a2, United States Patent
`US 6,584,336 B1
`(10) Patent No.:
`Jun. 24, 2003
`(45) Date of Patent:
`Ali et al.
`
`US006584336B1
`
`(54) UNIVERSAL/UPGRADING PULSE
`OXIMETER
`
`WO
`WO
`
`WO 97/22293
`WO 00/42911
`
`6/1997
`7/2000
`
`(75)
`
`Inventors:
`
`AmmarAIAli, Tustin, CA (US); Don
`Crothers, Mission Viejo, CA (US);
`David Dalke, Irvine, CA (US);
`MohamedK.Diab, Mission Viejo, CA
`(US); Julian Goldman,Irvine, CA
`(US); Massi E. Kiani, Laguna Niguel,
`CA (US); Michael Lee, Aliso Viejo, CA
`(US); Jerome Novak, Aliso Viejo, CA
`(US); Robert Smith, Lake Forest, CA
`(US); Val E. Vaden, Hillsborough, CA
`(US)
`
`(73)
`
`Assignee:
`
`Masimo Corporation, Irvine, CA (US)
`
`(*)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`US.C. 154(b) by 0 days.
`
`(21)
`
`(22)
`
`Appl. No.:
`Filed:
`
`09/516,110
`
`Mar.1, 2000
`
`OTHER PUBLICATIONS
`
`Mallinckrodt Product Catalog, Jan. 8, 2000.
`
`Primary Examiner—Enic F. Winakur
`(74) Attorney, Agent, or Firm—Knobbe, Martens, Olson &
`Bear, LLP.
`
`(57)
`
`ABSTRACT
`
`A Universal/Upgrading Pulse Oximeter (UPO) comprises a
`portable unit and a dockingstation together providing three-
`instruments-in-one functionality for measuring oxygen satu-
`ration and related physiological parameters. The portable
`unit functions as a handheld pulse oximeter. The combina-
`tion of the docked portable and the docking station functions
`as a standalone, high-performance pulse oximeter. The
`portable-docking station combination is also connectable to,
`and universally compatible with, pulse oximeters from vari-
`ous manufacturers through use of a waveform generator. The
`UPOprovides a universal sensor to pulse oximeter interface
`and a pulse oximetry measurement capability that upgrades
`the performance of conventional instruments by increasing
`low perfusion performance and motion artifact immunity,
`for example. Universal compatibility combined with port-
`ability allows the UPOto be transported along with patients
`transferred between an ambulance and a hospital ER, or
`between various hospital sites, providing continuouspatient
`monitoring in addition to plug-compatibility and functional
`upgrading for multiparameter patient monitoring systems.
`
`The image on the portable display is rotatable, either manu-
`ally when undocked or as a function of orientation. In one
`embodiment,
`the docking station has a web server and
`network interface that allows UPO data to be downloaded
`
`and viewed as web pages over a local area network or the
`Internet.
`
`Related U.S. Application Data
`
`Continuation of application No. 09/491,175,filed on Jan. 25,
`2000.
`Provisional application No. 60/117,097, filed on Jan. 25,
`1999, and provisional application No. 60/161,565,filed on
`Oct. 26, 1999.
`
`Tint, C17 occ cesescseseseecsesees A61B 5/00
`US. C1.
`cccccccccecceeteesensecseesecseeaeeasesseseeaeeaees 600/323
`Field of Search ............0..cc cece 600/300, 323;
`128/903, 904
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,687,717 A
`5,931,791 A
`
`11/1997 Halpern etal.
`8/1999 Saltzstein et al.
`
`FOREIGN PATENT DOCUMENTS
`
`(63)
`
`(60)
`
`(61)
`(52)
`(58)
`
`(56)
`
`EP
`
`0 601 589
`
`9/1993
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`37 Claims, 16 Drawing Sheets
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`U.S. Patent
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`Jun. 24, 2003
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`U.S. Patent
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`Jun. 24, 2003
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`US 6,584,336 B1
`
`1
`UNIVERSAL/UPGRADING PULSE
`OXIMETER
`
`This application is a continuation of prior application
`Ser. No. 09/491,175 filed Jan. 25, 2000, and claims the
`benefit of priority under 35 U.S.C. §119(e) from USS.
