Abstract:
A method of evaluating a chest wall protector comprises determining a flight time to impact on a subject of a projectile launched using a bow, determining an actuation time of a mechanism configured to release a string of the bow to launch the projectile based upon a desired time of receipt of energy from the projectile by a heart of the subject, determining an external location on an exterior surface of the subject corresponding to where a left ventricle of the heart of the subject is desirably close to the external surface, arranging at least one of the subject and the bow such that a flight path of the projectile is directed at the determined external location, disposing a protector device in the projectile&#39;s flight path in contact with the subject, actuating the mechanism at the actuation time, and monitoring a heartbeat of the subject before and after transfer of energy from the projectile to the subject.

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application Ser. No. 60/591,494, filed Jul. 27, 2004 and entitled, “Commotio Cordis Testing,” and to U.S. application Ser. No. 11/127,548, filed May 12, 2005 and entitled, “Chest Wall Protector,” each of which is herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Sudden (and usually immediate) death due to impact to the chest (a phenomenon known as commotio cordis) in the absence of underlying cardiac disease has occurred in at least 170 documented cases. The object that initiates commotio cordis generally travels at a speed greater than 25 miles per hour when it strikes the person, which initiates instantaneous ventricular fibrillation. The deaths typically result from impact during sports, e.g., by being hit by a baseball, a puck, a softball, a lacrosse ball, or a hand, foot, or elbow (e.g., in martial arts). Efforts have been undertaken to mandate the use of chest protection for at-risk sports participants, such as baseball and lacrosse players. Assessing the effectiveness of chest wall protection necessitates the development of a model of commotion cordis to understand the mechanism and to evaluate preventive measures. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention are directed to a method of evaluating a chest wall protector. The method includes determining a flight time to impact on a subject of a projectile launched using a bow, determining an actuation time of a mechanism configured to release a string of the bow to launch the projectile based upon a desired time of receipt of energy from the projectile by a heart of the subject, determining an external location on an exterior surface of the subject corresponding to where a left ventricle of the heart of the subject is desirably close to the external surface, arranging at least one of the subject and the bow such that a flight path of the projectile is directed at the determined external location, disposing a protector device in the projectile&#39;s flight path in contact with the subject, actuating the mechanism at the actuation time, and monitoring a heartbeat of the subject before and after transfer of energy from the projectile to the subject. 
     Implementations of the invention may include one or more of the following features. The method may include determining whether commotio cordis is induced in the subject due to the transfer of energy from the projectile to the subject. The actuation time can be a time relative to a reference point of a heartbeat cycle of the subject. The protector can be disposed in direct contact with the subject. The arranging can include using reference markings on a frame of the bow and sighting down the flight path of the projectile to aim the bow. 
     Further embodiments of the invention are directed to a system for evaluating a chest wall protector&#39;s effectiveness for inhibiting commotio cordis due to impact from a projectile. The system includes a launch mechanism configured to couple to the projectile and to launch the projectile toward a subject, the launch mechanism including a bow including a string, and a release mechanism configured to selectively retain the string with the bow in a drawn position, a retaining device configured to hold the subject in a desired position such that the subject can be held in a desired relationship relative to a flight path of the projectile, a monitor configured to monitor a heartbeat of the subject, and a controller coupled to the monitor and to the release and configured to actuate the release to release the string at a desired time relative to a heartbeat cycle of the subject. 
     Implementations of the invention may include one or more of the following features. The controller can be configured to determine a flight time to impact of the projectile from a test launch and to use the flight time, a period of the heartbeat cycle, a known delay of the release mechanism, and a desired time of energy transfer from the projectile to the heart to determine an actuation time for the release mechanism relative to the heartbeat cycle. 
     Various aspects of the invention may provide one or more of the following capabilities. Commotio cordis testing can be performed in a highly-repeatable manner. Timing, speed, and/or location of projectile impact for commotio cordis testing can be reproduced consistently. Projectile velocity can be adjusted. Timing of impact of a projectile against a subject relative to the subject&#39;s cardiac cycle can be adjusted and selected with a high degree of precision. 
