Patent Publication Number: US-2021169737-A1

Title: Compression belt assembly for a chest compression device

Description:
This application claims priority to U.S. Provisional Application 62/488,051, filed Apr. 20, 2017, now pending. 
    
    
     FIELD 
     The inventions described below relate to the field of CPR chest compression devices. 
     BACKGROUND 
     Cardiopulmonary resuscitation (CPR) is a well-known and valuable method of first aid used to resuscitate people who have suffered from cardiac arrest. CPR requires repetitive chest compressions to squeeze the heart and the thoracic cavity to pump blood through the body. In efforts to provide better blood flow and increase the effectiveness of bystander resuscitation efforts, various mechanical devices have been proposed for performing CPR. In one type of mechanical chest compression device, a belt is placed around the patient&#39;s chest and the belt is used to effect chest compressions, for example our commercial device, sold under the trademark AUTOPULSE®. 
     These devices have proven to be valuable alternatives to manual chest compression. The devices provide chest compressions at resuscitative rates and depths. A resuscitative rate may be any rate of compressions considered effective to induce blood flow in a cardiac arrest victim, typically 60 to 120 compressions per minute (the CPR Guidelines 2015 recommends 100 to 120 compressions per minute in adult victims), and a resuscitative depth may be any depth considered effective to induce blood flow, and typically 1.5 to 2.5 inches (the CPR Guidelines 2015 recommends 2 to 2.4 inches per compression in adults). 
     The AUTOPULSE® chest compression device uses a belt, which is releasably attached to a drive spool with the housing of the device. In a convenient arrangement, a spline is secured to the belt, and the spline fits into a slot in the drive spool of the device. The drive spool is accessible from the bottom, or posterior aspect, of the device. Before use, a fresh belt is fitted to the device, and this requires lifting the device to insert the spline into the drive spool. The patient is then placed on the housing of the device, and the belt is secured over the chest of the patient. Opposite ends of the belt are held together, over the chest of the patient, with hook and loop fasteners. The arrangement has proven effective for treating cardiac arrest victims and convenient to use. However, belt installation may not always be convenient. 
     SUMMARY 
     In certain embodiments, devices and methods are provided for a belt-driven chest compression device in which the compression belt is readily replaceable. The chest compression device includes a platform which houses drive components, and a compression belt which is connected to the drive components through releasably attachable couplings near the upper surface of the device. Removal and replacement of the belt may be accomplished while a patient is disposed on the housing. This arrangement helps avoid twisting of the belt and facilitates removal and replacement of the belt. The belt is tensioned upon installation by the control system that controls operation of the compression device. Also, the belt may be provided in an assembly including a liner sock, the belt, a guard slidably disposed on the belt, and/or an attachment feature or pin secured to the ends of the belt, while the housing of the device may include an aperture configured to securely receive the guard, and drive spools disposed within the housing, accessible through the apertures. Each drive spool may include a mating feature or slot for receiving a pin. A flange disposed about each drive spool, movable or slidable along the drive spool, is operable to trap the pins in the slots to keep the belt secured to the drive spools during operation. 
     The compression belt assembly for use with the chest compression device may comprise a compression belt, a guard slidably disposed on the compression belt, proximate the first end of the compression belt, and a sensor or sensor system component associated with the machine guard, and/or a liner sock disposed about the compression belt, and fixed to the guard. The attachment sensor or sensor system component may be interoperable with a corresponding sensor or sensor system component disposed on the chest compression device housing, or with a control system used to control the chest compression device. The control system may be operable to receive signals from the sensor or sensor system component or a corresponding sensor or sensor system component disposed on the chest compression device housing to control the device based on the signals. For example, the control system may be programmed so that it will not operate to perform chest compressions unless signals indicative of proper placement of the machine guard are transmitted to the control system. 