`Provisional Application No. 60/117,097, filed Jan. 25, 1999
`and Provisional Application No. 60/161,565 filed Oct. 26,
`1999,
`
`BACKGROUND OF THE INVENTION
`
`Oximetry is the measurementof the oxygenlevelstatus of
`blood. Early detection of low blood oxygenlevel is critical
`in the medical field, for example in critical care and surgical
`applications, because an insufficient supply of oxygen can
`result in brain damage and death in a matter -of minutes.
`Pulse oximetry is a widely accepted noninvasive procedure
`for measuring the oxygen saturation level of arterial blood,
`an indicator of oxygen supply. A pulse oximetry system
`consists of a sensor applied to a patient, a pulse oximeter,
`and a patient cable connecting the sensor and the pulse
`oximeter.
`
`The pulse oximeter may be a standalone device or may be
`incorporated as a module or built-in portion of a multipa-
`rameter patient monitoring system, which also provides
`measurements such as blood pressure, respiratory rate and
`EKG. A pulse oximeter typically provides a numerical
`readout of the patient’s oxygen saturation, a numerical
`readout of pulse rate, and an audible indicator or “beep” that
`occurs in response to each pulse. In addition,
`the pulse
`oximeter may display the patient’s plethysmograph, which
`provides a visual display of the patient’s pulse contour and
`pulse rate.
`
`SUMMARYOF THE INVENTION
`
`FIG. 1 illustrates a prior art pulse oximeter 100 and
`associated sensor 110. Conventionally, a pulse oximetry
`sensor 110 has LED emitters 112, typically one at a red
`wavelength and one at an infrared wavelength, and a pho-
`todiode detector 114. The sensor 110 is typically attached to
`an adult patient’s finger or an infant patient’s foot. For a
`finger, the sensor 110 is configured so that the emitters 112
`project light through the fingernail and through the blood
`vessels and capillaries underneath. The LED emitters 112
`are activated by drive signals 122 from the pulse oximeter
`100. The detector 114is positioned at the fingertip opposite
`the fingernail so as to detect the LED emitted light as it
`emerges from the finger tissues. The photodiode generated
`signal 124 is relayed by a cable to the pulse oximeter 100.
`The pulse oximeter 100 determines oxygen saturation
`(SpO.,) by computing the differential absorption byarterial
`blood of the two wavelengths emitted by the sensor 110. The
`pulse oximeter 100 contains a sensor interface 120, an SpO,,
`processor 130, an instrument manager 140, a display 150, an
`audible indicator (tone generator) 160 and a keypad 170.
`The sensor interface 120 provides LED drive current 122
`which alternately activates the sensor red and IR LED
`emitters 112. The sensor interface 120 also has input cir-
`cuitry for amplification and filtering of the signal 124
`generated by the photodiode detector 114, which corre-
`spondsto the red and infrared light energy attenuated from
`transmission through the patient tissue site. The SpO, pro-
`cessor 130 calculates a ratio of detected red and infrared
`
`intensities, and an arterial oxygen saturation value is empiri-
`cally determined based on that ratio. The instrument man-
`ager 140 provides hardware and software interfaces for
`
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`managingthe display 150, audible indicator 160 and keypad
`170. The display 150 shows the computed oxygenstatus, as
`described above. The audible indicator 160 provides the
`pulse beep as well as alarms indicating desaturation events.
`The keypad 170 provides a user interface for such things as
`alarm thresholds, alarm enablement, and display options.
