Patent Publication Number: US-2012029375-A1

Title: Respirations Activity and Motion Measurement Using Accelerometers

Description:
BACKGROUND 
     There is currently no low cost, accurate system to measure respirations (i.e., breaths per minute). In high acuity situations, a carbon dioxide monitor, including a nasal and/or mouth cannula, can be used to estimate respirations by monitoring airflow into and out of an individual&#39;s mouth or nose. However, such machines are complex, costly, and invasive. Otherwise, in lower acuity situations, a crude manual estimate of respirations can be made by a caregiver observing the speed and level of respirations of the individual. However, such a manual estimate is prone to inaccuracy and is incomplete, since the measurement is subjective and conducted only for the duration of time that the individual is observed by the caregiver. 
     SUMMARY 
     Embodiments of the present disclosure are directed to systems and methods for estimating respirations for an individual. In some examples described herein, an accelerometer is coupled to the individual to estimate respirations of the individual. 
     In one aspect, a system for estimating respirations includes: an accelerometer configured to be coupled to an individual&#39;s torso, the accelerometer being configured to measure a tilt of the accelerometer as the individual breathes; and a processor connected to the accelerometer, the processor being programmed to process tilt data from the accelerometer and to estimate a respiration rate based on the tilt data. 
     In another aspect, a method for estimating respirations includes: coupling a tilt sensor to a torso of an individual; measuring tilt data from the tilt sensor as the individual breathes; and estimating a respiration rate of the individual based on the tilt data. 
     In yet another aspect, a computer-readable data storage media encodes instructions that, when executed by a processor, cause the processor to: receive tilt data from a tilt sensor coupled to a torso of an individual; monitor the tilt data as the individual breathes; and estimate a respiration rate of the individual based on the tilt data. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present disclosure can be better understood with reference to the description below. Within the drawings, like reference numbers are used to indicate like parts throughout the various views. Differences between like parts may cause those like parts to be each indicated by different reference numbers. Unlike parts are indicated by different reference numbers. 
         FIG. 1  shows an example system for estimating respirations. 
         FIG. 2  shows an example sensor from the system of  FIG. 1 . 
         FIG. 3  shows the sensor of  FIG. 2 . 
         FIG. 4  shows the sensor and an example monitor from the system of  FIG. 1 . 
         FIG. 5  shows an example method for estimating respirations. 
         FIG. 6  shows another example method for estimating respirations. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are directed to systems and methods for estimating respirations for an individual. In some examples described herein, an accelerometer is coupled to the individual to estimate respirations of the individual. 
     Accelerometers can be used to measure both dynamic and static measurements of acceleration. Tilt is a static measurement. When measuring tilt, gravity is the acceleration that is measured. To achieve a tilt measurement, a low-gravity, high-sensitivity accelerometer is desirable. Such accelerometers experience acceleration in the range of +1 g to −1 g as the device is tilted from −90 degrees to +90 degrees. 
     By using an accelerometer to measure tilt, an individual&#39;s respirations can be estimated. For example, in some embodiments, a wearable accelerometer is used that measures multi-axis movement and multi-axis acceleration. The accelerometer is positioned on the individual&#39;s torso, and the accelerometer is used to measure the tilt of the accelerometer as the individual&#39;s chest moves during respirations. This tilt information is, in turn, used to estimate the respirations of the individual. 
     In one embodiment, the accelerometer is a DC-response sensor that measures tilt. As the orientation of the accelerometer changes (i.e., is tilted), the impact of gravity on the accelerometer changes in a cyclical and repeatable manner, and the accelerometer can be configured to measure this change. By processing the tilt patterns measured by the accelerometer, the individual&#39;s respirations are estimated. 
       FIGS. 1-3  show an example system  100  including a sensor  110 , a monitor  120 , and a server computer  130 . 
     In the example shown, the sensor  110  is an accelerometer that is coupled to a strap  112  that is positioned around the torso  104  of an individual  102 . In this example, the sensor  110  is a multi-axis accelerometer, such as an ADXL325 accelerometer manufactured by Analog Devices of Norwood, Me. 
     The sensor  110  is programmed to measure the tilt of the sensor  110  as the individual  102  breaths. For example, as shown in  FIG. 2 , the sensor  110  is positioned against the torso  104  of the individual, such as at the chest. In such an orientation, the force of gravity acting in a direction G can be measured by the sensor  110  throughout a respiration cycle. 
     Referring now to  FIG. 3 , as the individual breaths, the individual&#39;s lungs fill with air, causing the individual&#39;s torso to expand. Upon expansion, the orientation of the sensor  110  is changed. Upon such a tilt, a sensing axis  316  of the sensor  110  is changed, and an angle θ is formed between the sensing axis  316  and the force of gravity in the direction G. 
