Patent Publication Number: US-11020312-B2

Title: Adjustable piston

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/573,995, filed Dec. 17, 2014, which claims benefit under 35 U.S.C. § 119(e) of Provisional U.S. Patent Application No. 62/009,109, filed Jun. 6, 2014, the contents of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Cardiopulmonary resuscitation (CPR) is a medical procedure performed on patients to maintain some level of circulatory and respiratory functions when patients otherwise have limited or no circulatory and respiratory functions. CPR is generally not a procedure that restarts circulatory and respiratory functions, but can be effective to preserve enough circulatory and respiratory functions for a patient to survive until the patient&#39;s own circulatory and respiratory functions are restored. CPR typically includes frequent torso compressions that usually are performed by pushing on or around the patient&#39;s sternum while the patient is lying on the patient&#39;s back. For example, torso compressions can be performed as at a rate of about 100 compressions per minute and at a depth of about 5 cm per compression for an adult patient. The frequency and depth of compressions can vary based on a number of factors, such as valid CPR guidelines. 
     Mechanical CPR has several advantages over manual CPR. A person performing CPR, such as a medical first-responder, must exert considerable physical effort to maintain proper compression timing and depth. Over time, fatigue can set in and compressions can become less consistent and less effective. The person performing CPR must also divert mental attention to performing manual CPR properly and may not be able to focus on other tasks that could help the patient. For example, a person performing CPR at a rate of 100 compressions per minute would likely not be able to simultaneously prepare a defibrillator for use to attempt to restart the patient&#39;s heart. Mechanical compression devices can be used with CPR to perform compressions that would otherwise be done manually. Mechanical compression devices can provide advantages such as providing constant, proper compressions for sustained lengths of time without fatiguing, freeing medical personnel to perform other tasks besides CPR compressions, and being usable in smaller spaces than would be required by a person performing CPR compressions. 
     Mechanical CPR devices, and other medical devices, may provide advantages to performing medical tasks manually, for example, on patients having average dimensions. However, adjustability is needed in these devices to accommodate smaller and larger patients, to provide assistance in performing medical operations on these patients, without causing added risk. 
     SUMMARY 
     Illustrative embodiments of the present application include, without limitation, methods, structures, and systems. In one aspect, a mechanical CPR device may include a piston, for example, to drive chest compressions of a patient to perform CPR. The piston may have a suction cup attached to an end of the piston for contacting the sternum/torso of a patient. A drive component/controller may control the piston to extend the piston toward a patient&#39;s torso and retract the piston away from the patient&#39;s torso, to perform mechanical CPR. In order to accommodate patients having smaller dimensions, and particularly smaller chest or sternum heights, an extendable piston may be used to perform mechanical CPR. In one aspect, an extendable piston may include an inner piston having an outward surface, with at least one grove or recess disposed on the outward surface. An external piston sleeve, which may be part of or connected to a body of a mechanical CPR device, may be slidable over the inner piston. In some cases, the inner piston may be biased to at least partially slide into the external piston sleeve. A removable external piston spacer may be configured, when engaged to the at least one groove of the outward surface of the inner piston, to oppose the bias on the inner piston to prevent the inner piston from sliding into the external piston sleeve. The removable external piston spacer may, when attached to the inner piston, extend a length of the piston by a measurable distance, for example to enable the suction cup on an end of the piston to engage a smaller sternum of a patient. In some cases, the extendable piston, and/or mechanical CPR device, may include one or more sensors. The one or more sensors may detect the presence of the removable external piston spacer and/or determine the adjusted length of the piston itself, including the length of the inner piston and the external piston sleeve. This information may then be communicated to and used by a controller or motor of the mechanical CPR device to adjust motion of the piston to perform mechanical CPR. 
     In some cases, the sensor may be an inner piston sensor that detects the position of the inner piston relative to the external piston sleeve. In some implementations, the inner piston sensor may detect a displacement of the inner piston caused by the removable external piston spacer and communicate the displacement to a piston controller. The piston controller may subsequently modify movement or oscillation of the extendable piston to perform mechanical CPR. 
     In some examples, one or more spring members disposed about or around the inner piston may bias the inner piston to at least partially slide into the external piston sleeve. In some cases, a motor or drive component of the mechanical CPR device may bias the inner piston. 
     In some examples, the outward-facing surface of the inner piston may include two opposing grooves or recesses. The removable external piston spacer may correspondingly include two opposing flanges configured to engage the two opposing grooves of the inner piston. In some cases, the two opposing grooves may each define a substantially rectangular recess and each of the two opposing flanges may include a ridge having a substantially rectangular shape. 
