Secondary-emitter sensor position indicator

[0001] The present application claims priority benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/104,890, filed Oct. 13, 2008, titled Secondary-Emitter Sensor Position Indicator, hereby incorporated by reference herein.

[0002] Pulse oximetry is a technique that utilizes a noninvasive sensor to determine a person's oxygen status. An optical sensor used in pulse oximetry has light emitting diodes (LEDs) that transmit optical radiation of red and infrared wavelengths into a tissue site. A detector in the sensor 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 SpO₂ and pulse rate among other parameters. Pulse oximeters capable of reading through motion induced noise are available from Masimo Corporation (“Masimo”) of Irvine, Calif. Moreover, portable and other pulse oximeters capable of reading through motion induced noise are disclosed in at least U.S. Pat. Nos. 6,770,028, 6,658,276, 6,157,850, 6,002,952, and 5,769,785, which are owned by Masimo and are incorporated by reference herein. Corresponding low noise optical sensors are also available from Masimo and are disclosed in at least U.S. Pat. Nos. 6,985,764, 6,813,511, 6,792,300, 6,256,523, 6,088,607, 5,782,757, 5,758,644 and 5,638,818. Such reading through motion pulse oximeters and low noise sensors 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 types of monitoring scenarios. Moreover, pulse oximeters capable of reading through motion induced noise including Radical®, Rad-5™, Rad-8™, Rad-9™ and PPO+™ monitors and low noise optical sensors including LNOP®, LNCS® and SofTouch™ disposable, reusable, reSposable™ and multisite sensors and cables are also available from Masimo.

[0003] Further, noninvasive blood parameter monitors capable of measuring parameters in addition to SpO₂, such as HbCO, HbMet and Hbt and corresponding multiple wavelength optical sensors are also available from Masimo. Noninvasive blood parameter monitors and corresponding multiple wavelength optical sensors are described in at least U.S. patent application Ser. No. 11/367,013, filed Mar. 1, 2006, titled Multiple Wavelength Sensor Emitters and U.S. patent application Ser. No. 11/366,208, filed Mar. 1, 2006, titled Noninvasive Multi-Parameter Patient Monitor, both assigned to Masimo Laboratories, Irvine, Calif. (Masimo Labs) and both incorporated by reference herein. Moreover, multiple parameter monitors and multiple wavelength sensors including Radical-7™, Rad57™ and Rad87™ monitors and Rainbow™-brand adhesive and reusable sensors are available from Masimo. MS- and MX-brand processor boards are also available from Masimo.

[0004] Problems arise if a pulse oximeter or other blood parameter monitor is connected to an optical sensor that is not properly positioned on a tissue site or becomes partially or completely dislodged from a patient, a sensor out-of-position condition including sensor-off and sensor mis-position conditions. When an optical sensor is properly positioned on a tissue site, the detector only receives LED emitted light that has propagated via the tissue site to the detector after tissue scattering and absorption. Thus, the AC detector signal that results accurately reflects the differential absorption of constituents in the pulsatile arterial blood. If a sensor is off a tissue site or is mis-positioned on the tissue site, the detector may directly receive LED emitted light, i.e. light that has not propagated through any tissue. Despite a sensor out-of-position condition, a blood parameter monitor may continue to detect an AC signal, which can be induced at the detector by other than pulsatile arterial attenuation of LED emitted light. Small patient movements, vibrations, air flow or other perturbations may cause the pathlength between the LEDs and detector to vary, resulting in an AC detector signal that can be mistakenly interpreted by the monitor as due to pulsatile arterial blood. Further, ambient light may reach the detector, and any modulation of the ambient light due to AC power, power fluctuations, moving objects, such as a fan, among other perturbations can also be mistaken as a pulsatile arterial signal. Sensor out-of-position errors are serious because a blood parameter monitor may still display a normal measurement, potentially leading to critical missed events, such as an oxygen desaturation.

