Patent Application
20060089557
This invention relates generally to heart rate detection and more particularly to the use of light to detect a heart rate.
An individual's heart rate (i.e., the periodicity of that individual's heartbeats, typically denoted as beats per minute) comprises an important indicator of that individual's present or near-term physical well being. Detection of the pulse of the heart permits calculation of a corresponding beat-to-beat heart rate. The beat-to-beat heart rate, in turn, permits calculation of heart rate variability for that individual. Heart rate variability facilitates an ability to assess the potential onset of coronary distress such as ventricular arrhythmia. This has potential important application in certain public service applications. For example, recent statistics indicate that approximately 50% of all firefighter's job-related deaths result from a coronary event, and approximately 25% of job-related deaths for law enforcement personnel such as police are due to a similar cause.
Unfortunately, a cost-effective, robust, and reliable mechanism to permit on-the-job monitoring of this sort for public safety personnel remains unmet. There are, of course, numerous available products that provide a measure of an individual's heartbeat. One example is a heart rate sensor chest strap that uses electrodes to detect the heart's electrical performance. Such a form factor comprises an unsatisfactory solution for many public safety personnel. This mechanism requires separate, and early, careful placement and installation, and hence its usage remains at odds with the time-critical nature of the public safety paradigm. It may be expected that, at least some of the time, an individual will decline to take the required time to don and/or test the apparatus for proper placement and functionality.
Another prior art solution comprises a watch that measure heart rate. This device, however, does not provide continuous monitoring. It must usually be momentarily activated by the individual through contact with a finger on an opposing hand. Such an approach does not serve well to provide sufficient and on-going data to permit calculation of heart rate variability.
Yet another approach utilizes a ring bearing an infrared sensor that can measure the wearer's pulse. In many instances, however, public safety personnel such as firefighters often use their hands in an aggressive manner (pulling, pushing, carrying, or otherwise wielding heavy objects, for example). Such actions present the likelihood of introducing signal artifacts that will distort a resultant heart rate variability calculation.
Other mechanisms and form factors exist as well, including devices that clip to the ear lobe. In general, however, such prior art approaches tend to require an inappropriate amount of time to properly don and locate, are subject to dislodgement during anticipated use, and/or are unduly sensitive to the harsh operating conditions of a public safety worker and either readily fail to adequately track the beat of the heart or introduce sufficient noise to render their usage problematic when seeking to detect heart rate variability.
The above needs are at least partially met through provision of the method and apparatus to facilitate heart rate detection described in the following detailed description, particularly when studied in conjunction with the drawings, wherein:
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will also be understood that the terms and expressions used herein have the ordinary meaning as is usually accorded to such terms and expressions by those skilled in the corresponding respective areas of inquiry and study except where other specific meanings have otherwise been set forth herein.
Generally speaking, pursuant to these various embodiments, an apparatus to facilitate heart rate detection comprises at least one sensor cluster that comprises at least one light sensitive sensor and a plurality of light emitters that are disposed closely proximal to the light sensitive sensor and a heart rate detector that operably couples to the sensor cluster. In a preferred approach, a plurality of such sensor clusters are disposed in close proximity to a subject user. The light emitters are caused to each emit light and the light sensitive sensors detect interactions between the subject user and the emitted light. Those interactions are then used to determine a heart rate for the subject user.
Depending upon the needs of a given application, the light emitters can all emit light having a substantially same wavelength, or at least one or more of the light emitters can emit light having a different wavelength. Such emitted light can comprise, for example, an infrared wavelength, a visible light wavelength, and so forth. Pursuant to one approach, the light emitters and light sensitive sensor can be positioned as a grouped cluster. Pursuant to another approach such elements are disposed closely proximal to one another in a substantially co-linear orientation.
Pursuant to a preferred approach, when a plurality of sensor clusters are deployed with respect to a single individual, a determination can be made regarding at least one signal quality factor (such as, but not limited to, apparent noise content and/or apparent signal accuracy) for at least some of the detection interactions. This determination can be used to provide a corresponding alteration value. This alteration value, in turn, can be used to modify at least one of the interactions prior to using the interactions to determine the subject user's heart rate. For example, this alteration value can comprise a gain value that modifies such an interaction through application of the gain value to the interaction.