     In another aspect, an extendable piston may include a center piston having at least one locking rod extending outwardly from the center piston. An external piston sleeve of the extendable piston may be rotatably connected to or disposed around the center piston. The extendable piston may additionally include an internal bayonet sleeve, having a length, that is rotatably disposed along an outside surface of the center piston between a compression spring and a decompression spring also positioned on the outside surface of the center piston. The internal bayonet sleeve may include a plurality of locking grooves, located at different angular positions and having different lengths along the internal bayonet sleeve, configured to engage the at least one locking rod. The at least one locking rod may be alignable with at least one of the locking grooves, for example, by rotating the center piston relative to the internal bayonet sleeve. Rotating the center piston relative to the internal bayonet sleeve may, as a result, adjust a length of center piston relative to the external piston sleeve, thus increasing or decreasing the length of the extendable piston. In some aspects, the extendable piston may include a sensor, such as a center piston sensor, that can detect a position or displacement of the center piston relative to the external piston sleeve. The sensor may communicate the displacement to a piston controller, which may modify an oscillation of the extendable piston based on the displacement. In some cases, detection of the position/displacement of the center piston may include detecting which of the grooves of the internal bayonet sleeve is engaged by the at least one locking rod. In some examples, the sensor may be part of or associated with a controller of a drive component (e.g., a motor or drive shaft) of a mechanical CPR device attached to the center piston and/or the external piston sleeve. 
     In another aspect, an extendable piston may be realized through a piston adapter. The piston adapter may include a suction cup or other patient engagement device and a body attached to the suction cup having a gas check valve. The piston adapter may further include a piston connection surface disposed on an end of the body, opposed to the suction cup, configured to temporarily adhere to a planar or other surface in response to activation of the gas check valve. In some examples, the piston connection surface may adhere to a piston, for example, of a mechanical CPR device. The gas check valve may, when activated, exert a suction pressure against a surface of the piston, between the surface of the piston and the piston connection surface of the piston adapter. In some cases, the mechanical CPR device may further include a drive component or motor, controlled by a controller. One or more sensors, either disposed on the piston adapter or on the piston or other part of the mechanical CPR device, may detect when the piston connection surface of the piston adapter contacts a surface of the piston. The sensor may indicate the connection of the piston adapter to the controller, such that the control may modify movement of the piston to accommodate the extra length of the piston added by the piston adapter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Throughout the drawings, reference numbers may be re-used to indicate correspondence between referenced elements. The drawings are provided to illustrate example embodiments described herein and are not intended to limit the scope of the disclosure. 
         FIGS. 1A and 1B  depict an isometric view and a side view, respectively, of one embodiment of a mechanical CPR device. 
         FIGS. 2A, and 2B , depict example operations of a mechanical CPR device on a patient, in accordance with the present disclosure. 
         FIGS. 3A and 3B  depict example operations of a mechanical CPR device with an adjustable piston on a patient having a small sternum, in accordance with the present disclosure. 
         FIG. 4  depicts a side view of mechanical CPR device having an adjustable piston, in accordance with the present disclosure. 
         FIGS. 5A, 5B, 5C, 5D, 5E, 5F, and 5G  depict an example of an adjustable piston including a removable external piston spacer, according to an aspect of the present disclosure. 
         FIGS. 6A, 6B, 6C, 6D, and 6E , depict an example of an adjustable piston including an internal bayonet sleeve, according to an aspect of the present disclosure. 
         FIG. 7  depicts an example of an adjustable piston including a piston adapter, according to an aspect of the present disclosure. 
         FIG. 8  depicts an example method of adjusting the length of a piston of a mechanical CPR device, in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Mechanical CPR compression devices having an adjustable length piston can provide many advantages over manual CPR compressions and/or non-adjustable mechanical CPR compression devices. As will be described in greater detail below, the use of an adjustable piston with a mechanical CPR device may provide additional benefits, including adaptability to accommodate patients of different sizes. It should be appreciated that the devices and techniques described herein may similarly be used in other applications. These other applications may include other mechanical devices, particularly medical devices, where patients of different sizes may require treatment. 
       FIGS. 1A and 1B  depict an isometric view and a side view, respectively, of one embodiment of a mechanical CPR device  100 . The mechanical CPR device  100  includes a lower portion  105  and an upper portion  110 . The upper portion  110  can have a main portion  115  and two legs  120  and  125 . Each of the legs  120  and  125  can be releasably connected to one of the sides of the lower portion  105 . Items that are releasably connected are easily disconnected by a user, such as connections that can snap in and snap out, connection that do not require the use of tools to disconnect, quick-release connections (e.g., push button release, quarter-turn fastener release, lever release, etc.), and the like. Items are not releasably connected if they are connected by more permanent fasteners, such as rivets, screws, bolts, and the like. In the embodiment shown in  FIGS. 1A and 1B , the legs  120  and  125  are rotatably attached to the main portion  115  about axes  130  and  135 , respectively. However, in other embodiments, the legs  120  and  125  can also be fixed with respect to the main portion  115 . 
     The main portion  115  can include a piston  140  with an end  145 . The end  145  can be blunt, contoured, or otherwise configured to interact with a patient&#39;s torso. The end  145  can also have a suction cup that can temporarily attach to a patient&#39;s torso. The main portion  115  can include other components. For example, the main portion  115  can include a drive component, such as a motor or actuator, that can extend and retract the piston  140 . The main portion  115  can include a power source, such as a rechargeable battery, that can provide power for the drive component. The main portion  115  can also include a controller that can control the movement of the piston  140  by controlling the drive component. In one embodiment, the controller can include a processor and memory, and the memory stores instructions that can be executed by the processor. The instructions can include instructions for controlling the piston  140  by controlling the drive component. The main portion  115  can also include one or more sensors that can provide inputs to the controller. The one or more sensors can include one or more of a force sensor to sense a force exerted by the piston  140 , a spring sensor to sense a displacement of the piston  140 , a current sensor to sense an amount of current drawn by the drive component, or any other type of sensor. The main portion  115  can also include one or more user input mechanisms, such as buttons, keys, displays, and the like. A user can input information to adjust the operation of the mechanical CPR device  100 , such as a depth of compressions, a frequency of compressions, a maximum exertion force by the piston  140 , and the like. 
     In addition to the mechanical CPR device  100 ,  FIG. 1B  also depicts a cross section of a patient&#39;s torso  155  with the patient&#39;s back against the lower portion  105  and the patient&#39;s chest facing the piston  140 . While in the configuration depicted in  FIG. 1B , the piston can be extended in the space  160  to the patient&#39;s torso  155 , compress the patient&#39;s torso  155 , and retract from the patient&#39;s torso. This process, wherein the piston  140  compresses the patient&#39;s torso  155  and is then retracted from the patient&#39;s torso, can be performed repeatedly to mechanically perform CPR. 
       FIGS. 2A and 2B  depict example operations of a mechanical CPR device  100  on a patient  200 .  FIGS. 2A and 2B  depict a portion of a mechanical CPR device  100  that includes a piston  140 . The end of the piston  140  includes a suction cup  145 . The depictions in  FIGS. 2A and 2B  show cross sectional views of the mechanical CPR device  100 , the piston  140 , and the suction cup  145 . The mechanical CPR device  100  could also include other components that are not depicted in  FIGS. 2A and 2B , such as one or more components of mechanical CPR device  100  described above in reference to  FIGS. 1A and 1B . 
     In  FIG. 2A , the piston  140  is at first fully retracted into the mechanical CPR device  100 , such that the suction cup  145  is at a position  205  above a torso  220  of patient  200 . In this position, the suction cup  145  is not in contact with the patient&#39;s torso  220 . From this first position  210 , the piston  140  can be extended until the suction cup  145  of piston  140  is at a position or height  210 . At height  210 , the suction cup  145  is in contact with the patient&#39;s torso  220 . The piston  140  can be extended by a drive component, such as a motor or an actuator, in the mechanical CPR device  100 . A controller in the mechanical CPR device  100  may control the drive component. 
     From position  220 , depicted in  FIG. 2A , the piston  140 /suction cup  145  can be further extended toward the patient&#39;s torso  220  until a threshold is reached so that air is forced out from the lower side of the suction cup  145 , such as in position  225  depicted in  FIG. 2B . In one example, the threshold can be a force threshold and the controller in the mechanical CPR device  100  can measure the force exerted by the piston  140  as the air is forced out from the lower side of the suction cup  145  and air is forced out of the patient  200 . Once the force exerted on the patient&#39;s torso  220  by the piston  140  reaches the force threshold, the controller can stop the piston  140  from being extended any further, such as at position  225 . In another example, the threshold can be a distance threshold and the controller in the mechanical CPR device  100  can measure the distance travelled  230  by the piston  140  as the air is forced out of the patient  200 . Once the distance travelled  230  by the piston  140  reaches the distance threshold, the controller can stop the piston  140  from being extended any further. In yet another example, the threshold can be a pressure threshold and a pressure sensor can sense the pressure in the area between the suction cup  145  and the patient&#39;s torso  220 . As the air is forced out from the patient  200 , and the pressure reaches the pressure threshold, the controller in the mechanical CPR device  100  can stop the piston  140  from being extended any further. In any of these examples, the patient&#39;s torso  220  may be compressed as the piston  140  is extended, such as in the depiction in  FIG. 2B . At the position  225  depicted in  FIG. 2B , the suction cup  145  is attached to the patient&#39;s torso  220  and the patient&#39;s torso  220  is compressed by the piston  140 . 
     From position  230 , the piston  140  can be retracted to the position  210 , as depicted in  FIG. 2A , where the suction cup  145  originally came into contact with the patient&#39;s torso  220 . From the position  210 , the piston  140  can be further retracted until the position  235 , where the piston  140  reaches a second threshold. The second threshold can be a force threshold, such as a force exerted when pulling up on the patient&#39;s torso  220 . This second threshold can be measured by a spring activation sensor or other force sensor. For example, the piston  140  can be retracted until the spring activation sensor is activated and then the drive component can stop retracting the piston  140 . From the position  235 , the piston  140  can be extended toward the patient&#39;s torso  220 , contacting the patient&#39;s torso at  210 , compressing the patient&#39;s torso  220  by extending to position  225 , and decompressing the patient&#39;s torso  220  by moving away from the patient&#39;s torso  220  to position  235 . By repeating the movement of the piston  140  through positions  235 ,  210 ,  225 ,  210 , to  235 , mechanical CPR can be performed on patient  200 . 
     In some cases, position  210 , where the suction cup  145  engages the patient&#39;s torso  220 , may be defined as a reference point or position. From this position  210 , the compression and decompression stroke of the piston  140  can be determined. Defining and using reference position  210  as a position from which to measure the depth of CPR compressions and the height of CPR decompressions can help to avoid unintended injury to a patient. For example, a manual CPR device can be placed on a patient&#39;s torso and a user can manually push or pull on the manual CPR device to cause compressions or decompressions. However, the user of the manual CPR device does not have any reference position from which to measure the depth of compressions or the height of decompressions. Without a reference position, the user can cause additional injuries to the patient. For example, if the user pushes the manual CPR device down too far into the patient&#39;s chest during a compression, the compression might break one or more of the patient&#39;s ribs. When one or more of the patient&#39;s ribs are broken, it may be easier to compress the patient&#39;s chest and a subsequent compression by user of the manual CPR device can cause even more of the patient&#39;s ribs to be broken, and injury to the patient&#39;s internal organs. In contrast, establishing reference position  210  with respect to the patient&#39;s torso  220  can prevent CPR compressions from extending too deep. Moreover, even if one injury does occur (e.g., the breaking of a patient&#39;s rib), the reference position  230  will not change and the likelihood that a subsequent compression will cause even further injury can be reduced. 
     Using a reference position can also be beneficial is circumstances where the patient is not located in a stable or a flat position. For example, if a patient is being transported, such as on a stretcher or an ambulance, the patient may be jostled around or otherwise not in a stable position. However, if the mechanical CPR device is moving with the patient (e.g., if mechanical CPR is being performed in an ambulance while the patient is being transported), the reference position of the piston  140  or suction cup  145  can remain relatively fixed with respect to the patient and the mechanical CPR device can avoid over-compression and over-decompression. Thus, the benefits of avoiding unintended injury could still be realized if the patient is otherwise moving. In another example, the patient can be located in a position that is not flat, such as if the patient is being transported down stairs or the patient is on rough terrain. In these cases, if the mechanical CPR device is located with the patient in the same non-flat position, the reference position used by the mechanical CPR device would reflect the patient&#39;s non-flat position and the mechanical CPR device could avoid over-compression and over-decompression. A user performing manual CPR under such conditions may have difficulty in maintaining a desired compression depth and/or decompression height. 
     In some cases, the patient&#39;s torso may be of a smaller dimension, such that its maximum height is below position  210 . This position is depicted in  FIG. 3A  as position  305 . In this case, the piston  140  may not be of a sufficient length to extend to position  305  and extend further to compress the patient&#39;s torso  220 . As depicted in  FIG. 3B , the piston  140  may be modified by a device or mechanism  315  to extend the length of piston  140 , so that the piston  140  may extend a distance  310  to engage a patient&#39;s torso  220  at position  305 . In this way, by extending the piston  140  via device  315 , the piston&#39;s reference point may be set correctly to accommodate a patient having a smaller sternum with a height  305 . By adjusting the reference point of the piston  140 /suction cup  145  to height  305 , the movement of the piston may be recalibrated to correctly and safely perform mechanical CPR on patient  200 . 
       FIG. 4  depicts a side view of a mechanical CPR device  100  with an adjustable length piston  140 . By modifying piston  140  to include a length adjustment device  315 , the piston  140  may be extended to position  305  from position  210 . In some aspects, a change in the reference point or nominal height of the piston  140  from position  210  to position  305 , represented by displacement  310 , may be detected by one or more sensors. The change in height or displacement  310  of the reference point may then be communicated to a controller and/or drive component of the mechanical CPR device  100 . The controller/drive component may adjust the movement of the piston based on the detected change  415  in position or displacement of the piston  140 , for example, to calibrate the fully extended position and the retracted position of the piston  140  to safely perform mechanical CPR on a patent having a smaller torso/sternum. 
       FIGS. 5A, 5B, 5C, 5D, 5E, 5F, and 5G  depict multiple views, both side and cut-out views, of an example  500  of an external piston spacer  555  that may be used to extend the length of piston of a mechanical CPR device, such as piston  140  of mechanical CPR device  100 . In reference to  FIG. 5A , a piston of a mechanical CPR device, for example piston  140 , may include an external piston sleeve  505  and an inner piston  510  having an outward surface  512 . A portion of the length of the inner piston  510  may be slidably located within the external piston sleeve  505 . The amount or length by which the inner piston  510  is positioned within the external piston sleeve  505  may adjust a full piston length  522 . An end of the piston  515 , which in some cases may include a suction cup  145 , may be positioned a distance  520  away from the end of the external piston sleeve  505 . In some cases, the inner piston  510  may be biased to be located at least partially within the external piston sleeve  505 . In some cases, a spring  545  or a member having elastic or semi-elastic properties may be located along a length  522  of the inner piston  510 , for example inward from the outward facing surface  512 . The spring may at least partially bias the inner piston  510  to slide partially into the external piston sleeve  505 . In some cases, a drive component of the attached mechanical CPR device (not shown), such as mechanical CPR device  100 , may bias or determine a resting position of the inner piston  510 . 
     In some cases, the external piston spacer  555 , the inner piston  510 , and/or the external piston sleeve  505  may be defined by a circular or oval cross-section. In other cases, the external piston spacer  555 , the inner piston  510 , and/or the external piston sleeve  505  may be defined by other cross-sections, such as, rectangular, polygon, and so forth, such that the external piston spacer  555 , the inner piston  510 , and the external piston sleeve  505  have the same shaped-cross section (but not necessarily the same dimensions). In other examples, the external piston spacer  555 , the inner piston  510 , and/or the external piston sleeve  505  may have different-shaped cross-sections, that are engagable or slidable about each other. 
     As depicted in  FIG. 5B , the inner piston  510  may be extended  524  away from the external piston sleeve  505 . In some cases, the length from the piston end and the end of the external piston sleeve  505  may be extended to a length  521 , thus increasing the full piston length an equal amount to length  523 . In this scenario, the outward surface  512  of the extended portion of the inner piston  510  (not within the external piston sleeve  505 ), may include one or more grooves or recesses  530 . As depicted in  FIG. 5B , one groove  530  may be disposed on the outward surface  512  of the inner piston  510 . However, in other scenarios, the outward surface  512  of the inner piston  510  may have two opposed grooves  530 , or any other number of grooves or recesses in any angular arrangement/at any position along the outward surface  512  of inner piston  510 . 
       FIG. 5C  depicts a cutout-view of piston having extended length  523 . The inner piston  510  may include a center piston or center piston portion  535 , for example, that may be connected to a drive component or motor of a mechanical CPR device, such as device  100 . A slidable ring or inner sleeve  540  may be disposed about the center piston portion  535  at an end of the center piston portion  535  located distal to the external piston sleeve  505 . The inner sleeve  540  may contact a spring  545 , also positioned axially relative to the inner piston  510  and the inner piston portion  535 , between the sleeve  540 /center piston portion  535  and the piston end  515 . In some cases, the spring  545  may bias the inner piston  510  and/or the center piston portion  535  to move towards the external piston sleeve  505 . In yet some examples, the spring  545 , additionally or alternatively, may aid in determining and setting the correct compression and decompressions stroke of piston  140 , for example via sensing force exerted on the piston end  515 . In some examples, a drive component of the mechanical CRP device, and/or one or more other springs may bias the center piston portion  535 /ring  540  to contact spring  545 . In some examples, the one or more grooves  530  may extend through a thickness of the outward surface  512 , such that a portion of the center piston portion  535  and/or the piston ring  540  are exposed. 
     A removable external piston spacer  555 , as depicted in  FIG. 5D , having a circular cross-section, may include two flanges or ridges  560 ,  565 . The two flanges  560 ,  565 , may be located on an inward facing surface of the external piston spacer  555 . In some cases, the external piston spacer  555  may be ring-shaped in cross-section, having a thickness. In this scenario, the external piston spacer  555  may engage at least a portion of the inner piston  510 , for example, when the flanges  560 , 565  are aligned with grooves  530 . In some examples, the flanges  560 ,  565  may have a substantially rectangular shape to engage and fit within grooves  530 . In other cases, the flanges  560 ,  565  and the grooves  530  may have other corresponding shapes, such as circular, triangular, polygon shape, etc. In some cases, the flanges  560 ,  565  may extend inward from the external piston spacer  555  a distance. The distance may be equal to or greater than a thickness of the outward surface  512  of the inner piston  510 , so as to ensure stable engagement with the inner piston  510 . 
     As depicted in  FIG. 5E , the external piston spacer  555  may be placed on the outward surface  512  of the inner piston  510 , by aligning the flanges  560 ,  565  with the grooves  530 . In some cases, inserting the flanges  560 ,  565  into the grooves  530  may push or force  570  the center piston portion  535  and/or the ring  540  upward toward the external piston sleeve  505 . In some examples, the flanges  560 ,  565  may extend inward from the external piston spacer  555  a distance greater than a thickness of the outer surface  512  of the inner piston  510 , such that the flanges  560 ,  565  may separate the center piston portion  535  and/or the ring  540  from contacting the spring  545 , as depicted in  FIG. 5F . One or more sensors  570 , such as a wiper, potentiometer, or other sensor electrical, mechanical, or optical sensor may detect the change in length  523  of the piston  140  caused by the presence of the external piston spacer  555 . The sensor(s)  570  may communicate the detected change in position or displacement to a controller or drive component of the mechanical CPR device  100 . The controller or drive component may then modify the compression and decompression stroke, e.g., the oscillation of the piston  140  to accommodate the changed length. Modifying the movement of the piston  140  may ensure or help to ensure more safe operation of the mechanical CPR device  100  when a patient having a smaller sternum/torso is treated using the mechanical CPR device  100 . 
     In some examples, the one or more sensors  570  may be part of the drive component or motor of the mechanical CPR device  100 . In this scenario, the sensor(s)  570  may be wipers that detect the angular position of the motor or drive component, for example of a drive shaft of a motor. The drive component may be configured, for example via instructions such as computer code and the like, to adjust at least one of a stroke compression and stroke decompression based on the detected change in resting angular position of the drive shaft. 
     In the example illustrated, the flanges  560  and  565  may be spaced at 180 degrees apart from one another, each positioned at an external edge of the external piston spacer  555 . In this example, the external piston spacer  555  may also wrap approximately 180 degrees or less around the inner piston  510 . 
     In some examples, the external piston spacer may have a length that is less than the length of the inner piston  510 , so as to be engagable about the outward face  512 . In the example illustrated, the flanges  560 ,  565  may prevent the inner piston  510  from sliding, at least partially, into the external piston sleeve  505 , for example by opposing a bias created by spring  545 , a drive component, or any number of spring or elastic members. In other examples, a body of the external piston spacer  555  may prevent the inner piston  510  from sliding, at least partially, into the external piston sleeve  505 . 
       FIGS. 6A, 6B, 6C, 6D, and 6E  depict multiple views, both side and cut-out views, of an example  600  of an internal bayonet sleeve  620  that may be used to extend the length of a piston of a mechanical CPR device, such as piston  140  of mechanical CPR device  100 . In the example descried below, the piston, such as piston  140 , may include an external piston sleeve  505 , and an inner piston  510  having a piston end  515 , as described above in reference to  FIG. 5 . 
     The inner piston  510  may include a center piston  615 , which may include one or more aspects of center piston portion  535  described above. The center piston  615  may be axially positioned relative to the external piston sleeve  505 . The center piston  615  may contact a compression spring  605  at one end proximate to the piston end  515  and may contact a decompression spring  610  at an opposing end proximate to the external piston sleeve  505 . The compression spring  605  and/or the decompression spring  610  may bias the center piston  615  to at least partially slide into the external piston sleeve  505 . In some cases, the compression spring  605  may detect a force applied between the piston end  515 , for example against a patient, and the center piston  615 . The compression of the spring  605  may inform a controller or drive mechanism of the mechanical CPR device  100  when a fully compressed position has been reached. Similarly, the decompression spring  610  may detect a force applied between the center piston  615  and the external piston sleeve  505 . The decompression of the spring  610  may inform a controller or drive mechanism of the mechanical CPR device  100  when a fully decompressed position has been reached. The center piston  615  and/or the inner piston  510  may be rotatably connected to a mechanical CPR device (not shown), such as device  100 , by a retaining ring  640 . In some cases, the center piston  615  may be connected to and driven by a drive shaft or other drive component of the mechanical CPR device  100 . The drive component may drive the center piston  615  to extend away from and retract toward the CPR device  100  and the external piston sleeve  505 . 
     An internal bayonet sleeve  620  may slidably surround or engage a portion of an outside surface  616  of the center piston  615 . The internal bayonet sleeve  620  may form a ring or partial ring around the center piston  615 . The bayonet sleeve  620  may have a length  621  and may have a plurality of grooves  625 ,  630  on one end. The plurality of grooves  625 ,  630  may be located at different angular positions around the bayonet sleeve  620  and may have varying lengths relative to length  621  of the bayonet sleeve  620 . For example, groove  625  may only define a space having a short length, while groove  630  may define a space having a length equal to length  621  of the bayonet sleeve  620 . Any number of grooves  625 ,  630  having varying lengths may similarly define spaces on bayonet sleeve  620 . 
     One or more locking rods  635  may be positioned on the outside surface  616  of the center piston  615 . The locking rod(s)  635  may have any number of shapes, such as circular, rectangular, polygon, etc., and may extend beyond the outside surface  616  a distance. The distance may be short enough to allow the center piston  615  and the locking rods  635  to rotate  645  relative to the outward surface  512  and/or the internal bayonet sleeve  620 . In some cases, the one or more locking rods  635  may be connected to the outward surface  512 , such that rotating the inner piston  510  may rotate the center piston  615 . 
     The one or more locking rods  635  may have a width that is similar to or slightly smaller than a width of grooves  625 ,  630  of the internal bayonet sleeve  620 , such that the locking rod(s)  635  may engage one or more grooves  625 ,  630 . When one or more locking rods  635  engage one or more grooves  625 ,  630 , the center piston  615  may be locked or rotationally fixed relative to the internal bayonet sleeve  620  and/or the outward surface or plate  512 . 
     As depicted in  FIG. 6C , the inner piston  510  and/or center piston  615  may be extended  650  away from the external piston sleeve  505 , for example, by applying a force to piston end  515  and/or inner piston  510 . Extending the center piston  615  relative to the internal bayonet sleeve  620 , which may be fixed to the external piston sleeve  505 , may disengage the one or more locking rods  635  from one or more of the grooves  625 ,  630 . In one example, two locking rods  635  may be positioned on the center piston  615 , 180 degrees apart from each other. Similarly, two grooves  625 , having the same length, may also be positioned on the internal bayonet sleeve 180 degrees apart. By extending the center piston  615  away from the internal bayonet sleeve  620  and disengaging the locking rods  635  from grooves  625 , the center piston  615  may be made rotatable about the internal bayonet sleeve  620 . As depicted in  FIG. 6D , the center piston  615  may be rotated 90 degrees clockwise  655  relative to the bayonet sleeve  620 . The locking rods  635  may be aligned with grooves  630  (in this example, also spaced 180 degrees apart and having a same length). As depicted in  FIG. 6E , once aligned, the center piston  615  may be moved or pushed  660  toward the external piston sleeve  505  until the locking rods  635  engage or stop against an end of grooves  630  or at the decompression spring  610 , or until the internal bayonet sleeve  620  contacts the spring  605 . In some cases, one or more of springs  605 ,  610  may bias the center piston  615  to naturally rest at a position closest to the external piston sleeve  505 . 
     In some cases, one or more sensors  665  may be positioned on the outer piston  505  to detect a change in the length of the inner piston  510 /the entire piston  140  (including the inner piston  510  and the external piston sleeve  505 ), caused by positioning the locking rods  635  in different grooves  625 ,  630 . In some cases, the one or more sensors  665  may include a n electrical sensor, such as a wiper or potentiometer, a mechanical sensor, and/or an optical sensors. In some cases, the one or more sensors  665  may detect a position of the inner piston  510  relative to the external piston sleeve  505 , may detect the angular position of a drive component of the mechanical CPR device  100 , and/or may detect contact between the locking rods  635  and one or more grooves  625 ,  630 . In some examples, each contact position between a groove  625 ,  630  and a locking rod  635  may be associated with a predetermined or pre-measured distance or displacement. Upon detection by sensor(s)  665 , the corresponding displacement value may be accessed and used to calibrate a controller or drive component of the mechanical CPR device. 
       FIG. 7  depicts an example of an adjustable piston including a piston adapter  700 . The piston adapter  700  may be removably attachable to a surface  750  of piston, such as piston  140  attached to a mechanical CPR device  100 . In some cases the piston adapter  700  may be attachable to the bottom surface of suction cup  145 . The piston adapter  700  may include a piston connection surface  715  connected to one end  721  of a body  720 , which may be circular in cross section. At an opposite end of the body  720 , a suction cup  705  may be attached and configured, for example, to contact the torso/sternum of a patient. In some cases, suction cup  705  may be similar to and/or include one or more aspects of suction cup  145 . In some aspects, the piston connection surface  715  or plate may be connected to the suction cup  705  via one or more members  730 ,  735 , which may add rigidity to the piston adapter  700 . 
     To attach the piston adapter  700  to the piston  140 , the piston adapter  700  may be positioned beneath the piston surface  750  and the piston connection surface  715  may be moved to contact the piston surface  715 . Upon contact, a gas check valve  725  may be engaged to temporarily or removably adhere the piston connection surface  715  to the piston surface  750 . In some examples, the piston surface  750  or other part of piston  140  may include one or more sensors  755 . The one or more sensors  755  may detect when the surfaces  750  and  715  come into contact. The one or more sensors  755  may include any of pressure sensors, optical sensors, force sensors, etc. In some aspects, upon detecting contact between surfaces  750  and  715 , the piston  140  or a controller thereof may send an indication (e.g., via a wireless connection by a transceiver, a wired connection, etc.) to the piston adapter  700 . Upon receiving the indication, the gas check valve  725  may be made operational. A controller of the piston  140  may detect when the piston adapter  700  is attached to the piston  140 , and may prevent attachment of the piston adapter  700  to the piston  140  until the piston controller has detected and acknowledged, for example, the change in length of piston  140  due to the attachment of the piston adapter  700 . In this way, injury to a patient may be reduced or eliminated that may be caused by the piston  140  being extended toward a patient without proper calibration (e.g., accounting for the length added by the piston adapter  700 ). 
     In some cases, a length of the piston adapter may be detected by the piston/sensor  755  or communicated to the piston controller by the piston adapter  700 . The piston controller may then adjust a stroke of the piston  140  to account for the changed length of the piston  140 . 
       FIG. 8  depicts an example of a method  800  of configuring a mechanical CPR device, such as device  100 , to accommodate a patient, for example having a smaller torso/sternum. At block  805 , a height of a patient to be treated may be detected. This may include using one or more sensors. In some cases, a piston, such as piston  140 , may be extended toward a patient until contact with the patient is detected, for example, by analyzing the force exerted on one or more springs of the piston  140 , such as spring  545  and/or  605 . In other cases, one or more optical sensors may be used to detect the height of a patient. In yet some aspects, the height may be received by the mechanical CPR device  100 , for example from one or more inputs via an operator. 
     At block  810 , a reference point of the piston  140  may be adjusted based on the detected height of the patient. In some cases, the reference point may be adjusted and/or set according to the techniques described in reference to  FIGS. 3A and 3B , for example to height  305  from height  210 , which may be a nominal height of the mechanical CPR device  100 /piston  140 . 
     In some cases, method  800  may include operations performed at block  815 , including adjusting a length of the piston to contact the patient, for example according to the adjusted reference point. The operations at block  815  may be performed by placing an external piston spacer  500  on the piston, as described in reference to  FIGS. 5A through 5G , at block  816 . The operation at block  815  may additionally or alternatively include adjusting an internal bayonet sleeve  600 /one or more locking rods engagable about the bayonet sleeve, as described above in reference to  FIGS. 6A  though  6 E, at block  817 . The operation at block  815  may additionally or alternatively include attaching a removable piston adapter  700  to the end of the piston, as described above in reference to  FIG. 7 . 
     At block  820 , the stroke of the piston may be determined based on the adjusted reference position. Mechanical CPR may then be performed on a patient using the configured mechanical CPR device according to the determined stroke of the piston. In this way, compression and decompression of the piston may be calibrated to account for the added piston length. This may increase the number of patients that may be treated by a mechanical CPR device  100 . Additionally or alternatively, the use of an adjustable piston may help reduce risk associated with mechanical CPR, including injury to a patient due to the compression stroke of the piston not being adjusted to a patient having a smaller torso. 
     In a number of embodiments discussed here, a suction cup has been described on the end of a piston. The suction cup can attach to a patient&#39;s torso so that, among other benefits, active decompression is possible. However, other mechanisms could be used to attach an end of the piston to a patient&#39;s torso. For example, a sticker plate configured to stick to patient&#39;s torso could be used on the end of the piston to attach to a patient&#39;s torso to the piston. In many of the above embodiments, the suction cup could be replaced with a sticker plate. Similarly, the suction cup in many of the above embodiments could be replaced with any number of other mechanisms that can attach to a patient&#39;s torso to the piston. 
     Conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain examples include, while other examples do not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more examples or that one or more examples necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular example. The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. 
     In general, the various features and processes described above may be used independently of one another, or may be combined in different ways. For example, this disclosure includes other combinations and sub-combinations equivalent to: extracting an individual feature from one embodiment and inserting such feature into another embodiment; removing one or more features from an embodiment; or both removing a feature from an embodiment and adding a feature extracted from another embodiment, while providing the advantages of the features incorporated in such combinations and sub-combinations irrespective of other features in relation to which it is described. All possible combinations and subcombination are intended to fall within the scope of this disclosure. In addition, certain method or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described blocks or states may be performed in an order other than that specifically disclosed, or multiple blocks or states may be combined in a single block or state. The example blocks or states may be performed in serial, in parallel, or in some other manner. Blocks or states may be added to or removed from the disclosed example examples. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example examples. 
     Each of the processes, methods and algorithms described in the preceding sections may be embodied in, and fully or partially automated by, code modules executed by one or more computers or computer processors. The code modules may be stored on any type of non-transitory computer-readable medium or computer storage device, such as hard drives, solid state memory, optical disc and/or the like. The processes and algorithms may be implemented partially or wholly in application-specific circuitry. The results of the disclosed processes and process steps may be stored, persistently or otherwise, in any type of non-transitory computer storage such as, e.g., volatile or non-volatile storage. 
     It will also be appreciated that various items are illustrated as being stored in memory or on storage while being used, and that these items or portions of thereof may be transferred between memory and other storage devices for purposes of memory management and data integrity. Alternatively, in other embodiments some or all of the software modules and/or systems may execute in memory on another device and communicate with the illustrated computing systems via inter-computer communication. Furthermore, in some embodiments, some or all of the systems and/or modules may be implemented or provided in other ways, such as at least partially in firmware and/or hardware, including, but not limited to, one or more application-specific integrated circuits (ASICs), standard integrated circuits, controllers (e.g., by executing appropriate instructions, and including microcontrollers and/or embedded controllers), field-programmable gate arrays (FPGAs), complex programmable logic devices (CPLDs), etc. Some or all of the modules, systems and data structures may also be stored (e.g., as software instructions or structured data) on a computer-readable medium, such as a hard disk, a memory, a network or a portable media article to be read by an appropriate drive or via an appropriate connection. Such computer program products may also take other forms in other embodiments. Accordingly, the present invention may be practiced with other computer system configurations. 
     While certain example or illustrative examples have been described, these examples have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of certain of the inventions disclosed herein.