Patent Publication Number: US-8532729-B2

Title: Moldable ear sensor

Description:
BACKGROUND 
     The present disclosure relates generally to medical devices and, more particularly, to medical sensors with strain relief properties that may be applied to a patient&#39;s ear for sensing physiological parameters. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     In the field of healthcare, caregivers (e.g., doctors and other healthcare professionals) often desire to monitor certain physiological characteristics of their patients. Accordingly, a wide variety of devices have been developed for monitoring many such characteristics of a patient. Such devices provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, such monitoring devices have become an indispensable part of modern medicine. 
     One technique for monitoring certain physiological characteristics of a patient is commonly referred to as pulse oximetry, and the devices built based upon pulse oximetry techniques are commonly referred to as pulse oximeters. Pulse oximetry may be used to measure various blood flow characteristics, such as the blood-oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and/or the rate of blood pulsations corresponding to each heartbeat of a patient. 
     Pulse oximetry sensors, as well as other types of non-invasive optical sensors, transmit light through a patient&#39;s tissue and photoelectrically detect the absorption and/or scattering of the transmitted light in such tissue. One or more physiological characteristics may then be calculated based upon the amount of light absorbed or scattered. More specifically, the light passed through the tissue is typically selected to be of one or more wavelengths that may be absorbed or scattered by the blood in an amount correlative to the amount of the blood constituent present in the blood. The amount of light absorbed and/or scattered may then be used to estimate the amount of blood constituent in the tissue using various algorithms. 
     Accurate sensor measurements depend on the secure placement of the sensor on the desired measurement site on a patient. For example, a poor fit of the sensor with the tissue may allow ambient light to reach the photodetecting elements of the sensor, which may introduce error into the measurements. In addition, a poorly conforming sensor may become dislodged. To that end, sensors are manufactured with patient anatomy in mind. That is, sensors may be designed for a particular tissue placement site, e.g., a finger, and often for a particular type or size of patient, e.g., an adult. However, in critical care situations, an operator may apply a finger sensor to a patient&#39;s ear, which may result in inaccurate sensor measurements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the disclosed techniques may become apparent upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  illustrates a perspective view of a pulse oximetry system in accordance with an embodiment; 
         FIG. 2  is a block diagram of the pulse oximetry system of  FIG. 1 ; 
         FIG. 3  is a section view of an ear sensor including a moldable layer; 
         FIG. 4  is a perspective view of the sensor of  FIG. 3  applied to an earlobe; 
         FIG. 5  is a perspective view of the sensor of  FIG. 3  applied to an upper ear region; 
         FIG. 6  is a perspective view of a flexible cable sensor; 
         FIG. 7  is a is a perspective view of the senor of  FIG. 6  applied to an ear; 
         FIG. 8  is a is a perspective view of a flex circuit sensor with a moldable member applied to an ear; 
         FIG. 9  is a perspective view of a moldable sensor kit; 
         FIG. 10  is a view of a Y-shaped transmission-type sensor; 
         FIG. 11  is a is a perspective view of the sensor of  FIG. 10  applied to an ear; 
         FIG. 12  is a perspective view of a Y-shaped clip-type sensor applied to a patient&#39;s ear; 
         FIG. 13  is a perspective view of a Y-shaped sensor that includes a cinching mechanism. 
         FIG. 14  is a perspective view of a Y-shaped sensor with flat cables; 
         FIG. 15  is a perspective view of a Y-shaped reflectance-type sensor including an adhesive layer; 
         FIG. 16  is a perspective view of a Y-shaped reflectance-type sensor with a stabilizing branch applied to a patient&#39;s ear; 
         FIG. 17  is a perspective view of a Y-shaped reflectance-type sensor with a second reflectance-type sensor on an opposing branch applied to a patient&#39;s ear; 
         FIG. 18  is a perspective view of an ear sensor including a sliding clip applied to a patient&#39;s ear; 
         FIG. 19  is a perspective view of the sensor of  FIG. 18  in which the sensor is positioned in an open position; 
         FIG. 20  is a perspective view of the sensor of  FIG. 18  in which the sensor is positioned in a closed position; and 
         FIG. 21  is a perspective view of a sliding clip. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments of the present techniques will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     Medical sensors for sensing blood characteristics, such as arterial oxygen saturation measurement (SpO 2 ), may be placed on a patient in a location that is normally perfused with arterial blood. Common sensor placement sites include a patient&#39;s fingertips, toes, forehead, or earlobes. Often, a caregiver determines the appropriate placement of a sensor on a patient-by-patient basis. For example, a caregiver may initially apply a sensor to a patient&#39;s finger. If the sensor does not yield high quality measurements, e.g. because the patient is cold and his fingers are poorly perfused, the caregiver may then move the sensor to another tissue site, such as the ear. Rather than obtaining a new sensor for the new location, caregivers may attempt to adapt the original finger sensor for placement on the earlobe. This is particularly true for cases in which a disposable bandage-type finger sensor has been applied to the patient. While clip-type finger sensors may be too bulky to be easily placed on other tissue locations, bandage-type finger sensors are generally conformable. However, despite their conformability, bandage-type finger sensors are specifically calibrated for use on the finger. In addition, these finger sensors are too large to conform well to an earlobe and tend to peel off the earlobe under the weight of the sensor cable. Accordingly, the use of bandage-type finger sensors on the earlobe may result in measurement inaccuracies. While clip-style sensors are available that are designed to be used on a patient&#39;s ear, these sensors are reusable and are, therefore, more expensive than bandage-type sensors. In addition, clip-type sensors may be somewhat uncomfortable for a patient because of their rigidity and associated weight. 