[0005] An aspect of a sensor position indicator regards an optical sensor with a sensor-on condition in which the optical sensor is attached to and aligned with a tissue site so as to transmit light into the tissue site and detect the light after attenuation by pulsatile blood flow within the tissue site and a sensor out-of-position condition in which the sensor is unattached to or misaligned with the tissue site. The sensor position indicator comprises an optical sensor having primary emitters and a detector. The primary emitters generate light generally centered around each of multiple primary wavelengths. The primary emitters transmit light into a tissue site in a sensor-on condition. The detector, in the sensor-on condition, outputs a sensor signal responsive to the primary wavelength light after attenuation by pulsatile blood flow within the tissue site. A secondary emitter generates light generally centered around a secondary wavelength. The secondary emitter transmitted light is at least substantially attenuated by the tissue site. The detector, in the sensor-on condition, is at least substantially blocked by the tissue site from the secondary emitter so that the sensor signal is not responsive to the secondary wavelength light. The detector, in a sensor out-of-position condition, is at least partially exposed to the secondary emitter so that the sensor signal is responsive to the secondary wavelength light. A processor is responsive to the sensor signal so as to calculate a blood-related physiological parameter in the sensor-on condition and so as to indicate the sensor is unattached to or misaligned with the tissue site in the sensor out-of-position condition.

[0006] In various embodiments, the optical sensor has a sensor mis-positioned condition in which the optical sensor is misaligned with the tissue site. The sensor position indicator further comprises a second secondary emitter that generates light generally centered around the secondary wavelength. The detector, in the sensor mis-positioned condition, is at least substantially blocked from the second secondary emitter by the tissue site and is at least partially exposed to the secondary emitter so that the sensor signal is not responsive to the second secondary emitter and is responsive to the secondary emitter. The processor is responsive to the sensor signal so as to indicate the optical sensor is misaligned with the tissue site in the mis-positioned sensor condition. The optical sensor also has a sensor-off position in which the optical sensor is unattached to or substantially misplaced on the tissue site. The detector, in the sensor-off condition, is at least partially exposed to the secondary emitter and the second secondary emitter so that the sensor signal is responsive to both the secondary emitter and the second secondary emitter. The processor is responsive to the sensor signal so as to indicate that the optical sensor is unattached to or substantially misplaced on the tissue site in the sensor-off condition.

[0007] The optical sensor also has a sensor over-positioned condition where the tissue site is over-inserted into the optical sensor. The sensor position indicator further comprises a third secondary emitter that generates light generally centered around the secondary wavelength. The detector, in the sensor-on condition, is at least substantially exposed to the third secondary emitter so that the sensor signal is responsive to the third secondary emitter. The detector, in the sensor over-positioned condition, is at least substantially blocked from the third secondary emitter by the tissue site so that the sensor signal is not responsive to the third secondary emitter. The processor is responsive to the sensor signal so as to indicate the tissue site is over-inserted into the optical sensor in the sensor over-positioned condition. The primary wavelengths may include red and IR and the secondary wavelength may be blue or green. The secondary emitter may be located external to the optical sensor so that the secondary wavelength light is ambient light with respect to the optical sensor. The secondary emitter may be driven asynchronously relative to the primary emitters.

[0008] An aspect of an optical sensing method comprises providing an optical sensor having a primary emitter and a detector. The primary emitter is activated with a primary drive signal so as to transmit light having a primary wavelength into a fleshy tissue site. A secondary emitter is activated with a secondary drive signal so as to transmit light having a secondary wavelength proximate the fleshy tissue site. The primary wavelength light is detected after attenuation by pulsatile blood flow within the tissue site. The secondary wavelength light is detected. A physiological parameter is calculated according to detected primary wavelength light. A sensor position of the primary emitter and the detector relative to the fleshy tissue site is determined according to the detection of secondary wavelength light.