     These and other capabilities of the invention, along with the invention itself, will be more fully understood after a review of the following figures, detailed description, and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a simplified perspective view of a commotio cordis test system. 
         FIG. 2  is a perspective view of a projectile launch mechanism shown in  FIG. 1 . 
         FIG. 3  is a plot of an electrocardiogram output of a heartbeat from a subject shown in  FIG. 1 . 
         FIGS. 4-5  are side views of portions of the system shown in  FIG. 1  including the projectile launch mechanism also shown in  FIG. 2  and a cross-sectional view of a test subject and a subject-positioning sling shown in  FIG. 1  along a plane transverse to a sagital plane, with and without a chest protector between the subject and the sling. 
         FIG. 6  is a block flow diagram of a process of testing for commotio cordis in the subject shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Embodiments of the invention provide techniques for evaluating apparatus for guarding against commotio cordis. A test system is capable of precise control of speed, timing, and/or location of impact of a projectile upon a test subject. A bow is used to launch a rod with a projectile disposed on a leading end of the rod, with the projectile being or simulating an object of interest such as a sports ball, puck, etc. The bow is released using an electro-mechanical release device controlled by a controller that causes the bow&#39;s release to induce impact of the projectile with the subject at a desired time during the subject&#39;s heartbeat cycle. The projectile is test fired against the subject to determine timing of release and impact for each subject, and to determine proper sighting of the projectile. The subject is positioned relative to the bow such that the angle of impact of the projectile relative to the subject&#39;s chest is about 90°. Other embodiments are within the scope of the invention. 
     Referring to  FIG. 1 , a commotio cordis testing system  10  includes a sling  12 , a launch mechanism  14 , an electrocardiographic recorder  16 , a stimulator  18 , an echocardiogram  20 , and an anesthesia supply apparatus  22 . The sling  12  is configured to hold a test subject  24 , here a pig with its legs  26  dangling from either end of the sling  12 . The system  10  is configured to control the angle, location, timing, and speed of impact of a projectile into the subject  24  held in the sling  12 , and to measure effects of the impact on the subject&#39;s heartbeat. 
     Referring also to  FIG. 2 , the launch mechanism  14  includes a bow  30  (not shown in  FIG. 1 ), a rod  32 , a projectile  34 , a platform  36 , a support frame  38 , and a release mechanism  40 . The bow  30  is preferably a standard compound hunting bow. It has been found that using a bow provides for better, more repeatable testing than other devices, e.g., a pneumatic launcher, a baseball pitching machine (using one or more rotating wheels), etc. The bow  30  includes a frame  35 . The projectile  34  is the object of interest, for example, a baseball, lacrosse ball or hockey puck, or other object that may hit a person. The projectile  34  is attached to the rod  32 , such as an aluminum rod. The platform  36  supports and guides the rod  32  and the projectile  34  to hold the projectile  34  and the rod  32  before release of the bow  30  and to direct the projectile  34  to a desired portion of the subject  24 . The release mechanism  40  is preferably an electromechanical release under the control of the stimulator  18  that will release a string  31  of the bow  30  to launch the projectile  34  upon receiving a release command from the stimulator  18 . The release  40  is stationary such that the bow&#39;s string  31  can be pulled to substantially the same location for each use and the force on the string  31  of the bow  30  due to the release mechanism  40  holding the string is repeatable. The release  40  can hold the string  31  with the bow  30  in a drawn position and release the string  31  in response to being actuated to impel the rod  32  and the projectile  34  toward the subject  24 . The force applied to the rod  32  and the projectile  34  is thus repeatable, and thus the speed at which the projectile  34  hits the subject  24  is repeatable. The speed may be adjusted by altering the amount that the string  31  is pulled and by adjustment of the draw weight of the bow  30 . The stimulator  18  is configured to process data, e.g., by a processor executing stored software instructions, to perform operations as discussed below. 
