Personal health device

[0001] The present application claims priority benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/486,689 filed May 16, 2011, titled “Personal Health Device” hereby incorporated in its entirety by reference herein.

[0002] The present disclosure relates to the field of non-invasive physiological measurements.

[0003] The standard of care in caregiver environments includes patient monitoring through spectroscopic analysis using, for example, a pulse oximeter. Devices capable of spectroscopic analysis generally include a light source(s) transmitting optical radiation into or reflecting off a measurement site, such as, body tissue carrying pulsing blood. After attenuation by tissue and fluids of the measurement site, a photodetection device(s) detects the attenuated light and outputs a detector signal(s) responsive to the detected attenuated light. A signal processing device(s) process the detector(s) signal(s) and outputs a measurement indicative of a blood constituent of interest, such as glucose, oxygen, methemoglobin, total hemoglobin, other physiological parameters, or other data or combinations of data useful in determining a state or trend of wellness of a patient.

[0004] In noninvasive devices and methods, a sensor is often adapted to position a finger proximate the light source and light detector. For example, noninvasive sensors often include a clothespin-shaped housing that includes a contoured bed conforming generally to the shape of a finger.

[0005] The present disclosure provides solutions for determining physiological information using optical non-invasive processes by using an active pulse system. The system induces an artificial pulse at a frequency distinguishable from the frequency of a human arterial pulse. As a result, information related to both the arterial pulse as well as the artificial pulse is recoverable from the body. The redundant nature of both pieces of information provide additional information useful in determining physiological parameters.

[0006] In an embodiment, a sensor is described which facilitates producing and detecting optical radiation attenuated by body tissue. In an embodiment, a motor is detected which drives a piston into a detector assembly. As a result, the detector assembly creates the artificial pulse. In an embodiment, the detector assembly is configured to stay in constant contact with the body tissue.

[0020] Reference will now be made to the Figures to discuss embodiments of the present disclosure.

[0021] A typical heart beats around 1 Hz creating a fairly predictable heart rate. Determining the heart rate is important for many applications and particularly important for pulse oximetry and noninvasive determination of other parameters using pulse oximetry techniques. This is because the pulse affects light absorption rates at predictable amounts. Thus, knowing the pulse rate is essential to determining accurate non-invasive optical measurements. This information is useful for determining various physiological parameters. These parameters include, for example, a percent value for arterial carbon monoxide saturation (“SpCO”), a percent value for methemoglobin saturation (a brownish-red form of hemoglobin that cannot function as an oxygen carrier) (“SpMet”), fractional SpO₂ (“Fp0₂”) or the like. Additionally, caregivers often desire knowledge of Hb0₂, Hb, carboxyhemoglobin (“HbCO”), methemoglogin (“HbMet”), blood glucose and total hematocrit (Hct), bilirubin, perfusion quality, signal quality or the like

[0022] Similarly, introducing an artificial excitation can cause perturbations in the blood flow similar to the affects of a heart beat. These artificial excitations can be used as an alternative to the natural pulse rate or in addition to the natural pulse rate. Artificial excitations have the added benefit that the excitations introduced are introduced at known frequencies. Thus, it is not necessary to first determine the pulse rate of an individual. However, it is important to avoid providing artificial excitations at frequencies that over lap with the frequency of the heart rate or its harmonics. In one embodiment, an excitation frequency of five to six times the natural heart rate can be chosen. Moreover, it is also important to provide artificial excitations at frequencies that do not cause discomfort to the patient. Thus, a range of frequencies that are useful for artificial excitations includes a range of about 6 Hz to about 30 Hz. In an embodiment, an excitation in the range of 8 to 15 Hz is chosen. In one embodiment, an artificial excitation is provided at a frequency of about 12 Hz. In one embodiment, an artificial excitation is provided at a frequency of about 8 Hz. Alternatively, the excitation frequency can be chosen to be interspersed with the natural heart frequencies. For example, a frequency of 2.5 Hz can be chosen to avoid harmonics of a 1 Hz heart rate. In an embodiment, the artificial excitation is dynamically chosen based to avoid the heart rate frequencies and harmonics. This can be done by first determining the heart rate and then selecting an artificial excitation frequency once the heart rate is known. In an embodiment, the artificial excitation frequency can be changed during measurements if the heart rate changes. Introducing an artificial excitation generally does not affect the pulse rate or cause any other adverse physical effects on the patient. A typical arterial pulse can cause a pressure change of 2 to 4 psi (100 ml/Hg-200 ml/Hg), while an artificial excitation causes a much lower pressure change.

