Abstract:
A disposable active pulse sensor has an emitter that generates optical radiation having a plurality of wavelengths, a detector that is responsive to the optical radiation and an unbalanced electrical motor that vibrates when energized. A tape assembly removably attaches the emitter, the detector and the unbalanced electrical motor to a tissue site. The tape assembly also physically mounts the emitter, the detector and the unbalanced electrical motor in a spatial arrangement so that vibration from the unbalanced electrical motor induces pulsatile blood flow within the tissue site, the emitter transmits the optical radiation into the tissue site and the detector generates a sensor signal responsive to the intensity of the optical radiation after attenuation by the pulsatile blood flow within the tissue site.

Description:
REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 12/147,299, filed Jun. 26, 2008, titled “Disposable Active Pulse Sensor,” which application claims priority benefit under 35 U.S.C. §119(e) from U.S. Provisional Application No. 60/946,979, filed Jun. 28, 2007, entitled “Disposable Active Pulse Sensor.” All of the above-referenced application are hereby incorporated by reference herein in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     Pulse oximetry is widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of a person&#39;s oxygen supply. A typical pulse oximetry system utilizes a sensor applied to a patient tissue site. The sensor has emitters that transmit optical radiation of at least red and infrared (IR) wavelengths into the tissue site. A detector responds to the intensity of the optical radiation after attenuation by pulsatile arterial blood flowing within the tissue site. Based on this response, a processor determines measurements for oxygen saturation and pulse rate. In addition, a pulse oximeter may display a plethysmograph waveform, which is visualization of blood volume change within the illuminated tissue caused by the pulsatile arterial blood flow over time. 
     SUMMARY OF THE INVENTION 
     Pulse oximeters capable of reading through motion induced noise are available from Masimo Corporation (“Masimo”) of Irvine, Calif. Moreover, portable and other pulse oximeters capable of reading through motion induced noise are disclosed in at least U.S. Pat. Nos. 6,770,028, 6,658,276, 6,157,850, 6,002,952 5,769,785, and 5,758,644, which are assigned to Masimo and are incorporated by reference herein. Corresponding low noise sensors are also available from Masimo and are disclosed in at least U.S. Pat. Nos. 6,985,764, 6,813,511, 6,792,300, 6,256,523, 6,088,607, 5,782,757 and 5,638,818, which are assigned to Masimo and are incorporated by reference herein. Such reading through motion pulse oximeters and low noise sensors have gained rapid acceptance in a wide variety of medical applications, including surgical wards, intensive care and neonatal units, general wards, home care, physical training, and virtually all types of monitoring scenarios. 
     Further, noninvasive blood parameter monitors capable of measuring blood parameters in addition to Sp02, such as HbCO, HbMet and total hemoglobin (Hbt) and corresponding multiple wavelength optical sensors are also available from Masimo. Noninvasive blood parameter monitors and corresponding multiple wavelength optical sensors are described in at least U.S. patent application Ser. No. 11/367,013, filed Mar. 1, 2006 and entitled Multiple Wavelength Sensor Emitters and U.S. patent application Ser. No. 11/366,208, filed Mar. 1, 2006 and entitled Noninvasive Multi-Parameter Patient Monitor, both assigned to Masimo Laboratories, Irvine, Calif. (Masimo Labs) and both incorporated by reference herein. 
     Problems arise with pulse oximetry and other blood parameter monitoring systems when a tissue site has low blood perfusion and a corresponding weak sensor signal leading to invalid physiological measurements. To strengthen the sensor signal in low perfusion situations, an active pulse sensor actively induces a pulse in a controlled manner. That is, a sensor signal is generated according to a mechanically-induced active pulse rather than a heart-induced arterial pulse. Active pulse monitoring is described in U.S. Pat. No. 6,931,268 entitled Active Pulse Blood Constituent Monitoring, which is assigned to Masimo and incorporated by reference herein. 
     One aspect of a disposable active pulse sensor is an emitter that generates optical radiation having a plurality of wavelengths, a detector that is responsive to the optical radiation and an unbalanced electrical motor that vibrates when energized. A tape assembly removably attaches the emitter, the detector and the unbalanced electrical motor to a tissue site. The tape assembly also physically mounts the emitter, the detector and the unbalanced electrical motor in a spatial arrangement so that vibration from the unbalanced electrical motor induces pulsatile blood flow within the tissue site, the emitter transmits the optical radiation into the tissue site and the detector generates a sensor signal responsive to the intensity of the optical radiation after attenuation by the pulsatile blood flow within the tissue site. 
