Disposable active pulse sensor

[0001] The present 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,” which is incorporated herein by reference.

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

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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'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.

[0025] 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).

[0026] 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.

[0027] 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 dig ital 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.