     The chest compression device may also comprise a drive spool, having a first end and a second end and a motor operably connected to the belt through the drive shaft. The motor may be operably connected to the first end of the drive spool, and capable of operating the drive spool repeatedly to cause the belt to tighten about the thorax of the patient and loosen about the thorax of the patient. The drive spool may include a first spool portion having a longitudinally oriented first drive spool slot configured to receive a pin of a compression belt, and a first flange disposed proximate a first end of the spool portion. A compression belt may include a first pin secured to the belt, at the end of the belt, and extending transversely across the belt end. The first flange of the drive spool may be longitudinally translatable over the first spool portion, operable to translate to a first position along the first spool portion in which the slot is unobstructed by the flange and a second position in which the slot is partially obstructed by the flange, such that the pin is secured in the slot by the flange. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the CPR chest compression device installed on a patient. 
         FIGS. 2 and 3  are perspective views of the CPR chest compression device. 
         FIG. 4  is a zoomed in side view of the CPR chest compression device, illustrating the aperture in the housing which provides for access to the drive spool for connecting the compression belt to the drive spool. 
         FIG. 5  illustrates a see-through top view of the compression belt assembly, including a liner sock, guards, and connection pins. 
         FIGS. 6 and 7  are views of the guard. 
         FIGS. 8 and 9  illustrate the connection of the guard and the housing. 
         FIG. 10  illustrates a second embodiment of the guard. 
         FIG. 11  illustrates a third embodiment of the guard. 
         FIGS. 12 through 15  illustrate a drive spool and pin arrangement configured for releasable attachment of the belt to the drive spool. 
         FIGS. 16 through 19  illustrate a drive spool and pin arrangement configured for releasable attachment of the belt to the drive spool. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an embodiment of a chest compression device fitted on a patient  1 . The chest compression device  2  applies compressions with a compression belt or band  3 . The chest compression device  2  includes a belt drive platform  4  sized for placement under the thorax of the patient, upon which the patient rests during use and which provides a housing  5  for the drive train and control system for the device. The control system, provided anywhere in the device, can include a processor and may be operable to control tightening operation of the belt and to provide output on a user interface disposed on the housing. Operation of the device can be initiated and adjusted by a user through a control panel  6  and/or a display operated by the control system to provide feedback regarding the status of the device to the user. 
     The compression belt includes a wide load-distribution section  7  at the mid-portion of the belt and left and right belt ends  8 R and  8 L (shown in the illustration as narrow pull straps  9 R and  9 L), which serve as tensioning portions which extend from the load distributing portion, posteriorly relative to the patient, to drive spools within the housing. When fitted on a patient, the load distribution section is disposed over the anterior chest wall of the patient, and the left and right belt ends extend posteriorly over the right and left axilla of the patient to connect to their respective lateral drive spools shown in  FIG. 2 . 
       FIGS. 2 and 3  shows the CPR chest compression device in isolation.  FIG. 2  provides a view of the device with the housing anterior surface hidden. As illustrated in  FIG. 2 , drive spools  10 R and  10 L are disposed laterally on either side of the housing. The belt pull straps  9 R and  9 L are secured to these drive spools. The lateral drive spools are in turn driven by a motor  11  also disposed within the housing, through a drive shaft  12  and drive belt  13 . The belt pull straps  9 R and  9 L may be attached to the lateral drive spools such that, upon rotation of the drive spools, the pull straps  9 R and  9 L are pulled posteriorly, spooled upon the lateral spools, thereby drawing the compression belt downward to compress the chest of the patient. 
       FIG. 3  is a perspective view of the CPR chest compression device, illustrating the apertures in the housing which provide for access to the drive spools for connecting the belt to the drive spools. Alternatively, the chest compression device may not include apertures, and other connection or fastening components may be present on the lateral or anterior surface of the device for securing the belt to the drive spools. The apertures  14 R and  14 L on either side of the housing are disposed proximate the drive spools. The apertures are sized to allow passage of the belt end through the housing wall for insertion into the drive spools. The apertures can extend over the housing anterior surface  5 A and lateral surface  5 L as shown, or over the housing anterior surface  5 A alone, or the lateral surface  5 L alone, to preferably provide access to the drive spools from an anterior approach or lateral approach even while a patient is disposed on the anterior surface. Spindles  15 R and  15 L may be provided to guide the belt ends through the apertures. 