     Provided herein are disposable sensors for use on a patient&#39;s ear. These sensors provide the convenience of a reusable sensor while also conforming to the ear with sufficient pressure to facilitate accurate measurements. In particular embodiments, the ear sensors include attachment features such as movable clips. In other embodiments, the sensors include features that mitigate strain introduced by a cable or electrical connector. In additional embodiments, the sensors provided herein may include deformable features that may be specifically molded to the patient anatomy. For example, the sensors may include moldable putty that may be molded around the ear to affix the sensor to the patient. 
     With this in mind,  FIG. 1  depicts an embodiment of a patient monitoring system  10  that may be used in conjunction with a medical sensor  12 . Although the depicted embodiments relate to sensors for use on a patient&#39;s ear, it should be understood that, in certain embodiments, the strain relief features and/or attachment features of the sensor  12  as provided herein may be incorporated into sensors for use on other tissue locations, such as the finger, the toes, the heel, the forehead, or any other appropriate measurement site. In addition, although the embodiment of the patient monitoring system  10  illustrated in  FIG. 1  relates to photoplethysmography or pulse oximetry, the system  10  may be configured to obtain a variety of medical measurements with a suitable medical sensor. For example, the system  10  may, additionally or alternatively, be configured to determine patient temperature, transvascular fluid exchange volumes, tissue hydration, blood flow, cardiovascular effort, glucose levels, level of consciousness, total hematocrit, hydration, electrocardiography, electroencephalograpy, or any other suitable physiological parameter. As noted, the system  10  includes the sensor  12  that is communicatively coupled to a patient monitor  14  via a cable  16  through a plug  18  coupled to a sensor port  19 . Additionally, the monitor  14  includes a monitor display  20  configured to display information regarding the physiological parameters, information about the system, and/or alarm indications. The monitor  14  may include various input components  22 , such as knobs, switches, keys and keypads, buttons, etc., to provide for operation and configuration of the monitor. The monitor  14  also includes a processor that may be used to execute code such as code for implementing the techniques discussed herein. 
     The monitor  14  may be any suitable monitor, such as a pulse oximetry monitor available from Nellcor Puritan Bennett LLC. Furthermore, to upgrade conventional operation provided by the monitor  14  to provide additional functions, the monitor  14  may be coupled to a multi-parameter patient monitor  24  via a cable  26  connected to a sensor input port or via a cable  28  connected to a digital communication port. In addition to the monitor  14 , or alternatively, the multi-parameter patient monitor  24  may be configured to calculate physiological parameters and to provide a central display  30  for the visualization of information from the monitor  14  and from other medical monitoring devices or systems. The multi-parameter monitor  24  includes a processor that may be configured to execute code. The multi-parameter monitor  24  may also include various input components  32 , such as knobs, switches, keys and keypads, buttons, etc., to provide for operation and configuration of the a multi-parameter monitor  24 . In addition, the monitor  14  and/or the multi-parameter monitor  24  may be connected to a network to enable the sharing of information with servers or other workstations. 
     The sensor  12  may be any sensor suitable for detection of any physiological parameter. The sensor  12  may include optical components (e.g., one or more emitters and detectors), acoustic transducers or microphones, electrodes for measuring electrical activity or potentials (such as for electrocardiography), pressure sensors, motion sensors, temperature sensors, etc. In one embodiment, the sensor  12  may be configured for photo-electric detection of blood and tissue constituents. For example, the sensor  12  may be a pulse oximetry sensor, such as those available from Nellcor Puritan Bennett LLC. As shown in  FIG. 1 , the sensor  12  may be a bandage-type sensor having a generally flexible sensor body to enable conformable application of the sensor to a sensor site on a patient. However, in particular embodiments, certain aspects of the present disclosure may be used in conjunction with relatively rigid clip-type sensors. For example, clip-type sensors may benefit from the inclusion of moldable components that may prevent ambient light from reaching the optical components of the sensor  12 . 
     In one embodiment, the sensor  12  may include a sensor body  34  housing the optical components (e.g., an emitter for emitting light at certain wavelengths into a tissue of a patient and a detector for detecting the light after it is reflected and/or absorbed by the blood and/or tissue of the patient) of the sensor. In certain embodiments, the sensor  12  may be a wireless sensor  12 . Accordingly, the wireless sensor  12  may establish a wireless communication with the patient monitor  14  and/or the multi-parameter patient monitor  24  using any suitable wireless standard. By way of example, the wireless module may be capable of communicating using one or more of the ZigBee standard, WirelessHART standard, Bluetooth standard, IEEE 802.11x standards, or MiWi standard. In embodiments in which the sensor  12  is configured for wireless communication, the strain relief features of the cable  16  may be housed in the sensor body  34 . 
