Abstract:
Embodiments described herein may include devices and methods of manufacturing devices for sensing and monitoring physiological parameters of a patient. Specifically, certain embodiments disclose the use of conductive and nonconductive overmold materials to protect the device, increase reliability, increase comfort, and increase accuracy of the parameters measured.

Description:
BACKGROUND 
     The present disclosure relates generally to medical devices and, more particularly, to sensors used for sensing physiological parameters of a patient. 
     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 medicine, doctors often desire to monitor certain physiological characteristics of their patients. Accordingly, a wide variety of devices and techniques have been developed for monitoring physiological characteristics. Such devices and techniques provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, these monitoring devices and techniques have become an indispensable part of modern medicine. 
     One such monitoring technique is commonly referred to as pulse oximetry. Pulse oximetry may be used to measure various blood flow characteristics, such as the blood-oxygen saturation of hemoglobin in arterial blood and/or the rate of blood pulsations corresponding to each heartbeat of a patient. 
     The devices based upon pulse oximetry techniques are commonly referred to as pulse oximeters. Pulse oximeters typically utilize a non-invasive sensor that is placed on or against a patient&#39;s tissue that is well perfused with blood, such as a patient&#39;s finger; toe, forehead or earlobe. The pulse oximeter sensor emits light and photoelectrically senses the absorption and/or scattering of the light after passage through the perfused tissue. A photo-plethysmographic waveform, which corresponds to the cyclic attenuation of optical energy through the patient&#39;s tissue, may be generated from the detected light. Additionally, one or more physiological characteristics may be calculated based upon the amount of light absorbed or scattered. More specifically, the light passed through the tissue may be 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 a blood constituent, such as oxygen or oxyhemaglobin, present in the blood. The amount of light absorbed and/or scattered may then be used to estimate the amount of oxygen in the tissue using various algorithms. 
     For example, a reflectance-type sensor placed on a patient&#39;s forehead may emit light into the skin and detect the light that is “reflected” back after being transmitted through the forehead tissue. A transmission-type sensor may be placed on a finger, wherein the light waves are emitted through and detected on the opposite side of a finger. In either case, the amount of light detected may provide information that corresponds to valuable physiological patient data. The data collected by the sensor may be used to calculate one or more of the above physiological characteristics based upon the absorption or scattering of the light. For instance, the emitted light is typically selected to be of one or more wavelengths that are absorbed or scattered in an amount related to the presence of oxygenated versus de-oxygenated hemoglobin in the blood. The amount of light absorbed and/or scattered may be used to estimate the amount of the oxygen in the tissue using various algorithms. 
     The sensors generally include an emitter that emits the light and a detector that detects the light. The emitter and detector may be located on a flexible circuit that allows the sensor to conform to the appropriate site on the patient&#39;s skin, thereby making the procedure more comfortable for a patient. During use, the emitter and detector may be held against the patient&#39;s skin to facilitate the light being directed into and received from the skin of the patient. For example, a sensor may be clipped about a patient&#39;s finger tip with the emitter placed against the finger nail, and the detector placed against the under side of the finger tip. When fitted to the patient, the emitted light may travel directly through the tissue of the finger and be detected without additional light being introduced or the emitted light being scattered. 
     However, in practice, the shape and design of the sensor may be uncomfortable to the patient. Discomfort may be caused by shielding and protection provided on the optical devices, i.e. the photodetector and the emitter. For example, the detector and emitter may include materials or layers to protect measurement signals from being affected by external static electrical fields or external light. These materials can add to the bulkiness of the sensor. Further, after repeated use, the materials and layers may separate or delaminate, causing additional discomfort and resulting in potential erroneous measurements. Moreover, manufacturing the sensor, the optical devices and the protective layers may be a tedious and time consuming activity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the disclosure may become apparent upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  illustrates a patient monitoring system coupled to a multi-parameter patient monitor and a sensor assembly including a photodetector, in accordance with an embodiment; 
         FIG. 2  is a perspective view of a clip style embodiment of the sensor assembly shown in  FIG. 1 , in accordance with an embodiment, mounted in the hat; 
         FIG. 3  is a perspective view of the sensor assembly shown in  FIG. 1  placed on a patient&#39;s finger, in accordance with an embodiment; 
         FIG. 4  is a side view of the sensor assembly shown in  FIG. 1 , including a photodetector and an emitter, in accordance with an embodiment; 
         FIG. 5  illustrates a view of a bandage style embodiment of the sensor assembly, in accordance with an embodiment; 
         FIG. 6A-6C  are views of the photodetector assembly shown in  FIGS. 1-5 , shown prior to application of overmolds, in accordance with an embodiment; 
         FIG. 7A-7C  are views of the photodetector assembly shown in  FIGS. 1-5 , shown after the application of a nonconductive transparent overmold, in accordance with an embodiment; and 
         FIGS. 8A-8C  are views of the photodetector assembly shown in  FIGS. 1-5 , shown after the application of a nonconductive transparent overmold and a conductive overmold, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure 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. 