[0009] In various embodiments, the primary drive signal and the secondary drive signal are synchronized so that on periods of the secondary drive signal occur during off periods of the primary drive signal. Determining sensor position may comprise indicating a sensor-on condition according to undetected secondary wavelength light during an on period of the secondary drive signal and indicating a sensor out-of-position condition according to undetected secondary wavelength light during on periods of the secondary drive signal. A second secondary emitter may be activated with a second secondary drive signal and a sensor-off condition indicated according to the undetected secondary wavelength light during on periods of the secondary drive signal and second secondary drive signal. A sensor mis-position condition may be indicated according to detected secondary wavelength light during on periods of the secondary drive signal and according to undetected secondary wavelength light during on periods of the second secondary drive signal. A third secondary emitter may be activated with a third secondary drive signal and a sensor over-position condition indicated according to detected secondary wavelength light during on periods of the third secondary drive signal.

[0010] An aspect of a physiological measurement system comprises an optical sensor having primary emitters, at least one secondary emitter, a detector and an attachment assembly. A physiological monitor is in communications with the optical sensor. The primary emitters transmit light having a primary wavelengths. At least one secondary emitter transmits light having at least one secondary wavelength. The detector outputs a sensor signal in response to received light. The attachment assembly, in a sensor-on condition, positions the emitters and detector relative to a tissue site so that the sensor signal is substantially responsive to the primary wavelength light after attenuation by pulsatile blood flow within the tissue site and is negligibly responsive to the secondary wavelength light. The attachment assembly, in a sensor out-of-position condition, positions at least one secondary emitter relative to the tissue site so that the sensor signal is at least partially responsive to the at least one secondary wavelength.

[0011] In various embodiments, a first secondary emitter is located in a first position relative to the primary emitters. A second secondary emitter is located in a second position relative to the primary emitters. The attachment assembly, in a sensor mis-positioned condition, positions the secondary emitters relative to the tissue site so that the sensor signal is negligibly responsive to the first secondary emitter and at least partially responsive to the second secondary emitter. The attachment assembly, in a sensor-off condition, may position the secondary emitters relative to the tissue site so that the sensor signal is at least partially responsive to the first secondary emitter and the second secondary emitter. A third secondary emitter may be located in a third position relative to the primary emitters. The attachment assembly, in a sensor-on condition, positions the secondary emitters relative to the tissue site so that the sensor signal is negligibly responsive to the first and second secondary emitters and at least partially responsive to the third secondary emitter. The attachment assembly, in a sensor over-positioned condition, positions the secondary emitters relative to the tissue site so that the sensor signal is negligibly responsive to the first, second and third secondary emitters. A processor portion of the physiological monitor may operate on the sensor signal so as to determine the position of a finger relative to the sensor according to at least multiple ones of a sensor-on condition, a sensor out-of-position condition, a sensor off condition and a sensor mis-positioned condition. A display portion of the physiological monitor may be responsive to the processor determination of sensor and finger position so as to graphically depict the position of a finger relative to the sensor. An alarm portion of the physiological monitor may be responsive to the processor determination of sensor and finger position so as to audibly indicate the position of a finger relative to the sensor.

[0021] FIGS. 1-2 illustrate a physiological measurement system 100 which measures blood constituents and related parameters, such as oxygen saturation, pulse rate, perfusion index (PI), pleth variability index (PVI™), HbCO, HbMet and Hbt, to name a few. The physiological measurement system 100 includes an optical sensor 110 applied to a tissue site 10, a monitor 130 and a cable 150 that physically and electrically connects the sensor 110 to the monitor 130. Advantageously, the physiological measurement system 100 also utilizes a sensor position indicator responsive to improper placement of the sensor 110 on a finger or other tissue site 10, as described in detail below.