`Computation of SpO, relies on the differential
`light
`absorption of oxygenated hemoglobin, HbO., and deoxy-
`genated hemoglobin, Hb, to determine their respective con-
`centrations in the arterial blood. Specifically, pulse oximetry
`measurements are made at red and IR wavelengths chosen
`such that deoxygenated hemoglobin absorbs morered light
`than oxygenated hemoglobin, and, conversely, oxygenated
`hemoglobin absorbs more infrared light than deoxygenated
`hemoglobin, for example 660 nm (red) and 905 nm (IR).
`To distinguish between tissue absorption at
`the two
`wavelengths, the red and IR emitters 112 are provided drive
`current 122 so that only one is emitting light at a given time.
`For example, the emitters 112 may be cycled on and off
`alternately, in sequence, with each only active for a quarter
`cycle and with a quarter cycle separating the active times.
`This allows for separation of red and infrared signals and
`removal of ambient light levels by downstream signal pro-
`cessing. Because only a single detector 114 is used,
`it
`responds to both the red and infrared emitted light and
`generates a time-division-multiplexed (“modulated”) output
`signal 124. This modulated signal 124 is coupled to the input
`of the sensor interface 120.
`
`In addition to the differential absorption of hemoglobin
`derivatives, pulse oximetry relies on the pulsatile nature of
`arterial blood to differentiate hemoglobin absorption from
`absorption of other constituents in the surroundingtissues.
`Light absorption between systole and diastole varies due to
`the blood volume change from the inflow and outflow of
`arterial blood at a peripheral tissue site. This tissue site might
`also comprise skin, muscle, bone, venous blood, fat,
`pigment, etc., each of which absorbslight. It is assumed that
`the background absorption due to these surrounding tissues
`is invariant and can be ignored. Thus, blood oxygen satu-
`ration measurements are based upon a ratio of the time-
`varying or AC portion of the detected red and infrared
`signals with respect to the time-invariant or DC portion:
`
`RD/IR=(Red,,/Redp-/URaclIRpe)
`
`The desired SpO, measurementis then computed from this
`ratio. The relationship between RD/IR and SpO, is most
`accurately determined bystatistical regression of experi-
`mental measurements obtained from human volunteers and
`
`calibrated measurements of oxygen saturation. In a pulse
`oximeter device, this empirical relationship can be stored as
`a “calibration curve” in a read-only memory (ROM)look-up
`table so that SpO, can be directly read-out of the memory in
`response to input RD/IR measurements.
`Pulse oximetry is the standard-of-care in various hospital
`and emergency treatment environments. Demandhaslead to
`pulse oximeters and sensors produced by a variety of
`manufacturers. Unfortunately, there is no standard for either
`performance by, or compatibility between, pulse oximeters
`or sensors. As a result, sensors made by one manufacturer
`are unlikely to work with pulse oximeters made by another
`manufacturer. Further, while conventional pulse oximeters
`and sensors are incapable of taking measurements on
`patients with poor peripheral circulation and are partially or
`fully disabled by motionartifact, advanced pulse oximeters
`and sensors manufactured by the assignee of the present
`invention are functional under these conditions. This pre-
`18
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`US 6,584,336 B1
`
`3
`sents a dilemmato hospitals and other caregivers wishing to
`upgrade their patient oxygenation monitoring capabilities.
`They are faced with either replacing all of their conventional
`pulse oximeters, including multiparameter patient monitor-
`ing systems, or working with potentially incompatible sen-
`sors and inferior pulse oximeters manufactured by various
`vendors for the pulse oximetry equipment in use oat the
`installation.
`Hospitals and other caregivers are also plagued by the
`difficulty of monitoring patients as they are transported from
`onesetting to another. For example, a patient transported by
`ambulance to a hospital emergency room will likely be
`unmonitored during the transition from ambulanceto the ER
`and require the removal and replacement of incompatible
`sensors in the ER. A similar problem is faced within a
`hospital as a patient is moved between surgery, ICU and
`recovery settings. Incompatibility and transport problems
`are exacerbated by the prevalence of expensive and non-
`portable multiparameter patient monitoring systems having
`pulse oximetry modules as one measurement parameter.