     Turning to  FIG. 2 , a simplified block diagram of the medical system  10  is illustrated in accordance with an embodiment. The sensor  12  may include optical components such as an emitter  36  and a detector  38 . In addition, the sensor  12  may include an encoder  50 . The emitter  36  and the detector  38  may be arranged in a reflectance or transmission-type configuration with respect to one another. It should be noted that the emitter  36  may be capable of emitting at least two wavelengths of light, e.g., red and infrared am light, into the tissue of a patient, where the red wavelength may be between about 600 nanometers (nm) and about 700 nm, and the IR wavelength may be between about 800 nm and about 1000 nm. The emitter  36  may include a single emitting device, for example, with two light emitting diodes (LEDs) or the emitter  36  may include a plurality of emitting devices with, for example, multiple LED&#39;s at various locations. In some embodiments, the LEDs of the emitter  36  may emit three or more different wavelengths of light. Such wavelengths may include a red wavelength of between approximately 620-700 nm (e.g., 660 nm), a far red wavelength of between approximately 690-770 nm (e.g., 730 nm), and an infrared wavelength of between approximately 860-940 nm (e.g., 900 nm). Other wavelengths may include, for example, wavelengths of between approximately 500-600 nm and/or 1000-1100 nm. Regardless of the number of emitting devices, light from the emitter  36  may be used to measure, for example, oxygen saturation, water fractions, hematocrit, or other physiologic parameters of the patient. It should be understood that, as used herein, the term “light” may refer to one or more of ultrasound, radio, microwave, millimeter wave, infrared, visible, ultraviolet, gamma ray or X-ray electromagnetic radiation, and may also include any wavelength within the radio, microwave, infrared, visible, ultraviolet, or X-ray spectra, and that any suitable wavelength of light may be appropriate for use with the present disclosure. 
     In one embodiment, the detector  38  may be an array of detector elements capable of detecting light at various intensities and wavelengths. In one embodiment, light enters the detector  38  after passing through the tissue of the patient or being reflected by elements in the patent&#39;s tissue. The intensity of the received light may be directly related to the absorbance and/or reflectance of light in the tissue of the patient. That is, when more light is absorbed by the tissue, less light is available to be received by the detector  38 . After converting the received light to an electrical signal, the detector  38  may send the signal to the monitor  14 , where physiological characteristics may be calculated based at least in part on the absorption and/or reflection of light by the tissue of the patient. 
     In certain embodiments, the medical sensor  12  may also include an encoder  50  that may provide signals indicative of the wavelength of one or more light sources of the emitter  36 , which may allow for selection of appropriate calibration coefficients for calculating a physical parameter such as blood oxygen saturation. The encoder  50  may, for instance, be a coded resistor, EEPROM or other coding devices (such as a capacitor, inductor, PROM, RFID, parallel resident currents, or a colorimetric indicator) that may provide a signal to a microprocessor  56  related to the characteristics of the medical sensor  12  to enable the microprocessor  56  to determine the appropriate calibration characteristics of the medical sensor  12 . Further, the encoder  50  may include encryption coding that prevents a disposable part of the medical sensor  12  from being recognized by a microprocessor  56  unable to decode the encryption. For example, a detector/decoder  58  may translate information from the encoder  50  before it can be properly handled by the processor  56 . In some embodiments, the encoder  50  and/or the detector/decoder  58  may not be present. 
     Signals from the detector  38  and/or the encoder  50  may be transmitted to the monitor  14 . The monitor  14  may include one or more processors  56  coupled to an internal bus  60 . Also connected to the bus may be a RAM memory  62  and a display  64 . A time processing unit (TPU)  68  may provide timing control signals to light drive circuitry  70 , which controls when the emitter  36  is activated, and if multiple light sources are used, the multiplexed timing for the different light sources. TPU  68  may also control the gating-in of signals from detector  38  through a switching circuit  74 . These signals are sampled at the proper time, depending at least in part upon which of multiple light sources is activated, if multiple light sources are used. The received signal from the detector  38  may be passed through an amplifier  76 , a low pass filter  78 , and an analog-to-digital converter  80  for amplifying, filtering, and digitizing the electrical signals the from the ear sensor  12 . The digital data may then be stored in a queued serial module (QSM)  82 , for later downloading to RAM  62  as QSM  82  fills up. In an embodiment, there may be multiple parallel paths for separate amplifiers, filters, and A/D converters for multiple light wavelengths or spectra received. 
     In an embodiment, based at least in part upon the received signals corresponding to the light received by detector  38 , processor  56  may calculate the oxygen saturation using various algorithms. These algorithms may use coefficients, which may be empirically determined. For example, algorithms relating to the distance between an emitter  36  and various detector elements in a detector  38  may be stored in a ROM  84  and accessed and operated according to processor  56  instructions. 