[0022] As shown in FIGS. 1-2, the patient monitor 130 communicates with the sensor 110 to receive one or more intensity signals indicative of one or more physiological parameters. Drivers 134 convert digital control signals into analog drive signals 154 capable of driving primary emitters 112 that transmit optical radiation having multiple primary wavelengths. The drivers 134 also provide drive signals 156 capable of driving secondary emitters 116 having one or more secondary wavelengths. A detector 114 responds to the intensity of the optical radiation after attenuation by pulsatile blood flow within the tissue site 10 and generates a corresponding sensor signal 152. A front-end 132 converts the analog sensor signal 152 into digital data input to a digital signal processor (DSP) 138. The DSP 138 comprises any of a wide variety of data and signal processors capable of executing programs for determining physiological parameters from input data. The instrument manager 140 may comprise one or more microcontrollers providing system management, such as monitoring the activity of the DSP 138. The instrument manager 140 also has communications 142 with displays, alarms and user input/output (I/O) 144. In an embodiment, a display 144 depicts the position of a finger relative to the sensor according to any of a sensor on, a sensor out-of-position, a sensor off and a sensor mis-positioned condition.

[0023] Also shown in FIGS. 1-2, in an embodiment a sensor position indicator incorporates external secondary emitters 170 located outside of the sensor 110. In an embodiment, a sensor position indicator incorporates internal secondary emitters 116 located inside the sensor 110. The secondary emitters 116, 170 have one or more wavelengths selected to be at least substantially attenuated by tissue. In an embodiment, secondary emitter wavelengths are selected from the blue or green region of the visible spectrum so as to be highly absorbed by water and, hence, substantially attenuated by the substantial water content of tissue. In this manner, the sensor signal 152 responsive to a secondary emitter 116, 170 is indicative of a sensor-off or a sensor mis-positioned condition. That is, for the detector 114 to sense a secondary emitter 116, 170, the detector 114 must be at least partially uncovered by the tissue site 10.

[0024] As shown in FIG. 1, external secondary emitters 170 can be placed in one or more locations in or around the measurement system 100. These secondary emitters 170 enable the detection of a sensor-off or sensor mis-positioned condition via generation of ambient light having at least one secondary wavelength. As examples, external secondary emitters 170 can be disposed on the monitor 130, on the cable connector 160, in the surrounding room, such as on a wall 180, or on other instruments in the room (not shown), or combinations of these locations. External secondary emitters 170 may be free running, driven by the monitor in sync with primary emitters or may be driven by another instrument.

[0025] As shown in FIG. 2, one or more internal secondary emitters 116 are placed in a sensor proximate a primary emitter 112 and distal a detector 114 used for blood parameter measurements. These secondary emitters 116 enable the detection of a sensor-off or sensor mis-positioned condition via generation of sensor generated light having at least one secondary wavelength. Internal secondary emitters 116 may be free running or driven by the monitor in sync with the primary emitters.

[0026] FIGS. 3A-B illustrate a sensor 200 having a secondary emitter configured for sensor position indication. The sensor 200 has primary emitters 210 capable of transmitting light having primary wavelengths (λp) 212 into a tissue site 10. A detector 240 is capable of detecting the transmitted light 212 after attenuation by the tissue site 10 and outputting a primary signal 250 responsive to the detected light 214. The primary signal 250 is indicative of at least one physiological parameter corresponding to the tissue site 10. Advantageously, the sensor 200 is associated with at least one secondary emitter 220 having at least one secondary wavelength (λs) 213 that is at least substantially attenuated by the tissue site 10. In this manner, the response of the detector signal 250 to the secondary emitter 220 is indicative of sensor position, as described in further detail below.

[0027] As shown in FIG. 3A, a sensor-on condition 201 is where the tissue site 10 is properly placed relative to the detector 240 so that accurate physiological measurements can be made. In particular, a primary emitter 210 is placed so as to illuminate a blood-perfused tissue site 10, such as a nail bed, and the detector 240 is positioned so that only light transmitted by the primary emitter 210 and attenuated by pulsatile blood flowing within the tissue site 10 is received by the detector 240. Specifically, in a sensor-on condition 201, the detector 240 is not exposed to ambient light or light transmitted directly from emitter 210 to detector 240 without tissue site attenuation, such as by light-piping or reflection around the tissue site or otherwise. For example, in a sensor-on condition 201, constraints on the placement and relative location of emitter, tissue site and detector result in a sensor signal having a negligible contribution from light having a secondary wavelength λs 213.