`The Universal/Upgrading Pulse Oximeter (UPO) accord-
`ing to the present invention is focused on solving these
`performance, incompatibility and transport problems. The
`UPOprovides a transportable pulse oximeter that can stay
`with and continuously monitor the patient as they are
`transported from setting to setting. Further, the UPO pro-
`vides a synthesized output that drives the sensor input of
`other pulse oximeters. This allows the UPO to function as a
`universal interface that matches incompatible sensors with
`other pulse oximeter instruments. Further, the UPO acts as
`an upgrade to existing pulse oximeters that are adversely
`affected by low tissue perfusion and motion artifact.
`Likewise,
`the UPO can drive a SpO, sensor input of
`multiparameter patient monitoring systems, allowing the
`UPO to integrate into the associated multiparameter
`displays, patient record keeping systems and alarm manage-
`ment functions.
`
`One aspect of the present invention is a measurement
`apparatus comprising a sensor, a first pulse oximeter and a
`waveform generator. The sensorhas at least one emitter and
`an associated detector configured to attach to a tissuesite.
`The detector provides an intensity signal responsive to the
`oxygen content of arterial blood at the tissue site. Thefirst
`pulse oximeter is in communication with the detector and
`computes an oxygen saturation measurement based on the
`intensity signal. The waveform generator is in communica-
`tion with the first pulse oximeter and provides a waveform
`based on the oxygen saturation measurement. A second
`pulse oximeter is in communication with the waveform
`generator and displays an oxygen saturation value based on
`the waveform. The waveform is synthesized so that the
`oxygen saturation value is generally equivalent to the oxy-
`gen saturation measurement.
`In another aspect of the present invention, a measurement
`apparatus comprises a first sensor port connectable to a
`sensor, an upgrade port, a signal processor and a waveform
`generator. The upgrade port
`is connectable to a second
`sensor port of a physiological monitoring apparatus. The
`signal processor is configured to compute a physiological
`measurementbased on a signal inputto the first sensorport.
`The waveform generator produces a waveform based on the
`physiological measurement, and the waveform is available
`at the upgrade port. The waveform is adjustable so that the
`physiological monitoring apparatus displays a value gener-
`ally equivalent to the physiological measurement when the
`upgrade port is attached to the second sensorport.
`Yet another aspect of the present invention is a measure-
`ment method comprising the steps of sensing an intensity
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`signal responsive to the oxygen content of arterial blood at
`a tissue site and computing an oxygen saturation measure-
`ment based on the intensity signal. Other steps are generat-
`ing a waveform based on the oxygen saturation measure-
`ment and providing the waveform to the sensor inputs of a
`pulse oximeterso that the pulse oximeter displays an oxygen
`saturation value generally equivalent to the oxygen satura-
`tion measurement.
`An additional aspect of the present invention is a mea-
`surement method comprising the steps of sensing a physi-
`ological signal, computing a physiological measurement
`based upon the signal, and synthesizing a waveform as a
`function of the physiological measurement. A further step is
`outputting the waveform to a sensor input of a physiological
`monitoring apparatus. The synthesizing step is performed so
`that the measurement apparatus displays a value correspond-
`ing to the physiological measurement.
`A further aspect of the present invention is a measurement
`apparatus comprising a first pulse oximeter for making an
`oxygen saturation measurement and a pulse rate measure-
`ment based upon an intensity signal derived from a tissue
`site. Also included is a waveform generation means for
`creating a signal based upon the oxygen saturation measure-
`ment and the pulse rate measurement. In addition, there is a
`communication meansfor transmitting the signal to a second
`pulse oximeter.
