Abstract:
A pulse oximetry sensor has an emitter adapted to transmit optical radiation of at least two wavelengths into a tissue site and a detector adapted to receive optical radiation from the emitter after tissue site absorption. A tape assembly is adapted to attach the emitter and detector to the tissue site. A flexible housing is disposed around and optically shields the detector.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application relates to and claims the benefit of prior U.S. Provisional Patent Application No. 60/534,331 entitled Pulse Oximetry Sensor, filed Jan. 05, 2004 and incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Pulse oximetry is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of a person&#39;s oxygen supply. Early detection of low blood oxygen level is critical in the medical field, for example in critical care and surgical applications, because an insufficient supply of oxygen can result in brain damage and death in a matter of minutes. A pulse oximetry system consists of a sensor applied to a patient, a monitor, and a patient cable connecting the sensor and the monitor. The sensor is attached to a tissue site, such as an adult patient&#39;s finger. The sensor has an emitter configured with both red and infrared LEDs that, for finger attachment, project light through the fingernail and into the blood vessels and capillaries underneath. A detector is positioned at the finger tip opposite the fingernail so as to detect the LED emitted light as it emerges from the finger tissues. In general, the emitter is adapted to transmit optical radiation of at least two wavelengths into a tissue site, and the detector is adapted to receive optical radiation from the emitter after absorption by pulsatile blood flowing within the tissue site. 
     SUMMARY OF THE INVENTION 
     There are various noise sources for a sensor including electromagnetic interference (EMI), ambient light and piped light. Light that illuminates the detector without propagating through the tissue site, such as ambient light and piped light, is unwanted optical noise that corrupts the desired sensor signal. Ambient light is transmitted to the detector from external light sources, i.e. light sources other than the emitter. Piped light is stray light from the emitter that is transmitted around a tissue site along a light conductive surface, such as a reflective inner surface of face stock material, directly to the detector. A pulse oximetry sensor advantageously provides EMI shielding and optical shielding, including multiple barriers to ambient light and piped light. 
     One aspect of a pulse oximetry sensor comprises an emitter adapted to transmit optical radiation of at least two wavelengths into a tissue site and a detector adapted to receive optical radiation from the emitter after tissue site absorption. A tape assembly is adapted to attach the emitter and detector to the tissue site. A flexible housing is disposed around and optically shields the detector. 
     Another aspect of a pulse oximetry sensor comprises a detector adapted to receive optical radiation from an emitter after absorption by pulsatile blood flowing within a tissue site. A shielded detector assembly has an EMI shield disposed around the detector. A housing assembly has a flexible housing disposed around the shielded detector assembly. A tape assembly is folded around the housing assembly and is adapted to attach the detector and emitter to the tissue site. 
     A further aspect of a pulse oximetry sensor is a method providing an emitter adapted to transmit optical radiation of at least two wavelengths into a tissue site and a detector adapted to receive optical radiation from the emitter after absorption by pulsatile blood flowing within the tissue site. The emitter and detector are incorporated within a cable assembly adapted to provide electrical communications between the emitter and detector and a monitor. The detector is EMI shielded so as to reduce electromagnetic noise, and the EMI shielded detector is optically shielded with an opaque, flexible housing so as to reduce optical noise from ambient and piped light. The cable assembly is disposed within a tape assembly adapted to attach the emitter and detector to a tissue site. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-C  are assembled top plan, assembled perspective and packaged perspective views, respectively, of a pulse oximetry sensor; 
         FIG. 2  is an exploded perspective view of a pulse oximetry sensor; 
         FIGS. 3A-D  are shielded bottom, untaped top, untaped side and taped bottom views, respectively, of a cable assembly; 
         FIGS. 4A-F  are unassembled bottom, unfolded bottom, folded top, folded side, folded bottom and light barrier covered top views, respectively, of a shielded detector assembly; 
         FIGS. 5A-B  are unassembled and assembled bottom plan views, respectively, of a housing assembly; 
         FIGS. 6A-D  are top plan views of a tape assembly; 
         FIGS. 7A-H  are top perspective, bottom perspective, top, back, side, side cross sectional, bottom, and back cross sectional views, respectively, of a housing. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1A-C  illustrate a pulse oximetry sensor  100  having a body  110 , a cable  120  and a connector  130 . The body  110  is configured to wrap around a fingertip and incorporates an emitter  310  ( FIG. 2 ) and a detector  350  ( FIG. 2 ) that provide physiological measurements responsive to a patient&#39;s blood oxygen saturation, as described above. The body  110  also incorporates a flexible housing  700  configured to enclose a shielded detector assembly  400  ( FIG. 2 ). Advantageously, the flexible housing  700  optically shields the detector  350  ( FIG. 2 ), blocking ambient and piped light. The cable  120  provides electrical communication between the emitter  310  ( FIG. 2 ) and detector  350  ( FIG. 2 ) and the connector  130 . The connector  130  is adapted to a patient cable, which electrically and mechanically connects the sensor  100  to a monitor (not shown). 