       FIG. 4  is a zoomed in side view of the CPR chest compression device corresponding to the view of  FIG. 3 , illustrating the aperture in the housing which provides for access to the drive spool for connecting the compression belt to the drive spool. In this view, the aperture  14 L is shown with a guard, such as machine guard  16 L, configured to fit into the aperture  14 L which spans anterior surface  5 A and lateral surface  5 L, to cover the drive spool  10 L and spindle  15 L. 
       FIG. 5  illustrates one embodiment of a compression belt assembly, including the pins, with machine guards, and liner socks. The compression belt  3  includes the load distribution section  7 , the left and right belt ends  8 R and  8 L (shown in the illustration as narrow pull straps  9 R and  9 L) shown in  FIG. 1 , along with machine guards  16 R and  16 L and liner socks  17 R and  17 L, and pins  18 R and  18 L. The guards are slidably disposed on their respective belt ends, so that the belt can move freely through the guard while the drive spool is tightening and loosening the belt during operation. The liner socks  17 R and  17 L are secured at their outer ends to their respective guards ( 16 R and  16 L), and fixed at their inner ends to the load distributing section  7 , but loosely fitted over the belt ends/pull straps so that the belt end/pull straps may translate within the liner socks while the drive spool is tightening and loosening the belt during operation. The pins  18 R and  18 L are secured to the left and right belt ends  8 R and  8 L, respectively, with a long axis of the pins arranged perpendicularly to the long axis of the belt ends. The pins are slightly longer than the width of the compression belt, so that tips or ends of the pins extend beyond the long edge of the belt. These pins are configured to fit within slots in the drive spools, and also to be captured within the slots by flanges, as illustrated in  FIGS. 12 to 19 . The compression belt assembly may also include a buckle or fastener, disposed on a portion of the belt assembly, e.g.,at a medial portion of one of the pullstraps  9 R and  9 L and connecting the pull strap to the remainder of the compression belt assembly, operable to open the belt should it be necessary before or after the compression belt assembly is fitted around a patient and secured to the drive spools. 
       FIGS. 6 and 7  are views of one embodiment of a guard. Though the guards may take many forms, to match various apertures, receptacles, slots, or other connection or fastening components in the housing, the embodiments of  FIGS. 6 and 7  are suitable for use in the housing illustrated in  FIGS. 1 through 3 . The machine guard  16  may be generally L-shaped, with a “vertical” lateral portion  16 V configured to fit within the lateral side of the housing aperture and a “horizontal” anterior portion  16 A configured to fit within the anterior portion of the housing aperture. Each portion may include a first fastener component configured to mate with a second fastener component on the housing (proximate the aperture). Fasteners may include a latch, clip, clamp or other fastening connection mechanism. For example, the upper fastener component  19  may be a latch such as snap-fit latching component such as non-releasing cantilever beam, configured to slip under a lug under the anterior housing surface (see  FIG. 9 ). The lower fastener component  20  may be a latch, e.g. a hook, configured to engage latch component in the form of a long ridge disposed along the inside of the lateral housing surface. As seen in the perspective view of  FIG. 7 , the machine guard includes a slot  21 , and the belt end is disposed within the slot. The belt may include a pin or other connector  18 , secured to belt end. The pin and/or belt end may be disposed on the inner side of the machine guard. The machine guard may be slightly flexible, so that it may be compressed to fit into an aperture to align the snap fit component with corresponding components in the housing. 
     Various other configurations may be used to secure the machine guard to the housing. For example, the first fastener component may be a fixed hinge component interoperable with the hinge component proximate the aperture of the chest compression device, and the second fastener component may be a flexible fastener component, interoperable with a fixed catch component proximate the aperture of the chest compression device. The first fastener component may comprise a rigid cantilever with a lug interoperable with a first bead component proximate the aperture of the chest compression device, and the second fastener component may be a deflectable cantilever with a lug, interoperable with a second fixed bead component proximate the aperture of the chest compression device. The first fastener component may comprise a cantilever snap fit beam for securing the first portion of the machine guard over the aperture in the chest compression device disposed on the first portion, and a second fastener component disposed on the second portion, where the second fastener component is a flexible fastener component, interoperable with a fixed catch component within the housing proximate the aperture of the chest compression device. The machine guard may also be secured to the housing with rotating latches, snaps, toggle bolts, or any other means for releasably fastening the machine guard to the housing. 