[0023] FIG. 1 is a frequency plot illustrating an embodiment of an active pulse system. As discussed above, a typical heart beats at a frequency around 1 Hz. The pulse typically includes a number of harmonics, usually at 2, 3, 4 and possibly 5 Hz. Thus, a bandpass filter 103 can be selected in order to isolate the expected frequencies of the heart rate. Also illustrated in FIG. 1 is an artificial excitation introduced at 12 Hz. As illustrated the artificial excitation also includes harmonics at 9, 10, 11, 13, 14 and 15 Hz. Because the 12 Hz frequency is known, a narrow bandpass filter 105 can be used to isolate the 12 Hz frequency.

[0024] The information from the artificial excitation can then be used to determine either a bulk measurement or venous information. Bulk measurement information can provide a better estimate of mean path length. In order to obtain a bulk measurement, a wavelength of around 1300 nm can be used. Other wavelengths around 1300 nm can also be used. For example, a wavelength of between 1200 nm and 1900 nm can be used. A venous measurement can be obtained by using wavelengths typically associated with standard pulse oximetry measurements, include 660 and 905. In one embodiment, the emitter can emit optical radiation in the form of pulses at wavelengths about 905 nm, about 1050 nm, about 1200 nm, about 1300 nm, about 1330 nm, about 1610 nm, about 1640 nm, and about 1665 nm. In another embodiment, the emitter can emit optical radiation ranging from about 860 nm to about 950 nm, about 950 nm to about 1100 nm, about 1100 nm to about 1270 nm, about 1250 nm to about 1350 nm, about 1300 nm to about 1360 nm, and about 1590 nm to about 1700 nm. Of course, the emitter can transmit any of a variety of wavelengths of visible or near-infrared optical radiation Of course, it will be understood from the disclosure herein that multiple artificial excitations can be introduced at the same time or at different times and at the same or different frequencies in order to obtain both bulk and venous information using the respective wavelengths associated with each measurement.

[0025] According to the Beer-Lambert law, light absorption is related to the properties of the materials it passes through as follows:
I=I_oe^−(μd)  Eq. 1

[0026] The pulse rate and artificial excitations affect different portions of the Eq. 1 as follows:
I=I_oe^{−(μ+Δμ)(d+Δd)}  Eq. 2
where Δμ is caused by the heart rate and Δd is due to the artificial excitation.

[0027] FIG. 2 illustrates a block diagram for extracting information from the DC portion of the detected light signal. At 201, the DC signal is inputted into the system. The DC signal is then sent along two paths as illustrated. At 203 and 205, the respective DC signals are sent through a log conversion. Log conversions simplify the data so that it is not necessary to know the power of the emitters used. At steps 207 and 209 a bandpass filter is applied to both signals. The bandpass filter in step 207 corresponds to a filter which passes pulse rate frequencies as illustrated in FIG. 1. Similarly, the bandpass filter at step 209 corresponds to the filter which passes the artificial excitation frequency. The output from bandpass 207 is arterial information. The output from 209 is bulk and/or venous information, again depending on the wavelength used.

[0028] In an embodiment, the measurements can be continuous or discrete. In an embodiment of a discrete measurement system, or “spot-check” device, three measurements are taken and the two closest measurements are averaged or weighted to determine a displayed measurement. This results in an improved accuracy of 0.1 to 0.2 g/dl in the case of a glucose measurement.

[0029] In an embodiment, the metabolic breakdown of glucose is measured over a period time. This can be measured by continuously measuring glucose levels over time and monitoring how glucose levels drop. In an embodiment, the subject being measured is provided with food or drink before the test is started so that the subject has a higher glucose count at the start of the test. The measurement can be displayed as glucose metabolism in g/dl per period of time, such as a minute, ten minutes or per hour.