     Furthermore, one or more functions of the monitor  14  may also be implemented directly in the sensor  12 . For example, in some embodiments, the sensor  12  may include one or more processing components capable of calculating the physiological characteristics from the signals obtained from the patient. In accordance with the present techniques, the sensor  12  may be configured to provide optimal contact between a patient, the detector  38 , and/or the emitter  36 , may have varying levels of processing power, and may output data in various stages to the monitor  14 , either wirelessly or via the cable  16 . For example, in some embodiments, the data output to the monitor  14  may be analog signals, such as detected light signals (e.g., pulse oximetry signals), or processed data. 
     Sensors  12  as provided herein may be applied to a patient&#39;s ear to generate a signal related to a physiological parameter. In particular, the disclosed sensors  12  may be securely and comfortably attached to the ear with reduced strain on the electrical components. For example, for relatively rigid clip-type sensors, the weight of the sensor housing components may introduce strain on the cable, which in turn may result in movement of the sensor relative to the tissue and inaccuracies in the measured signal. In addition, ear sensors are typically positioned with the cable hanging down from the sensor, and gravity may exacerbate the effects of such strain. Even for patients in a supine position, the cable tends to hang down from the ear, which puts pressure on both the sensor and the tissue itself. The disclosed sensors  12  provide flexibility in the positioning and attachment of the sensing components to the ear, which may result in decreased strain on the sensor  12 . 
     In particular embodiments, the sensors  12  may include moldable members that may be shaped and molded around the irregular profile of the ear. Such sensors  12  may be shaped around the tissue at the time of application to the patient, which facilitates a secure and conforming fit for a patient regardless of individual anatomy. In addition, the moldable members may seal any light paths from outside of the sensor and may provide flexible and custom-fitted shunt barriers to prevent shunting of light from the emitter  36  to the detector  38 . While bandage-type sensors are generally conformable, such sensors still retain enough rigidity that ambient light may leak into the sensor. Sensors with moldable members may create a tissue-contact surface that bends around the tissue to protect the detector from any undesired light. 
     Moldable members as provided may include putties, clays, polymers, or waxes that are deformable by an operator (e.g., easily deformed by hand). For example, the moldable members may include impression wax or wax compositions, hydrocolloidal impression masses and rubber impression masses. The molding material may further be a gelatin or agar having a calcium sulfate reactor. In one embodiment, the moldable material may be a dental impression material or gum-type composition. In other embodiments, the moldable member may be a medical paste, such as Moldable Strip Paste, (Coloplast, Minn.). The moldable material may also be characterized by its hardness on the Shore OO scale. For example, in one embodiment, the moldable member may have a hardness of less than 40 Shore OO or less than 20 Shore OO. In certain embodiments, the moldable member may be configured to harden or cure upon exposure a specific wavelength of light, heat, or a chemical catalyst for hardening. Examples of suitable material include Triad® light-curing materials (DENTSPLY, Pa.). In particular embodiments, room temperature vulcanizing silicones may be used to form the moldable member. In such embodiments, the moldable member may not only provide a conforming fit, but may also contribute to the overall rigidity of the sensor  12  and may provide a fixed optical distance between the emitter  36  and the detector  38 . In this manner, a sensor  12  may combine the tissue-conforming advantages of bandage-type sensors with the stability and motion-resistance of more rigid sensors. In another embodiment, to facilitate the appropriate interaction with undesired light, the moldable member may be opaque and/or dark in color. 
       FIG. 3  is a section view of a transmission-type sensor  12  including a moldable layer  200 . As depicted, the sensor body  34  may also include a backing layer  210  that is generally conformable. For example, the backing layer  210  may be one or more cloth or bandage layers. Alternatively, the backing layer  210  may be relatively resilient and may be scored or hinged at a fold point  214  to facilitate bending or folding of the sensor body  34  around the tissue. For example, a relatively rigid clip-type sensor may benefit from an interior moldable layer  200 , which may prevent light leakage onto the detector  38  by filling in any gaps between the sensor  12  and the tissue. The cable  16 , or other suitable electrical connector, may be embedded in or otherwise coupled to the backing layer  210 . The backing layer  210  may also include suitable coatings or shielding layers for preventing cross-talk between the electrical couplings of the emitter  36  and the detector  38 . 
     The moldable layer  200  is disposed on a tissue-contacting surface  218  of the sensor body  34  such that the moldable layer  34  is in direct contact with the tissue when the sensor  12  is applied to the patient. When the sensor is applied, an operator may squeeze or press the sensor  12  to fit the sensor around the tissue. To prevent the moldable material from migrating over the optical components, the emitter  36  and the detector  38  may be disposed within housing members  220  that include ends  222  that serve as a barrier to lateral movement of the moldable layer  200  over the optical components. The emitter  36  and detector  38  may be covered by optically transparent windows  224  that are positioned within the housing members  220 . In certain embodiments, the ends  222  may be slightly raised relative to the moldable layer  200 , which may facilitate shaping of the moldable layer  200  around each optical component. That is, when the sensor  12  is squeezed around the ear, the moldable layer  200  may accumulate around ends  222 . In addition, the sensor body  34  may include a raised lip around all or part of the outside edge to prevent migration of the moldable layer  200  outside the sensor. In other embodiments, such migration outside the sensor may serve as a barrier to infiltration of ambient light. 
