patientenmonitor, der konfiguriert ist, um die Plethysmograph-Wellenform einzugeben und einen Plethysmograph-Variabilitätsindex (PVI) gemäß dem folgenden Verfahren auszugeben:

    Ableiten mehrerer Perfusionsindizes (PIs) entsprechend den mehreren Pulsen in der Plethysmograph-Wellenform;

    Speichern der mehreren Perfusionsindizes in einem ersten Speicher;

    Sortieren der mehreren Perfusionsindizes von dem minimalen Perfusionsindex an dem einen Ende des ersten Speichers zu dem maximalen Perfusionsindex an dem anderen Ende des ersten Speichers;

    Aussortieren mindestens eines der größten Perfusionsindizes und mindestens eines der kleinsten Perfusionsindizes aus dem ersten Speicher;

    Berechnen eines Plethysmograph-Variabilitätsindexes (PVI) wie folgt:

    wobei PIMax der in dem ersten Speicher verbleibende maximale Perfusionsindex ist und PIMin der in dem ersten Speicher verbleibende minimale Perfusionsindex ist; und

    eine Patientenmonitorausgabe (180), die konfiguriert ist, um den Plethysmograph-Variabilitätsindex (PVI) anzuzeigen.


     
    9. System nach Anspruch 8, wobei Ableiten mehrerer Perfusionsindizes (PIs) aufweist:

    Identifizieren von Spitzen und Tälern für die mehreren Pulse;

    Berechnen von AC-Werten für die mehreren Pulse aus den Spitzen und Tälern;

    Berechnen von DC-Werten für die mehreren Pulse; und

    Normalisieren der AC-Werte mit den DC-Werten.


     
    10. System nach Anspruch 9, wobei Berechnen des Plethysmograph-Variabilitätsindexes (PVI) ferner aufweist:

    Speichern der PIs in mehreren Speichern; und

    Berechnen eines PVI für jeden der mehreren Speicher.


     
    11. System nach Anspruch 10, wobei der digitale Signalprozessor ferner konfiguriert ist, um die folgenden Schritte durchzuführen:

    Sortieren von PIs in jedem der mehreren Speicher von dem größten der PIs zu dem kleinsten der PIs; und

    Aussortieren mindestens eines der größten PIs und mindestens eines der kleinsten PIs aus jedem der mehreren Speicher.


     
    12. System nach Anspruch 11, wobei Berechnen eines PVI ferner aufweist: Berechnen eines Medianwerts der PVIs.
     
    13. System nach Anspruch 12, wobei der digitale Signalprozessor ferner konfiguriert ist, um die folgenden Schritte durchzuführen:

    Identifizieren von physiologisch akzeptablen der mehreren Pulse; und

    Bestimmen einer minimalen Zeitdauer von akzeptablen Daten in jedem der mehreren Speicher.


     
    14. System nach Anspruch 13, wobei der digitale Signalprozessor ferner konfiguriert ist, um die Plethysmograph-Wellenform unter Verwendung eines IR-Kanals einzugeben; und Identifizieren aufweist: Verwenden eines roten Kanals, um die akzeptablen der mehreren Pulse zu verifizieren.
     


    Revendications

    1. Procédé de traitement de variabilité pléthysmographique comprenant les étapes ci-dessous consistant à :

    appliquer en entrée une forme d'onde pléthysmographique présentant une pluralité d'impulsions correspondant à un flux sanguin pulsatile au sein d'un site tissulaire, à un processeur de signal numérique (DSP), ladite forme d'onde pléthysmographique correspondant à des données numériques représentatives d'un changement dans l'absorption de longueurs d'onde spécifiques de la lumière en fonction des changements dans les tissus corporels qui résultent de pulsations sanguines ;

    dériver une pluralité d'indices de perfusion (PI) correspondant à la pluralité d'impulsions ;

    stocker ladite pluralité d'indices de perfusion dans une première mémoire tampon ;

    trier la pluralité d'indices de perfusion, de l'indice de perfusion minimal à une extrémité de la première mémoire tampon à l'indice de perfusion maximal à l'autre extrémité de ladite première mémoire tampon ;

    ajuster au moins l'un des plus grands indices de perfusion et au moins un des plus petits indices de perfusion à partir de la première mémoire tampon ;

    calculer un indice de variabilité pléthysmographique (PVI), comme suit :

    dans lequel « PIMax » est l'indice de perfusion maximal restant dans ladite première mémoire tampon, et « PIMin » est l'indice de perfusion minimal restant dans ladite première mémoire tampon ; et

    afficher l'indice de variabilité pléthysmographique (PVI).


     
    2. Procédé de traitement de variabilité pléthysmographique selon la revendication 1, dans lequel l'étape de dérivation d'une pluralité d'indices de perfusion (PI) comprend les étapes ci-dessous consistant à :

    identifier des crêtes et des creux pour la pluralité d'impulsions ;

    calculer des valeurs de courant alternatif, AC, pour la pluralité d'impulsions à partir des crêtes et des creux ;

    calculer des valeurs de courant continu, DC, pour la pluralité d'impulsions ; et

    normaliser les valeurs AC avec les valeurs DC.


     
    3. Procédé de traitement de variabilité pléthysmographique selon la revendication 2, dans lequel l'étape de calcul d'un indice de variabilité pléthysmographique (PVI) comprend en outre les étapes ci-dessous consistant à :

    accumuler les indices PI dans une pluralité de mémoires tampons ; et

    calculer un indice PVI pour chaque mémoire tampon de la pluralité de mémoires tampons.