     As described herein, various embodiments of sensors are provided featuring various coatings to prevent shunting and interference from external light as well as external static forces. Further the embodiments of sensors discussed are designed to fit a range of patient application areas and are designed to provide a simplified method for manufacturing. In general, embodiments of the sensors include optical components (e.g., emitters and detectors) that are coated with a material that blocks the passage of light from external sources as well as directly between the emitter and detector. In certain embodiments, one or more of the optical components may also be coated with a material that prevents or reduces electrical interference. 
     Prior to discussing examples of such sensor assemblies in detail, it should be appreciated that such sensors may be typically designed for use with a patient monitoring system. For example, referring now to  FIG. 1 , sensor  10  may be used in conjunction with patient monitor  12 . Sensor  10 , as depicted in  FIG. 1 , is designed to be placed on a patient&#39;s finger. In the depicted embodiment, cable  14  connects sensor  10  to patient monitor  12 . Sensor  10  and/or cable  14  may include or incorporate one or more integrated circuit or electrical devices, such as a memory processor chip, that may facilitate or enhance communication between sensor  10  and patient monitor  12 . Similarly, cable  14  may be an adaptor cable, with or without an integrated circuit or electrical device, for facilitating communication between sensor  10  and various types of monitors, including different versions of patient monitor  12  or other physiological monitors. In other embodiments, sensor  10  and patient monitor  12  may communicate via wireless means such as using radio frequency, infrared, or optical signals. In such embodiments, a transmission device may be connected to sensor  10  to facilitate wireless transmission between sensor  10  and patient monitor  12 . As will be appreciated by those of ordinary skill in the art, cable  14  (or a corresponding wireless connection) may be used to transmit control or timing signals from patient monitor  12  to sensor  10  and/or to transmit acquired data from sensor  10  to patient monitor  12 . 
     In one embodiment, patient monitor  12  may be a suitable pulse oximeter, such as those available from Nellcor Puritan Bennett L.L.C. In other embodiments, patient monitor  12  may be a monitor suitable for measuring tissue water fractions, or other body fluid related metrics, using spectrophotometric or other techniques. Furthermore, patient monitor  12  may be a multipurpose monitor suitable for performing pulse oximetry and measurement of tissue water fraction, or other combinations of physiological and/or biochemical monitoring processes, using data acquired via the sensor  10  and/or other sensors. Moreover, to upgrade conventional monitoring functions provided by the system, patient monitor  12  may be coupled to a multi-parameter patient monitor  16  via cable  18  connected to a sensor input port and/or a cable connected to a digital communication port. 
     In an embodiment, the sensor  10 , as depicted in  FIG. 1 , may be a clip-style sensor assembly. In such an embodiment, the clip-style sensor may utilize transmission spectrophotometric techniques to monitor one or more parameters. In other embodiments, the sensor  10  may be a reflectance type sensor assembly using reflectance spectrophotometric techniques. The sensor  10  may include optical components, such as detector  22  and emitter  24 , which may be of any suitable type. For example, in one embodiment the emitter  24  may be one or more light emitting diodes adapted to transmit one or more wavelengths of light, such as in the red to infrared range, and the detector  22  may be a photodetector, such as a silicon photodiode package, selected to receive light in the range emitted from the emitter  24 . In the present context, detector  22  may be referred to as a photodetector, a detector device, a detector assembly or a detector component. Further, detector  22  and emitter  24  may be referred to as optical components or devices. 
     In the depicted embodiment, the sensor  10  is coupled to a cable  14  that is responsible for transmitting electrical and/or optical signals to and from the emitter  24  and the detector  22  of the sensor  10 . The cable  14  may be permanently coupled to the sensor  10 , or it may be removably coupled to the sensor  10 —the latter alternative being more useful and cost efficient in situations where the sensor  10  is disposable. In an embodiment where sensor  10  is disposable, the unitary assemblies of emitter  24  and detector  22  as described herein may allow them to be easily removed from the sensor body, which may be disposed of after use on a patient. The emitter  24  and detector  22  may then be cleaned and placed in a new sensor body for use on a new patient. 