[0030] FIG. 2A is a flow diagram according to an embodiment of the disclosure. At block 251, an artificial pulse is applied to the measurement site. At block 253, optical radiation is emitted into the measurement site. This can include one or more different wavelengths. At block 255, the emitted optical radiation is detected after attenuation by body tissue which is undergoing an active pulse stimulation. At block 257, the detected optical radiation is used to determine both arterial pulse information and active pulse information. The two different sets of information can then be used to enhance physiological measurement.

[0031] FIG. 3 illustrates an example of a monitoring device 300. In the depicted embodiment, the monitoring device 300 includes a finger clip sensor 301 connected to a monitor 309 via a cable 312. In the embodiment shown, the monitor 309 includes a display 310, control buttons 308 and a power button 311. Moreover, the monitor 309 can advantageously include various electronic processing, signal processing, and data storage devices capable of receiving signal data from said sensor 301, processing the signal data to determine one or more output measurement values indicative of one or more physiological parameters of a monitored patient, and displaying the measurement values, trends of the measurement values, combinations of measurement values, and the like.

[0032] The cable 312 connecting the sensor 301 and the monitor 309 can be implemented using one or more wires, optical fiber, flex circuits, or the like. In some embodiments, the cable 312 can employ twisted pairs of conductors in order to minimize or reduce cross-talk of data transmitted from the sensor 301 to the monitor 309. Various lengths of the cable 312 can be employed to allow for separation between the sensor 301 and the monitor 309. The cable 312 can be fitted with a connector (male or female) on either end of the cable 312 so that the sensor 301 and the monitor 309 can be connected and disconnected from each other. Alternatively, the sensor 301 and the monitor 309 can be coupled together via a wireless communication link, such as an infrared link, radio frequency channel, or any other wireless communication protocol and channel.

[0033] The monitor 309 can be attached to the patient. For example, the monitor 309 can include a belt clip or straps that facilitate attachment to a patient's belt, arm, leg, or the like. The monitor 309 can also include a fitting, slot, magnet, LEMO snap-click connector, or other connecting mechanism to allow the cable 312 and sensor 301 to be attached to the monitor 309.

[0034] The monitor 309 can also include other components, such as a speaker, power button, removable storage or memory (e.g., a flash card slot), an AC power port, and one or more network interfaces, such as a universal serial bus interface or an Ethernet port. For example, the monitor 309 can include a display 310 that can indicate a measurement for glucose, for example, in mg/dL. Other analytes and forms of display can also appear on the monitor 309. In an embodiment, the monitor 309 includes an integral or detachable glucose strip reader. A detachable glucose strip reader can be separately housed and configured to communicate wirelessly with monitor 309 or by attachment to a network interface, universal serial bus interface or Ethernet port. In an embodiment, an invasive glucose strip test device can be integrated into the monitor 309. The strip test device can be used as a secondary measure in the case of glucose or in addition to other measurements performed by the monitor 309. In an embodiment, the invasive glucose strip test can be used to calibrate a non-invasive optical glucose measurement. In an embodiment, blood pressure measurements can also be integrated into the monitor 309.

[0035] In addition, although a single sensor 301 with a single monitor 309 is shown, different combinations of sensors and device pairings can be implemented. For example, multiple sensors can be provided for a plurality of differing patient types or measurement sites or even patient fingers. In an embodiment, a resposable sensor can be used. A resposable sensor integrates both reusable and disposable components. For example, the emitters, detectors and motor assembly can be reused while the components used to attach the sensor to the patient can be disposable.

[0036] FIG. 4 illustrates an example of a data collection system 400. In certain embodiments, the data collection system 400 noninvasively measures a blood analyte, such as oxygen, carbon monoxide, methemoglobin, total hemoglobin, glucose, proteins, glucose, lipids, a percentage thereof (e.g., saturation) or for measuring many other physiologically relevant patient characteristics. The system 400 can also measure additional blood analytes and/or other physiological parameters useful in determining a state or trend of wellness of a patient.

[0037] The data collection system 400 can measuring optical radiation from the measurement site. The optical radiation can be used to determine analyte concentrations, including glucose, total hemoglobin, methemoglobin, carboxyhemoglobin, oxygen saturation, etc., at least in part by detecting light attenuated by a measurement site 402. The measurement site 402 can be any location on a patient's body, such as a finger, foot, ear lobe, or the like. For convenience, this disclosure is described primarily in the context of a finger measurement site 402. However, the features of the embodiments disclosed herein can be used with other measurement sites 402.

