Abstract:
The present disclosure relates to the acquisition and use of an arterial pulse signal that may be used to synchronize the measurement of other physiological characteristics. In one embodiment, a sensor is provided that emits light toward a pulsing artery and detects the transmitted light to generate a signal representative of the amount of light detected. In another embodiment, a sensor is provided that acquires physiological data from a first emitter and first detector placed proximate to a perfused tissue site and acquires arterial pulse data from a second emitter and second detector placed proximate to an artery. Embodiments related to systems, tangible media, and methods of operation are also provided.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority from U.S. Patent Application No. 61/009,453 which was filed on Dec. 28, 2007, and is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally to medical devices and, more particularly, to sensors used for sensing physiological parameters of a patient. 
         [0003]    This section is intended to introduce the reader to various aspects of art that may be related to various aspects of disclosed embodiments, 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. 
         [0004]    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. 
         [0005]    Non-invasive medical devices may be particularly useful and desirable, as they generally provide immediate feedback and do not traumatize a patient. For example, certain types of non-invasive sensors transmit electromagnetic radiation, such as light, through a patient&#39;s tissue. Such sensors photoelectrically detect the absorption and/or scattering of the transmitted or reflected light in the tissue. The light emitted into the tissue is typically selected to be of one or more wavelengths that may be absorbed and scattered by particular tissue constituents under investigation. One or more physiological characteristics may then be calculated based upon the amount of light absorbed and/or scattered as the light passes through tissue. 
         [0006]    For example, one such non-invasive 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. In fact, the “pulse” in pulse oximetry refers to the time varying amount of arterial blood in the tissue during each cardiac cycle. 
         [0007]    Pulse oximetry readings measure the pulsatile, dynamic changes in amount and type of blood constituents in tissue. However, events other than the pulsing of arterial blood, such as noise caused by patient motion, may lead to modulation of the light path, direction, and/or the amount of light detected by the sensor, introducing error to the measurements. As a result, pulse oximetry measurements that are performed in the presence of patient motion may suffer due to the arterial portion of the signal being overwhelmed, obscured or distorted by the portion of the signal attributable to the patient motion. 
       SUMMARY 
       [0008]    Certain aspects commensurate in scope with this disclosure are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms any claimed invention might take and that these aspects are not intended to limit the scope of any claimed invention. Indeed, any claimed invention may encompass a variety of aspects that may not be set forth below. 
         [0009]    According to an embodiment, there may be provided a sensor. The sensor may comprise an emitter configured to emit light toward a pulsing artery. The sensor may also comprise a detector configured to detect the transmitted or reflected light and to generate a signal representative of the amount of light detected. 
         [0010]    According to an embodiment, there may be provided a sensor. The sensor may comprise a first emitter and a first detector configured to optically acquire physiological data when placed proximate to a perfused tissue site. The sensor may also comprise a second emitter and a second detector configured to optically acquire arterial pulse data when placed proximate to an artery. 
         [0011]    According to an embodiment, there may be provided a monitoring system. The monitoring system may comprise a processor. The processor may be configured to process data representing a physiological characteristic of interest and data representing an arterial pulse. The processor may also be configured to generate a measure of the physiological characteristic of interest based upon the processed physiological characteristic and pulse data. 
         [0012]    According to an embodiment, there may be provided a method for measuring a physiological characteristic. The method may includes the acts of acquiring data related to a physiological characteristic of interest and of acquiring data related to an arterial pulse. The arterial pulse may be derived from the data related to the arterial pulse. A measure of the physiological characteristic of interest may be derived using the data related to a physiological characteristic and the arterial pulse. 
         [0013]    According to an embodiment, there may be provided one or more tangible media encoded with a processor-executable program. The program may comprise code for deriving an arterial pulse based upon data acquired from a sensor or part of a sensor placed proximate to an artery. The program may also comprise code for deriving a measure of a physiological characteristic of interest based upon data acquired related to the physiological characteristic and upon the arterial pulse. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Advantages of this disclosure may become apparent upon reading the following detailed description and upon reference to the drawings in which: 
           [0015]      FIG. 1  illustrates a patient monitoring system coupled to a multi-parameter patient monitor and corresponding sensors, in accordance with aspects of an embodiment; 
           [0016]      FIG. 2  is a block diagram of a monitoring system, in accordance with aspects of an embodiment; 
           [0017]      FIG. 3  is a block diagram of a monitoring system, in accordance with aspects of a further embodiment; 
           [0018]      FIG. 4  is a block diagram of a monitoring system, in accordance with aspects of an additional embodiment; and 
           [0019]      FIG. 5  is a block diagram of a monitoring system, in accordance with aspects of another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    One or more specific embodiments 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. 