`Anotheraspect of the present invention is a measurement
`apparatus comprising a portable portion having a sensor
`port, a processor, a display, and a docking connector. The
`sensor port
`is configured to receive an intensity signal
`responsive to the oxygen content ofarterial blood ata tissue
`site. The processor is programmed to compute an oxygen
`saturation value based upon the intensity signal and to
`output the value to the display. A docking station has a
`portable connector and is configured to accommodate the
`portable so that
`the docking connector mates with the
`portable connector. This provides electrical connectivity
`between the docking station and the portable. The portable
`has an undocked position separate from the docking station
`in which the portable functions as a handheld pulse oxime-
`ter. The portable also has a docked position at least partially
`retained within the docking station in which the combination
`of the portable and the docking station has at least one
`additional function compared with the portable in the
`undocked position.
`A further aspect of the present invention is a measurement
`apparatus configured to function in both a first spatial
`orientation and a second spatial orientation. The apparatus
`comprises a sensor port configured to receive a signal
`responsive to a physiological state. The apparatus also has a
`tilt sensor providing an output responsive to gravity. In
`addition, there is a processor in communication with the
`sensor port and the tilt sensor output. The processor is
`programmedto compute a physiological measurement value
`based upon the signal and to determine whether the mea-
`surement apparatus is in the first orientation or the second
`orientation based upon the tilt sensor output. A display has
`a first mode and a second mode and is driven by the
`processor. The display shows the measurementvalue in the
`first mode when the apparatusis in the first orientation and
`showsthe measurementvalue in the second mode whenthe
`
`apparatus is in the second orientation.
`Anotheraspect of the present invention is a measurement
`method comprising the steps of sensing a signal responsive
`to a physiological state and computing physiological mea-
`surement based on the signal. Additional steps are deter-
`mining the spatial orientation of a tilt sensor and displaying
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`US 6,584,336 B1
`
`5
`the physiological measurementin a modethat is based upon
`the determining step.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a prior art pulse oximeter,
`FIG. 2 is a diagram illustrating a patient monitoring
`system incorporating a universal/upgrading pulse oximeter
`(UPO)according to the present invention;
`FIG. 3 is top level block diagram of a UPO embodiment;
`FIG. 4 is a detailed block diagram of the waveform
`generator portion of the UPO embodiment shownin FIG. 3;
`FIG. 5 is an illustration of a handheld embodimentofthe
`UPO;
`FIG. 6 is a top level block diagram of another UPO
`embodiment incorporating a portable pulse oximeter and a
`docking station;
`FIG. 7 is a detailed block diagram of the portable pulse
`oximeter portion of FIG. 6;
`FIG. 8A is an illustration of the portable pulse oximeter
`user interface, including a keyboard and display;
`FIGS. 8B-Care illustrations of the portable pulse oxime-
`ter display showing portrait and landscape modes, respec-
`tively;
`FIG. 9 is a detailed block diagram of the docking station
`portion of FIG. 6;
`FIG. 10 is a schematic of the interface cable portion of
`FIG. 6;
`FIG. 11A is a front view of an embodimentof a portable
`pulse oximeter,
`FIG. 11B is a back view of a portable pulse oximeter;
`FIG. 12A is a front view of an embodiment of a docking
`station;
`FIG. 12Bis a back view of a docking station;
`FIG. 13 is a front view of a portable docked to a docking
`station; and
`FIG. 14 is a block-diagram of one embodimentof a local
`area network interface for a dockingstation.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`FIG. 2 depicts the use of a Universal/Upgrading Pulse
`Oximeter (“UPO”) 210 to perform patient monitoring. A
`pulse oximetry sensor 110 is attached to a patient (not
`illustrated) and provides the UPO 210 with a modulated red
`and IR photo-plethysmograph signal through a patient cable
`220. The UPO 210 computesthe patient’s oxygen saturation
`and pulse rate from the sensor signal and, optionally, dis-
`plays the patient’s oxygen status. The UPO 210 may incor-
`porate an internal power source 212, such as common
`alkaline batteries or a rechargeable power source. The UPO
`210 mayalso utilize an external power source 214, such as
`standard 110V AC coupled with an external step-down
`transformer and an internal or external AC-to-DC converter.