[0038] In the depicted embodiment, the system 400 includes an optional tissue thickness adjuster or tissue shaper 405, which can include one or more protrusions, bumps, lenses, or other suitable tissue-shaping mechanisms. In certain embodiments, the tissue shaper 405 is a flat or substantially flat surface that can be positioned proximate the measurement site 402 and that can apply sufficient pressure to cause the tissue of the measurement site 402 to be flat or substantially flat. In other embodiments, the tissue shaper 405 is a convex or substantially convex surface with respect to the measurement site 402. Many other configurations of the tissue shaper 405 are possible. Advantageously, in certain embodiments, the tissue shaper 405 reduces thickness of the measurement site 402 while preventing or reducing occlusion at the measurement site 402. Reducing thickness of the site can advantageously reduce the amount of attenuation of the light because there is less tissue through which the light must travel. Shaping the tissue into a convex (or alternatively concave) surface can also provide more surface area from which light can be detected.

[0039] The embodiment of the data collection system 400 shown also includes an optional noise shield 403. In an embodiment, the noise shield 403 can be advantageously adapted to reduce electromagnetic noise while increasing the transmittance of light from the measurement site 402 to one or more detectors 406 (described below). For example, the noise shield 403 can advantageously include a conductive coated glass or metal grid electrically communicating with one or more other shields of the sensor 401 or electrically grounded. Also included is an active pulse motor 420 (described below).

[0040] The data collection system 400 can include a sensor 401 (or multiple sensors) that is coupled to a processing device or physiological monitor 409. In an embodiment, the sensor 401 and the monitor 409 are integrated together into a single unit. In another embodiment, the sensor 401 and the monitor 409 are separate from each other and communicate one with another in any suitable manner, such as via a wired or wireless connection. The sensor 401 and monitor 409 can be attachable and detachable from each other for the convenience of the user or caregiver, for ease of storage, sterility issues, or the like. The sensor 401 and the monitor 409 will now be further described.

[0041] In the depicted embodiment shown in FIG. 4, the sensor 401 includes an emitter 404, a tissue shaper 405, a set of detectors 406, and a front-end interface 408. The emitter 404 can serve as the source of optical radiation transmitted towards measurement site 402. As will be described in further detail below, the emitter 404 can include one or more sources of optical radiation, such as LEDs, laser diodes, incandescent bulbs with appropriate frequency-selective filters, combinations of the same, or the like. In an embodiment, the emitter 404 includes sets of optical sources that are capable of emitting visible and near-infrared optical radiation.

[0042] In some embodiments, the emitter 404 is used as a point optical source, and thus, the one or more optical sources of the emitter 404 can be located within a close distance to each other, such as within about a 2 mm to about 4 mm. The emitters 404 can be arranged in an array, such as is described in U.S. Publication No. 2006/0211924, filed Sep. 21, 2006, titled “Multiple Wavelength Sensor Emitters,” the disclosure of which is hereby incorporated by reference in its entirety. In particular, the emitters 404 can be arranged at least in part as described in paragraphs [0061] through [0068] of the aforementioned publication, which paragraphs are hereby incorporated specifically by reference. Other relative spatial relationships can be used to arrange the emitters 404.

[0043] The data collection system 400 also includes a driver 411 that drives the emitter 404. The driver 411 can be a circuit or the like that is controlled by the monitor 409. For example, the driver 411 can provide pulses of current to the emitter 404. In an embodiment, the driver 411 drives the emitter 404 in a progressive fashion, such as in an alternating manner. The driver 411 can drive the emitter 404 with a series of pulses of about 1 milliwatt (mW) for some wavelengths that can penetrate tissue relatively well and from about 40 mW to about 100 mW for other wavelengths that tend to be significantly absorbed in tissue. A wide variety of other driving powers and driving methodologies can be used in various embodiments.

[0044] The driver 411 can be synchronized with other parts of the sensor 401 and can minimize or reduce jitter in the timing of pulses of optical radiation emitted from the emitter 404. For example, in an embodiment, the timing of the pulses is synchronized with the timing of the motor 420 revolutions. In some embodiments, the driver 411 is capable of driving the emitter 404 to emit optical radiation in a pattern that varies by less than about 10 parts-per-million.