       FIGS. 8 and 9  illustrate the connection of the machine guard and the housing, according to one embodiment. As shown in  FIG. 8 , the machine guard may fit into the aperture over the drive spool and spindle. The belt end passes through the slot in the machine guard. The liner sock is secured to the anterior surface of the machine guard, and fits loosely around the belt end. As shown in the cross section of  FIG. 9 , the machine guard fastening components  19  and  20  mate with corresponding fastening components  22  and  23  on the inside of the housing. Also as shown in  FIG. 9 , the belt end  8  is secured within a slot  24  in the drive spool  10 , and may be secured in place with a flange  25  which is disposed over the drive spool, near the outer edge of the belt end (trapping the tips of the pins that extend outside of the edge of the belt). The spindle  15  is also more clearly shown in  FIG. 9 . 
       FIG. 9  also shows sensors operable to detect the presence and proper installation of the guard. One or more sensors, e.g., first or second sensor components or proximity or contact sensor component pairs  26  may be fixed or otherwise coupled to or associated with the machine guard and/or housing, operable to detect proximity or contact of the machine guard-mounted sensor component with the housing mounted sensor component, and generate a signal for transmission to the control system. The control system may be operable to detect the signal corresponding to proximity or contact of the machine guard, indicating proper attachment or securement of the machine guard to the housing, and control operation of the device accordingly. For example, the control system may prevent tightening or loosening operation of the belt unless a signal corresponding to proper proximity or contact is received from the sensor. Operation of the belt is prevented unless a signal indicating proper attachment or securement of the machine guard to the housing is received by the control system. Ensuring attachment or securement of the machine guard before permitting operation of the belt provides safety for the user, e.g., by protecting a user&#39;s fingers or other body parts or clothing from coming into contact with the rotating drive spool and belt during device operation, thereby preventing potential injury to a user or damage to the device. The control system may also operate an annunciator or display to alert the user that the machine guards are or are not properly installed, e.g., providing an alarm or other alert or indicator, or a message on a user interface or display. 
     A variety of sensors or attachment sensors may be used, e.g., contact sensors or proximity sensors, including contact relays, contact switches, magnetic sensors, capacitive sensors inductive sensors, optical sensors, photocells, ultrasonic sensor, or any other means for sensing contact or proximity of the machine guard to the housing. Sensors may include a first sensor component and second sensor component, e.g., a sensor target and a sensing component operable to sense the presence or location of the sensor target, and either sensor component may be disposed on the guard or on the housing. A relay switch may comprise an electromagnetic switch operated by a small electric current, with a magnet or electromagnet on one structure (the housing or the guard) and a spring-loaded switch on the other structure, where proximity of the magnet or electromagnet functions to close or open the spring-loaded switch. A change in the switch position may be taken by the control system as a signal indicative of proper placement of the guard. A contact switch may comprise a switch on one structure (the housing or the guard) activated by contact with an impinging component on the other structure. For example, a reed switch disposed on the housing, operable to be closed by a protrusion on the guard, or the guard itself, when the guard is inserted properly into the aperture. Closure of the switch may be taken by the control system as a signal indicative of proper placement of the guard. A magnetic sensor may comprise a Hall effect sensor on one structure (the housing or the guard), and a magnet on the other structure. Detection of the magnetic field of the magnet may be taken by the control system as a signal indicative of proper placement of the guard. A capacitive sensor may comprise a capacitive sensor probe with a sensing electrode on one structure (the housing or the guard), and a conductive target, or a capacitive sensor probe on one structure, combined with a conductive target on the same structure on the opposite side of a channel which accommodates the other structure, operable to sense the entry of the other structure (whether conductive or non-conductive) by its effect on the capacitance measured by the capacitive sensor probe. Detection of the target may be taken by the control system as a signal indicative of proper placement of the guard. An inductive sensor may comprise a magnetic field oscillator on one structure (the housing or the guard), and a conductive target on the other structure. Detection of a change in the amplitude of the oscillator may be taken by the control system as a signal indicative of proper placement of the guard. An optical sensor may comprise photoelectric detectors and optical encoders. Optical encoders, for example, may comprise an encoder scanner on one structure (the housing or the guard), and an encoder scale on the other structure. Detection of the encoder scale by the encoder scanner may be taken by the control system as a signal indicative of proper placement of the guard. A photoelectric sensor may comprise an emitter light source on one structure (the housing or the guard), and a photodetector the other structure (or a reflector on the other structure and a photodetector on the first structure). Detection of light, or loss of detection of light, from the emitter light source by the photodetector may be taken by the control system as a signal indicative of proper placement of the guard. An ultrasonic sensor may comprise a transducer on one structure (the housing or the guard), and a reflective target on the other structure (the structure itself may constitute the target), in a through-beam or reflective arrangement. Detection of ultrasound from reflected by the target, or alteration of the ultrasound by transmission through the target may be taken by the control system as a signal indicative of proper placement of the guard. 
     In one example, one or more magnets may be positioned on the guard, e.g., on a machine guard fastening component  19 ,  20  or elsewhere on the machine guard. The magnet may be detected by a magnetic sensor positioned on or in the device housing, e.g., in a location on or near where the machine guard couples to the housing. Alternatively, a magnet may be positioned on the device housing and the magnetic sensor on the guard. In another example, a portion of the machine guard, e.g., the machine guard fastening component or first sensor component,  19  or  20 , as shown in  FIG. 6 , may actuate a contact switch or second sensor component, which transmits a signal corresponding to proper attachment or securement of the machine guard to the housing, to the control system. Various contact switch arrangements may be utilized. For example, the machine guard fastening component or protrusion may actuate a rod or pin located within the housing, which rod or pin comes into contact with a contact switch, (e.g., directly or indirectly e.g., via a lever), resulting in the transmission of a signal to the control system. Alternatively, a contact switch may be positioned on the guard and a protrusion or other actuator may be positioned on the housing. In response to receiving any of the generated signals described herein, the control system may control operation of the chest compression device, e.g., by preventing or allowing motor operation to perform repeated chest compression cycles. 
       FIG. 10  illustrates a second embodiment of a machine guard  16 . The machine guard includes upper and lower fastener components  19  and  20 . The lower fastener component  20  may include two more latches or ridges, separated by a slot or receptacle for holding a first sensor component  26 . Optionally, the first sensor component may be positioned in a different location on the machine guard, to provide for optimal communication with a second sensor component located on the chest compression device or device housing. 
       FIG. 11  illustrates a third embodiment of the machine guard. In this embodiment, the machine guard  16  is also generally L-shaped, with a “vertical” lateral portion  16 L configured to fit within the lateral side of the housing aperture and a “horizontal” anterior portion  16 A configured to fit within the anterior portion of the housing aperture. The belt end passes through an aperture in the “horizontal” anterior portion  16 A of the machine guard. A tongue running around the edge of the “vertical” lateral portion  16 V fits into a corresponding groove in the lateral wall  5 L. The “horizontal” anterior portion  16 A may include a fastening component configured to engage a corresponding fastening component fixed to the anterior surface of the housing. One or more sensors, as described above, may be located on the machine guard. 
     In another embodiment, a chest compression device having a platform housing a motor and a drive spool operable to tighten a compression belt about the thorax of a patient is provided. The compression belt includes a first end and a second end. The first end is releasably attachable to the drive spool. A guard is fixed or otherwise coupled to the platform. The guard may be positioned in a secured position, which conceals the drive spool from the user, protecting the user or other objects from contacting the drive spool during operation, or an unsecured position, which exposes the drive spool. A first sensor component is disposed on the guard and is interoperable with a second sensor component disposed on the platform housing. The first sensor component is detectable by the second sensor component or vice versa, for detection of the attachment of the guard to the chest compression device. Detection of the first or second sensor component indicates whether the guard is in the secured position, and a control system of the chest compression device can control operation of the compression belt in response to the guard being in a secured or unsecured position. By preventing operation of the chest compression device unless the guard is in a secured position where it provides a barrier between the user and the drive spool, potential injury to the user or damage to the device is prevented. As described herein, a guard may be coupled or connected to a compression belt assembly (and releasably attached to a compression device platform, to cover a drive spool or operating mechanism), or alternatively, the guard may be fixed or coupled to the platform of the chest compression device, and after attaching the belt to the drive spool, rotated or slid into a secured position, to cover the drive spool or other operating mechanism. Any of the sensors or sensor components described herein may be utilized in the above embodiments. 