[0028] As shown in FIG. 3B, a mis-positioned sensor condition or a sensor-off condition 202 is where the tissue site 10 is displaced relative to the detector 240 so that light having a secondary wavelength λs 213 reaches the detector 240, i.e. the detector signal 250 is also responsive to a secondary emitter 220. For example, in a mis-positioned sensor condition or a sensor-off condition 202, a sensor signal could have a substantial contribution from ambient light or other transmitted light that has not reach the detector 240 via tissue site 10 attenuation. Various embodiments of a sensor position indicator utilizing a secondary emitter are described with respect to FIGS. 4-9, below.

[0029] FIGS. 4A-B illustrate a secondary emitter sensor embodiment in a sensor-on condition and a mis-positioned sensor condition, respectively. The sensor 400 has a primary emitter 410 that emits light having multiple primary wavelengths λp into a tissue site 10 and a detector 420 that detects the emitted light after attenuation by the tissue site 10.

[0030] As shown in FIG. 4A, in a sensor-on condition 405, the tissue site 10 completely covers the detector 420. As such, light having a secondary wavelength λs is at least substantially attenuated by the tissue site 10 so that the detector 420 is not responsive to a secondary emitter. That is, the failure to detect emission from one or more secondary emitters indicates a sensor-on condition 405.

[0031] As shown in FIG. 4B, in a mis-positioned sensor condition 406, the detector 420 is exposed to light having a secondary wavelength λs including light from one or more secondary emitters. That is, the detection of wavelength λs from one or more secondary emitters indicates either a mis-positioned sensor condition 406 or a sensor-off condition (not shown).

[0032] As shown in FIGS. 4A-B, one or more external secondary emitters 170 (FIG. 1) or internal secondary emitters 116 (FIG. 2) have at least one secondary wavelength λs that is at least substantially attenuated by the tissue site 10. Accordingly, a sensor position relative to the tissue site 10 is indicated according to whether a secondary wavelength is detected. In an embodiment, internal secondary emitters, if any, are driven synchronously with the primary emitters, as described with respect to FIGS. 5A-B, below. In an embodiment, external secondary emitters, if any, are free-running, i.e. driven asynchronously from the primary emitters, as described with respect to FIG. 5C, below. In an embodiment, a detector response in one or more time slots where no primary emitters are activated indicates a sensor-off condition, as described with respect to FIGS. 5A-C, below. In an embodiment, the emitter 410 is an array of LEDs including LEDs that emit primary wavelengths and LEDs that emit one or more secondary wavelengths. An emitter array is described in U.S. patent application Ser. No. 11/367,013, cited above and incorporated by reference herein.

[0033] FIGS. 5A-C illustrate time diagrams for an emitter drive signal 500 and corresponding detector signals 520, 540 with synchronous and asynchronous secondary emitters, respectively. These emitter drive 500 and detector signals 520, 540 correspond to a sensor utilizing an internal or external secondary emitter, such as described with respect to FIGS. 4A-C, above. As shown in FIG. 5A, during primary emitter enable periods 501-503, drive current is supplied from monitor drivers 134 (FIG. 2) to selected primary emitters in sequence, causing the selected emitters to turn on and emit optical energy at a particular wavelength. During OFF periods 511-513, no drive current is supplied to any emitter, allowing demodulation of the detector signal. Detector signal demodulation is described in U.S. Pat. No. 5,919,134 entitled “Method and Apparatus for Demodulating Signals in a Pulse Oximetry System,” which is assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein.