[0045] The detectors 406 capture and measure light from the measurement site 402. For example, the detectors 406 can capture and measure light transmitted from the emitter 404 that has been attenuated or reflected from the tissue in the measurement site 402. The detectors 406 can output a detector signal 407 responsive to the light captured or measured. The detectors 406 can be implemented using one or more photodiodes, phototransistors, or the like.

[0046] In addition, the detectors 406 can be arranged with a spatial configuration to provide a variation of path lengths among at least some of the detectors 406. That is, some of the detectors 406 can have the substantially, or from the perspective of the processing algorithm, effectively, the same path length from the emitter 404. However, according to an embodiment, at least some of the detectors 406 can have a different path length from the emitter 404 relative to other of the detectors 406. Variations in path lengths can be helpful in allowing the use of a bulk signal stream from the detectors 406. In some embodiments, the detectors 406 may employ a linear spacing, a logarithmic spacing, or a two or three dimensional matrix of spacing, or any other spacing scheme in order to provide an appropriate variation in path lengths.

[0047] Active Pulse Motor 420 rotates providing an agitation at a known frequency which is transferred through the sensor to the measurement site. The motor 420 is driven by driver 411. The vibration created by the motor 420 is useful in determining further information regarding the physiological state of the patient as described in more detail below.

[0048] The front end interface 408 provides an interface that adapts the output of the detectors 406, which is responsive to desired physiological parameters. For example, the front end interface 408 can adapt a signal 407 received from one or more of the detectors 406 into a form that can be processed by the monitor 409, for example, by a signal processor 410 in the monitor 409. The front end interface 408 can have its components assembled in the sensor 401, in the monitor 409, in connecting cabling (if used), combinations of the same, or the like. The location of the front end interface 408 can be chosen based on various factors including space desired for components, desired noise reductions or limits, desired heat reductions or limits, and the like.

[0049] The front end interface 408 can be coupled to the detectors 406 and to the signal processor 410 using a bus, wire, electrical or optical cable, flex circuit, or some other form of signal connection. The front end interface 408 can also be at least partially integrated with various components, such as the detectors 406. For example, the front end interface 408 can include one or more integrated circuits that are on the same circuit board as the detectors 406. Other configurations can also be used.

[0050] The front end interface 408 can be implemented using one or more amplifiers, such as transimpedance amplifiers, that are coupled to one or more analog to digital converters (ADCs) (which can be in the monitor 409), such as a sigma-delta ADC. A transimpedance-based front end interface 408 can employ single-ended circuitry, differential circuitry, and/or a hybrid configuration. A transimpedance-based front end interface 408 can be useful for its sampling rate capability and freedom in modulation/demodulation algorithms. For example, this type of front end interface 408 can advantageously facilitate the sampling of the ADCs being synchronized with the pulses emitted from the emitter 404 and/or vibrations from the motor 420.

[0051] The ADC or ADCs can provide one or more outputs into multiple channels of digital information for processing by the signal processor 410 of the monitor 409. Each channel can correspond to a signal output from a detector 406.

[0052] In some embodiments, a programmable gain amplifier (PGA) can be used in combination with a transimpedance-based front end interface 408. For example, the output of a transimpedance-based front end interface 408 can be output to a PGA that is coupled with an ADC in the monitor 409. A PGA can be useful in order to provide another level of amplification and control of the stream of signals from the detectors 406. Alternatively, the PGA and ADC components can be integrated with the transimpedance-based front end interface 408 in the sensor 401.

[0053] In another embodiment, the front end interface 408 can be implemented using switched-capacitor circuits. A switched-capacitor-based front end interface 408 can be useful for, in certain embodiments, its resistor-free design and analog averaging properties. In addition, a switched-capacitor-based front end interface 408 can be useful because it can provide a digital signal to the signal processor 410 in the monitor 409.

[0054] As shown in FIG. 4, the monitor 409 can include the signal processor 410 and a user interface, such as a display 412. The monitor 409 can also include optional outputs alone or in combination with the display 412, such as a storage device 414 and a network interface 416. In an embodiment, the signal processor 410 includes processing logic that determines measurements for desired analytes, such as glucose and total hemoglobin, based on the signals received from the detectors 406. The signal processor 410 can be implemented using one or more microprocessors or subprocessors (e.g., cores), digital signal processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), combinations of the same, and the like.