     By monitoring this periodic tilt of the sensor  110  as the individual breaths, the sensor  110  can be used to estimate a rate of respiration. Further, by estimating the magnitude of the angle θ, the quality of each of the breaths (e.g., shallow, deep, etc.) can also be estimated. The sensor  110  can also be programmed to measure the dynamic acceleration of the sensor  110  as the individual breathes to supplement the estimate of the rate and/or quality of respirations. 
     Further, the sensor  110  can be used to estimate a status of the individual as the respiration measurements are taken. For example, an estimate of whether the individual is prone or upright can be made as the respiration estimates are taken. In addition, an estimate of whether the individual is moving or still can also be made. If moving, an estimate of the type of movement (e.g., ascending, descending, level) can also be made. These characteristics can be examined as the respirations estimates are made to provide further detail to supplement the data. For example, the respirations may increase as the individual runs or ascends a large hill. Other configurations are possible. 
     Referring again to  FIG. 1 , in the examples shown, the sensor  110  communicates with the monitor  120  using wireless or wired technologies. For example, in one embodiment, the sensor  110  communicates with the monitor  120  using a wireless protocol such as Bluetooth. Additional details of the pairing of the sensor  110  with the monitor  120  are disclosed in U.S. patent application Ser. No. 12/723,726 filed on Mar. 15, 2010 and U.S. patent application Ser. No. 12/827,817 filed on Jun. 30, 2010, the entireties of which are hereby incorporated by reference. Other configurations are possible. 
     Once paired, in a first embodiment, the sensor  110  sends data related to the tilting of the sensor  110  to the monitor  120 . The monitor  120 , in turn, estimates respirations based on the tilt data from the sensor  110 . In a second embodiment, the sensor  110  is programmed to estimate respirations based on the data sensed by the sensor  110 . The sensor  110  thereupon sends the estimated respirations to the monitor  120 . 
     The monitor  120  can display the estimated respiration data to a user, such as a caregiver. For example, the monitor  120  can display the rate of respiration (e.g., breaths per minute), the quality of respiration (e.g., shallow, deep, etc.), and/or the activity level of the individual (e.g., lying down, upright, moving, etc.). 
     In the examples shown, the monitor  120 , in turn, communicates with a server computer  130 . The monitor  120  can communicate the respiration data to the server computer  130 . The server computer  130  can further process the data, display the data to a caregiver (e.g., at a central monitoring station in a hospital), and/or store the data (e.g., in the individuals electronic medical record). 
     Referring now to  FIG. 4 , additional details about the sensor  110  and the monitor  120  are shown. 
     The sensor  110  including an orientation detector  402 , an optional processor  404 , a memory  406 , a radio  408 , and a power source  410 . 
     The orientation detector  402  is the accelerometer that can measure the tilt and/or acceleration of the sensor  110 . In one example, the orientation detector is a three-dimensional accelerometer. The orientation detector  402  is configured to measure orientation at given intervals, such as every 20 seconds, once per minute, once per hour, once every hour, etc. For example, the orientation detector  402  is configured to estimate a tilt and/or an orientation of the sensor  110 , as described herein, to estimate respirations and/or body position. The orientation detector  402  can be set to custom sampling times (e.g., spot check versus monitoring) and to average times depending on the application. 
     In one example, the orientation detector  402  samples three difference axis (X, Y, Z) of orientation to determine what position the individual is in and what axis is predominate to extract respiratory cycles. The relevant axis can vary depending on the position of the individual (i.e., lying down versus sitting up versus angled in bed, etc.). A most relevant axis can be derived from a combination of X, Y, and Z. 
     In some examples, the sensor  110  includes the processor  404  that takes the orientation data from the orientation detector  402  and can manipulate the data to estimate respirations and body position. For example, the processor  404  can obtain the tilt data from the orientation detector  402  and use that tilt data to estimate a rate of respirations for the individual. In other examples, the processor  404  can be omitted, and the data from the orientation detector  402  can be sent to another device to estimate respirations (e.g., the monitor  120 ). 
     The memory  406  is used to store instructions that are executed by the processor  404 , as well as to store data from the orientation detector  402 . In the example shown, the memory  406  includes a random access memory (“RAM”) and/or a read-only memory (“ROM”). In some examples, the memory  406  can also include a mass storage device. The mass storage device stores software instructions and data. 
     The mass storage device and its associated computer-readable data storage media provide non-volatile, non-transitory storage. Computer-readable data storage media include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable software instructions, data structures, program modules or other data. Example types of computer-readable data storage media include, but are not limited to, RAM, ROM, EPROM, EEPROM, flash memory or other solid state memory technology, CD-ROMs, digital versatile discs (“DVDs”), other optical storage media, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the monitor  120 . 