     Turning now to  FIG. 2 , a perspective view of a clip-style embodiment of sensor  10  is shown, according to an embodiment. The assembly of sensor  10  includes an upper clip portion  26  and a lower clip portion  28 . As depicted, upper clip portion  26  includes a housing  30  that features a cavity for detector  22 , while the lower clip portion  28  includes a cavity for emitter  24 . In other embodiments the emitter  24  and detector  26  may be reversed. Further, housing  30  may be configured to allow detector  22  to be removed either through the outer portion of housing  30  or the skin contacting portion of upper clip portion  26 . As depicted, the sensor assembly  10  may allow the optical devices to be easily removed for cleaning of the sensor body and the devices. Further, the components and/or sensor body may be covered with an overmold that would facilitate cleaning, such as by rinsing off the device or body with water or a solution. 
       FIG. 3  shows the clip-style embodiment of sensor assembly  10  in operation. As depicted, upper clip portion  26  and lower clip portion  28  have been separated, allowing a patient&#39;s finger  34  to be inserted in the clip-style sensor assembly  10 . In one embodiment, light waves may be emitted by emitter  24  into the bottom of patient finger  34 . The light waves may then be transmitted through the patient&#39;s finger tissue and received by detector  22 . A signal corresponding to the detected light waves may be sent to the patient monitor via cable  14 . In one embodiment, the skin contacting components of sensor assembly  10  may be formed to be as comfortable as possible so as not to irritate the skin while the sensor is on a patient&#39;s finger. Therefore, utilizing suitable materials for sensor assembly  10  improves overall comfort and performance of clip style sensor assembly  10 . 
     With the foregoing discussion in mind and turning now to  FIG. 4 , a cut-away side view of a clip-style embodiment of sensor assembly  10  is illustrated. In one embodiment, detector device  22  may be located on the skin contacting side of upper clip portion  26 . Similarly, emitter device  24  may be located on the skin contacting side of lower clip portion  28 . Signals may be routed to or from the optical devices by component lead wires  36  which may be bundled into cable  14 . Detector device  22  and emitter device  24  may each include or be proximate to a transparent window which allows light to be transmitted between the optical components via light transmission path  38 , which may pass through a patient&#39;s finger tissue. 
     In other embodiments, the sensor may not be a clip-style sensor. For example, turning now to  FIG. 5 , an embodiment of a bandage style sensor  40  is illustrated. The bandage style sensor  40  may be applied to any well perfused area of a patient, such as a patient&#39;s forehead. As depicted, the bandage style sensor  40  may include optical devices photodetector  22  and emitter  24 . In one embodiment, the optical devices each feature windows that allow light to be transmitted to and received from the patient&#39;s tissue. In one embodiment, signals may be transmitted to and from the optical devices by lead wires  36 . In the depicted embodiment, lead wires  36  route signals to the monitor via cable  14 . In one embodiment, the bandage style sensor  40  may use an adhesive layer to attach the sensor  40  to the patient&#39;s skin. The adhesive layer may include an acrylic or synthetic rubber adhesive or other suitable adhesives. Alternatively, in another embodiment, the bandage style sensor  40  may be applied without adhesive, instead being made from a foam PVC or foam polyurethane material and attached to the skin by medical tape. 
     With the foregoing discussion of various sensor and optical component assemblies in mind,  FIGS. 6A through 8C  show embodiments of a photodetector assembly for use in accordance with the present disclosure. In particular,  FIGS. 6A through 8C  show various stages of one embodiment of a manufacturing process for the photodetector assembly.  FIGS. 6A-6C  show perspective, front and side views of the photodetector assembly prior to the application of overmold materials. In the depicted embodiment, the photodetector assembly includes detector face  42 , lead frame  44 , and ground lead  46 . In one embodiment, detector face  42  receives light waves that are converted into electrical signals which are transmitted to an associated patient monitor via lead frame  44  and attached cables.  FIG. 7A-7C  illustrates the photodetector assembly after the application of an overmold material, in accordance with an embodiment. For example, in one such embodiment, the photodetector assembly includes transparent non-conductive overmold  48  disposed about detector face  42  and a portion of lead frame  44 . In the depicted embodiment, the transparent non-conductive overmold  48  includes a protruding window  50 . In one such embodiment, window  50  is located in front of detector face  42 , thereby permitting light to be received by the detector face  42  through the window  50 . 
       FIGS. 8A-8C  show perspective, front and side views of a photodetector assembly after the application of transparent non-conductive overmold  48  and conductive overmold  52 , in accordance with an embodiment. In one embodiment, the conductive overmold  52  may cover a portion of lead frame  44  and transparent non-conductive overmold  48 . In the depicted embodiment, conductive overmold  52  does not cover window  50  which allows detector face  42  to receive incoming light waves. Further, in the depicted embodiment, conductive overmold  52  is approximately the same thickness as the protrusion of window  50 , meaning that the surface of conductive overmold  52  is flush with the surface of window  50 . In one embodiment, ground lead  46  is in contact with conductive overmold  52 , enabling the conductive overmold  52  to be connected via cable to a ground located on a monitor. 