`
`In addition to providing pulse oximetry measurements,
`the UPO 210 also separately generates a signal, which is
`received by a pulse oximeter 268 external to the UPO 210.
`This signal is synthesized from the saturation calculated by
`the UPO 210 such that the external pulse oximeter 268
`calculates the equivalent saturation and pulse rate as com-
`puted by the UPO 210. The external pulse oximeter 268
`receiving the UPO signal may be a multiparameter patient
`monitoring system (MPMS) 260 incorporating a pulse
`oximeter module 268,
`a standalone pulse oximeter
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`instrument, or any other host instrument capable of measur-
`ing SpO,. The MPMS260 depicted in FIG. 2 has a rack 262
`containing a number of modules for monitoring such patient
`parameters as blood pressure, EKG, respiratory gas, and
`SpO,. The measurements made by these various modules
`are shown on a multiparameter display 264, which is typi-
`cally a video (CRT) device. The UPO 210 is connected to an
`existing MPMS 260 with a cable 230, advantageously
`integrating the UPO oxygen status measurements with other
`MPMSmeasurements. This allows the UPO calculations to
`be shown on a unified display of important patient
`parameters, networked with other patient data, archived
`within electronic patient records and incorporated into alarm
`management, which are all MPMSfunctions convenient to
`the caregiver.
`FIG. 3 depicts the major functions of the UPO 210,
`including an internal pulse oximeter 310, a waveform gen-
`erator 320, a power supply 330 and an optional display 340.
`Attached to the UPO 210 is a sensor 110 and an external
`pulse oximeter 260. The internal pulse oximeter 310 pro-
`vides the sensor 110 with a drive signal 312 that alternately
`activates the sensor’s red and IR LEDs,as is well-known in
`the art. A corresponding detector signal 314 is received by
`the internal pulse oximeter 310. The internal pulse oximeter
`310 computes oxygen saturation, pulse rate, and, in some
`embodiments, other physiological parameters such as pulse
`occurrence, plethysmograph features and measurement con-
`fidence. These parameters 318 are output to the waveform
`generator 320. A portion of these parameters may also be
`used to generate display drive signals 316 so that patient
`status may be read from, for example, an LED or LCD
`display module 340 on the UPO.
`The internal pulse oximeter 310 may be a conventional
`pulse oximeteror, for upgrading an external pulse oximeter
`260, it may be an advanced pulse oximeter capable of low
`perfusion and motion artifact performance not found in
`conventional pulse oximeters. An advanced pulse oximeter
`for use as an internal pulse oximeter 310 is described in U.S.
`Pat. No. 5,632,272 assigned to the assignee of the present
`invention and incorporated herein by reference. An
`advanced pulse oximetry sensor for use as the sensor 110
`attached to the internal pulse oximeter 310 is described in
`US. Pat. No. 5,638,818 assigned to the assignee of the
`present
`invention and incorporated herein by reference.
`Further, a line of advanced Masimo SET® pulse oximeter
`OEMboards and sensorsare available from the assignee-of
`the present invention.
`The waveform generator 320 synthesizes a waveform,
`such as a triangular waveform having a sawtooth or sym-
`metric triangle shape, that is output as a modulated signal
`324 in response to an input drive signal 322. The drive input
`322 and modulation output 324 of the waveform generator
`320 are connected to the sensor port 262 of the external
`pulse oximeter 260. The synthesized waveform is generated
`in a manner such that
`the external pulse oximeter 260
`computes and displays a saturation and a pulse rate value
`that is equivalent to that measured by the internal pulse
`oximeter 310 and sensor 110.In the present embodiment, the
`waveforms for pulse oximetry are chosen to indicate to the
`external pulse oximeter 260 a perfusion level of 5%. The
`external pulse oximeter 260, therefore, always receives a
`strong signal. In an alternative embodiment, the perfusion
`level of the waveforms synthesized for the external pulse
`oximeter can be set to indicate a perfusion level at or close
`to the perfusion level of the patient being monitored by the
`internal pulse oximeter 310. As an alternative to the gener-
`ated wavefor, a digital data output 326, is connected to the
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`US 6,584,336 B1
`
`7
`data port 264 of the external pulse oximeter 260. In this
`manner, saturation and pulse rate measurements and also
`samples of the unmodulated, synthesized waveform can be
`communicated directly to the external pulse oximeter 260
`for display, bypassing the external pulse oximeter’s signal
`processing functions. The measured plethysmograph wave-
`form samples output from the internal pulse oximeter 310
`also may be communicated through the digital data output
`326 to the external pulse oximeter 260.