     As mentioned above, the mass storage device and the RAM can store software instructions and data. The software instructions can include an operating system suitable for controlling the operation of the sensor  110 . The mass storage device and/or the RAM also store software instructions, that when executed by the processor  404 , cause the sensor  110  to provide the functionality of the sensor  110  described herein. For example, the mass storage device and/or the RAM can store software instructions that, when executed by the processor  404 , cause the sensor  110  to monitor and estimate respirations as described herein. 
     The radio  408  is used to communicate with other devices, such as the monitor  120 . In some examples, the radio  408  communicates using Bluetooth, although other networking protocols such as 802.15.4, ZigBee, UWB, a low-power 802.11 network, or a proprietary network could be used. 
     The power source  410  powers the sensor  110 . In one example, the power source  410  is a battery. In another example, the power is harvested from the individual and/or is provided from an external source (e.g., mains power). Other configurations are possible. 
     The monitor  120  includes a processor  422 , a memory  424 , a radio  426 , and an input/output device  428 . 
     Similar to the sensor  110 , the processor  422  of the monitor  120  is programmed to take the orientation data from the orientation detector  402  and manipulate the data to estimate respirations and body position. The memory  424  is likewise configured to store data and instructions for execution. The radio  426  is programmed for wireless communications (wired communications are also possible) with the sensor  110 . 
     The input/output device  428  can be one or more of a number of different devices. For example, the device  428  can be a display that displays various parameters associated with respirations to the caregiver, such as rate of respiration (e.g., breaths per minute), the quality of respiration (e.g., shallow, deep, etc.), and/or the activity level of the individual (e.g., lying down, upright, moving, etc.). The device  428  can also be an input device, such as a keyboard or touch screen. Other types of possible devices include a mouse, a printer, or other type of input or output devices. 
     In one example, the monitor  120  is a patient monitor device such as that disclosed in U.S. patent application Ser. No. 12/751,579 filed on Mar. 31, 2010, the entirety of which is hereby incorporated by reference. 
     Referring now to  FIG. 5 , an example method  500  for estimating respirations information is shown. 
     Initially, at operation  502 , the tilt of the sensor is measured at periodic intervals. Next, at operation  504 , the tilt data is used to estimate respiration information, as described herein. 
     Referring to  FIG. 6 , another example method  600  for estimating respirations information is shown. 
     Initially, at operation  602 , the input signals from the different axis of a multi-axis accelerometer are processed. Next, at operation  604 , the signals are run through a high-pass filter to reduce extraneous noise. 
     Next, at operation  606 , a pause is used to wait for the signals to stabilize. For example, in some embodiments, the pause is about 1 second, 5 seconds, 10 seconds, 15 seconds, 20 seconds, or 30 seconds. Next, at operation  608 , a determination is made as to whether or not the signals have stabilized. If the signals have not stabilized, control is passed back to operation  606  for additional waiting. 
     Otherwise, control is passed to operation  610 , at which a search routine is used to determine the best respiration signal candidate from the various input signals (i.e., the signals from the X, Y, and Z axis). In one example, a band-pass filter is applied within the ¼ to ½ hertz range in an attempt to find the best respiration signal candidate. Signals falling below that range are typically associated with gravity, and signals above the range are typically associated with activity. 
     Next, at operation  614 , a test is performed to determine if the signal is likely respiration or noise. One example of such as test is to determine if there are multiple occurrences of cyclical changes having a period that represents a reasonable human respiration rate. At operation  616 , a determination is made regarding whether the signal is a respiration candidate. If not, control is passed back to operation  606 . 
     If so, control is instead passed to operation  620 , where the rate of respiration is estimated, and, in some embodiments, the rate is displayed for the caregiver to review. Next, at operation  622 , a refresh pause is instituted, such as 0.5 seconds, 1 second, 2 seconds, or 5 seconds depending on how quickly updating of the display is desired. Finally, after the refresh pause, control is passed back to operation  618 . 
     Various embodiments disclosed herein can be implemented (1) as a sequence of computer implemented acts or program modules running on a computing system and/or (2) as interconnected machine logic circuits or circuit modules within the computing system. The implementation is a matter of choice dependent on the performance requirements of the computing system. Accordingly, logical operations including related algorithms can be referred to variously as operations, structural devices, acts or modules. It will be recognized by one skilled in the art that these operations, structural devices, acts and modules may be implemented in software, firmware, special purpose digital logic, and any combination thereof without deviating from the spirit and scope of the present disclosure. 
     Although the disclosure has been described in connection with various embodiments, those of ordinary skill in the art will understand that many modifications may be made thereto. Accordingly, it is not intended that the scope of the disclosure in any way be limited by the above description.