[0034] Also shown in FIG. 5A, the drive signal 500 represents emitter drive currents activated and deactivated to various emitters. Included are emitter currents 501-503 for activating primary emitters 112 (FIG. 2) that transmit light having multiple wavelengths λ_p1, λ_p2, . . . λ_pn into a tissue site 10 (FIG. 2). Also included are emitter currents 506 for synchronously activating one or more secondary emitters having one or more wavelengths during an inactive period 510 for the primary emitters. For example, a single internal secondary emitter 116 (FIG. 2) of wavelength λ_s may be activated after the primary emitters 112 (FIG. 2) have each be activated in sequence and before the start of another primary activation sequence, as shown. In another embodiment, there are no synchronous emitter currents 506 for activating secondary emitters. Rather, secondary emitters, either internal or external are free-running or are otherwise activated asynchronously from the primary drive currents, as described with respect to FIG. 5C, below.

[0035] As shown in FIG. 5B, a detector signal 520 represent detector current 152 (FIG. 2) in response to the emitter transmitted light after absorption by pulsatile bloodflow within the tissue 10 (FIG. 2). In particular, the detector signal 520 has response periods 521-523 corresponding to the primary emitter enable periods 501-503 (FIG. 5A) and off periods 531-533 corresponding to the primary emitter off periods 511-513 (FIG. 5A). Advantageously the detector signal 520 may also have one or more secondary emitter response intervals 530 that indicate a sensor-off condition. The DSP 138 (FIG. 2), for example, processes a secondary emitter response interval 530 so as to detect a synchronous secondary emitter response 526, which indicates a sensor-off condition. Correspondingly, failure to detect a synchronous secondary emitter response 526 within the interval 530 when a secondary emitter is activated 506 (FIG. 5A) is indicative of a sensor-on condition.

[0036] As shown in FIG. 5C, a detector signal 540 also represents detector current 152 (FIG. 2) in response to the emitter transmitted light after absorption by pulsatile blood flow within the tissue 10 (FIG. 2), including response periods 541-543 corresponding to the primary emitter enable periods 501-503 (FIG. 5A) and off periods 551-553 corresponding to the primary emitter off periods 511-513 (FIG. 5A). Advantageously the detector signal 540 may also have one or more secondary emitter response intervals 550 used to detect an asynchronous secondary emitter response 546 indicative of a sensor-off condition. That is, the DSP 138 (FIG. 2), may process an interval 550 known to be outside of any primary emitter activation sequence so as to determine if there is a detector response to an asynchronous secondary emitter, such as a free-running external emitter. Detection of a known secondary emitter activation sequence within the interval 550 is indicative of a sensor-off condition, and failure to detect such a sequence may be indicative of a sensor-on condition. As described above, the secondary emitter response intervals 530, 550 may include one or more on/off cycles of one or more synchronously or asynchronously activated secondary emitters.

[0037] FIGS. 6A-C illustrate a multiple secondary-emitter sensor 600 advantageously configured to indicate multiple improper sensor placement conditions. In particular, the multiple secondary-emitter sensor 600 has a sensor-on condition 605, a sensor mis-positioned condition 606 and a sensor-off condition 607. The sensor 600 has a primary emitter 610 that emits light having multiple primary wavelengths λ_p into a tissue site 10 and a detector 620 that detects the emitted light after attenuation by the tissue site 10. In the embodiment shown, the sensor 600 has two secondary emitters 630, 640 that emit light having a secondary wavelength λs and that are placed relative to the primary emitter 610 so as to indicate the two improper placement sensor conditions.

[0038] As shown in FIG. 6A, in the sensor-on condition 605, tissue completely covers the detector 620 so that the detector 620 is not responsive to secondary emitters 630-640 of wavelength λ_s. As shown in FIG. 6B, in the sensor mis-positioned condition 606, the detector 620 is exposed to at least one secondary emitter 630 and is blocked by tissue from at least one secondary emitter 640. As shown in FIG. 6C, in the sensor-off condition 607, the detector 620 is exposed to light transmitted from multiple secondary emitters 630-640. Advantageously, a sensor mis-positioned condition 606 is differentially indicated from a sensor-off position 607 so that an attached monitor can more accurately inform a healthcare professional or monitor operator of an appropriate corrective action.

