Medical device with optical module

Abstract

An implantable medical device (IMD) comprising a first light emitter arranged to generate a first light beam of emitted light, a second light emitter arranged to generate a second light beam of emitted light, a light detector arranged to sense backscattered light, and at least one optical layer comprising a light beam directing feature and / or a crosstalk feature.

Description

Cross Reference to Related Applications

[0001] This application claims priority to U.S. Patent Application 63 / 535,258, filed August 29, 2023, which is incorporated by reference in its entirety. TECHNICAL FIELD

[0002] Examples of the present disclosure relate to medical devices and systems that sense physiological parameters using optical sensors. BACKGROUND

[0003] Implantable medical devices (IMDs) can be configured to sense physiological parameters and / or provide therapy. Examples of IMDs include implantable cardiac monitors, implantable loop recorders, and the like, which can be configured to be implanted subcutaneously in a patient to monitor one or more physiological parameters, such as physiological parameters associated with the heart and / or lungs. SUMMARY

[0004] In Example 1, an implantable medical device (IMD) comprising: a first light emitter arranged to generate a first light beam of emitted light; a second light emitter arranged to generate a second light beam of emitted light; a light detector arranged to sense backscattered light in response to the first light beam and the second light beam; and at least one optical layer comprising a beam steering feature and / or a cross-talk feature.

[0005] In Example 2, the IMD of Example 1, wherein the beam steering feature is a lens or a grating.

[0006] In Example 3, the IMD of Example 1, wherein the beam steering feature is a Fresnel lens.

[0007] In Example 4, the IMD of any of Examples 1-3, further comprising a first wall positioned between the first light emitter and the light detector, wherein the first wall is arranged to at least partially block non-backscattered light.

[0008] In Example 5, the IMD of Example 4, wherein the first wall is positioned between the second light emitter and the detector.

[0009] In Example 6, the IMD of any of Examples 1-4, further comprising a second wall positioned between the second light emitter and the light detector.

[0010] In Example 7, the IMD of any of Examples 1-6, wherein the cross-talk feature is a region of dark material.

[0011] In Example 8, the IMD of any of Examples 1-7, wherein the first emitter and the second emitter are part of a single integrated circuit package.

[0012] In Example 9, the IMD of any of Examples 1-8, wherein the first emitter and the second emitter are light emitting diodes.

[0013] In Example 10, the IMD of any of Examples 1-9, wherein the first emitter, the second emitter, and the detector have respective top surfaces facing a bottom surface of the optical layer.

[0014] In Example 11, the IMD of any of Examples 1-10, wherein the cross-talk feature includes a plurality of filter layers.

[0015] In Example 12, the IMD of any of Examples 1-11, wherein the first light emitter, the second light emitter, and the detector are coupled to a single circuit board.

[0016] In Example 13, the IMD of any of Examples 1-12, wherein an edge of the first light emitter is positioned 3-6 mm from an adjacent edge of the detector.

[0017] In Example 14, the IMD of any of Examples 1-13, wherein the first light beam includes infrared light, wherein the second light beam includes red light.

[0018] In Example 15, the IMD of any of Examples 1-14, wherein the emitter and the detector are part of an optical module positioned within a housing of the IMD.

[0019] In Example 16, an IMD includes an optical module. The optical module includes: a first light emitter arranged to generate a first light beam of emitted light; a second light emitter arranged to generate a second light beam of emitted light; a light detector arranged to sense backscattered light in response to the first light beam and the second light beam; and at least one optical layer including a beam steering feature and / or a cross-talk feature.

[0020] In Example 17, the IMD of Example 16, wherein the at least one optical layer includes the beam steering feature, and wherein the beam steering feature is a lens or a grating.

[0021] In Example 18, the IMD of Example 16, wherein the at least one optical layer includes the beam steering feature, and wherein the beam steering feature is a Fresnel lens.

[0022] In Example 19, the IMD of Example 16, further comprising a first wall positioned between the first light emitter and the light detector, wherein the first wall is arranged to at least partially block non-backscattered light.

[0023] In Example 20, the IMD of Example 19, wherein the first wall is positioned between the second light emitter and the detector.

[0024] In Example 21, the IMD of Example 19, further comprising a second wall positioned between the second light emitter and the light detector.