By so altering a value as corresponds to at least one such interaction as a function, at least in part, of likely validity of the value, and then using the altered value when using the interactions to determine a subject user's heart rate, more robust performance can be expected. This, in turn, permits greater latitude with respect to the form factor and interface requirements of a useful heart rate detection system.
These and other benefits may become more evident upon making a thorough review and study of the following detailed description. Referring now to the drawings, and in particular to
Pursuant to one approach, and referring momentarily to
This sensor cluster 11 can be configured in a wide variety of form factors. As illustrated, the individual sensors and emitters can be closely clustered proximal to one another and share a common housing or other support platform. If desired, and referring momentarily to
Such light sensitive sensors 12 and light emitters 14 are generally well understood in the art. Further, these teachings are not particularly sensitive to selection of a particular sensor or emitter and are generally applicable to many such elements. Therefore, for the sake of brevity and the preservation of focus additional elaboration will not be provided here regarding such devices.
Referring again to
If desired, and as may be preferred for many applications, the heart rate detector 16 can further operably couple to one or more additional sensor clusters 11a and 11b. Use of additional sensor clusters can provide useful information to permit more reliable detection of the subject user's heart rate as will be described more fully below. In general, such additional sensor clusters can be similar or identical to the sensor cluster 11 described above and can each include one or more light sensitive sensor and a corresponding plurality of light emitters that are again disposed closely proximal to the light sensitive sensor. When using additional sensor clusters, it is also possible to have the light emitters of, for example, a second sensor cluster 11a use a light wavelength that is different than the light emitters of the first sensor cluster 11. Other combinations are of course possible if desired. For example, a first one of the sensor cluster could comprise light emitters that all use a common light wavelength and another of the sensor clusters could comprise light emitters that use a mix of light wavelengths.
In many cases, when using a plurality of sensor clusters, it will be desirable to dispose at least some of the sensor clusters substantially distal to one another. For example, and referring now to
So configured, light emitted from the light emitters impinges upon the skin of the wearer. This light interacts with the user in a known manner that varies in a relatively predictable manner as a function of the wearer's pulse rate. That is, the momentary increase of blood pressure due to a heartbeat will cause a variation in the reflected light as sensed by a corresponding light sensitive sensor. Use of light for the general purpose of detecting a heartbeat comprises a known area of endeavor. The above-described embodiments, however, offer particular advantages in this regard when deployed in more difficult monitoring situations such as those mentioned above. In particular, the use of multiple light emitters as described can aid in assuring a usable signal notwithstanding a physically noisy and highly dynamic operating environment.
Such an apparatus, or any other enabling apparatus as may be available in a given instance, can be employed to effect a heart rate detection process 60 such as that illustrated in
So deployed, this process 60 then causes 63 the plurality of light emitters that comprise the sensor clusters to each emit light. If desired, such light emission can be continuous or substantially continuous. Since power consumption will often comprise a design concern, however, it will usually be preferable to effect this process using a reduced duty cycle. For example, useful results can be expected using a duty frequency of 10% when employing a light frequency of 400 Hz. (The fastest adult human heart typically will not exceed 4 Hz, so a pulse signal sampled at 400 Hz will provide 100 data points per beat under even these relatively extreme circumstances.)
This process 60 then uses 64 the light sensitive sensors to detect the expected interactions between the subject user and the light as emitted by the plurality of light emitters. These interactions are then used 65, in turn, to determine a corresponding heart rate for the subject user. The heart rate can then be used to calculate heart rate variability for the subject user as noted above if desired. In a preferred embodiment, and as will be described in more detail below, when a plurality of sensor clusters are deployed, this step preferably comprises processing the interaction information from each of the sensor clusters in combination with each other in order to determine the subject user's heart rate.
One advantage of deploying multiple sensor clusters in a distal orientation with respect to one another is that each sensor cluster will experience a different local physical environment. For example, when deployed within a face mask for breathing equipment, some of the sensor clusters may have a relatively optimum placement with respect to the wearer's skin while other sensor clusters may be less optimally placed at any given moment depending upon, for example, movement of the wearer, contact between the face mask and other objects, and so forth. In many cases, momentary dislocation of one or more of the sensor clusters will nevertheless not unduly adversely impact one of more of the remaining sensor clusters.
