Patent Publication Number: US-2007112287-A1

Title: System and method for detecting deviations in nominal gait patterns

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation-in-part of pending U.S. patent application Ser. No. 10/925,765, filed Aug. 25, 2004, and additionally claims the benefit of U.S. Provisional Patent Application No. 60/716,624, filed Sep. 13, 2005. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to the field of medical monitoring. More particularly, the present invention is directed to a system and method for detecting deviations in nominal gait patterns by employing a monitoring device adaptable for at least partial insertion within or, alternatively, for attachment in close proximity to the auditory canal.  
      2. Description of the Prior Art  
      The manner in which an individual traverses movements on foot is referred to as gait. The most basic of human gaits are walking and running. Such basic movements are regulated by the human body&#39;s neuromuscular and musculoskeletal systems. Through the combined coordination of muscle contractions, joint movements and sensory perception, an individual may traverse a path of travel in any desirable manner.  
      Assessing an individual&#39;s gait pattern can be useful for identifying particular areas of impairment and neurological defects affecting motor control. For example, information pertaining to an individual&#39;s particular gait pattern may generally be used to determine the existence of a physical impairment associated with weakened muscle development, limited range in the movement of joints or poor posture. Typically, an individual&#39;s gait pattern is assessed in connection with pathological conditions such as cerebral palsy, multiple sclerosis, Parkinson&#39;s disease, frontal lobe disease and various other neuromuscular disorders. However, providing a means for assessing an individual&#39;s gait pattern is not only useful for identifying physical impairments and neurological diseases, but rather it is also tremendously useful for monitoring the progress of rehabilitative measures and the recovery of patients after, for example, an injury resulting in bone fractures or orthopedic related surgical procedures. When properly assessed, an individual&#39;s particular gait pattern can help guide caregivers in determining the appropriate treatments and preventative measures to be implemented.  
      Gait analysis entails the process of quantifying and interpreting an individual&#39;s manner of movement. Modern means for analyzing gait have been known to employ a variety of sophisticated equipment. For instance, one commonly employed means for analyzing an individual&#39;s particular gait involves the use of video cameras positioned around a walkway having markers designating anatomical landmark points. The video cameras record the individual&#39;s movements as he/she traverses the walkway, wherein the recorded movements are then applied to a computer model for determining the underlying gait related motions of the individual. Other means for monitoring gait have employed the use of multiple wearable body sensors strategically positioned and attached to the upper torso of an individual, such as those described in U.S. Pat. No. 5,919,149, for diagnosing stability and balance impairments resulting from disorders.  
      These aforementioned gait assessment techniques, although non-invasive and likely effective in assessing the gait of an individual, require the use of expensive and intricate equipment set-ups. In addition, they are deficient in that they limit the extent of medically related applications in which gait assessment can be made useful. A lab type environment is typically required due to the sophistication and intricacies of these gait assessment techniques and, therefore, there are obvious limitations on the scope for which these gait assessment techniques can be used. For example, it would very difficult and costly to provide the aforementioned gait assessment techniques as a means for allowing continuous monitoring of individuals undergoing recovery. Existing gait assessment techniques lack ease of mobility. Moreover, every individual possesses a unique gait. In fact, gait is actively studied as a potential biometric marker For this reason, it is difficult to build an absolute gait classifier to indicate whether a particular gait is normal or pathological. Because the range of human gaits is so expansive, what may be a normal gait for one individual may be indicative of a health problem for another.  
      Accordingly, there exists a need for an improved system and method that can be employed through use of a monitoring device that is minimally invasive and maximizes mobility to allow for the detection of a deviation in an individual&#39;s unique nominal gait pattern.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide a minimally invasive monitoring device employing a light weight and cost effective design, thereby further providing a less cumbersome and highly mobile means for monitoring an individual&#39;s gait pattern.  
      It is another object of the present invention to provide a minimally invasive and mobile monitoring device capable of providing continuous monitoring of an individual&#39;s gait pattern to evaluate the effectiveness of rehabilitative measures, drug efficacy and restricted movements by an individual undergoing recovery.  