     The moldable layer  200  may be covered by a release layer, which may be removed, e.g., peeled off, prior to application of the sensor  12 . The release layer may protect the moldable layer  200  from exposure to air, which may prematurely harden the sensor  12 . The release layer may be disposed on the tissue-contacting surface  218  of the sensor  12  such that the moldable layer  200  is between the release layer and the backing layer  210 . For example, the release layer and the backing layer  210  may form a substantially air-tight seal around the moldable layer  200 . In addition, in embodiments in which the moldable layer  200  is tacky, adhesive, or coated in an adhesive layer, the release layer may prevent self-adhesion of the sensor  12  prior to application. 
       FIG. 4  is a perspective view of the sensor  12  of  FIG. 3  applied to a patient&#39;s ear. The sensor  12  is bent around the earlobe such the emitter  36  and the detector  38  are aligned on opposing sides of the earlobe. The moldable layer  200  is on the interior of the sensor in contact with the tissue. To facilitate the positioning of the sensor, the exterior, i.e., visible to an observer when the sensor  12  is applied, the exterior surface  234  of the sensor  12  may include one or more alignment indicators. For example, a folding indicator  236  on the fold point  214  may indicate the location of the sensor body that is configured to be positioned on an underside  238  of the earlobe. In addition, optical component indicators  240  may be positioned at locations on the exterior surface  234  that correspond to the emitter  36  and the detector  38 . In a particular embodiment, the sensor  12  may include magnetic components that are configured to align the emitter  36  and detector  38 . For example, the optical housing members  220  (see  FIG. 3 ) may include magnetic features. When the optical housing members  220  are positioned correctly on opposing sides of the earlobe, the housing members  220  experience a maximum of magnetic force and are more difficult to pull apart, indicating proper alignment to an operator. In addition, the sensor  12  may be cured or hardened in place on the patient, for example by exposing the sensor  12  to a harmless wavelength of light. 
     While the sensor  12  may be applied to an earlobe, depending on the configuration of the sensor body, the sensor  12  may be bent around other parts of the ear, such as an upper curve, i.e., a helix, as shown in  FIG. 5 , or the tragus. In addition, the disclosed features may also be incorporated into reflectance-type sensors. For example, a reflectance-type sensor may include a sensor body  34  that is configured to be wrapped around an earlobe. In such an embodiment, the emitter  36 /detector  38  pair are positioned on the same side of the ear. In a particular embodiment, the sensor body  34  may include magnetic components configured to mate across the tissue. In such an embodiment, one magnetic component on one side of the earlobe may be positioned proximate to the emitter  36 /detector  38  pair. 
     In addition to embodiments in which a moldable member may form a layer on a sensor body, in particular embodiments, the moldable member may be used instead of a sensor body or may be used to affix electrical connectors to the tissue.  FIG. 6  is a perspective view an embodiment in which a moldable member  250  is used in conjunction with a Y-shaped sensor  12  formed from an electrical connector (e.g. cable  16 ). The emitter  36  and the detector  38  are disposed at the ends of the branches  252  and  254  of the Y-shaped member while the main body  256  extends towards the monitor. The moldable member  250  may be molded around the branches  252  and  254  to affix the sensor  12  to the patient, as shown in  FIG. 7 . 
     In an alternative embodiment in which a sensor body  34  is formed from a flexible circuit, as shown in  FIG. 8 , the sensor body  34  may be affixed to the tissue with the moldable member  250 . For example, the sensor body  34  may be scored at the fold line to facilitate the proper placement and alignment of the emitter  36  and detector  38 . In addition, the moldable member  250  may be used to affix the cable  16  to the tissue as well to promote strain relief. As depicted, the cable  16  is affixed to the upper ear with an additional moldable member  258 . 
     Regardless of whether the moldable member forms a tissue-contacting layer on a sensor body  34  or a removable affixing member for the sensor  12 , in certain embodiments, the sensor  12  may be provided as a kit  260  with the moldable member  250  provided as a separate component, as shown in  FIG. 9 . The kit may also include an appropriate applicator  262 , such as a syringe, tube, or knife. In addition, where appropriate, the kit may include a curing agent  264  that may be mixed with the moldable member  250  to promote its hardening. In such embodiments, the moldable member  250  may only be deformable for a set period of time after exposure to the curing agent. The kit may also include instructions for applying the curing agent  264  and/or applying the moldable member  250  to the sensor  12 . 