       FIGS. 12 through 15  illustrate a drive spool and pin arrangement configured for releasable attachment of the belt to the drive spool. The drive spool  10  comprises a spool shaft component  31  which is operably connected to the motor drive shaft  12  through the drive belt  13  (both shown in  FIG. 2 ), and also comprises a spool portion  32  (which may be integral with the shaft, or disposed about the shaft) with a channel  33  for receiving the pin  18 . The channel runs the length of the spool portion, and is long enough to receive the pin. The spool shaft component and spool portion are supported within the housing by a support walls  34  and  35 . Two flanges are provided to trap the pin ends  36 . A first flange  37  is slidably disposed over the spool portion, and includes an aperture  38  for receiving the pin, so that it may be translated longitudinally along the spool portion to uncover the channel sufficiently to allow insertion of the pin into the channel, and then translated longitudinally along the spool portion to trap the end of the pin within the channel. This first flange  37  may be disposed at either end of the spool shaft, and is preferably biased toward the opposite end of the spool portion, with a spring  39  disposed between the flange and the support wall  35 , but can be secured in the trapping position with detents, latches or other means for holding the flange in the trapping position. The second flange  40  on the opposite end of the spool portion may be fixed longitudinally on the spool portion, or may be longitudinally translatable and biased as with the first flange.  FIG. 13  illustrates the drive spool and pin arrangement with the first flange in the trapping position, and held there by the spring.  FIG. 14  is a cross section of the spool portion, showing the pin  18  disposed with the channel  33  of the spool portion  32 . The depth of the channel may be varied between the right and left side drive spools, where the drive spools are otherwise symmetrically disposed on the left and right side of the device, to account for differences in belt travel arising from different directions spooling.  FIG. 15  is a perspective view of a segment of the spool portion  32  illustrating two variations in the configuration. In the embodiment shown in  FIG. 15 , the spool portion  32  includes a wrench flat  41  (a flat surface milled into the otherwise round outer contour of the spool) along the length of the spool, on the trailing side of the channel. Also, the channel is a half-pipe or partial-pipe configuration, and the flanges include circular apertures  38  extending beyond the outer diameter of the spool portion, to receive the tips of the pins. 
       FIGS. 16 through 19  illustrate a drive spool and pin arrangement configured for releasable attachment of the belt to the drive spool. As in the previous figures, the drive spool  10  comprises a spool shaft component  42  which is operably connected to the motor drive shaft  12  through the drive belt  13  (both shown in  FIG. 2 ), and also comprises a spool portion  32  (which may be integral with the shaft, or disposed about the shaft) with a channel  33  for receiving the pin  18 . The channel runs the length of the spool portion, and is long enough to receive the pin. The spool shaft component and spool portion are supported within the housing by support walls  34  and  35 . Two flanges are provided to trap the pin ends  36 . A first flange  43  is slidably disposed relative to the spool portion, so that it may be translated longitudinally relative to the spool portion to allow insertion of the pin into the channel, and then translated longitudinally along the spool portion to trap the end of the pin within the channel and the aperture  44  of the flange. This first flange  43  is disposed at the end opposite the spool shaft, and is supported on a journal bearing  45  (which is also longitudinally translatable relative to the spool portion), which in turn is supported by the journal shaft  46  supported by the support wall  35 . The flange and journal bearing are biased toward the opposite end of the spool portion, with a spring  47  disposed between the flange and the support wall  35  (within or about the journal bearing), but can be secured in the trapping position with detents, latches or other means for holding the flange in the trapping position. A second flange  48  on the opposite end of the spool portion may be fixed longitudinally on the spool portion, or may be longitudinally translatable and biased as with the first flange. One or more guide rails  49  are fixed to the first flange, and extend into corresponding guide channels  50  within the spool portion, and are slidable within the guide channels. The rails and guide channels may be disposed off-center in the spool portion, or they may have non-circular cross sections, to aid in torque transfer. The pin and flange pockets may be centered in the spool portion (and the flanges) or may be disposed off-center.  FIG. 16  shows this embodiment with the first flange in a retracted position, which allows insertion of the pin into the channel, while  FIG. 17  shows the embodiment with the first flange in the trapping position, biased toward the opposite end of the spool portion by the spring.  FIG. 18  is a cross section of the spool portion of  FIG. 16 , showing the location of the guide channels and pin channel, and a sloped slot  51  which may be incorporated into the flange  48  which helps guide the pin into the channel.  FIG. 19  is a cross section of the guide rail components, showing the location of the guide rails  49  which extend from the first flange  43 , and a sloped slot  52  which may be incorporated into the first flange  43  which helps guide the pin into the channel and/or the aperture. 