Using 65 the detected interactions to determine a user's heart rate can therefore beneficially further comprise making a determination regarding at least one signal quality factor (such as but not limited to noise content and/or apparent signal accuracy) for at least some (and preferably all) of the interactions to provide at least one alteration value and use of that alteration value to modify at least one of the interactions prior to using the interactions to determine the user's heart rate. For example, and as will be described below in more detail, such dynamic modifications can be employed to alter a gain value that is, in turn, applied to a signal that corresponds to the interaction information to thereby facilitate minimizing reliance upon interaction information that appears suspect while fostering reliance upon interaction information that appears to be more reliable.
Referring now to
The signal processing unit 70 provides a block 71 comprising a frequency and magnitude range and noise level detector and pre-filter that receives the light sensitive sensor 12a output. This frequency and magnitude range and noise level detector and pre-filter 71 provides four outputs with a first output coupling to a first amplifier 75 having a variable gain Gp. This variable gain Gp is increased or decreased depending on the detected frequency and magnitude range and noise level. A second output is coupled to a second amplifier 77 having a variable gain Gd. This variable gain Gd is reduced or increased by the range and noise level detection of the block 71. The third output signal from this block 71 is a pre-filtered signal 12a directed to a low pass filter system 72 with cut off frequencies, in this embodiment, of 40 Hz and below. The fourth output signal from this block 71 is the pre-filtered signal 12a coupled to a derivative processor 73 that extracts the derivative of the incoming signal. The low pass filter 72 and the derivative processor 73 then each provide an output to a corresponding one of the first and second amplifier 75 and 77 wherein the first amplifier 75 has a variable gain Gp and the second amplifier 77 has a variable gain Gd. Each amplifier's 75 and 77 variable gain value is continuously influenced by the two outputs of this block 71.
In a preferred approach, these gain values are also influenced by corresponding prediction calculations. In the case of the amplifier 75 that couples to the low pass filter 72, the low pass filter 72 further couples to a predictor 74 that processes that incoming data in comparison with respect to a current overall heart rate calculation as per the function f(t) from a heart rate calculation unit 78. The resultant signal represents a sense of how well, or how poorly, the current trajectory of the incoming low pass signal corresponds to a current trajectory of a best overall calculation of the heart rate. This, in turn, is used to vary the gain Gp of the amplifier 75 for the low pass filter 72. So configured, when the behavior of the low pass filtered version of the signal from this particular light sensitive sensor 12a appears to correspond well with an overall view of the subject's heart beat, that low pass filtered version of the signal can be emphasized or at least not de-emphasized with respect to its subsequent use during calculation of the heart rate. Similarly, when the low pass filtered version of the signal from this light sensitive sensor 12a appears suspect (due to noise or any other cause or reason), the low pass filtered version of the signal can be de-emphasized accordingly and hence ameliorate the influence of that suspect signal with respect to calculation of the subject user's heart rate.
A similar process occurs for the derivative processed signal path. A derivative predictor 76 processes incoming information from the derivative processor 73 and compares that result against a similarly processed version of the overall heart rate calculation. Again, that comparison serves to provide information that is used to influence the gain Gd and thereby influence the extent to which this calculation impacts the heart rate calculation.
The gain modified outputs of the low pass filter 72 and the derivative processor 73 are then linearly combined, respectively, with the corresponding signals from other available light sensitive sensors 12b with the resultant combined signals then informing a standard heart rate calculation process 78 to yield a present determination f(t) regarding the subject's heart rate.
So configured, a plurality of sensor clusters can be disposed in various ways and/or in various monitoring locations with respect to a wearer's skin. By providing processing that aids in dynamically minimizing the contribution from sensor clusters that are presently providing unreliable information, one can also avoid, to a significant extent, a need for specialized placement and/or attention to the sensor clusters during use. In effect, to a large degree, a user can simply don their usual work apparel and/or pay only brief attention to installation of the sensor cluster(s) carrier item. Upon installation and/or during use, some of the sensor clusters may well be non-optimally placed, but other sensor clusters are more likely to be sufficiently well situated to permit accurate heart rate detection. To illustrate, and referring now to
Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept.