     In addition to sensors that include moldable components, the sensors  12  as provided herein may include generally conformable or shapeable components to relieve strain on the sensor.  FIG. 10  depicts a generally Y-shaped sensor  12  that is configured to be placed upside down on the ear, as shown in  FIG. 11 . As provided the sensor  12  may include a sensor body  34  that generally refers to the portion of the sensor  12  that is applied to the patient, e.g., affixed to and/or wrapped around the ear, to facilitate patient monitoring. The sensor body  34  may house the electrical connections from the emitter  36  and the detector  38 . In certain embodiments, the housing or body of the cable  16  may form all or part of the sensor body  34 . In one embodiment, the cable  16  may be a 2-wire cable that takes a single wire branched form in the portion that wraps around the ear. The sensor body  34  may include the branched portion and, in particular embodiments, a section of the cable  16  immediately adjacent to the branch point to form a generally Y-shaped sensor body  34 . In such an embodiment, the outer plastic shield or other covering of the cable  16  may form the sensor body  34 . In other embodiments, the sensor body portion of the cable  16  may be formed or shaped (e.g. flattened) to achieve a particular arrangement of the sensor body  34 . In other embodiments, the sensor body may include bandage layers, surfaces for attachment to the patient, rigid outer shells, or different types of shields or housing for electrical wires or connectors. 
     In one embodiment, the Y-shape may include a main branch  300 , a first fork  310 , and a second fork  312 . The main branch  300  may extend away from the ear and form the cable  16 . A junction  314  of the main branch  300  with the forks  310  and  312  is positioned above the ear, and the first fork  310  and the second fork  312  run down opposite sides of the ear. The emitter  36  is positioned at an end  316  of the first fork and the detector  38  is positioned at an end  318  of the second fork  312 . The electrical connectors for the emitter  36  and the detector  38  may be contained within the first fork  310  and the second fork  312  and may run along the main branch  300  into cable  16 . It should also be understood that the positions of the emitter  36  and the detector  38  may be reversed. In the depicted configuration, the weight of the sensor hangs down from above the ear rather than hanging below the ear from the earlobe. This may reduce the tendency of the sensor  12  to be pulled off the ear. That is, a traditional clip-type sensor may be pulled off by a downward tug on the cable. However, an upside-down Y-shape is less vulnerable to being pulled off because the cable  16  does not hang down from the ear. In addition, the attachment points of the sensor  12  may be positioned on the head or neck and not the ear. This reduces the effects of motion on the sensor because tugs on the cable  16  pull at the attachment points, and not on the emitter  36  and the detector  38 . 
     As shown in  FIG. 11 , the junction  314  may rest on a top  320  of the ear. The sensor  12  may form a curve  322  that is shaped to conform to the top  320  of the ear, e.g., the curve  322  may conform to the thickness and curvature of the tissue at the top of the ear. Accordingly, the top  320  of the ear may hold some of the weight of the sensor. The sensor may also be adhered to the tissue along the main branch  300  or the first fork  310  and the second fork  312 . In addition, the emitter  36  and the detector  38  may be coated with an adhesive to facilitate attachment to the tissue. Magnetic components or moldable components may be employed to facilitate attachment of the sensor  12 . In the embodiment shown in  FIG. 12 , the junction  314  may form a hinge  324  (e.g., a spring clip or a spring-loaded hinge) such that first fork  310  and the second form  312  may be biased towards one another. In such an embodiment, the first fork  310  and the second fork  312  may be formed from relatively rigid materials. 
     The first fork  310  and the second fork  312  may be substantially equal in length. In another embodiment, the second fork  312  may be a different length than the first fork  310 . For example, depending on the path of the second fork  312  along the back of the ear, the second fork  312  may be longer than the first fork  310 . The first fork  310  and the second fork may be about a length of an average ear, from the earlobe  330  to the top  320  of the ear. In a particular embodiment, the first fork  310  and the second fork  312  may be at least about 1 inch in length, or may be between 1 inch and 4 inches in length. 
     The Y-shaped sensor  12  may be formed all or in part from conformable or shapeable materials. It particular embodiments, the materials may include traditional medical sensor materials and shielded cable or wire materials that may be placed directly against a patient&#39;s skin. For example, in one embodiment, the main branch  300 , the first fork  310 , and the second fork  312  are all formed from a flexible cable. In other embodiments, the Y-shaped sensor  12  may include a flexible circuit. In another embodiment, first fork  310  and the second fork  312  form a sensor body  34  and are a different material than the main branch  300 . In such an embodiment, the curve  322  may be relatively rigid while the rest of the sensor body  34  is flexible, or the entire sensor body  34  may be relatively rigid while the main branch  300  is conformable. In yet another embodiment, the main branch  300  is relatively rigid at least for a portion of its length adjacent to the junction  314 . In another specific embodiment, the first fork  310  and/or the second fork  312  are formed from shapeable wires. That is, the first fork  310  and/or the second fork  312  may be bent around the ear, but the wires, one bent, tend to hold their position. In this manner, the sensor  12  may be formed to the shape of a particular patient&#39;s ear. 
       FIG. 13  illustrates an embodiment in which the sensor  12  includes a cinching mechanism  328  that may pull the first fork  310  and the second fork  312  taut against the ear. The cinching mechanism may be a loop that slides down over the junction  314  and is capable of being tightened to hold the first fork  310  and the second fork  312  at a desired position. In such an embodiment, the first fork  310  and the second fork  312  may be relatively conformable. The cinching mechanism  328  may be a knotted loop that becomes tighter as it slides further down the main branch  300 . In other embodiments, the cinching mechanism may have teeth or other adjustment features to fix its diameter around the first fork  310  and the second fork  312 , similar to a zip tie. 