[0055] The signal processor 410 can provide various signals that control the operation of the sensor 401. For example, the signal processor 410 can provide an emitter control signal to the driver 411. This control signal can be useful in order to synchronize, minimize, or reduce jitter in the timing of pulses emitted from the emitter 404 or motor vibrations from motor 420. Accordingly, this control signal can be useful in order to cause optical radiation pulses emitted from the emitter 404 to follow a precise timing and consistent pattern. For example, when a transimpedance-based front end interface 408 is used, the control signal from the signal processor 410 can provide synchronization with the ADC in order to avoid aliasing, cross-talk, and the like. As also shown, an optional memory 413 can be included in the front-end interface 408 and/or in the signal processor 410. This memory 413 can serve as a buffer or storage location for the front-end interface 408 and/or the signal processor 410, among other uses.

[0056] The user interface 412 can provide an output, e.g., on a display, for presentation to a user of the data collection system 400. The user interface 412 can be implemented as a touch-screen display, an LCD display, an organic LED display, or the like. In addition, the user interface 412 can be manipulated to allow for measurement on the non-dominant side of the patient. For example, the user interface 412 can include a flip screen, a screen that can be moved from one side to another on the monitor 409, or can include an ability to reorient its display indicia responsive to user input or device orientation. In alternative embodiments, the data collection system 400 can be provided without a user interface 412 and can simply provide an output signal to a separate display or system.

[0057] A storage device 414 and a network interface 416 represent other optional output connections that can be included in the monitor 409. The storage device 414 can include any computer-readable medium, such as a memory device, hard disk storage, EEPROM, flash drive, or the like. The various software and/or firmware applications can be stored in the storage device 414, which can be executed by the signal processor 410 or another processor of the monitor 409. The network interface 416 can be a serial bus port (RS-232/RS-485), a Universal Serial Bus (USB) port, an Ethernet port, a wireless interface (e.g., WiFi such as any 802.1x interface, including an internal wireless card), or other suitable communication device(s) that allows the monitor 409 to communicate and share data with other devices. The monitor 409 can also include various other components not shown, such as a microprocessor, graphics processor, or controller to output the user interface 412, to control data communications, to compute data trending, or to perform other operations. In an embodiment, the measurements are encrypted and decrypted inside the processor in hardware. As a result, the measurements can be safely stored and communicated to, for example, a cloud based storage medium without compromising the security of the data.

[0058] Although not shown in the depicted embodiment, the data collection system 400 can include various other components or can be configured in different ways. For example, the sensor 401 can have both the emitter 404 and detectors 406 on the same side of the measurement site 402 and use reflectance to measure analytes. The data collection system 400 can also include a sensor that measures the power of light emitted from the emitter 404.

[0059] FIGS. 5-10 illustrate more detailed examples of embodiments of the sensor 301. Referring to FIG. 5, the sensor 501 in the depicted embodiment is a clothespin-shaped clip sensor that includes an enclosure 502 for receiving a patient's finger. The enclosure 502 is formed by an upper section or emitter shell 504, which is pivotably connected with a lower section or detector shell 506. The emitter shell 504 can be biased with the detector shell 506 to close together around a pivot point 503 and thereby sandwich finger tissue between the emitter and detector shells 504, 506.

[0060] In an embodiment, the pivot point 503 advantageously includes a pivot capable of adjusting the relationship between the emitter and detector shells 504, 506 to effectively level the sections when applied to a tissue site. In another embodiment, the sensor 501 includes some or all features of the finger clip described in U.S. Publication No. 2006/0211924, incorporated above, such as a spring that causes finger clip forces to be distributed along the finger. Paragraphs [0096] through [0105], which describe this feature, are hereby specifically incorporated by reference.

[0061] The emitter shell 50a can position and house various emitter components of the sensor 501. It can be constructed of reflective material (e.g., white silicone or plastic) and/or can be metallic or include metalicized plastic (e.g., including carbon and aluminum) to possibly serve as a heat sink. The emitter shell 504 can also include absorbing opaque material, such as, for example, black or grey colored material, at various areas, such as on one or more flaps 507, to reduce ambient light entering the sensor 501.

