Pulse oximetry sensor

[0001] 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.

[0002] Pulse oximetry is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of a person'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'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.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0014] 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'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).

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.