         [0021]    In accordance with the present disclosure, systems for pulse oximetry, or other applications utilizing spectrophotometry, may be provided that identify arterial pulses using optical or other techniques. In certain embodiments, this identification is performed utilizing data obtained from a sensor package configured to acquire the arterial pulse data. In certain embodiments, this sensor package may be separate from or part of an existing sensor package for measuring a physiological parameter, such as a pulse oximeter sensor. 
         [0022]    For example, referring now to  FIG. 1 , a pulse sensor  8  and physiological sensor  10  according to the present invention may be used in conjunction with a patient monitor  12 . In the depicted embodiment, a cable  14  connects both the pulse sensor  8  and the physiological sensor  10  to the patient monitor  12 . In other embodiments, the pulse sensor  8  and physiological sensor  10  may be separately connected to the patient monitor  12  by separate respective cables. Likewise, in other embodiments, the components of the pulse sensor  8  and the physiological sensor  10  may be provided in a common sensor package, i.e., as a combined sensor. 
         [0023]    In certain embodiments, one or more of the sensors  8 ,  10  and/or the cable  14  may include or incorporate one or more integrated circuit devices or electrical devices, such as a memory, processor chip, or resistor, that may facilitate or enhance communication between the sensors  8 ,  10  and the patient monitor  12 . Likewise the cable  14  may be an adaptor cable, with or without an integrated circuit or electrical device, for facilitating communication between the sensors  8 ,  10  and various types of monitors, including older or newer versions of the patient monitor  12  or other physiological monitors. In other embodiments, the sensors  8 ,  10  and the patient monitor  12  may communicate via wireless means, such as using radio, infrared, or optical signals. In such embodiments, a transmission device (not shown) may be connected to the sensors  8 ,  10  to facilitate wireless transmission between the sensors  8 ,  10  and the patient monitor  12 . As will be appreciated by those of ordinary skill in the art, the cable  14  (or a corresponding wireless transmission) is typically used to transmit control or timing signals from the monitor  12  to the sensors  8 ,  10  and/or to transmit acquired data from the sensors  8 ,  10  to the monitor  12 . In some embodiments, the cable  14  may be an optical fiber that enables optical signals to be conducted between the patient monitor  12  and the sensors  8 ,  10 . 
         [0024]    In one embodiment, the patient monitor  12  may be a suitable pulse oximeter, such as those available from Nellcor Puritan Bennett LLC and/or Covidien. In other embodiments, the 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, the patient monitor  12  may be a multi-purpose 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 sensors  8 ,  10 . Furthermore, to upgrade conventional monitoring functions provided by the monitor  12  and to provide additional functions, the patient monitor  12  may be coupled to a multi-parameter patient monitor  16  via a cable  18  connected to a sensor input port and/or a cable  20  connected to a digital communication port. 
         [0025]    In the depicted embodiment, the physiological sensor  10  is configured as a transmission-type sensor and includes optical components, such as one or more emitters  22  and a detector  24 , which may be of any suitable type. Likewise, in the depicted embodiment, the pulse sensor  8  is configured as a reflectance-type sensor and includes a respective emitter  26  and detector  28 . In certain embodiments, one or more of the emitters  22 ,  26  may include light emitting diodes adapted to transmit one or more wavelengths of light, such as in the red to infrared range, and one or both of the detectors  24 ,  28  may be photodetectors, such as silicon photodiode packages, selected to receive light in the ranges emitted by the respective emitters  22 ,  26 . 
         [0026]    In the depicted embodiment, the pulse sensor  8  and physiological sensor  10  are jointly coupled to a cable  14  that is responsible for transmitting electrical and/or optical signals to and from the emitters  22 ,  26  and the detectors  24 ,  28 . The cable  14  may be permanently coupled to one or both of the pulse sensor  8  and the physiological the sensor  10 , or it may be removably coupled to one or both of these sensors—the latter alternative being more useful and cost efficient in situations where one or more of the sensors is disposable. Further, as noted above, in certain embodiments, the pulse sensor  8  and the physiological sensor  10  may have separate respective cables  14  such that the sensors are separately connectable to the monitor  12 . 
         [0027]    With the foregoing system description in mind, we refer now to  FIG. 2  where an embodiment of a monitor  12 , pulse sensor  8 , and physiological sensor  10  are discussed. In particular,  FIG. 2  illustrates a block diagram depicting a pulse sensor  8 , physiological sensor  10 , and monitor  12  for use in a monitoring system in accordance with an exemplary embodiment. As previously described the pulse sensor  8  and physiological sensor  10  respectively include one or more emitters  22 ,  24  as well as respective photodetectors  24 ,  28 . In the depicted embodiment, the emitters  22 ,  26  of the respective pulse sensor  8  and physiological sensor  10  are configured to transmit electromagnetic radiation, such as light, into the tissue  40  of a patient. 
         [0028]    In an embodiment where the monitoring system is a pulse oximetry system, the emitters  22  of the physiological sensor  10  may be configured to emit light at wavelengths that are differentially absorbed by oxygenated and deoxygenated hemoglobin, such as at a red and infrared wavelengths. For example, in such a pulse oximetry implementation, the emitter  22  may include two light emitting diodes (LEDs) where one LED emits light at a first wavelength where the absorption of HbO 2  differs from the absorption of reduced Hb. In this example, the second wavelength, i.e., the wavelength of light emitted by the second LED, may be a wavelength where the absorption of Hb and HbO 2  differs from those at the first wavelength. For example, LED wavelengths for measuring normal blood oxygenation levels typically include a red light emitted at approximately 660 nm and an infrared light emitted at approximately 900 nm. In one such an embodiment, the LEDs of the emitter  22  are activated alternately such that only one wavelength is being emitted and detected at a time. 
         [0029]    In one embodiment, the physiological sensor  10  includes a detector  24  configured to detect the scattered and reflected light and to generate a corresponding electrical signal. Examples of such detectors  24  include one or more photodiodes configured to detect light at one or more of the emitted wavelengths of interest. For example, in an embodiment in which emitter  22 , such as a pair of LEDs in an oximetry implementation, only emit light at the wavelengths of interest and in which the emissions alternate, i.e., only light at one wavelength is emitted, a single detector  24  may be provided as long as the detector  24  is configured to detect light at each wavelength of interest. In the depicted embodiment, the physiological sensor  10  is depicted as a reflectance-type sensor, i.e., the emitters  22  and detector  24  are provide on the same side of the tissue  40  and the detector  24  detects lights that enters and exits the same surface of the tissue  40 , i.e., the light is reflected back by interactions with the tissue  40 . 
         [0030]    In one embodiment, the pulse sensor  8  includes an emitter  26 , such as a single LED. For example, in one embodiment the emitter  26  of the pulse sensor  8  is a single LED emitting at an infrared wavelength, such as the aforementioned 900 nm, though other wavelengths in the near-infrared spectrum (750 nm to 2500 nm) or in the infrared spectrum in general may also be employed. The detector  28  of the pulse sensor  8  may be a photodiode or of the suitable detector of the wavelengths emitted by the emitter  26 . In this depicted embodiment, the pulse sensor  8  is also depicted as being a reflectance-type sensor. 
         [0031]    In an embodiment where the physiological sensor  10  is a pulse oximetry sensor, the physiological sensor  10  may be situated above blood perfused tissue, such as on a fingertip, toe, earlobe, or forehead of the patient. In such an embodiment, the pulse sensor  8  may be situated above a pulsing artery  38 , such as the temporal artery of the head. Such a position over a pulsing artery is generally not suitable to acquire data for measuring blood oxygen saturation (SpO 2 ), i.e., such a site is generally not suitable for pulse oximetry. However, in such an embodiment, the plethysmographic signal acquired by the pulse sensor  8  placed over such a pulsing artery  38  may provide a strong signal that indicates arterial pulsation and this signal may be used to synchronize processing of the data acquired elsewhere using the physiological sensor  10 , such as a pulse oximetry sensor. 