[0039] Although a multiple secondary-emitter sensor 600 is described above with two secondary emitters 630, 640 placed proximate to and on either side of the primary emitter 610, in other embodiments there may be more than two secondary-emitters. In other embodiments, the secondary emitters may both be located on the same side of the primary emitter, the secondary emitters may be placed at various locations around the primary emitter, the secondary emitters may be co-located within the primary emitter package or the secondary emitters may be placed at various combinations of the above-described sensor locations. Further, some or all of the secondary emitters may have the same or similar wavelengths λ_s or some or all of the secondary emitters may have distinct wavelengths λs₁, λs₂, . . . λs_n.

[0040] FIGS. 7A-D illustrate sensor timing diagrams corresponding to a sensor having multiple secondary emitters, such as described with respect to FIGS. 6A-C, above. As shown in FIG. 7A, emitter drive signals 700 include activated and deactivated drive currents to multiple primary emitters 701-703 and multiple secondary emitters 705-706. In particular, during a secondary emitter activation interval 710, secondary emitters 630, 640 (FIGS. 6A-C) are activated 705, 706 in sequence with intervening OFF periods.

[0041] As shown in FIGS. 7B-D, a detector signal 720 corresponding to the emitter drive signals 700 is generated by the detector 114 (FIG. 2) and transmitted to the monitor 130 (FIG. 2) as a detector current 152 (FIG. 2). As shown in FIG. 7B, in a sensor-on condition 605 (FIG. 6A), light transmitted from the secondary emitters 630, 640 (FIG. 6A) is at least substantially absorbed by tissue 10 (FIG. 6A) properly placed between the emitters and the detector 620 (FIG. 6A). Hence, there is no detector current corresponding to secondary emitter activation during the activation interval 730 (FIG. 7B). Thus, the monitor 130 (FIGS. 1-2) can determine that there is proper placement of the sensor 110 (FIGS. 1-2).

[0042] As shown in FIG. 7C, in a mis-positioned sensor condition 606 (FIG. 6B), light transmission from at least one secondary emitter 630 (FIG. 6B) is not at least substantially absorbed by tissue, because the tissue site 10 (FIG. 6B) is not properly placed between the emitters 630, 640 (FIG. 6B) and the detector 620 (FIG. 6B). Hence, there is detector current 725 corresponding to a secondary emitter drive current 705 (FIG. 7A) during the activation interval 730. Thus, the monitor 130 (FIGS. 1-2) can determine that the sensor 110 (FIGS. 1-2) is mis-positioned.

[0043] As shown in FIG. 7D, in a sensor-off condition 607 (FIG. 6C), light transmission from all secondary emitters 630, 640 (FIG. 6C) is not at least substantially absorbed by tissue, as the sensor is substantially misplaced on the tissue site or is completely off of the tissue site 10 (FIG. 6C). Hence, there is detector current 725-726 corresponding to each secondary emitter drive current 705, 706 (FIG. 7A) during the activation interval 730. Thus, the monitor 130 (FIGS. 1-2) can determine that the sensor 110 (FIGS. 1-2) is substantially or completely off of the tissue site.

[0044] FIGS. 8A-D illustrate a secondary emitter/detector sensor 800 having secondary emitters and a secondary detector advantageously configured to indicate a sensor on condition and multiple improper sensor conditions. In particular, the secondary emitter/detector sensor 800 has a sensor-on condition 805, an over-positioned sensor condition 806, a sensor mis-positioned condition 807, and a sensor-off condition 808. In an over-positioned sensor condition 806, the sensor 800 indicates that the tissue site is inserted too far into the sensor. An over-positioned sensor condition 806 may occur, for example, in a removable finger clip sensor where a fingertip is over inserted, such as when a finger nail or other finger structure bypasses a blocking structure or indent.