[0025] In Example 22, the IMD of Example 16, wherein the at least one optical layer comprises a cross-talk feature, wherein the cross-talk feature is a dark material region.

[0026] In Example 23, the IMD of Example 16, wherein the first emitter and the second emitter are light emitting diodes.

[0027] In Example 24, the IMD of Example 16, wherein the at least one optical layer comprises a cross-talk feature, wherein the cross-talk feature comprises a plurality of filter layers.

[0028] In Example 25, the IMD of Example 16, wherein the first light emitter, the second light emitter, and the detector are coupled to a single circuit board.

[0029] In Example 26, the IMD of Example 16, wherein an edge of the first light emitter is positioned 3 mm to 6 mm from an adjacent edge of the detector.

[0030] In Example 27, the IMD of Example 16, wherein the first light beam comprises infrared light, wherein the second light beam comprises red light.

[0031] In Example 28, the IMD of Example 16, further comprising a housing and an electrode, wherein the optical module is positioned within the housing, wherein the electrode is coupled to the housing.

[0032] In Example 29, the IMD of Example 16, wherein the at least one optical layer is part of a single window, wherein the single window is arranged such that the first light beam, the second light beam, and the backscattered light pass through the single window.

[0033] In Example 30, the IMD of Example 29, further comprising a single seal around a perimeter of the single window.

[0034] In Example 31, the IMD of Example 16, wherein the optical module is configured to consume a maximum of 5 milliamps of power during operation.

[0035] In Example 32, the IMD of Example 16, wherein the light detector is a single light detector, wherein the light detector is the only light detector of the IMD.

[0036] In Example 33, an IMD having an optical module, comprising: a first light emitter arranged to generate a first light beam of emitted light; a second light emitter arranged to generate a second light beam of emitted light; a light detector arranged to sense backscattered light in response to the first light beam and the second light beam; and means for directing the first light beam and the second light beam.

[0037] In Example 34, the IMD of Example 33, further comprising means for reducing interference with the backscattered light.

[0038] In Example 35, the IMD of Example 34, wherein the first light beam comprises infrared light, wherein the second light beam comprises red light.

[0039] While a number of embodiments have been disclosed herein, other embodiments will become apparent to those skilled in the art upon reading the following detailed description, and to the accompanying drawings. The detailed description is presented only for the purpose of illustrating illustrative embodiments of the present application. Therefore, the drawings and detailed description are to be regarded as illustrative in nature rather than restrictive. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a schematic diagram depicting an illustrative medical system in accordance with certain examples of the present disclosure.

[0041] Figure 2 An implantable medical device in accordance with certain examples of the present disclosure is shown.

[0042] Figure 3 A side cross-sectional view of a portion of an optical sensor assembly in accordance with certain examples of the present disclosure is shown.

[0043] Figure 4 A side cross-sectional view of a portion of an optical sensor assembly in accordance with certain examples of the present disclosure is shown.

[0044] Figure 5 A top view of a portion of an optical sensor assembly in accordance with certain examples of the present disclosure is shown.

[0045] Figure 6A and Figure 6B Different arrangements of an optical sensor assembly in accordance with certain examples of the present disclosure are shown.

[0046] While the application is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail in the following description. It should be understood, however, that the intention is not to limit the application to the particular examples described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the application as defined by the appended claims. DETAILED DESCRIPTION

[0047] Optical sensor devices can be used to measure physiological parameters, such as oxygen saturation in blood. For example, an optical sensor device can be placed on a body part of a person (e.g., a finger, an earlobe) such that light passes through the body part to an optical sensor. The oxygen saturation of the person can be estimated based on how the light is absorbed when it passes through blood flowing in the body part. However, the measurement accuracy of these types of external optical sensor devices can be negatively affected by iron deficiency of the person, their skin pigmentation, ambient light, etc.

[0048] Accordingly, certain examples of the present disclosure are directed to optical sensor devices that can be implanted in a patient’s body. Medical device system

[0049] Figure 1 An illustrative medical device system 100 is shown that includes an implantable medical device 102 (hereinafter referred to for brevity as an “IMD”) configured to be implanted in the body of a subject 104 and an external receiver or monitoring device 106 (EMD). In Figure 1 In examples, the IMD 102 and the EMD 106 are configured to communicate with each other over a communication link 108.

[0050] The IMD 102 can be implanted subcutaneously in an implant location or pocket in the chest or abdomen of the patient and can be configured to monitor (e.g., sense and / or record) one or more physiological parameters. The IMD 102 can be an implantable cardiac monitor (ICM) (e.g., an implantable diagnostic monitor (IDM), an implantable loop recorder (ILR)) configured to record physiological parameters such as, for example, one or more cardiac electrical signals, heart sounds, heart rate, blood pressure measurements, etc. For example, the IMD 102 can include sensors or circuitry to detect respiratory system signals, cardiac system signals, heart sounds.

[0051] The EMD 106 can be a device configured to be carried with the subject 104, e.g., by being integrated into a vest, belt, harness, patch; placed in a pocket, purse, or backpack; held in the subject's hand; and / or the like, or otherwise operatively (and / or physically) coupled to the subject 104. The EMD 106 can be configured to receive data from the IMD 102 and / or monitor physiological parameters associated with the subject 104 and / or provide therapy to the subject 104. In some cases, the EMD 106 is a cellular phone or other device having a user interface that can be used to view aspects of the physiological parameters recorded by the IMD 102.

[0052] The IMD 102 includes an optical sensor assembly 110, which can be used to sense one or more physiological parameters, as described in greater detail below. Implantable medical device

[0053] Figure 2 is a side view of a medical device 200 (hereinafter referred to as "IMD 200"). The IMD 200 can be or can be similar to the IMD 102 depicted in Figure 1 and can be used in the system 100 of Figure 1 .

[0054] The IMD 200 includes an outer housing extending between a first end 202 and a second end 204. When assembled, the outer housing can form a sealed enclosure. The IMD 200 can include one or more electrodes 206, 208 for sensing electrical activity of a patient. The IMD 200 can also include features such as an antenna for communicating with external devices, a battery for powering electrical components of the IMD 200, and circuitry.

[0055] Figure 2 The IMD 200 is shown with an optical sensor assembly or optical module 210 (hereinafter referred to as "optical module 210" for brevity). In some cases, the IMD 200 includes features described in U.S. Patent Application No. 15 / 242,470, which is incorporated by reference herein in its entirety, and adds the optical module described herein. Optical module

[0056] Figure 3A side cross-sectional view of one example of an optical module 210 is shown. The optical module 210 includes one or more emitters 212 (hereinafter “emitters 212”) and one or more detectors 214 (hereinafter “detectors 214”). The optical module 210 includes one or more optical layers 216 (hereinafter “optical layers 216”) that allow light to pass through (e.g., like a window) but protect the emitters 212 and detectors 214 from the environment outside of the optical module 210 or IMD 200. As shown, both the emitters 212 and detectors 214 have a top surface (e.g., an emission surface for the emitters 212 and a detection surface for the detectors 214) that faces a bottom surface of the optical layers 216. In some cases, the optical layers 216 (with their one or more layers) create a common window for both light exiting and entering the optical module 210, while in other cases, the optical layers 216 include separate windows (e.g., one or more layers for light exiting and one or more layers for light entering the optical module 210). In either case, as discussed below, one or more portions of the optical layers 216 can have different properties or characteristics (e.g., beam directing / filtering / blocking properties or characteristics) than other portions of the optical layers 216. An example with a common window can only require one seal 217 (e.g., a seal around the perimeter as shown), which can be preferable for manufacturability and reliability. Whether using one window or multiple windows, the window(s) can include glass, sapphire, etc. Figure 3 Figure 2 As shown, both the emitters 212 and detectors 214 have a top surface (e.g., an emission surface for the emitters 212 and a detection surface for the detectors 214) that faces a bottom surface of the optical layers 216. In some cases, the optical layers 216 (with their one or more layers) create a common window for both light exiting and entering the optical module 210, while in other cases, the optical layers 216 include separate windows (e.g., one or more layers for light exiting and one or more layers for light entering the optical module 210). In either case, as discussed below, one or more portions of the optical layers 216 can have different properties or characteristics (e.g., beam directing / filtering / blocking properties or characteristics) than other portions of the optical layers 216. An example with a common window can only require one seal 217 (e.g., a seal around the perimeter as shown), which can be preferable for manufacturability and reliability. Whether using one window or multiple windows, the window(s) can include glass, sapphire, etc.

[0057] As described in more detail below, the emitters 212 (e.g., one or more light sources such as light emitting diodes) can be selectively powered such that the emitters 212 emit light out of the optical module 210 and toward tissue of a patient. At least some of the light will be reflected back (e.g., backscattered light) to the optical module 210 and sensed by the detectors 214 (e.g., one or more light sensors such as photodetectors or another type of light sensor). The IMD 200 can use the sensed backscattered light to measure a physiological parameter such as the blood oxygen content (e.g., Sp02) of the patient.

[0058] There are multiple challenges with emitting and sensing backscattered light with an optical sensing device. One challenge is directing sufficient backscattered light to the detectors 214, which is due to light being reflected back in directions that are not aligned with the detectors 214 such that the reflected light cannot be sensed by the detectors 214. To help address this challenge, the optical module 210 can incorporate one or more beam directing features 218.

[0059] ​One example beam-directing feature 218 is a lens (e.g., a Fresnel lens, a contact lens). The lens can be incorporated into the optical layer proximate the emitter 212. The lens can direct or focus light in a direction that increases the amount of backscattered light that will eventually be reflected back to and sensed by the detector 214. Because lenses such as Fresnel lenses can have rough surfaces, the lens can be covered by another layer of optical material to produce a smooth outer surface for the optical module 210. Another example beam-directing feature 218 is a grating designed to direct light in a direction that increases the amount of backscattered light that will be reflected back to and sensed by the detector 214.

[0060] Another challenge for optical sensing devices is that non-backscattered light can interfere with backscattered light. For example, not all light from the emitter 212 can exit the optical module 210, which can result in interference with backscattered light. To help address this challenge, the optical module 210 can incorporate one or more crosstalk features into the optical layer 216. The example crosstalk features described below are not mutually exclusive and can be used with one another. Similarly, the optical module 210 can use both one or more crosstalk features and one or more beam-directing features 218.

[0061] As one example of a crosstalk feature, the material and / or dimensions (e.g., thickness) of the optical layer 216 and / or the relative position of the optical layer 216 relative to the emitter 212 and the detector 214 can be selected to reduce the risk of crosstalk. The relative positions of the optical layer 216, the emitter 212, and the detector 214 can be selected so that light is less likely to reflect back toward the emitter 212. In other words, the selection of the relative positions of the optical layer 216, the emitter 212, and the detector 214 can help control the amount of light that is internally reflected due to its angular relationship with the critical angle of the optical layer 216.

[0062] As another example of a crosstalk feature, the optical layer 216 can include a segment 220 (in Figure 3(Indicated by dashed lines). Some of the emitted light can be “captured” in optical layer 216 and directed toward a portion of optical layer 216 adjacent to (e.g., directly above) detector 214. Segment 220 can act as a wall or block within optical layer 216 to help prevent backscattered light reflected toward detector 214 from being interfered with by light internally reflected within optical layer 216. For example, segment 220 can include dark areas diffused into optical layer 216. This segment 220 of dark material can function as a wall through which internally reflected light cannot pass. Additionally or alternatively, optical module 210 can include one or more walls 222 positioned between emitter 212 and detector 214 such that emitted light does not travel within optical module 210 from the housing portion of the emitter to the housing portion of the detector.

[0063] Figure 4 An example layer structure is shown to help prevent light interference with backscattered light. For example... Figure 4 As shown in the side view, optical layer 216 comprises multiple layers. The number and arrangement of the layers can be... Figure 4 The difference is shown in the diagram. This layer may include an anti-reflective material layer 224 closest to the emitter 212 and detector 214. One or more filter layers 226, 228, and 230 may be positioned between the anti-reflective layer 224 and the optical substrate 232. Filter layers 226-230 may be designed to help prevent light generated from sources outside the optical module 210 from reaching the detector 214 and / or to tune the light generated by the emitter 212. If the IMD 200 is oriented such that the optical module 210 is close to and faces the patient's skin, light such as sunlight can pass through the patient and reach the optical module 210. Therefore, filter layers 226-230 may each be designed / selected to filter out certain undesired wavelengths of light (e.g., sunlight, fluorescence) most likely to reach the optical module 210. Additionally or alternatively, one or more filters may be directly coupled to the emitter 212 and / or detector 214. As previously described, a portion of optical layer 216 may have features (e.g., one or more filters, doping) that are different from other portions of optical layer 216. Therefore, the portion of optical layer 216 directly above emitter 212 may use one or more types of filters that are different from the portion of optical layer 216 directly above detector 214.