[0062] The detector shell 506 can position and house one or more detector portions of the sensor 501. The detector shell 506 can be constructed of reflective material, such as white silicone or plastic. As noted, such materials can increase the usable signal at a detector by forcing light back into the tissue and measurement site (see FIG. 1). The detector shell 506 can also include absorbing opaque material at various areas, such as lower area 508, to reduce ambient light entering the sensor 501.

[0063] FIG. 6 illustrates another view of the sensor 301, which includes an embodiment of a partially cylindrical protrusion 605. The finger bed 510 includes a generally curved surface shaped generally to receive tissue, such as a human digit. The finger bed 510 also includes the ridges or channels 514. The finger bed 310 shown also includes the protrusion 605.

[0064] FIG. 7 illustrates an exploded view of certain of the components of the sensor 301 described above. A heat sink 751 and a cable 781 attach to an emitter shell 704. The emitter shell attaches to a flap housing 707 attached to an emitter submount 702, which is attached to a circuit board 719. flap housing 707 includes emitter window 709.

[0065] A spring 787 attaches to a detector shell 706 via pins 783, 785, which hold the emitter and detector shells 704, 706 together. A support structure 791 attaches to the detector shell 706. A motor assembly 713 attaches to the support structure 791 and presses against the detector submount 700. In an embodiment, submount 700 is floating, in other words, it is not fixedly attached but is allowed to float within the surrounding support structures. This allows the submount 700 to move freely when pressed by the motor assembly 713. Submount 712 attaches to support structure 791. A finger bed 710 provides a surface for placement of the patient's finger. Finger bed 710 can comprise a gripping surface or gripping features, which can assist in placing and stabilizing a patient's finger in the sensor. A partially cylindrical protrusion 705 can also be disposed in the finger bed 710. As shown, finger bed 710 attaches to the noise shield 703. The noise shield 703 may be configured to reduce noise, such as from ambient light and electromagnetic noise. For example, the noise shield 703 may be constructed from materials having an opaque color, such as black or a dark blue, to prevent light piping.

[0066] Noise shield 703 may also comprise a thermistor. The thermistor can be helpful in measuring the temperature of a patient's finger. For example, the thermistor may be useful in detecting when the patient's finger is reaching an unsafe temperature that is too hot or too cold. In addition, the temperature of the patient's finger may be useful in indicating to the sensor the presence of low perfusion as the temperature drops. In addition, the thermistor may be useful in detecting a shift in the characteristics of the water spectrum in the patient's finger, which can be temperature dependent.

[0067] A flex circuit cover 760 attaches to the pins 783, 785. A flex circuit can also be provided that connects the circuit board 719 with the submount 700 (or a circuit board to which the submount 700 is connected). A flex circuit protector 760 may be provided to provide a barrier or shield to the flex circuit. In particular, the flex circuit protector 760 may also prevent any electrostatic discharge to or from the flex circuit. The flex circuit protector 760 may be constructed from well known materials, such as a plastic or rubber materials.

[0068] FIGS. 8 and 9 illustrate different perspective views of some of the components of FIG. 7.

[0069] FIG. 10A is an exploded view of the motor assembly 713. The motor assembly 713 includes a motor 1001, actuator 1003, actuator housing 1007, piston 1005 and servo controller 1009. The motor 1001 rotates an axle 1011 upon application of an electric current. The axle 1011 is coupled to shaft 1013 of actuator 1003. The shaft 1013 is configured to be off-balance or decentralized. The actuator 1003 is placed inside the actuator housing 1007 along with piston 1005. Servo controller 1009 is also included in the actuator housing 1007 as illustrated. The servo controller monitors the rotation of the motor 1001 and provides feedback to the driver 411. Based on the feedback from the servo controller 1009, the driver 411 adjusts power to the motor 1001 to achieve a desired rotations speed. An important aspect of the motor is the ability to tightly control the speed of the motor in order to achieve and accurate desired frequency of rotation. As depicted, the motor 1001 is a DC motor that is controlled using a servo encoder. In an alternative embodiment, a brushless or step-motor is used.

[0070] In operation, the motor 1001 spins the axle 1011. The axle 1011 rotates the actuator 1003. Due to the off-balance nature of the actuator 1003, the actuator will spin unevenly. This uneven rotation moves the piston 1005 up and down, perpendicular to the rotational axis of the motor 1011. The piston 1005 then pushes against submount 700 which pushes cylindrical protrusion 705 into the patient's tissue causing an artificial vibration at a known frequency.