         [0032]    As discussed herein, in embodiments where the components of the pulse sensor  8  and the physiological sensor  10  are provided as separate sensors, these separate sensors may be placed on different parts of the patient&#39;s body and need not be proximate to one another. For example, in embodiments where the pulse sensor  8  and the physiological sensor  10  are separate, the physiological sensor  10  may be placed on the finger of the patient while the pulse sensor  8  is placed on the temporal artery or another pulsing artery  38  that may or may not be proximate to the location of the physiological sensor  10 . 
         [0033]    While the preceding examples disclose the use of optical techniques for acquiring arterial pulse data via the pulse sensor  8 , in other embodiments other types of techniques may be employed to acquire the arterial pulse data. For example, in other embodiments the pulse sensor  8  may measure arterial pressure (such as via accelerometers or other pressure sensitive instrumentation) as an indication of arterial pulse. Likewise, in yet another embodiment, the pulse sensor  8  may measure impedance or other electrical indicia as an indicator of arterial pulse. In one other embodiment, the pulse sensor  8  may utilize acoustical data (such as via a microphone placed proximate the heart or a major artery) to detect arterial pulses. 
         [0034]    In an exemplary embodiment, the pulse sensor  8  and the physiological sensor  10  provide their respective detected signals to a monitor  12 . In this embodiment, the monitor  12  may have a microprocessor  42  that calculates a physiological parameter (such as blood oxygen saturation (SpO 2 ) in one example) based on the data provided by the physiological sensor  10  and the pulse sensor  8 . In such an embodiment, the microprocessor  42  may be connected to other component pails of the monitor  12 , such as a ROM  46 , a RAM  48 , and input device(s)  50 . In one embodiment, the ROM  46  holds the algorithms used to process the measured signals and the RAM  48  stores the detected signal values or data for use in the algorithms. 
         [0035]    In one embodiment, input device  50  allows a user to interface with the monitor  12 , such as via buttons of an operator interface, a keypad or keyboard, or a mouse or other selection mechanism for use with a provided control interface. For example, a user may input or select parameters specific to the patient undergoing monitoring or may specify a monitor protocol where multiple protocols are available. For example, different wavelengths or wavelength combinations and/or different light emission timing schemes or measurement cycle lengths may be utilized in different protocols. As a result, different protocols may be desirable depending on the placement of the physiological sensor  10  and/or the pulse sensor  8 . 
         [0036]    As noted above, in certain embodiments detected signals are passed from the pulse sensor  8  and the physiological sensor  10  to the monitor  12  for processing. In the depicted embodiment, the signals are amplified and filtered in the monitor  12  by respective amplifiers  32 ,  60  and filters  34 ,  62  respectively, before being converted to digital signals by an analog-to-digital converters  36 ,  64 , respectively. The signals may then be used to determine an arterial pulse and a blood oxygen saturation (or other physiological parameter) based on the arterial pulse. The monitor  12  may be configured to display the calculated parameters, such as the measured blood oxygen saturation based on the detected arterial pulses, on display  74 . 
         [0037]    In one embodiment, light drive units  38 ,  66  in the monitor  12  control the timing of one or more of the emitters  22 ,  26 , respectively. While the depicted embodiment discloses the use of a separate light drive  66 , amplifier  60 , filter  62 , and analog-to-digital converter for the pulse sensor  8 , in other embodiments one or more of these components may support both the pulse sensor  8  and the physiological sensor  10 . In other words, in other embodiments, there may be only one light drive, amplifier, filter, and/or analog-to-digital converter that supports both the pulse sensor  8  and the physiological sensor  10 . 