      It is another object of the present invention to provide a minimally invasive and mobile monitoring device capable of detecting various deviations in the unique nominal gait pattern of an individual under surveillance, thereby identifying early signs of neurological problems, deterioration rate of motor control and warning signs of imminent falls.  
      These and other objects are accomplished in accordance with the principles of the present invention, wherein the novelty of the present invention will become apparent ftom the following detailed description and appended claims.  
      In accordance with the present invention, a monitoring device configured for at least partial insertion within the auditory canal of an individual is provided. The monitoring device employs a system and method for detecting a deviation in a nominal gait pattern through use of an accelerometer embodied therein and positioned securely within an individual&#39;s auditory canal. In an alternate embodiment, the accelerometer is positioned in close proximity to the auditory canal by securely attaching the monitoring device between an auricle of an ear and a head of the individual. The accelerometer measures acceleration in three orthogonal directions aligned with the principal directions of the body. Acceleration measurements are digitized and processed through use of a Kalman filter, providing an estimation of the current state of the body. Gait features associated with the current state of the body are continuously extracted and accumulated to determine the unique nominal gait pattern of the individual. As new gait features associated with a current state of the body are extracted they are compared with previously accumulated gait feature statistics to detect deviations in the established nominal gait pattern of the individual. Suitable notification procedures are subsequently executed in response to detected deviations in the nominal gait pattern. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects and advantages of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:  
       FIG. 1  is a block diagram depicted within an exemplary monitoring device suitable for insertion within the auditory canal in accordance with a preferred embodiment of the present invention.  
       FIGS. 2A and 2B  are illustrations of an exemplary monitoring device suitable for placement between an auricle of an ear and a head in accordance with another embodiment of the present invention.  
       FIG. 3  is a flowchart illustrating the steps employed in detecting a deviation in a nominal gait pattern in accordance with a preferred embodiment of the present invention. 
    
    
      It is to be understood that the above-identified drawing figures are for purposes of illustrating the concepts of the present invention and may not be to scale, and are not intended to be limiting in terms of the range of possible shapes and proportions of the present invention.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The present invention is directed towards a system and method for detecting a deviation from an individual&#39;s nominal gait pattern. The present invention also serves as a means for providing continuous medical monitoring. For purposes of clarity, and not by way of limitation, illustrative views of the present invention are described with references made to the above-identified figures. Various modifications obvious to one skilled in the art are deemed to be within the spirit and scope of the present invention.  
      An exemplary monitoring device  10  is illustrated in  FIG. 1 . In accordance with a preferred embodiment of the present invention, monitoring device  10  is constructed and configured for at least partial insertion within an auditory canal of an individual. Monitoring device  10  is comprised of a housing  12  having gait change detection system  20  enclosed therein. A moldable exterior shell  14  may be provided circumferentially about the exterior surface of housing  12  of monitoring device  10 . Moldable exterior shell  14  is preferably constructed of a soft, yet durable, material capable of conforming to the interior walls of an individual&#39;s auditory canal in order to provide a comfortable and secure fitting of monitoring device  10 . For example, moldable exterior shell  14  may be constructed of a memory foam that can be compressed and inserted into the auditory canal. When the memory foam is released it expands and provides a secure custom fitting within the individual&#39;s auditory canal. It will be understood that the use of a memory foam is one of many suitable materials that may be used to construct a moldable exterior shell  14  and is merely provided as an example.  
      In an alternative embodiment, monitoring device  10  of  FIG. 1  may be constructed so as to be situated only partially within the auditory canal of an individual. For example, as illustrated in  FIGS. 2A and 2B , an exemplary monitoring device  10 ′ is comprised of a housing  11 , a processing extension  13  and a plug  15 . Monitoring device  10 ′ is configured for suitable placement between an auricle  17  of an ear and a head  19  of an individual. As illustrated in the enlarged view of  FIG. 2B , housing  11  is shaped to the curved contour of the ear of an individual. Processing extension  13  extends from an end of housing  11  to plug  15 , which is inserted within the auditory canal of the individual. Plug  15  may similarly be constructed with a moldable exterior shell  14  (not shown) to provide a secure custom fitting within the auditory canal of the individual.  