[0064] Figure 5 A top view is shown of a portion of an optical sensor assembly or optical module 300 (hereinafter referred to as "optical module 300" for simplicity), which can be incorporated into, for example... Figures 1 to 4 In the IMDs of 100 and 200. Therefore, Figures 2 to 4 The feature shown can be with Figure 5 The features shown are used together.

[0065] Figure 5 The optical module 300 includes multiple sets of transmitters. For example, the optical module 300 includes a first set of transmitters 302A, a second set of transmitters 302B, and a third set of transmitters 302C. The optical module 300 also includes one or more detectors 304 (e.g., photodetectors or other types of light sensors).

[0066] Each group of emitters may include an infrared emitter 306 and one or more visible light emitters, such as a blue light emitter 308, a green light emitter 310, and / or a red light emitter 312. Although Figure 5 An infrared emitter 306 is shown as part of an integrated circuit package 314, and a visible light emitter is shown as part of another integrated circuit package 316; however, the emitters may all be integrated into a single package or a separate package. The optical module 300 also includes a wall 318, which helps prevent light from the emitters from interfering with the backscattered light directed at the detector 304. Each of the above components may be attached to a substrate 320, such as a printed circuit board or a flexible circuit board. When completed, the substrate 320 may be positioned within the IMD or subsequently incorporated into a separate module within the IMD. In some cases, the substrate 320 is a single substrate to which all the above components are attached; however, in other cases, the components may be attached to separate substrates.

[0067] During use, the transmitters can be selectively powered to emit light. In some cases, the transmitters are selectively powered to determine which transmitter or group of transmitters provides the optimal amount (or highest quality) of backscattered light to detector 304. Because each transmitter has a different position relative to detector 304, each transmitter will produce a different optical path from the corresponding transmitter to detector 304. The transmitters can be cycled one by one, group by group, or by some combination thereof to determine which transmitter(s) should be used to measure and record physiological parameters. For example, one or more transmitters in the first group of transmitters 302A can be powered first, followed by the second group of transmitters 302B, and then the third group of transmitters 302C. The circuitry or logic in an IMD, EMD, or other device can determine which group of transmitters provides the optimal amount (or highest quality) of backscattered light to detector 304 compared to the other groups. For example, the transmitter that produces the highest measurement amplitude can ultimately be selected for measuring and recording physiological parameters. With multiple detectors 304, different emitter-detector combinations can be tested to see which produces the optimal amount (or highest quality) of sensed backscattered light.

[0068] Figure 6A and 6B Other example optical modules are shown, which can be incorporated into, for example... Figures 1 to 4of the IMD 100 and 200. Thus, Figures 1 to 5 The features shown in FIGS. 1-3 can be used with the features shown in Figure 6A and 6B The features shown in FIGS. 1-3 can be used with the features shown in

[0069] From Figure 6A Optical module 400 includes a first emitter 402A, a second emitter 402B, one or more detectors 404, a first wall 406A, and a second wall 406B, all of which can be coupled to one or more substrates 408. Although only two emitters and one detector are shown in Figure 6A Additional emitters and detectors can be used.

[0070] In certain embodiments, first emitter 402A is a light emitting diode (LED) designed to emit red light (e.g., a wavelength of about 620 nm to 750 nm), while second emitter 402B is a LED designed to emit infrared light (e.g., a wavelength of about 800 nm to 1 mm). First emitter 402A and second emitter 402B can be spaced apart from detector 404 along a longitudinal axis 410 of optical module 400 or an IMD. In the example of Figure 6A detector 404 is positioned between first emitter 402A and second emitter 402B, and respective walls 406A and 406B are each positioned between detector 404 and one of emitters 402A and 402B. In some cases, an edge of first emitter 402A and an edge of second emitter 402B are positioned 3 mm to 6 mm (e.g., 4 mm, 5 mm) from an edge of detector 404 (e.g., along longitudinal axis 410, such as a central longitudinal axis of optical module 400). This range of distances has been found to be sufficient for detector 404 to receive sufficient backscattered light from tissue. Although each of the above components is shown as being coupled to a single substrate 408 (e.g., a single printed circuit board or a single flexible circuit board), the components can be attached to different substrates. Because the IMD is designed to be compact and because the emitters and detector(s) should be spaced apart from one another, the space between the emitters and detector(s) can be used for other components of optical module 400 or the IMD. Thus, the respective emitters and detector(s) can be coupled to separate substrates, such that other components can be more easily positioned between the emitters and detector(s).