     Another aspect of a disposable active pulse sensor is a method for inducing pulsatile blood flow within a tissue site so as to determine at least one constituent of the pulsatile blood flow. An emitter, a detector and an unbalanced electric motor are removably attached to a tissue site. The tissue site is illuminated with optical radiation having a plurality of wavelengths from the emitter. A sensor signal is generated from the detector responsive to the optical radiation after attenuation by pulsatile blood flow within the tissue site. If there is insufficient arterial pulsatile blood flow to measure a desired constituent of the pulsatile blood flow in response to the sensor signal, the unbalanced electric motor is energized so as to induce a sufficient pulsatile blood flow within the tissue site from motor vibrations. 
     A further aspect of a disposable active pulse sensor is an emitter means for transmitting optical radiation having a plurality of wavelengths into a tissue site and a detector means for generating a sensor signal responsive to the optical radiation after attenuation by pulsatile blood flow within the tissue site. An active pulse means induces pulsatile blood flow within the tissue site of sufficient volume so as to allow the measurement of a plurality of blood constituents within the pulsatile blood flow. A tape means mounts the emitter means, detector means and active pulse means in a predetermined configuration and removably attaching the emitter means, detector means and active pulse means to the tissue site. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a disposable active pulse sensor; 
         FIG. 2  is an exploded perspective view of a disposable active pulse sensor; 
         FIG. 3  is a perspective view of an unbalanced electric motor for inducing an active pulse in a tissue site; 
         FIG. 4  is an untaped top view of a disposable active pulse sensor assembly; and 
         FIG. 5  is a general block diagram of a patient monitoring system including an active pulse sensor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates a disposable active pulse sensor  100  having a body  110 , a cable  120  and a connector  130 . In an embodiment, the body  110  is configured to wrap around a fingertip. The body incorporates an emitter  210  ( FIG. 2 ) and a detector  220  ( FIG. 2 ) that generates a sensor signal responsive to blood oxygen saturation, as described above. Advantageously, the body  110  also incorporates an active pulse element, such as an unbalanced electric motor  300  ( FIG. 3 ) adapted to induce pulsatile blood flow in a tissue site so as to provide a sufficiently strong sensor signal for meaningful physiological measurements. 
     As shown in  FIG. 1 , an emitter marking  140  may designate the location of the emitter  210  ( FIG. 2 ) within the body  110  allowing easy placement of the emitter  210  ( FIG. 2 ) over a fingernail, for example, so as to transmit optical radiation into the blood perfused fingernail bed tissue underneath. Likewise, a detector marking  150  may designate the location of the detector  220  ( FIG. 2 ) within the body  110  allowing easy placement of the detector  220  ( FIG. 2 ) on the fingertip opposite the fingernail and the emitter  210  ( FIG. 2 ). A housing  250  described in further detail below covers an unbalanced electric motor, which is located so as to mechanically vibrate the fingertip proximate the detector at a predetermined frequency so as to induce pulsatile blood flow at that frequency. 
     In the illustrated embodiment, the electric motor is located behind the detector  220  ( FIG. 2 ), i.e. such that the detector is between the electric motor and the end of the finger tip. The electric motor may also be placed at other locations relative to the detector  220  ( FIG. 2 ). In an embodiment, the electric motor is located in front of the detector  220  ( FIG. 2 ), i.e. such that the motor is between the detector and the end of the fingertip. In an embodiment, the electric motor is located on or near the very end of the fingertip. In an embodiment, the electric motor is located on either side of the detector  220  ( FIG. 2 ) along the fingertip. 
     In the illustrated embodiment, the electric motor is located immediately behind the detector  220  ( FIG. 2 ), sharing the fingertip with the detector. In other embodiments, the electric motor is located at any of various other distances from the detector, such as between the first and second finger joints for example. In yet other embodiments, the electric motor is placed at any of various distances behind the emitter along the top of the finger. 
     Also shown in  FIG. 1 , the cable  120  provides electrical communication between the emitter  210  ( FIG. 2 ), the detector  220  ( FIG. 2 ), the motor  300  ( FIG. 3 ) and the connector  130 . The connector  130  is adapted to electrically and mechanically connect the sensor  100  to a monitor  500  ( FIG. 5 ) either directly or via a patient cable. The monitor  500  ( FIG. 5 ) drives the emitters  210  ( FIG. 2 ), receives the detector signal, provides physiological measurements and controls the electric motor  300  ( FIG. 3 ), as described in further detail with respect to  FIG. 5 , below. 