     
    4. Procédé de traitement de variabilité pléthysmographique selon la revendication 3, comprenant en outre les étapes ci-dessous consistant à:

    trier des indices PI au sein de chaque mémoire tampon de la pluralité de mémoires tampons, du plus grand des indices de perfusion (PI) au plus petit des indices PI ; et

    ajuster au moins l'un des plus grands indices PI et au moins l'un des plus petits indices PI à partir de chaque mémoire tampon de la pluralité de mémoires tampons.


     
    5. Procédé de traitement de variabilité pléthysmographique selon la revendication 4, dans lequel l'étape de calcul d'un indice PVI consiste en outre à calculer une valeur médiane des indices PVI.
     
    6. Procédé de traitement de variabilité pléthysmographique selon la revendication 5, comprenant en outre les étapes ci-dessous consistant à:

    identifier des impulsions physiologiquement acceptables de la pluralité d'impulsions ; et

    déterminer une durée minimale de données acceptables dans chaque mémoire tampon de la pluralité de mémoires tampons.


     
    7. Procédé de traitement de variabilité pléthysmographique selon la revendication 6, dans lequel l'étape d'application en entrée comprend l'étape consistant à utiliser un canal infrarouge, IR, pour la forme d'onde pléthysmographique ; et l'étape d'identification comprend l'étape consistant à utiliser un canal rouge pour vérifier les impulsions acceptables de la pluralité d'impulsions.
     
    8. Système de traitement de variabilité pléthysmographique comprenant :

    un capteur optique (106) configuré de manière à transmettre de multiples longueurs d'onde de rayonnement optique dans un site tissulaire, à détecter le rayonnement optique après atténuation par du sang pulsatile circulant au sein du site tissulaire, et à générer un signal de capteur en réponse au rayonnement optique détecté ;

    un moniteur de patient (102) configuré de manière à démoduler le signal de capteur de manière à générer une forme d'onde pléthysmographique présentant une pluralité d'impulsions correspondant à un flux sanguin pulsatile au sein d'un site tissulaire ;

    un processeur de signal numérique (140), au sein du moniteur de patient, qui est configuré de manière à appliquer en entrée la forme d'onde pléthysmographique et à fournir en sortie un indice de variabilité pléthysmographique (PVI) selon le processus suivant consistant à :

    dériver une pluralité d'indices de perfusion (PI) correspondant à la pluralité d'impulsions dans la forme d'onde pléthysmographique ;

    stocker ladite pluralité d'indices de perfusion dans une première mémoire tampon ;

    trier la pluralité d'indices de perfusion, de l'indice de perfusion minimal à une extrémité de la première mémoire tampon à l'indice de perfusion maximal à l'autre extrémité de ladite première mémoire tampon ;

    ajuster au moins l'un des plus grands indices de perfusion et au moins un des plus petits indices de perfusion à partir de la première mémoire tampon ;

    calculer un indice de variabilité pléthysmographique (PVI), comme suit :

    dans lequel « PIMax » est l'indice de perfusion maximal restant dans ladite première mémoire tampon, et « PIMin » est l'indice de perfusion minimal restant dans ladite première mémoire tampon ; et

    une sortie de moniteur de patient (180) qui est configurée de manière à afficher l'indice de variabilité pléthysmographique (PVI).


     
    9. Système selon la revendication 8, dans lequel l'étape de dérivation d'une pluralité d'indices de perfusion (PI) comprend les étapes ci-dessous consistant à :

    identifier des crêtes et des creux pour la pluralité d'impulsions ;

    calculer des valeurs de courant alternatif, AC, pour la pluralité d'impulsions à partir des crêtes et des creux ;

    calculer des valeurs de courant continu, DC, pour la pluralité d'impulsions ; et

    normaliser les valeurs AC avec les valeurs DC.


     
    10. Système selon la revendication 9, dans lequel l'étape de calcul de l'indice de variabilité pléthysmographique (PVI) comprend en outre les étapes ci-dessous consistant à :

    accumuler les indices PI dans une pluralité de mémoires tampons ; et

    calculer un indice PVI pour chaque mémoire tampon de la pluralité de mémoires tampons.


     
    11. Système selon la revendication 10, dans lequel le processeur de signal numérique est en outre configuré de manière à mettre en oeuvre les étapes ci-dessous consistant à :

    trier des indices PI au sein de chaque mémoire tampon de la pluralité de mémoires tampons, du plus grand des indices de perfusion (PI) au plus petit des indices PI ; et

    ajuster au moins l'un des plus grands indices PI et au moins l'un des plus petits indices PI à partir de chaque mémoire tampon de la pluralité de mémoires tampons.


     
    12. Système selon la revendication 11, dans lequel l'étape de calcul d'un indice PVI consiste en outre à calculer une valeur médiane des indices PVI.
     
    13. Système selon la revendication 12, dans lequel le processeur de signal numérique est en outre configuré de manière à mettre en oeuvre les étapes ci-dessous consistant à :

    identifier des impulsions physiologiquement acceptables de la pluralité d'impulsions ; et

    déterminer une durée minimale de données acceptables dans chaque mémoire tampon de la pluralité de mémoires tampons.


     
    14. Système selon la revendication 13, dans lequel le processeur de signal numérique est en outre configuré de manière à appliquer en entrée la forme d'onde pléthysmographique en utilisant un canal IR ; et dans lequel l'étape d'identification comprend l'étape consistant à utiliser un canal rouge pour vérifier les impulsions acceptables de la pluralité d'impulsions.
     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



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    Patent documents cited in the description