[0045] The secondary emitter/detector sensor 800 has a primary emitter 810 that emits light having multiple primary wavelengths λp into a tissue site 10 and a primary detector 820 that detects the emitted light after attenuation by the tissue site 10. In the embodiment shown, the sensor 800 also has three secondary emitters 830-840 that emit light having a secondary wavelength λs, which are placed relative to the primary emitter 810 so as to indicate the three improper placement sensor conditions.

[0046] As shown in FIG. 8A, in the sensor-on condition 805, tissue completely covers the detector 820 so that the primary detector 820 is not responsive to secondary emitters 830-840. The secondary detector 825, however, is responsive to a secondary emitter 835 placed distal the primary emitter 810.

[0047] As shown in FIG. 8B, in the sensor over-positioned condition 806, the secondary detector 825 is not responsive to the secondary emitter 835. That is, light transmission from the secondary emitter 835 is at least substantially absorbed when tissue is over inserted between a secondary emitter 835 and secondary detector 825.

[0048] As shown in FIG. 8C, in the sensor mis-positioned condition 807, the detector 820 is exposed to at least one secondary emitter 830 and is blocked by tissue from at least one secondary emitter 840. As shown in FIG. 8D, in the sensor-off condition 808, the detector 620 is exposed to light transmitted from multiple secondary emitters 630-640. Advantageously, the various improperly placed sensor conditions 806-808 are differentially indicated from each other so that an attached monitor can more accurately inform a healthcare professional or monitor operator of an appropriate corrective action.

[0049] FIGS. 9A-E illustrate sensor timing diagrams corresponding to a secondary emitter/detector sensor 800 (FIGS. 8A-D), such as described above. These timing diagrams including input emitter drive signals 900 and corresponding combined primary and secondary detector output signals 950-980 indicating a sensor-on condition and various improper sensor position conditions. As shown in FIG. 9A, emitter drive signals 900 include drive currents activated and deactivated to multiple primary emitters 901-903 and multiple secondary emitters 905-907 during a secondary emitter activation interval 910.

[0050] As shown in FIG. 9B, in a sensor-on condition 805 (FIG. 8A), a primary detector response current 921-923 is generated by the primary detector 820 (FIG. 8A) in response to light received during emitter activation 901-903. Also, a secondary detector response current 927 is generated by the secondary detector 825 (FIG. 8A) in response to light received during a secondary response interval 930 in response to secondary emitter activation 907.

[0051] As shown in FIG. 9C, in a sensor over-positioned condition 806 (FIG. 8A), a primary detector response current 921-923 is generated by the primary detector 820 (FIG. 8A) as described with respect to FIG. 9B, above. However, the secondary detector response current 927 for a sensor over-position condition is substantially null during the secondary activation interval 930 as light transmission at wavelength λs is at least substantially absorbed by the tissue over-inserted between the detector and the secondary emitter 825, 835 (FIG. 8B).

[0052] As shown in FIG. 9D, in a mis-positioned sensor condition 807 (FIG. 8C) light transmission from at least one secondary emitter 830 (FIG. 8C) is not at least substantially absorbed by tissue, which is not properly placed between the secondary emitters 830, 840 (FIG. 8C) and the primary detector 820 (FIG. 8C). Hence, there is primary detector current 925 corresponding to a secondary emitter drive current 905 (FIG. 9A) during the activation interval 930. Thus, the monitor 130 (FIGS. 1-2) can determine that the sensor is mis-positioned.

[0053] As shown in FIG. 9E, in a sensor off condition 808 (FIG. 8D) light transmission from all secondary emitters 830 is not at least substantially absorbed by tissue, which is either substantially misplaced between the secondary emitters 830, 840 (FIG. 8D) and the primary detector 820 (FIG. 8D) or the sensor is entirely off of the tissue site. Hence, there is detector current 925-927 corresponding to secondary emitter drive current 905-907 (FIG. 9A) during the activation interval 930. Note that primary detector current 921-923 in response to primary emitter drive current 901-903 may have an AC component that appears normal, i.e. due to pulsatile blood absorption, despite the absence of tissue, as described in the summary, above.

[0054] A secondary-emitter sensor position indicator 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.