       FIG. 2  further illustrates a pulse oximetry sensor  100  having a cable assembly  300 , a shielded detector assembly  400 , a housing assembly  500 , a tape assembly  600  and a flexible housing  700 . The cable assembly  300  has the cable  120 , the emitter  310 , the shielded detector assembly  400  and insulating tape  390 , as described in detail with respect to  FIGS. 3A-D . The shielded detector assembly  400  has the detector  350 , an electromagnetic interference (EMI) shield  401  and a light barrier  440 , as described in detail with respect to  FIGS. 4A-F . The housing assembly  500  has the cable assembly  300  and the flexible housing  700 , as described in detail with respect to  FIGS. 5A-B . The tape assembly  600  has a face tape  610 , a trifold wrap  620  and a release liner  630 , as described in detail with respect to  FIGS. 6A-D . The flexible housing  700  is described in detail with respect to  FIGS. 7A-H . 
       FIGS. 3A-D  illustrate a cable assembly  300  having an emitter  310 , a shielded detector assembly  400  and a cable  120 . The detector  350  is incorporated within the shielded detector assembly  400 . The cable  120  has an emitter portion  122  and a detector portion  124 . A pair of emitter wires  123  extend from the emitter portion  122  and are soldered to corresponding emitter leads  312 . A pair of detector wires  125  extend from the detector portion  124  and are soldered to corresponding detector leads  352 . A cable shield  126  also extends from the detector portion  124  and is dressed for attachment to the EMI shield  401  ( FIGS. 4A-B ), as described below. As shown in  FIG. 3D , insulating tape  390  is wrapped around the emitter wires  123  and emitter leads  312  at the emitter portion  122  and wrapped around the detector wires  125  and detector leads  352  at the detector portion  124 . 
       FIGS. 4A-F  illustrate a shielded detector assembly  400  having a detector  350 , insulating tape  390  and an EMI shield  401 . The EMI shield  401  has a front portion  410 , a foldable back portion  420  and a cable portion  430 . The front portion  410  is disposed between the back  420  and the cable  430  portions. A conductive grid  450  is disposed on the front portion  410 . Foldable sides  440  extend from the side edges of the front portion  410  and the cable portion  430 . Tabs  442  extend from some of the foldable sides  440 . An aperture  432  is defined in the cable portion  430 . 
     As shown in  FIG. 4A , the detector  350  is placed on the inside of the EMI shield  401  so that the light sensitive areas of the detector  350  are proximate the grid  450 . As shown in  FIG. 4B , the back portion  420  and the sides  440  are folded back to cover the detector  350 . As shown in  FIGS. 4C-E , the tabs  442  secure the sides  440  and the back  420  in a closed position. The EMI shield  401  reduces electromagnetic interference at the detector  350 . The grid  450  allows light from the emitter  410  that is attenuated by tissue to pass through to the detector  350 . The cable shield  126  is placed through the aperture  432  and soldered or otherwise electrically connected to the cable portion  430  of the EMI shield  401 . Any excess cable shield  126  is trimmed. As shown in  FIG. 4F , a light barrier  440  is placed over the back of the EMI shield  401 . In one embodiment, the light barrier  440  is a metal foil, such as aluminum. 
       FIGS. 5A-B  illustrate a housing assembly  500  having a cable assembly  300  attached to a flexible housing  700 . The cable assembly  300  has an emitter  310  and the shielded detector assembly  400 , as described above with respect to  FIGS. 3A-D  and  FIGS. 4A-F , respectively. The housing  700  has an aperture  750  and an opening  760 . The shielded detector assembly  400  is inserted into the housing  700  through the opening  760  and secured within a pocket  770  ( FIG. 7F ) so that the grid  450  is aligned with the aperture  750 . The aperture  750  allows emitted light to pass to the detector  350  ( FIG. 2 ) via the grid  450 . 
       FIGS. 6A-D  illustrate a tape assembly  600  having a face tape  610 , a trifold wrap  620  and a release liner  630 . As shown in  FIG. 6A , the trifold wrap  620  has a center portion  621  disposed between foldable side portions  625 , which are symmetrical about the center portion  621 . The center portion  621  has an emitter aperture  622  and a detector aperture  624 . The emitter aperture  622  passes light from the emitter  310  ( FIG. 6B ) and the detector aperture  624  passes light to the detector  350  (not visible). The side portions  625  have cutouts  626  configured to accommodate the housing  700  when the side portions  625  are folded. The trifold wrap  620  has a pressure sensitive adhesive (PSA) on the component side and a Med  3044  adhesive on the center portion  621  of the patient side. The release liner  630  is removably attached to the patient side of the trifold wrap  620 . 
     As shown in  FIG. 6B , the housing assembly  500  is attached to the center portion  621  on the side opposite the release liner  630  so that the emitter  310  is aligned with the emitter aperture  622  and the housing aperture  750  ( FIG. 5B ) is aligned with the detector aperture  624 . As shown in  FIG. 6C , the side portions  625  are folded around the housing assembly  500  so that the housing  700  protrudes through the cutouts  626 . As shown in  FIG. 6D , the face tape  610  is fixedly attached to the trifold wrap  620  and removably attached to the release liner  630 . A face tape aperture  612  also accommodates the protruding housing  700 . In one embodiment, the trifold wrap  620  is polypropylene and the face tape  610  is a laminate of Bioflex RX848P and 3M 1527ENP. 
       FIGS. 7A-H  illustrate a housing  700  that advantageously functions as both a light barrier and an optical cavity and is flexible and easy to manufacture. In one embodiment, the housing is injection molded as single piece of opaque, gray, medical grade PVC. As shown in  FIGS. 7A-H , the housing  700  has a base  710 , a cover  720 , a cable strain relief  730 , and a flange portion  740  of the base  710  disposed around the periphery of the cover  720 . The cover  720  defines a pocket  770 , which receives the detector assembly  400  ( FIGS. 4A-F ), as described above with respect to  FIGS. 5A-B . The base  710  defines a generally centered, generally circular aperture  750  and an opening  760  for the pocket  770 . The flange  740  provides a structure for securing the housing  700  to the trifold wrap  620  ( FIGS. 6A-D ). The pocket  770  is raised above the base  710 , which advantageously recesses the detector  350  ( FIG. 2 ) to reduce ambient and piped light from entering the detector  350  ( FIG. 2 ) from the sides. In particular, the aperture  750  provides an optical cavity that allows optical radiation from the emitter  310  ( FIG. 2 ) that propagates through the tissue site to reach the detector  350  ( FIG. 2 ), while rejecting optical noise sources. 
     Further shown in  FIGS. 7A-H , the housing  700  has a width  712 , a length  714 , a cover thickness  702 , a side angle  772 , a front angle  724  and a back angle  726 . In one embodiment, the width  712  is about 0.44 inches, the length  714  is about 0.598 inches, the cover thickness  702  is about 0.02 inches, the side angle  722  is about 5°, the front angle  724  is about 10° and the back angle  726  is about 52.5°. Further, the aperture diameter  752  is about 0.117 inches, the pocket width  762  is about 0.2 inches and the cover height  728  is about 0.14 inches. 
     A pulse oximetry sensor 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.