     A Y-shaped sensor as provided may have a relatively low profile to provide a more comfortable fit for the patient. In certain embodiments, all or part of the sensor  12  is formed from substantially flat cables.  FIG. 14  is a perspective view of a Y-shaped sensor  12  with flat portions along the main branch  300 , the first fork  310 , and the second fork  312 . Flat cables may conform to the tissue better than rounded structures. In addition, a relatively flat surface may provide increased surface area for an adhesive. Alternatively, the sensor  12  may include an adhesive layer  340 , as shown in  FIG. 15 , that extends away from the sensor  12  to provide more surface area for adhesion. In particular, the adhesive layer  340  may be highly flexible to facilitate a conforming fit. In addition, the adhesive layer  340  may be transparent so that an operator may easily view the sensor  12  during application. 
     A Y-shaped sensor  12  may also be implemented in a reflectance-type configuration. For example, rather than an opposing emitter  36  and detector  38 , an emitter  36 /detector  38  pair may be positioned on a single fork. The opposing fork may be used to stabilize the attachment of the sensor  12 .  FIG. 16  is a perspective view of a Y-shaped reflectance-type sensor with a stabilizing branch applied to a patient&#39;s ear. As shown, the emitter  36  and the detector  38  are disposed on the first fork  310 , which runs along the front of the ear. The second fork  312  runs behind the ear and is affixed to the neck. The second fork  312  stabilizes the sensor  12  and may be formed from more rigid materials relative to the first fork  310 . In other embodiments, the second fork  312  may include a magnetic component configured to align across the tissue of the ear with a magnetic component on the first fork  310 . 
       FIG. 17  is a perspective view of a Y-shaped reflectance-type sensor  12  with a plurality of optical components. In the depicted configuration, the first fork  310  includes a first emitter  36   a  and first detector  38   a  and the second fork  312  includes a second emitter  36   b  and a second detector  38   b . The emitter/detector pairs may be offset from one another along the ear so that they may operate simultaneously without interfering with one another. Alternatively, the timing of the emitter/detector pairs may be controlled via the monitor  14  so that they are configured to emit and detect light at different times. In other implementations, the sensor  12  may include a transmission-type sensing arrangement as well as a reflectance-type sensing arrangement or two transmission-type arrangements. Further, the first emitter  36   a  and first detector  38   a  and the second emitter  36   b  and a second detector  38   b  may both be configured to sense the same physiological parameter. That is, the depicted configuration may allow measurement of oxygen saturation at two different sites on the ear. The monitor  14  may arbitrate the signals to determine which measurement site has the highest quality measurements. In other embodiments, the emitter/detector pairs may be configured to sense different physiological parameters. For example, the first emitter  36   a  and first detector  38   a  may be configured for pulse oximetry while the second emitter  36   b  and a second detector  38   b  may be configured for determining a tissue water fraction. 
     Sensors  12  with improved strain relief properties may also include sensor configurations with a traditional clip-type arrangement in which the sensor cable  16  hangs down from the earlobe. As noted, this configuration may introduce strain from the weight of the electrical connectors as well as the weight of the sensor housing. In certain embodiments, the pull of the sensor  12  may be mitigated by reducing the weight of the sensor components and the attachment mechanism. Provided herein are sensors  12  that combine conformable bandage-type sensor bodies  34  with lightweight rigid clips.  FIG. 18  is a perspective view of an ear sensor  12  with a sliding clip  360  applied to a patient&#39;s ear. It is envisioned that the depicted sensor  12  is disposable. In the depicted embodiment, the sensor body  34  is formed from flexible bandage-type materials. The sensor cable  16  runs along an axis  364  of the sensor body  34  and extends away from the sensor  12 . 
       FIG. 19  is a perspective view of the sensor  12  in which the clip is positioned along the cable  16 . The sliding clip  360  is capable of sliding along axis  364  and down the cable  16 . The cable terminates in a plug  18 . The sensor body  34  is generally Y-shaped and includes a first portion  370  and a second portion  372  that are joined at the stem portion  374  at junction  376  and that are configured to be positioned on opposing side of the earlobe. As depicted, the sensor  12  is in an open configuration, and the first portion  370  and the second portion  372  are not biased towards one another. A foam layer  378  may be positioned on the tissue-contacting side of the first portion  370  and the second portion  372  to provide additional thickness. In another embodiment, a pressure-sensitive adhesive layer may be disposed on the side of the first portion  370  and the second portion  372 . The emitter  36  and the detector  38  are disposed on opposing portions. However, it should be understood that the emitter  36  and the detector  38  may be arranged in a reflectance configuration. The sensor body may include features that allow the sliding clip to move easily from the stem portion  374  to the cable  16 . As shown, the stein portion  374  includes notches  379  to prevent the sliding clip  360  from catching on the sensor body  34 , 
       FIG. 20  shows the sensor in the closed position in which the sliding clip  360  is positioned to bias the first portion  370  and the second portion  372  towards one another. In certain embodiments, the sliding clip  360  is not removable from the sensor  12  by an operator without breaking or tearing the clip  360  or the sensor  12 . This may provide the advantage of having an all-in-one sensor assembly without removable parts that may be misplaced. To that end, the clip  360  encircles the sensor  12  in a dimension substantially orthogonal to the axis  364 . 