     The electrocardiogram is configured to monitor the heartbeat of the subject  24  and the stimulator  18  is configured to trigger the launcher  14  based upon the subject&#39;s heartbeat and a desired timing of impact of the projectile  34  relative to the subject&#39;s cardiac cycle. The electrocardiographic recorder  16  can monitor electric signals from the subject&#39;s heart and provide R-wave data to the stimulator  18 . Referring also to  FIG. 3 , a plot  50  shows that approximately 60 ms passes from a beginning QRS  52  of a beat, to a trough  54 . A peak  56  of the T-wave is approximately 300 to 350 ms after the onset of the QRS  52 . It has been found that a window  58  from about 30 ms to about 15 ms before the peak  56  of the T-wave is a period of particular vulnerability for chest impact inducing commotio cordis. The release  40  has a solenoid delay of about 5 ms from receipt of actuation signal to release of the bow&#39;s string. The launch mechanism  14  is positioned relative to the subject  24  such that the flight time of the projectile  34  from release to impact is of a length such that if the release  40  is actuated at the beat beginning  52 , the projectile  34  will hit the subject  24  during the window  58  of the T-wave. The stimulator  18  marks each QRS  52  and puts out an electrical stimulus to the release  40  which causes release of the rod  32 . The time interval from the QRS  52  to the output electrical stimulus is adjustable in 1 ms time intervals. The flight time of the rod  32  and projectile  34  is between 150 and 400 ms, depending on the velocity. The flight time is determined by a test shot in which the projectile  34  is released toward a leg of the subject  24 . 
     Referring to  FIGS. 4-5 , with further reference to  FIGS. 1-2 , the subject  24  is arranged, and the launcher  14  is set up, such that the projectile  34  is directed at substantially the center of the heart  70  of the subject  24 . Only the rod  32  and the projectile  34  of the launcher  14  are shown in  FIGS. 4-5  for simplicity. The subject  24  and the launcher  14  are arranged such that the projectile  34  will be directed at about a 90° angle relative to the chest wall  72  of the subject  24  and hit the chest wall  72  where the distance from the chest wall  72  to the left ventricle is at or near its minimum. The echocardiogram  20  is used to probe the subject  24  to determine where the left ventricle is closest to the chest wall  72 . While this location varies from subject to subject, for a pig this location typically means that the angle of impact of the projectile  34  is at about a 15° upward angle relative to horizontal. Thus, as shown, the launch mechanism  14  is set up to fire the projectile  34  horizontally and the subject is tilted approximately 15° away from the launcher  34  relative to a standing, upright position (relative to the sagital plane  74 ). In  FIG. 5 , a chest wall protector  76  is inserted between the chest wall  72  and the sling  12  between the projectile  34  and the heart  70 . Adjustments in the release time of the projectile  34  to account for the depth of the protector  76  may be made such that the force transferred to the subject  24  from the projectile  34  reaches the heart  70  at a desired time, e.g., in the known critical window for inducing commotio cordis. Using this setup, and by firing the projectile  34  such that the heart  70  receives the force of the projectile&#39;s impact in the known critical time window, the ability and/or effectiveness of the heart/chest wall protector  76  in inhibiting commotio cordis may be evaluated. Further, results using this setup, with the protector  76 , and with a setup without the protector  76  can be compared to evaluate the effectiveness of the protector  76  in inhibiting commotio cordis or other effects of the projectile&#39;s impact. 
     In operation, referring to  FIG. 6 , with further reference to  FIGS. 1-5 , a process  100  for testing chest wall protectors using the system  10  includes the stages shown. The process  100 , however, is exemplary only and not limiting. The process  100  may be altered, e.g., by having stages added, removed, or rearranged. 
     At stage  102 , the location of the subject  24  where substantially the center of the heart  70  is closest to the chest wall  72  is determined. The user of the system  10  operates the echocardiogram  20  to take measurements, and evaluates the measured data to determine the point where the heart  70  is closest to the wall  72 . 