     In one embodiment, a substantial portion of the photodetector assembly is shielded from electromagnetic and static fields by conductive overmold  52 , which serves as a Faraday shield for the optical device. In one such embodiment, transparent non-conductive overmold  48  insulates detector face  42  and other assembly components from electrical contact with conductive overmold  52 . Transparent non-conductive overmold  48  and conductive overmold  52  may be composed of any suitable material, such as neoprene, silicone, plastic, polyurethane, polypropylene, nylon, urethane, epoxy, and/or other suitable materials. Moreover, different materials or combinations of materials may be used for each of the overmolds. For instance, in one embodiment, the conductive overmold  52  may be composed of a medical grade silicone, epoxy, and/or polypropylene containing a conductive additive, such as metal fibers, carbon fibers, carbon powders or carbon nanotubes. In one embodiment, conductive overmold  52  may be completely or partially opaque, however, in other embodiments, conductive overmold  52  is not opaque. 
     In one embodiment, the optical component and associated overmold layers constitute an assembly that may be inserted and removed from the sensor body. For example, in one embodiment, a photodetector assembly, as shown in  FIGS. 6A-8C , may be utilized in a suitable pulse oximetry sensor, including the bandage-style sensor of  FIG. 5  or the clip-style sensor of  FIGS. 1-4 . In addition, the arrangement of the overmold layers in such an embodiment protects the photodetector device from contaminants and other debris by providing a hermetic seal about the components. 
     In certain embodiments, the use of overmolded optical components also allows a simplified approach to cleaning and replacing the optical components within a sensor assembly. For example, in one embodiment the photodetector assembly may be removed as an integral unit from a housing or frame of a clip style sensor by application of a mechanical force to overcome a force that may be exerted by the housing to keep the assembly in place. As described herein, in certain embodiments the photodetector assembly may include a cable connected to the lead frame  44  and covered in a rubber casing, which, along with the overmolds, provide protection for the entire detector assembly. In one such embodiment, the rubber casing and overmold allow the assembly to be easily cleaned with water or a solution. After removal of such an overmolded detector assembly, the housing may also be easily cleaned. Similarly, the easy removal and insertion of the detector assembly allows for simplified replacement of the device in the sensor housing. 
     The application of transparent nonconductive overmold  48  and/or conductive overmold  52  to the optical components, such as the photodetector, may be accomplished by any suitable means. For example, in one embodiment, a detector assembly may be formed by an injection molding process. In one example of such a process the lead frame  44  and detector  22  may be positioned within a die or mold of the desired shape for the assembly. A molten or otherwise unset overmold material may then be injected into the die or mold. For example, in one implementation, a molten thermoplastic elastomer at between about 400° F. to about 450° F. is injected into the mold. The overmold material may then be set, such as by cooling for one or more minutes or by chemical treatment, to form the overmold layer about the lead frame  44  and detector  22 . Further, the application of an overmold, as described herein, may be applied to any suitable electronic component, including LEDs and photodiodes. 
     The configuration, thickness, and number of overmold layers may vary depending upon several factors including size and weight constraints as well as costs, materials used, manufacturing limitations and environment. In one embodiment, the use of one or two overmold layers may reduce the complexity of the detector assembly, thereby reducing overall size and bulkiness of the photodetector assembly. For example, the use of conductive overmolding instead of metallic mesh for the device&#39;s Faraday shield may be more compact, resist separation/delamination and eliminate a source of discomfort for the patient. In other embodiments, additional overmold layers, such as an addition nonconductive overmold layer may be utilized. Further, the simplified approach to shielding the photodetector may increase robustness of the photodetector and sensor assembly by providing an overmolded material that will resist delamination or degradation after repeated use. Moreover, the assembly may allow for easy removal of the unitary optical device, thereby enabling the device to be removed and replaced for cleaning or maintenance. The arrangement also allows for a simplified manufacturing process for the optical device, thereby reducing costs and complexity of the sensor assembly. 
     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 disclosure is not intended to be limited to the particular forms provided. Rather, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the following appended claims. Indeed, the present disclosed methods may not only be applied to transmission type sensors for use in pulse oximetry, but also to other sensor designs. Likewise, the present disclosure is not limited to use on ears, digits, or foreheads but may also be applied to placement on other body parts.