      Gait change detection system  20  provided within housing  12  of  FIG. 1  is comprised of at least one accelerometer  22 , an analog-to-digital (ADC) converter  28 , a processor  30 , an extraction unit  32 , a memory component  34 , a detection unit  36 , a notification alarm  38 , a speaker  40 , a wireless transmitter/receiver  42 , and an antenna  44 . The components of system  20  may, similarly, be provided entirely within housing  11  (not shown) or, alternatively, distributed between housing  11  and plug  15  and connected by processing extension  13  of  FIG. 2B . For example, accelerometer  22  may be fixed within bud  15 , wherein corresponding signals are transmitted to ADC  28  and processor  30  provided in housing  11  via processing extension  13 .  
      Various neurological diseases that affect motor control and gait possess unique identifiable characteristics. For example, in frontal lobe disease an individual is prone to small shuffling steps. These small shuffling steps might be detected from features such as forward velocity, vertical acceleration and step frequency. As another example, in Parkinson&#39;s disease an individual is prone to small rapid steps, small backward steps after attempting to stop and difficultly turning quickly. The small rapid steps and backward steps are also detectable as a signature identifier of this particular disease. The progression of neurological diseases that affect motor control, as well as imminent dangers of falling due to dizziness, vertigo or blackout, can be detected simply by employing a monitoring means for assessing the distinguishable random direction and step frequencies associated with each. Therefore, accelerometer  22  is preferably a three-axis accelerometer that can be used to measure acceleration in the three orthogonal directions aligned with the principal directions of the human body.  
      In order for accelerometer  22  to be useful in monitoring an individual&#39;s gait, it must be of the type sensitive to low frequency and low amplitude motions. In addition, accelerometer  22  is preferably of small circuit design and low power consumption, such as those produced by Hitachi Metals, Ltd., so that it may be properly integrated within the limited space allotted by housing  22 . A gyroscope  24  and a level meter  26  may also be integrated into system  20  to supplement the acceleration measurements taken by accelerometer  22 . A gyroscope is typically used to measure and maintain orientation. For example, gyroscope  24  may be integrated in conjunction with accelerometer  22  of system  20  to correct for horizontal motions of an individual&#39;s head not related to body movement. Similarly, level meter  26  may be provided to correct for vertical motions of the head not related to body movement.  
      Accelerometer  22 , gyroscope  24  and level meter  26  are coupled to processor  30  through ADC  28 . Acceleration signals measured by accelerometer  22 , as well as corrective measurements provided by gyroscope  24  and level meter  26 , are digitized by ADC  28  after any necessary signal conditioning and pre-processing. Processor  30  is further coupled to extraction unit  32  and detection unit  36  in order to, respectively, extract and analyze relevant gait features corresponding to the acceleration measurements provided by accelerometer  22 . Relevant gait features are continuously extracted and may be stored in memory component  34  in order to accumulate gait feature statistics and derive the nominal gait pattern of a particular individual.  
       FIG. 3  is an illustrative depiction of the steps employed by system  20  for monitoring and detecting a deviation in an individual&#39;s nominal gait pattern. System  20  is initiated, at step  302 , after proper and secure positioning of monitoring device  10  or housing  11  and plug  15  of monitoring device  10 ′, respectively, within the auditory canal or between the auricle  17  and head  19  of an individual. Upon the proper positioning of monitoring device  10  or  10 ′ at step  302 , system  20  is activated and acceleration is measured, at step  304 , in the three orthogonal directions aligned with the principal directions of the individual&#39;s body. Necessary conditioning, pre-processing and digitizing of the acceleration signals measured by accelerometer  22  are then performed at step  306 . After acceleration signals measured by accelerometer  22  are digitized at step  306 , the digitized acceleration signals are processed by processor  30  at step  308 . Processor  30  may employ a Kalman filter in conjunction with the digitized acceleration measurements to derive estimations of the current state of the individual, comprising of the individual&#39;s position, velocity and acceleration in three axes at a particular point in time. Thereafter, relevant gait features are extracted from the estimations at step  312 .  