       FIG. 2  further illustrates a disposable active pulse sensor  100  having a cable assembly  400 , a motor housing  250  and a tape assembly  203 . The cable assembly  400  has an emitter  210 , a detector  220  and an unbalanced electric motor  300 , which are interconnected to the cable  120  opposite the monitor connector  130 . The emitter  210  is configured with at least red and infrared LEDs that, for finger attachment, project light through the fingernail and into the blood vessels and capillaries underneath. The detector  220  is positioned at the fingertip opposite the fingernail so as to detect the LED emitted light as it emerges from the finger tissues. In an embodiment, the unbalanced motor  300  is also positioned at the fingertip opposite the fingernail and configured to vibrate the fingertip while the motor  300  is activated so as to induce blood flow in the finger tissues. The motor housing  250  accommodates the motor  300  and facilitates securing the motor  300  within the tape assembly  203 . An electromagnetic interference (EMI) shield  230  is attached to the detector  220  so as to reduce detector noise. Electrically insulating tapes  240  are attached to the emitter  210  and the shielded detector  220 . The cable assembly  400  is terminated at the monitor connector  130 . A monitor  500  ( FIG. 5 ) activates the emitter  210  and motor  300  and receives a corresponding sensor signal from the detector  220  all via the monitor connector  130 , as described in detail with respect to  FIG. 5 . 
     As shown in  FIG. 2 , the tape assembly  203  is adapted to attach the emitter  210 , the detector  220  and the electric motor  300  to a tissue site, such as a fingertip. The tape assembly  203  has a face tape  260 , a trifold wrap  270  and a release liner  280 . The trifold wrap  270  has a center portion  271  disposed between foldable side portions  275 , which are symmetrical about the center portion  271 . The center portion  271  is attached to the emitter  210 , the detector  220  and the electric motor  300  with an emitter aperture  272  aligned so as to pass light from the emitter  210  and a detector aperture  274  aligned so as to pass light to the detector  220 . The trifold wrap  270  has a pressure sensitive adhesive (PSA) on the component side and a patient adhesive, such as Med  3044 , on the center portion  271  of the patient side. The release liner  280  is removably attached to the patient side of the trifold wrap  270 . The face tape  260  has a housing aperture  262  allowing the motor housing  250  to protrude through the aperture  262 . The face tape  260  is fixedly attached to the trifold wrap  270  and removably attached to the release liner  280 . In one embodiment, the trifold wrap  270  is polypropylene and the face tape  260  is a laminate. 
     In other embodiments, not shown, a disposable active pulse sensor utilizes a flexible circuit for physical and electrical attachment and interconnection of the emitter, detector and unbalanced electric motor components. The flexible circuit may have an integrated connector for attachment to a sensor cable or patient cable, which communicates with a monitor or the flexible circuit may be soldered to or otherwise permanently attached to an integrated sensor cable. Further, in other embodiments, the tape assembly may be layered without a tri-fold wrap, or the sensor assembly may have a tissue attachment mechanism in lieu of or in addition to adhesive tape. 
     In other embodiments, the disposable active pulse sensor may include multiple emitters, multiple detectors or multiple unbalanced motors or combinations of such multiple components. The emitter(s) may incorporate light sources other than or in addition to LEOs, such as laser diodes or fiber optics transmitting light from an external source. The LEOs or other light sources may emit light having multiple wavelengths in addition to or instead of pulse oximetry-related red and infrared wavelengths. For example, multiple wavelengths emitters may be utilized with a disposable active pulse sensor for the detection of blood constituents other than oxyhemoglobin and reduced hemoglobin and for the measurement of blood parameters other than oxygen saturation, such as carboxyhemoglobin (HbCO), methemoglobin (HbMet) and other abnormal hemoglobin constituents. Other blood parameters that may be measured to provide important clinical information are fractional oxygen saturation, total hemaglobin (Hbt), bilirubin and blood glucose, to name a few. 
     In other embodiments, a disposable active pulse sensor is configured as a reflectance or transflectance sensor. Other embodiments may be configured to attach to other tissue sites rather than a fingertip, such as ear, nose, forehead, foot, cheek and lip sites, to name a few. Further, other embodiments of a disposable active pulse sensor may have additional components to those described above, such as an information element (IE) as described in U.S. patent application Ser. No. 11/367,036, filed Mar. 1, 2006 and entitled Configurable Physiological Measurement System, or a sensor life indicator (SLI), as described in U.S. Pat. No. 7,186,966 entitled Amount of use Tracking Device and Method for Medical Product, both incorporated by reference herein. 
       FIG. 3  illustrates an unbalanced electric motor  300  having a motor body  320 , a rotary shaft  340  and an unbalanced flywheel  360 . The motor body  320  is generally cylindrical and accommodates the shaft  340 , which extends along a center axis of the body  320 . Electrical leads  380  extend from the body  320  opposite the shaft  340  so as to electrically connect the motor  300  to the cable  120  ( FIG. 1 ). When the motor  300  is activated by a monitor  500  ( FIG. 5 ) via the cable  120  ( FIG. 1 ), the shaft  340  rotates the flywheel  360 . In an embodiment, the flywheel  360  is a generally semi-circular disc centrally mounted to the shaft  340 . When the shaft  340  rotates, the flywheel&#39;s eccentric imbalance causes the motor as a whole to vibrate at a predetermined frequency according to the motor rotational speed. This vibration “pulses” a tissue site, which creates a pulsatile blood flow. In other embodiments, the unbalanced motor  300  is configured with rotational elements other than the semi-circular flywheel, such as a circular flywheel composed of two or more materials of differing weights or densities, or an otherwise unsymmetrical flywheel. In other embodiments, the unbalanced motor is replaced with an alternative, electrically-activated vibrating component such as a piezo-electric element. 
       FIG. 4  illustrates a cable assembly  400  having an emitter  210 , a detector  220 , an unbalanced electric motor  300  and a cable  120 . The cable  120  has an emitter portion  122 , a detector portion  124  and a motor portion  126 . A pair of emitter wires  123  extend from the emitter portion  122  and are soldered to corresponding emitter leads  212 . A pair of detector wires  125  extend from the detector portion  124  and are soldered to corresponding detector leads  222 . A pair of motor wires  127  extend from the motor portion  126  and are soldered to corresponding motor leads  380 . The cable wires  123 ,  125 ,  127  terminate at the monitor connector  130  ( FIG. 2 ). 
       FIG. 5  illustrates a patient monitoring system  500  that generates one or more blood parameter measurements, such as Sp02, perfusion index (PI), HbCO, HbMet, and Hbt, to name a few. The patient monitoring system  500  is adapted to trigger an active pulse sensor as needed. In one embodiment, an active pulse is advantageously triggered when the monitor measures poor perfusion at the tissue site. In a particular embodiment, the active pulse is activated by a PI measurement below a predetermined threshold and deactivated between successful measurements. In an embodiment, an active pulse is triggered upon any measure indicating poor signal strength or signal quality. Signal quality and data confidence measures are described in U.S. Pat. No. 6,996,427 entitled Pulse Oximetry Data Confidence Indicator, assigned to Masimo and incorporated by reference herein. In an embodiment, an active pulse is triggered to induce a venous blood pulse so as to measure venous oxygen saturation or related venous blood parameters. 
     Also shown in  FIG. 5 , the patient monitor  502  communicates with the sensor  100  to receive one or more intensity signals indicative of one or more physiological parameters. Drivers  510  convert digital control signals into analog drive signals  512  capable of driving the emitter  210 . A front-end  520  converts composite analog intensity signal(s)  522  from the detector(s)  220  into digital data input to the DSP  540 . The DSP  540  comprises any of a wide variety of data and signal processors capable of executing programs for determining physiological parameters from input data. The DSP  540  generates an activation signal  532  from a motor driver  530  to the electric motor  300  when an active pulse is needed or desired. 
     In an embodiment, the patient monitoring system  500  controls the active pulse so as to accentuate a natural, heart-induced pulse. In particular, the patient monitor  502  generates an activation signal  532  so that an active pulse frequency and phase matches the frequency and phase of the natural pulse. In an embodiment, the DSP  540  executes a phase-locked-loop algorithm that has as inputs the natural pulse and the induced active pulse as derived from the detector signal  522  and an output that controls the activation signal  532  accordingly. 
     The instrument manager  560  may comprise one or more microcontrollers providing system management, such as monitoring the activity of the DSP  540 . The instrument manager  560  also has an input/output (I/O) port  568  that provides a user and/or device interface for communicating with the monitor  502 . In an embodiment, the I/O port  568  provides threshold settings via a user keypad, network, computer or similar device, as described below. 
     Further shown in  FIG. 5  are one or more user I/O devices  580  including displays  582 , audible indicators  584  and user inputs  588 . The displays  582  are capable of displaying indicia representative of calculated physiological parameters such as one or more of a pulse rate (PR), plethysmograph, perfusion index (PI), signal quality and values of blood constituents in body tissue, including for example, oxygen saturation (Sp02), carboxyhemoglobin (HbCO) and methemoglobin (HbMet). The monitor  502  may also be capable of storing or displaying historical or trending data related to one or more of the measured parameters or combinations of the measured parameters. The monitor  502  may also provide a trigger for the audible indictors  584 , which operate beeps, tones and alarms, for example. Displays  582  include for example readouts, colored lights or graphics generated by LEDs, LCDs or CRTs to name a few. Audible indicators  584  include speakers or other audio transducers. User input devices  588  may include, for example, keypads, touch screens, pointing devices, voice recognition devices, or the like. 
     A disposable active pulse 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.