     As shown in  FIG. 21  in perspective view, the sliding clip  360  includes an annular base member  380  that defines a passage  382 . The passage  382  is large enough to accommodate the cable  16  and the stein portion  374 . The base member  380  may include a bump  383  or notch configured to accommodate a slightly thicker cable  16 . In addition, the sensor body  34  may include a wider or thicker portion that is larger than the passage  382  and that stops movement of the sliding clip  360  past the stem portion  374 . For example, the first portion  370  and the second portion  372  may include an additional layer, such as the foam layer  378 , that results in a greater combined thickness of the first and second portions  370  and  372  relative to the stein portion  374 . At the other end of the sensor  12 , the passage  382  of the sliding clip  360  is smaller than the plug  18 . 
     The sliding clip  360  also includes a first end  384  and a second end  386  that provide the biasing force. The biasing force may be determined by the size and shape of the first end  384  and the second end  386 . The first end  384  and the second end  386  may also include cutouts  388  that may adjust the amount of force applied. In certain embodiments, it is contemplated that the sliding clip  360  or other biasing mechanism applies sufficient pressure to the tissue to exceed the typical venous pressure of a patient, but not the diastolic arterial pressure. If the sensor  12  applies a pressure greater than the venous pressure, excess venous blood will be squeezed from the earlobe, thus enhancing the sensitivity of the sensor to variations in the arterial blood signal. In addition, in such an embodiment, the effect of venous pulsations may be dampened. Since the pressure applied by the sensor  12  is designed to be less than the arterial pressure, the application of pressure to the tissue does not interfere with the arterial pulse signal. In certain embodiments, the sensor  12  may be adjusted to overcome venous pressure in the tissue of the ear (e.g., the earlobe), which may be as low as an average pressure of 3-5 mmHg. In certain embodiments, the sensor  12  applies at least enough pressure to overcome about 3-5 mm Hg, about 5 mm Hg, or about 10-15 mm Hg. These pressures may vary because of the location of the vascular bed and the patient&#39;s condition. For example, a patient with poor perfusion may have lower venous pressure. It is contemplated that removing venous blood contribution without arterial blood exsanguination may improve the arterial pulse signal. Further, the pressure applied by the sensor  12  may be less than arterial pressure, e.g., the diastolic arterial pressure or the systolic arterial pressure. Typical diastolic arterial pressure and systolic arterial pressures may be about 80 mmHg and 120 mmHg, respectively. However, venous pressure or arterial pressure may be assessed on a patient-by-patient basis. 
     The sensor  12  may also include alignment features or indicators to facilitate application to the ear. In one embodiment, the sliding clip  360  may slide only to the junction point  376  of the main stem  374  and the first portion  370  and the second portion  372  because the size of the passageway  382  prevents further movement along the axis  364 . At that stopping point, the sliding clip  360  is correctly aligned with the sensor body  34  and the emitter  36  and detector  38  to provide the appropriate securing force. In such an embodiment, the correct alignment may be achieved by intuitive feel, which may be advantageous. In other embodiments, the interior surface  392  of the first end  384  and/or the second end  386  may include depressions or protrusions that may mate with complementary features on an exterior surface of the first portion  370  and/or the second portion  372 . 
     The biasing mechanism is depicted as a sliding clip  360 . However, the sensor  12  may be secured with a flat spring, a coiled torsion spring, a hinged clip, or other biasing component. Further, in certain embodiments, the biasing mechanism may be removable from the sensor  12 . In such embodiments, the sensor  12  may be affixed to the earlobe with a removable flat clip or U-shaped clip that does not encircle the sensor body  34  when applied to the sensor  12 . In such embodiments, the sensor body  34  and/or the biasing mechanism may include text or other alignment indicators, for example indicating the position of the emitter  36  and the detector  38 , to facilitate proper positioning of the biasing mechanism. The biasing mechanism may be constructed from a variety of materials or combinations of materials that provide the desired resiliency and clamping force. For example, in certain embodiments, the biasing mechanism is constructed from stainless steel. In other embodiments, the biasing mechanism is constructed from polymeric materials, such as acrylonitrile butadiene styrene. 
     While the disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the embodiments provided herein are not intended to be limited to the particular forms disclosed. Indeed, the disclosed embodiments may not only be applied to measurements of blood oxygen saturation, but these techniques may also be utilized for the measurement and/or analysis of other blood constituents. For example, using the same, different, or additional wavelengths, the present techniques may be utilized for the measurement and/or analysis of carboxyhemoglobin, met-hemoglobin, total hemoglobin, fractional hemoglobin, intravascular dyes, and/or water content. Rather, the various embodiments may cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the following appended claims.