      In some instances, specific gait feature may be predefined in system  20  and associated with an indication that an individual has fallen or is in clear imminent danger of falling. When these predefined gait feature values are identified, system  20  may be configured to bypass other processing procedures and automatically trigger notification procedures to alert a third party that an individual under surveillance has fallen or is on the verge of an imminent fall. The notification procedures may also be configured to warn the individual of a potential loss of balance and an imminent fall. Therefore, if a gait feature value extracted from current state estimations generated at processing step  308  matches a predefined gait feature value, or is classified within a predefined range of values identified at step  310 , system  20  may bypass intermediate steps  314  and  316  (discussed in further detail below) and execute notification procedures in connection with step  320 .  
      If predefined gait feature values, as described above, are not matched at step  310 , system  20  proceeds with the execution of step  312 . At step  312 , relevant gait features are extracted from the current state readings provided at processing step  308 , generating a time-to-space mapping of locally stationary relevant gait features that have been extracted. Statistics of these relevant gait features are accumulated over a period of time and stored, for example, in memory component  34  of system  20 . Alternatively, for substantially longer periods of time involving the monitoring of an individual, statistics of relevant gait features may be transmitted via wireless transmitter/receiver  42  employing antenna  44  to a remote monitoring location (not shown) for storage and analysis.  
      As relevant gait features are extracted from current state estimations and accumulated into memory, system  20  is continuously comparing the values associated with current state gait features to previously accumulated gait features statistics, as provided in step  314 . This continuous comparison and accumulation of gait feature statistics permits system  20  to determine the nominal gait pattern for the particular individual under surveillance. Once an nominal gait pattern is recognizable, system  20  becomes highly efficient in detecting deviations exceeding a predefined permissible range. Deviation detection is performed at step  316  using, for example, detection unit  36  of  FIG. 1 . Current gait feature values acquired by extraction unit  32  and previously accumulated gait feature statistics stored in memory component  34  are made accessible to detection unit  36 , allowing detection unit  36  to execute a comparison and determine whether there is a deviation exceeding a predefined permissible threshold.  
      If a deviation is not detected, currently extracted gait features are accumulated with previously extracted gait features at step  318 , furthering contributing to the derivation of the nominal gait pattern of the individual under surveillance. The accumulation of gait features stored at step  318  is linked back to step  314  to allow for ongoing comparison of incoming gait features with previously accumulated gait features statistics. However, if a deviation is detected at step  316 , detection unit  36  of system  20  may report the detected deviation back to processor  30 , triggering the execution of notification procedures at step  320 . System  20  may be configured so that notification procedures executed at step  320  may continue to be executed until the particular notification alarm is reset at step  322 . Once the notification alarm is reset, system  20  may return to step  304  to continue measuring acceleration of the individual under surveillance.  
      Notification procedures executed at step  320  may include the transmission of a notification alarm to the caregiver and an audible alarm or a predefined notification message to the individual under surveillance. For example, in the case of detecting an imminent fall, an audible alarm may be sounded to the patient via speaker  40  of monitoring device  10 , as well as to the caregiver via a wireless transmission using transmitter/receiver  42  coupled to antenna  44  of monitoring device  10 . The notification procedures executed at step  320  may also include the transmission of a notification message by a caregiver from a remote location to the individual under surveillance upon receiving a notification alarm indicating a deviation in the individual&#39;s nominal gait pattern or, alternatively, triggering of a predefined notification message stored in memory component  34  of system  20  to be aurally presented to the individual via speaker  40  of monitoring device  10 . For example, a notification message may be wirelessly transmitted by the caregiver from a remote location to system  20  of monitoring device  10  or  10 ′ upon receipt of a notification alarm and aurally presented to the individual under surveillance. It should be understood that the notification procedures described above are provided merely as examples and that various notification procedures may be implemented in accordance with the principles of the invention.  
      One skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which are presented for purposes of illustration and not by way of limitation, and the present invention is limited only by the claims that follow.