         [0038]    The depicted embodiment also includes an encoder  68  provided in at least the physiological sensor  10 . Such an embodiment may be desirable where the emitter  22  (such as two LEDs in a pulse oximetry implementation) is manufactured to operate at one or more certain wavelengths and where variances in the wavelengths actually emitted by the emitter  22  may occur which may result in inaccurate readings. To help avoid inaccurate readings, an encoder  68  and decoder  70  may be used to calibrate the monitor  12  to the actual wavelengths being generated. The encoder  68  may be a resistor, for example, whose value corresponds to coefficients stored in the monitor  12 . The coefficients may then be used in the processing algorithms. Alternatively, the encoder  68  may also be a memory device, such as an EPROM, that stores information, such as the coefficients themselves. Once the coefficients are determined by the monitor  12 , they may be utilized to calibrate the monitor  12 . Though the encoder  68  is depicted in the physiological sensor  10 , the encoder may, alternatively, be provided in a cable  14  in embodiments in which the physiological sensor  10  and cable  14  are not separable. Further, an encoder as described herein may also be utilized in the pulse sensor  8  to provide calibration information to the monitor  12  for use in the calculation of arterial pulses by the microprocessor  42 . 
         [0039]    Turning now to  FIG. 3 , an embodiment is depicted where the physiological sensor  10  is configured as a transmission-type sensor. In this embodiment, the physiological sensor  10  may be configured to emit light from the emitter  22  through the tissue  40 , such as the tissue of the finger or earlobe, toward the detector  24  positioned opposite the emitter  22  with respect to the tissue  40 . Thus, in this embodiment, the detector  24  detects the light that has passed through the tissue as opposed to the light reflected by the tissue. Such an embodiment may be suitable for use where the pulse sensor  8  is utilized on or near tissue that is better suited for reflectance-type sensing, such as above the temporal artery or other suitable arteries, but where the physiological sensor  10  is utilized on or near tissue that is suitable for transmission-type sensing, such as fingers or earlobes. 
         [0040]    Unlike  FIGS. 2 and 3  which depict separate pulse and physiological sensors,  FIGS. 4 and 5  depict embodiments where there is a common sensor package  80  that includes both the emitter  22  and detector  24  used for sensing the physiological characteristic of interest as well as the emitter  26  and detector  28  used for sensing arterial pulses. For example, the embodiment depicted in  FIG. 4  includes a common sensor package  80  configured as a reflectance-type sensor. In this embodiment, a single sensor package is provided that is configured such that the emitter  22  and detector  24  used for sensing a physiological signal of interest can be positioned suitably, such as over perfused tissue in an oximetry implementation. In addition, the single sensor package is configured such that the emitter  26  and detector  28  used to detect arterial pulse can be positioned over a suitable artery  30 . Such an embodiment may be suitable for placement on the head of a patient such that the emitter  26  and detector  28  may be positioned over the temporal artery while the emitter  22  and detector  24  may be positioned over the perfused tissue of the forehead. Indeed, the common sensor package  80  may be configured to facilitate alignment and/or positioning of the respective emitters and detectors in such an implementation. 
         [0041]    Likewise,  FIG. 4  depicts an embodiment in which the common sensor package  80  is configured as a transmission-type sensor, with the emitter  22  and detector  24  situated opposite one another with respect to the perfused tissue  40 . Similarly, the emitter  26  and detector  28  may be situated opposite one another with respect to a suitable artery  38 . While the embodiments of  FIGS. 4 and 5  generally depict a common sensor package  80  in which the optical components are all configured for reflectance or transmission-type sensing, in other embodiments the common sensor package  80  may be provided for a combination of transmission and reflectance-type sensing. For example, in one embodiment suitable for use on the hand, the emitter  22  and detector  24  for sensing the physiological trait of interest may be configured for transmission-type sensing, such as for placement on a finger tip. In this embodiment, the emitter  26  and detector  28  may be configured for reflectance type sensing, such as on the top or palm of the hand. 
         [0042]    Thus in view of these embodiments, one or more sensor configurations may be provided that utilize optical or other data to provide a monitor with arterial pulse data that may be used to improve determination of a physiological trait, such as blood oxygen saturation levels. Such embodiments may be useful, for example, in the presence of patient motion where it is desirable to more readily identify those portions of a signal that correspond to an arterial pulse, as opposed to the motion component of the signal. 
         [0043]    While any claimed invention 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 any claimed invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.