     In use, a CPR provider will assemble the CPR chest compression device about a patient, placing the device under the patient&#39;s thorax, placing the compression belt around the patient&#39;s thorax, and inserting the pins into the drive spools, and inserting the machine guard into the apertures. The belt may be secured to the drive spools, and thereafter closed over the patient&#39;s thorax using a buckle or fastener disposed along the belt. Alternatively, the belt may be placed about the patient&#39;s thorax and thereafter secured to the drive spools. The CPR provider will then provide input to the control system of the CPR chest compression device to cause the device to perform repeated chest compression cycles. 
     To attach compression belt assembly to a chest compression device, the CPR provider will insert one of the pins secured to an end of the compression belt assembly through an aperture in a housing of the compression device into a receiving channel in a drive spool, forcing the sliding flange as necessary to expose the receiving channel so as to fit the pin in the channel, and then slide a machine guard (which is slidably disposed on the compression belt assembly) along the compression belt; and releasably attach the machine guard to the housing to occlude the aperture. In a symmetrical system, the CPR provider will attach both belt ends in similar fashion. Once the system is assembled about the patient, the CPR provider will operate the control system to initiate compressions. If the machine guard sensors or sensor components are used, operator initiation of compressions will cause the control system to receive analysis signals from the sensors to determine whether the machine guard is attached to the housing, and control operation of the compression belt in response to the absence or presence of the machine guard. 
     Referring again to  FIG. 3 , the system may be enhanced with various features. For example, the housing may be trimmed with a gasket joining upper and lower portions of the housing to prevent fluid entry and seal the device, and the housing may be trimmed along lateral surfaces and corners with resilient bumpers. The bumpers may comprise leaf sprigs over-molded with rubber, to protect the system from mechanical shock. The surface of the device, especially the anterior surface, which supports the patient and is in contact with the patient during use, may comprise a low durometer polymer such as rubber or silicone to aid in positioning the patient while installing the system, and/or to help grip or hold the patient in position on the device. The upper surface can be configured with a depression, to aid in positioning the patient so that the load distributing portion of the belt is located over the sternum of the patient. 
     The several embodiments have been described in the context of a symmetrical CPR chest compression device, illustrated in embodiments which include various components in matching left and right pairs. However, the benefits of the various configurations of components may be achieved in asymmetric embodiments. For example, the benefits of the belt end configuration with the pin, machine guard slidably secured to the belt ends or pull straps, and/or the liner sock secured to the machine guard, can be obtained by applying those features to one side of the belt, while the other side of the belt is configured for attachment to its corresponding drive spool through other means. Likewise, the benefits of the drive spool configuration, with the channel for receiving the pin and the slidable flange for capturing the pin, can be applied by applying those features to one drive spool, while the other drive spool is configured for attachment to its corresponding belt end through other means. 
     While the preferred embodiments of the devices and methods have been described in reference to the environment in which they were developed, they are merely illustrative of the principles of the inventions. The elements of the various embodiments may be incorporated into each of the other species to obtain the benefits of those elements in combination with such other species, and the various beneficial features may be employed in embodiments alone or in combination with each other. Other embodiments and configurations may be devised without departing from the spirit of the inventions and the scope of the appended claims.