[0071] Importantly, protrusion 705 maintains contact with the patient's tissue. As a result, the detector(s) 406 are kept at the same distance relative to the patient's tissue throughout the operation of the artificial vibration. This prevents optical errors from being introduced into the system. The force provided to the piston 1005 should be sufficiently high to affect the perfusion of the tissue site while not exceeding mechanical or patient comfort constraints. In an embodiment, the piston is driven with a force that drives the protrusion 705 about 0.3 mm into the tissue site. In an embodiment, sufficient force is provided to drive the protrusion 705 between about 0.1 mm and about 0.5 mm into the tissue site. In an embodiment, the pressure required to drive the protrusion 705 into the tissue site is between about 80 g and 120 g. In an embodiment, the pressure required to drive the protrusion 705 into the tissue site is about 5 g to about 20 g of pressure higher than the pressure applied by the spring clip of the sensor 501.

[0072] FIG. 10B illustrates another embodiment of a motor assembly 713. In the embodiment shown in FIG. 10B, the actuator 1015 has a generally oval cylindrical shape with shaft 1017. The oval shape allows the motor assembly to produce two times the active pulses per revolution as actuator 1003. The oval shape also provides a different shape to the pulse wave than actuator 1003. Piston 1019 is also shaped to be driven by actuator 1015.

[0073] In an embodiment, the personal health device disclosed herein is packaged with instructions for using the personal health device. In an embodiment, the instructions are purely graphical in nature so as to be universally understood by all users independent of reading capabilities or language skills.

Phase Shift Effects

[0074] Applying an artificial pulse or excitation can induce a phase shift in measurements among wavelengths used. Each wavelength probes the finger in different regions depending on scattering. Wavelengths with lower scattering probe the finger in a straight path from source to detector. Wavelengths with higher scattering probe the finger in a curved and broader path. Because the arterial pressure wave has a delay when it travels through the arteries and capillaries, the wavelengths with lower scattering are modulated by a pressure wave that travels closer to the finger's center and therefore has a smaller delay. The wavelengths with higher scattering are modulated by pressure waves that cover a broader area in the finger and therefore have a larger delay. The result is a measureable shift in time among wavelengths depending on the scattering values, absorption and finger/sensor geometry. This measurable shift can be used to estimate scattering properties and finger geometry which will remove errors observed from one finger to another. For example, in an embodiment, measureable phase shifts can be compared to empirically obtained data based on a cross section of the population. The comparison can then be used to compensate for error observed in the empirical data.

[0075] FIG. 11 illustrates an example of phase shift. In the example of FIG. 11, graph 1100 illustrates a phase plot of two wavelengths when an active pulse of 13.7 Hz is applied to the measurement site. Wavelength 1660 nm (1101) has an observed phase shift of 20 degrees or 4 ms with respect to wavelength 970 nm (1102).

[0076] FIG. 12 is a flow diagram of a phase shift measurement process. At block 1201, an artificial pulse is applied to the measurement site. At 1203, optical radiation of at least two different wavelengths is projected into the measurement site. At 1205, the optical radiation is detected after attenuation by the tissue undergoing the active pulse stimulation. At block 1207, a phase shift is determined between the wavelengths. At block 1209, the phase shift determination is used to compensate measurement data.

Terminology/Additional Embodiments

[0077] Conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment.

[0078] Depending on the embodiment, certain acts, events, or functions of any of the methods described herein can be performed in a different sequence, can be added, merged, or left out all together (e.g., not all described acts or events are necessary for the practice of the method). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores, rather than sequentially.

[0079] The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosure.

[0080] The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein can be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0081] The blocks of the methods and algorithms described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of computer-readable storage medium known in the art. An exemplary storage medium is coupled to a processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The processor and the storage medium can reside in an ASIC. The ASIC can reside in a user terminal. In the alternative, the processor and the storage medium can reside as discrete components in a user terminal.

[0082] While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices or algorithms illustrated can be made without departing from the spirit of the disclosure. As will be recognized, certain embodiments of the inventions described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others. The scope of certain inventions disclosed herein is indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.