`It will be understood from the above discussion that the
`synthesized waveform is not physiological data from the
`patient being monitored by the internal pulse oximeter 310,
`but is a waveform synthesized from predetermined stored
`waveform data to cause the external pulse oximeter 260 to
`calculate oxygen saturation and pulse rate equivalent to or
`generally equivalent (within clinical significance) to that
`calculated by the internal pulse oximeter 310. The actual
`physiological waveform from the patient received by the
`detector is not provided to the external pulse oximeter 260
`in the present embodiment. Indeed, the waveform provided
`to the external pulse oximeter will usually not resemble the
`plethysmographic waveform of physiological data from the
`patient being monitored by the internal pulse oximeter 260.
`The cable 230 (FIG. 2) attached between the waveform
`generator 320 and external pulse oximeter 260 provides a
`monitor ID 328 to the UPO, allowing identification of
`predetermined external pulse oximeter calibration curves.
`For example, this cable may incorporate an encoding device,
`such as a resistor, or a memory device, such as a PROM
`1010 (FIG. 10) that is read by the waveform generator 320.
`The encoding device provides a value that uniquely identi-
`fies a particular type of external pulse oximeter 260 having
`knowncalibration curve, LED drive and modulation signal
`characteristics. Although the calibration curves of the exter-
`nal pulse oximeter 260 are taken into account, the wave-
`lengths of the actual sensor 110, advantageously, are not
`required to correspond to the particular calibration curve
`indicated by the monitor ID 328 or otherwise assumed for
`the external pulse oximeter 260. That is, the wavelength of
`the sensor 110 attached to the internal pulse oximeter 310 is
`not relevant or knownto the external pulse oximeter 260.
`FIG. 4 illustrates one embodimentof the waveform gen-
`erator portion 320 of the UPO 210 (FIG. 3). Although this
`embodimentis illustrated and described as hardware, one of
`ordinary skill will recognize that the functions of the wave-
`form generator may be implemented in softwareorfirmware
`or a combination of hardware, software and firmware. The
`waveform generator 320 performs waveform synthesis with
`a waveform look-up table (“LUT”) 410, a waveform shaper
`420 and a waveform splitter 430. The waveform LUT 410 is
`advantageously a memory device, such as a ROM (read only
`memory) that contains samples of one or more waveform
`portions or segments containing a single waveform. These
`stored waveform segments may be as simple as a single
`period of a triangular waveform, having a sawtooth or
`symmetric triangle shape, or more complicated, such as a
`simulated plethysmographic pulse having various physi-
`ological features,
`for example rise time,
`fall
`time and
`dicrotic notch.
`
`The waveform shaper 420 creates a continuous pulsed
`waveform from the waveform segments provided by the
`waveform LUT 410. The waveform shaper 420 has a shape
`parameter input 422 and an eventindicator input 424 that are
`buffered 470 from the parameters 318 output from the
`internal pulse oximeter 310 (FIG. 3). The shape parameter
`input 422 determines a particular waveform segmentin the
`waveform LUT 410. The chosen waveform segment
`is
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`specified by the first address transmitted to the waveform
`LUT 410 on the address lines 426. The selected waveform
`
`segment is sent to the wavefo