[0071] Figure 6B Optical module 400 is shown with a first emitter 402A and a second emitter 402B positioned on a first side of the optical module and a detector 404 positioned on a second side of the optical module. Figure 6AMost of the components are the same as shown in FIG. 1, but are rearranged for a more compact design. Because the first emitter 402A and the second emitter 402B are arranged on the same side of the detector 404, the total length of the optical module 400 can be reduced compared to the design of FIG. 1. In some cases, the edge of the first emitter 402A and the edge of the second emitter 402B are positioned 3 mm to 6 mm (e.g., 4 mm, 5 mm) from the edge of the detector 404 (e.g., along the longitudinal axis 410, such as the central longitudinal axis of the optical module 400). Figure 6A The total length of the optical module 400 can be reduced compared to the design of FIG. 1. In some cases, the edge of the first emitter 402A and the edge of the second emitter 402B are positioned 3 mm to 6 mm (e.g., 4 mm, 5 mm) from the edge of the detector 404 (e.g., along the longitudinal axis 410, such as the central longitudinal axis of the optical module 400).

[0072] In any of the examples described above, the emitters can be selected and operated under certain constraints. For example, the emitters can be operated such that surrounding tissue is not heated by the emitted light from the optical module. As another example, the emitters can be collectively powered (e.g., at any given point in time) by no more than 5 mA of current to conserve power and help prevent heat generation.

[0073] Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present application. For example, while the embodiments described above refer to particular features, the scope of this application also includes embodiments that do not include all of these features. Thus, embodiments of the present application can include any combination of the features described above. Accordingly, the scope of the present application is intended to embrace all such alternatives, modifications and variations as falling within the scope of the claims, together with all equivalents thereof.

Claims

1. An implantable medical device (IMD), comprising: A first light emitter is arranged to generate a first beam of emitted light; A second light emitter is arranged to generate a second beam of emitted light; A photodetector, the photodetector being arranged to sense backscattered light in response to the first beam and the second beam; as well as At least one optical layer, including a beam guiding feature and / or a crosstalk feature.

2. The IMD according to claim 1, wherein, The beam guiding feature is a lens or a grating.

3. The IMD according to claim 1, wherein, The beam guiding feature is a Fresnel lens.

4. The IMD according to any one of claims 1 to 3, further comprising a first wall positioned between the first light emitter and the photodetector, wherein, The first wall is arranged to at least partially block non-backscattered light.

5. The IMD according to claim 4, wherein, The first wall is positioned between the second light emitter and the detector.

6. The IMD according to any one of claims 1 to 4, further comprising a second wall positioned between the second light emitter and the photodetector.

7. The IMD according to any one of claims 1 to 6, wherein, The crosstalk feature is a dark material region.

8. The IMD according to any one of claims 1 to 7, wherein, The first transmitter and the second transmitter are part of a single integrated circuit package.

9. The IMD according to any one of claims 1 to 8, wherein, The first emitter and the second emitter are light-emitting diodes.

10. The IMD according to any one of claims 1 to 9, wherein, The first transmitter, the second transmitter, and the detector have corresponding top surfaces facing the bottom surface of the optical layer.

11. The IMD according to any one of claims 1 to 10, wherein, The crosstalk feature includes multiple filter layers.

12. The IMD according to any one of claims 1 to 11, wherein, The first light emitter, the second light emitter, and the detector are coupled to a single circuit board.

13. The IMD according to any one of claims 1 to 12, wherein, The edge of the first light emitter is positioned 3 mm to 6 mm from the adjacent edge of the detector.

14. The IMD according to any one of claims 1 to 13, wherein, The first beam includes infrared light, while the second beam includes red light.

15. The IMD according to any one of claims 1 to 14, wherein, The transmitter and the detector are part of an optical module located within the housing of the IMD.

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