     At stage  104 , the QRS and T-wave characteristics of the subject&#39;s heart  70  are determined. The user operates the electrocardiographic recorder  16  to measure the time from onset of the QRS  52  to the peak  56  of the T-wave. The time to vulnerable period  58  is determined by taking the time in ms from the QRS  52  to the peak of the T-wave  56  and subtracting 15 to 30 ms. Other characteristics may also be determined. 
     At stage  106 , the flight time of the projectile  34  is determined. The subject  24  is positioned with a point of impact on the subject&#39;s leg being at the same distance from the projectile  34  as the point of impact will be for impact at the subject&#39;s heart  70 . The projectile is test fired/launched and the T-wave electrocardiogram monitored for disturbance. The flight time of the projectile  34  is determined by measurement on the electrocardiographic recorder  16  by determining the time from release to impact based on the monitored electrocardiogram disturbance. 
     At stage  108 , the subject  24  and/or the launcher  14  is(are) positioned to provide for a desired impact of the projectile  34  against the subject  24 . The flight path and/or point of impact of the projectile  34  is determined by sighting down the launch mechanism  14  from a proximal portion (e.g., the release  32 ) toward the subject  24 . The subject  24  and launcher  14  are arranged with respect to each other such that the flight time will be substantially the same as for the test launch, and such that the projectile&#39;s flight path is directed at the spot on the chest wall  72  closest to the left ventricle of the heart  70  and at an angle approximately perpendicular to the chest wall  72  at that point. For a pig, and with the rod  32  substantially horizontal before release, this orientation typically means tilting the subject  24  about 15° from a standing orientation of the subject  24 , exposing the underside of the subject  24  slightly to the launcher  14 . If a protector is being evaluated, the protector  76  is preferably placed in the flight path of the projectile  34  covering the location of the chest wall  72  closest to the left ventricle of the heart  70 . Preferably, the protector  76  is disposed in direct contact with the subject  24  as shown, although the protector  76  could be disposed in indirect contact with the subject  24 , e.g., externally to the sling  12 , with the sling  12  between the protector  76  and the subject  24 . 
     At stage  110 , the launcher  14  is programmed and actuated, and results of projectile impact analyzed. The flight time is subtracted from the time to the vulnerable window  58  (in msec) and this is the time that the stimulator  18  triggers the release  40 . Thus the time from QRS  52  to the impact is the addition of the time from QRS  52  to release and the flight time, allowing for the vulnerable time window  58  to be struck. The stimulator  18  detects the beginning  52  of a cycle, and actuates the release at the determined actuation time. The launcher  14  launches the projectile  34 , that hits the subject  24  and transfers energy to the subject  24  and the protector  76 . The electrocardiographic recorder  16  records the electrocardiogram measurement. The data is analyzed to determine whether commotio cordis was induced and to assess whether the impact occurred during the vulnerable window  58 . The process  100  may be repeated with the protector  76 , and with different protectors, and the effectiveness of the protector(s) evaluated. The process  100  is preferably repeated without using the protector  76  to determine the effect of the projectile&#39;s impact on an unprotected subject. Results of protected and unprotected impacts are analyzed/compared at stage  110  to determine the effectiveness of the protector  76 . 
     In embodiments of the invention, the stimulator  18  can use information from a test firing of the projectile  34  to determine the flight time to the subject  24 . The stimulator  18  can use the flight time information and input data as to a desired time of impact relative to the T-wave cycle to determine an actuation time for the release  40  relative to the beginning  52  of a QRS cycle. The stimulator  18  can be configured to receive information about the T-wave from the electrocardiographic recorder  16  and determine the beat frequency by determining the average time between beginnings  52  of beats. The stimulator  18  can also be configured to determine the timing of the peak  56  of the T-wave relative to the T-wave cycle, and thus the window  58  of commotio cordis vulnerability (from about 30 ms before the peak  56  to about 15 ms before the peak  56 ). 
     Other embodiments are within the scope and spirit of the appended claims. For example, due to the nature of software, functions described above can be implemented using software, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations.