Abstract:
A CPR chest compression system includes a retention structure that retains the body of a patient, and a motor and a compressor that can perform CPR compressions to the chest of the patient. The motor is powered by a battery that is located on the retention structure but away from the motor, and is electrically connected to the motor via one or more wires. Accordingly the weight and volume of the battery can be located away from a top portion of the retention structure. This renders the CPR system is less heavy at the top, and therefore less likely to tilt and start compressing the chest at a different point. Moreover, this permits X-Rays of a larger footprint to go through the CPR system and reach the patient, in embodiments where the components are transparent to X-Rays.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This patent application claims priority from U.S. Provisional Patent Application Ser. No. 62/290,188, filed on Feb. 2, 2016, the disclosure of which, as initially made, is hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    In certain types of medical emergencies a patient&#39;s heart stops working, which stops the blood from flowing. Without the blood flowing, organs like the brain will start becoming damaged, and the patient will soon die. Cardiopulmonary resuscitation (CPR) can forestall these risks. CPR includes performing repeated chest compressions to the chest of the patient, so as to cause the patient&#39;s blood to circulate some. CPR also includes delivering rescue breaths to the patient, so as to create air circulation in the lungs. CPR is intended to merely forestall organ damage and death, until a more definitive treatment is made available. Defibrillation is one such a definitive treatment: it is an electric shock delivered deliberately to the patient&#39;s heart, in the hope of restoring the heart rhythm. 
         [0003]    Guidelines by medical experts such as the American Heart Association provide parameters for CPR to cause the blood to circulate effectively. The parameters are for aspects such as the frequency of the chest compressions, the depth that they should reach, and the full release that is to follow each of them. If the patient is an adult, the depth is sometimes required to reach 5 cm (2 in.). The parameters for CPR may also include instructions for the rescue breaths. 
         [0004]    Traditionally, CPR has been performed manually. A number of people have been trained in CPR, including some who are not in the medical professions, just in case they are bystanders in a medical emergency event. 
         [0005]    Manual CPR may be ineffective, however. Indeed, the rescuer might not be able to recall their training, especially under the stress of the moment. And even the best trained rescuer can become fatigued from performing the chest compressions for a long time, at which point their performance may become degraded. In the end, chest compressions that are not frequent enough, not deep enough, or not followed by a full release may fail to maintain the blood circulation required to forestall organ damage and death. 
         [0006]    The risk of ineffective chest compressions has been addressed with CPR chest compression machines. Such machines have been known by a number of names, for example CPR chest compression machines, CPR machines, mechanical CPR devices, cardiac compressors, CPR devices, CPR systems, and so on. 
         [0007]    CPR chest compression machines typically hold the patient supine, which means lying on his or her back. Such machines then repeatedly compress and release the chest of the patient. In fact, they can be programmed to automatically follow the guidelines, by compressing and releasing at the recommended rate or frequency, while reaching a specific depth. 
         [0008]    The repeated chest compressions of CPR are actually compressions alternating with releases. The compressions cause the chest to be compressed from its original shape. During the releases the chest is decompressing, which means that the chest is undergoing the process of returning to its original shape. This decompressing does not happen immediately upon a quick release. In fact, full decompression might not be attained by the time the next compression is performed. In addition, the chest may start collapsing due to the repeated compressions, which means that it might not fully return to its original height, even if it were given ample opportunity to do so. 
         [0009]    Some CPR chest compression machines compress the chest by a piston. Some may even have a suction cup at the end of the piston, with which these machines lift the chest at least during the releases. This lifting may actively assist the chest, in decompressing the chest faster than the chest would accomplish by itself. This type of lifting is sometimes called active decompression. 
         [0010]    Active decompression may improve air circulation in the patient, which is a component of CPR. The improved air circulation may be especially critical, given that the chest could be collapsing due to the repeated compressions, and would thus be unable by itself to intake the necessary air. 
       BRIEF SUMMARY 
       [0011]    The present description gives instances of Cardio-Pulmonary Resuscitation (CPR) chest compression systems and methods, the use of which may help overcome problems and limitations of the prior art. 
         [0012]    In embodiments, a CPR chest compression system includes a retention structure that retains the body of a patient, and a motor and a compressor that can perform CPR compressions to the chest of the patient. The CPR chest compression system is powered by a battery that can be replaced by the rescuer. The retention structure has a well, and a rescuer can slide a battery into the well. The inserted battery becomes locked in the well until the rescuer actuates a release handle. 
         [0013]    An advantage is that a CPR chest compression system retains a patient, and is powered by battery that can be replaced while the patient continues to be retained. As such, a battery of the CPR system can be replaced without needing to pause for a significant time duration, which is useful in case a medical emergency event for a single patient lasts for a long time. One or more batteries can be replaced in the field, which further relaxes the design requirement that a single battery be used that has enough charge for operation during a prolonged event. 
         [0014]    In embodiments, a CPR chest compression system includes a retention structure that retains the body of a patient, and a motor and a compressor that can perform CPR compressions to the chest of the patient. The CPR chest compression system&#39;s motor is powered by a battery that is located away from the motor, and is electrically connected to the motor via one or more wires. 
         [0015]    An advantage over the prior art is that the weight and volume of the battery can be located away from a top portion of the retention structure. This renders the CPR system is less heavy at the top, and therefore less likely to tilt and start compressing the chest at a different point. Moreover, this permits X-Rays of a larger footprint to go through the CPR system and reach the patient, in embodiments where the components are transparent to X-Rays. 
         [0016]    In embodiments, a CPR chest compression system includes a retention structure that retains the body of a patient, and a motor and a compressor that can perform CPR compressions to the chest of the patient. The CPR chest compression system is powered by two or more batteries. The CPR system includes a receiving circuit between the batteries and the motor. In embodiments, the receiving circuit is smart and permits one of the batteries to be used preferentially over the other. The battery that is used is drained faster. In embodiments, a battery that already has less charge can be drained preferentially. 
         [0017]    An advantage over the prior art is that a rescuer then needs to recharge only one depleted battery, at a time when the CPR system is using the better-charged battery that it has preserved. 
         [0018]    These and other features and advantages of the claimed invention will become more readily apparent in view of the embodiments described and illustrated in the present disclosure, namely from the present written specification and the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1A  is a perspective diagram of a conventional CPR system. 
           [0020]      FIG. 1B  is a diagram showing an elevation view of the CPR system of  FIG. 1A . 
           [0021]      FIG. 2A  is a partly conceptual diagram of sample components of a CPR system made according to embodiments that have a well, and where a battery block has not yet been inserted into a well. 
           [0022]      FIG. 2B  is the diagram of  FIG. 2A , and where the battery block has been inserted into the well. 
           [0023]      FIG. 3  is a partly conceptual diagram of a sample battery block made according to embodiments, and which could also be the battery block of the embodiments of  FIG. 2A  and  FIG. 2B . 
           [0024]      FIG. 4  is a diagram showing sample details of a well of a CPR system made according to embodiments, and which could also be the well of the embodiments of  FIG. 2A  and  FIG. 2B . 
           [0025]      FIG. 5  is an elevation diagram of a sample CPR system made according to embodiments. 
           [0026]      FIG. 6  is an elevation diagram of a sample CPR system made according to embodiments. 
           [0027]      FIG. 7  is a diagram showing a detail of a sample instrument locking component and a complementary sample accessory locking component of a CPR system that are made according to embodiments, and which are shown artificially separated for clarity. 
           [0028]      FIGS. 8A-8C  are diagrams of successive sample configurations of the components of  FIG. 7 , as they may become engaged and disengaged when operated by a rescuer according to embodiments. 
           [0029]      FIG. 9  is a diagram showing a detail of a sample instrument locking component and a complementary sample accessory locking component of a CPR system that are made according to other embodiments, and which are shown artificially separated for clarity. 
           [0030]      FIG. 10  is a flowchart for illustrating methods according to embodiments. 
           [0031]      FIG. 11  is a partly conceptual diagram of sample components of a CPR system made according to additional embodiments. 
           [0032]      FIG. 12  is a partly conceptual diagram of sample components of a CPR system made according to embodiments, and in a larger scale than those in  FIG. 11 , so as to show a possible detail according to an embodiment. 
           [0033]      FIG. 13  is a partly conceptual diagram of sample components of a CPR system made according to embodiments, and further showing a more particular embodiment in which the battery block of  FIG. 11  is supported at or in one of the legs of the retention structure. 
           [0034]      FIG. 14A  is a partly conceptual diagram of sample mechanical and electrical details of a leg and a back plate of a CPR system at a time when they are apart, and made according to embodiments in which the back plate supports a battery block. 
           [0035]      FIG. 14B  is the partly conceptual diagram of  FIG. 14A , in which further the back plate and the leg have been brought together. 
           [0036]      FIG. 15  is a partly conceptual diagram of sample components of a CPR system, made according to embodiments that include two batteries and a receiving circuit. 
           [0037]      FIG. 16  is a block diagram of sample components for implementing a receiving circuit such as the receiving circuit of  FIG. 15  according to embodiments. 
           [0038]      FIG. 17  is a sample decision diagram for a receiving circuit such as the receiving circuit of  FIG. 15  according to an embodiment. 
           [0039]      FIG. 18  is a block diagram of sample components for implementing a receiving circuit such as the receiving circuit of  FIG. 15  according to embodiments. 
           [0040]      FIG. 19  is a flowchart for illustrating methods according to embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0041]    As has been mentioned, the present description is about Cardio-Pulmonary Resuscitation (CPR) systems that are usable by a rescuer to care for a patient. A conventional such system is now described with reference to  FIGS. 1A and 1B , which is presently being sold by Physio-Control under the trademark Lucas®. 
         [0042]    A CPR system  100  includes components that form a retention structure. The components include a central member  141 , a first leg  121 , a second leg  122  and a back plate  110 . Central member  141  is coupled with first leg  121  and second leg  122  using joints  181 ,  182 , such that first leg  121  and second leg  122  can be partly rotated around joints  181 ,  182  with respect to central member  141 . This rotation can help minimize the overall volume of CPR system  100 , for easier storage at times when it is not used. In addition, the far ends of legs  121 ,  122  can become coupled with edges  131 ,  132  of back plate  110 . 
         [0043]    These couplings form the retention structure that retains the patient. In this particular case, central member  141 , first leg  121 , second leg  122  and back plate  110  form a closed loop, in which the patient is retained. For storage, back plate  110  can be uncoupled from legs  121 ,  121 , which can be further rotated so that their edges are brought closer to each other. 
         [0044]    Central member  141  includes a battery that stores energy, a motor that receives the energy from the battery, and a compression mechanism that can be driven by the motor. The compression mechanism is driven up and down by the motor using a rack and pinion gear. The compression mechanism includes a piston  148  that can compress and release the patient&#39;s chest. Here, piston  148  terminates in a suction cup  199  for active decompression. In this case the battery, the motor and the rack and pinion gear are not shown, because they are completely within a housing of central member  141 . 
         [0045]    Embodiments are now described in more detail.  FIGS. 2A &amp; 2B  are partly conceptual, in that some elements are depicted substantially accurately while other elements substantially conceptually, as will be understood by a person skilled in the art. 
         [0046]    In one or more implementations, as shown in  FIG. 2A , a Cardio-Pulmonary Resuscitation (CPR) system  200  is provided. CPR system  200  is a chest compression system, usable to care for a patient  282 . CPR system  200  is usable by a rescuer (not shown) to care for patient  282 . As will be appreciated, the rescuer will thus place patient  282  in CPR system  200 , and turn on CPR system  200 . Head  283  of patient  282  is shown for perspective. Afterwards, CPR system  200  may operate automatically and largely autonomously, while the rescuer is observing, making adjustments, performing other tasks, or making logistical arrangements for transport and subsequent care of patient  282 . 
         [0047]    CPR system  200  includes a retention structure  240  that is configured to retain a body of patient  282 . Retention structure  240  may be implemented in a number of ways. In some embodiments, retention structure  240  includes the earlier described components, sometimes with modifications. One such modification can be that one of the legs is missing. In some embodiments, retention structure  240  includes a backboard. Some embodiments are described later in this document. 
         [0048]    CPR system  200  also includes a motor  249  that is coupled to retention structure  240 . In this example, motor  249  is provided in an optional housing  241  that is located generally above patient  282 , while patient  282  is retained by retention structure  240 . 
         [0049]    CPR system  200  additionally includes a compression mechanism  248 . As shown conceptually in  FIG. 2A , compression mechanism  248  could include a piston such as piston  148  of  FIG. 1A . In this example, at least some of compression mechanism  248  is shown within optional housing  241 . 
         [0050]    Other configurations are also possible. For example, the retention structure could include a backboard, and the compression mechanism could include a belt wrapped around the chest of patient  282 . In such a case, motor  249  could be located generally at a location other than above patient  282 . Of course, the implementation of compression mechanism  248  is preferably done in consideration of the implementation of retention structure  240 . For example, in some embodiments, compression mechanism  448  is a piston that emerges from a housing that is placed against the patient&#39;s chest. In such embodiments, retention structure  440  can include a belt with two ends attached to the housing. The belt is also wrapped around the back of the patient. Batteries can be inserted in the housing as described below. 
         [0051]    This description presents details about batteries of CPR systems. It is necessary for this description to sometimes distinguish between a) the cell that stores the electrical energy, and b) the battery housing that contains the cell. As will be seen in this description, a battery housing according to embodiments may have properties that permit easier handling by the rescuer. Accordingly, to maintain the distinction between the cell and the battery housing, the term “battery block” is used in this document as necessary. Where the distinction is not important, the simpler term “battery” may be used. In addition, it is anticipated that rescuers will use the simpler term “battery” for the object they are replacing, recharging, and so on. 
         [0052]    CPR system  200  additionally includes a battery block  261 . Battery block  261  has a battery housing and a cell within the battery housing that is configured to store energy, neither of which are indicated separately in  FIG. 2A  due to scale. Detailed sample embodiments of battery block  261  are now described. 
         [0053]      FIG. 3  shows a sample battery block  361  that could also be battery block  261 . Battery block  361  has a battery housing  360  and a cell  362  within battery housing  360 . Cell  362  is configured to store energy  363  in ways that are well known in the art. Moreover, battery housing  360  has electrical contacts  368 ,  369 . Within battery housing  360 , wires make electrical connections between cell  362  and electrical contacts  368 ,  369 . 
         [0054]    In the example of  FIG. 3 , battery block  361  also has an accessory locking component  364 , whose implementation and function will be understood in view of the below similarly named and numbered component of  FIG. 2A . 
         [0055]    Returning to  FIG. 2A , battery block  261  also has an accessory locking component  264 . Moreover, retention structure  240  has a well  251 , and an instrument locking component  254  that is associated with well  251 . Well  251  can be formed as part of retention structure  240 , or in any of its components, as described later in this document. 
         [0056]    In some embodiments, battery block  261  is configured to be inserted into well  251 . This configuration may be implemented by making the battery housing of battery block  261  have a shape substantially complementary to well  251 . In embodiments, therefore, the battery housing of battery block  261  is configured to be inserted into well  251 . Inserting can be performed by the rescuer sliding the battery housing into well  251 , according to the direction of an arrow  253 . Such sliding within the well can be by at least 1.5 cm in depth or even deeper, depending on the component sizes. 
         [0057]    In  FIG. 2A  battery block  261  has not yet been inserted into well  251  according to arrow  253 .  FIG. 2B  shows where the battery block has been so inserted. In embodiments, CPR system  200  further includes an ejection spring  255 , and optionally also a stop  256 . Detailed sample embodiments are now described. 
         [0058]    Referring briefly to  FIG. 4 , a sample well  451  is shown with an ejection spring  455  and a stop  456 , all of which could be similar to those of  FIG. 2A . A battery block (not shown in  FIG. 4  but shown in  FIG. 3 ) may be inserted in well  451  according to a direction  453 . Ejection spring  455  is positioned relative to well  451  such that ejection spring  455  becomes compressed when the battery housing of the battery block has been thus inserted into well  451  down to a threshold depth D. 
         [0059]    Moreover, in this embodiment, stop  456  is at about the threshold depth D, and defines the desired end of the travel of the battery housing being inserted into well  451 . In particular, stop  456  may prevent the battery housing being inserted any deeper into the well. Based on the above, threshold depth D could be deeper than the above mentioned 1.5 cm. 
         [0060]    In this embodiment, stop  456  includes electrical contacts  459 ,  458  within well  451 . These electrical contacts  459 ,  458  could become electrically coupled to contacts  369 ,  368  when the battery housing has been fully inserted into well  451 . Accordingly, energy  363  could be received from battery block  361  via wires  447 ,  446  that are coupled to electrical contacts  459 ,  458 . In other embodiments, the electrical contacts are provided within the well, but at a side wall of the well, etc. 
         [0061]    Returning again to  FIG. 2B , battery block  261  has been inserted into well  251  until it has reached stop  256 , and ejection spring  255  has become compressed. In equivalent embodiments, an ejection spring could have been extended, etc. 
         [0062]    In  FIGS. 2A, 2B, 3 and 4 , instrument locking component  254  and accessory locking component  264  are shown mostly conceptually. Implementations for instrument locking component  254  and accessory locking component  264  are described later in this document. Still, as shown, when the battery housing is inserted into well  251  down to the threshold depth, accessory locking component  264  is brought close to instrument locking component  254 . In embodiments, instrument locking component  254  can become interlocked with accessory locking component  264 , so as to lock battery block  261  within well  251 . This locking would prevent battery block  261  from partially sliding out or completely falling out of well  251 . In other words, instrument locking component  254  of well  251  and accessory locking component  264  of the battery housing of battery block  261  are such that, thus inserting the battery housing into well  251  down to the threshold depth permits instrument locking component  254  and accessory locking component  264  to become engaged with each other. Engagement can effectuate locking, such that the thus inserted battery housing can no longer slide out of well  251 , even if a force of  50  Newton (Nt) were to be applied to the battery housing against retention structure  240 . 
         [0063]    Motor  249  is configured to receive the stored energy from the cell of battery block  261 , while the battery housing of battery block  261  has been thus inserted into well  251 . If well  251  has been placed close to motor  249 , the stored energy can be received over a short distance, perhaps over a node. Else wires may be used, for example as later described in this document for battery wire  1146 . A sample optional battery wire  246  is shown. 
         [0064]    Compression mechanism  248  can be configured to be driven by motor  249 , while motor  249  thus receives energy. Compression mechanism  248  can be configured to perform, while thus driven and the patient&#39;s body is retained by retention structure  240 , automatically CPR compressions alternating with releases to a chest of the patient&#39;s body. The CPR compressions may thus cause the chest to become compressed by at least 2.5 cm. 
         [0065]    In embodiments, one of the instrument locking component and the accessory locking components includes a release handle. Examples of such a release handle are described later in this document, for example with reference to at least  FIGS. 7-9 . In such embodiments, when the release handle is actuated by the rescuer, the thus engaged instrument locking component  254  and accessory locking component  264  become disengaged from each other, such that the battery housing can again slide out of well  251  if a force of 50 Nt were to be applied to the battery housing against retention structure  240 . 
         [0066]    Moreover if, as is preferred, ejection spring  255  is indeed provided, then the ejection spring may eject at least partially the battery housing from well  251 , responsive to the release handle being thus actuated. 
         [0067]    An advantage of embodiments is that a rescuer can replace a depleted battery with a freshly charged one rather easily and quickly. Such embodiments are easy to teach to medical personnel who would use CPR system  200 . 
         [0068]    Regarding the location of well  251  relative to retention structure  240 , there are many possibilities. In embodiments, retention structure  240  and well  251  are configured such that the rescuer can slide the battery housing of battery block  261  into well  251  while retention structure  240  thus retains the body of patient  282 . In other words, a mouth of well  251 , and its main depth direction, can be oriented such that they are accessible by the rescuer during the medical emergency event, and without the retained patient&#39;s body presenting an obstruction. 
         [0069]    An advantage, therefore, is that the rescuer can replenish a battery by interrupting the chest compressions for only a short time, and without having to move the patient. In fact, batteries can be made smaller, if they can be changed during a single such event. 
         [0070]    In some embodiments, retention structure  240  includes a central member, a first leg, a second leg and a back plate. The central member can be configured to become coupled to the back plate via the first leg and the second leg. This could be as in  FIG. 1A , where the back plate can be totally separated from the other three components. Or, these components may be capable of being coupled together and separable in different combinations, for example using hinges or not, etc. In such embodiments, the well is in one of the legs, such as in the first leg. An example is now described. 
         [0071]      FIG. 5  is an elevation diagram of a sample CPR system  500  made according to embodiments. CPR system  500  includes a central member  541 , a first leg  521 , a second leg  522  and a back plate  510 . A compression mechanism  548  can be coupled to central member  541 . Central member  541  can be configured to become coupled to back plate  510  via first leg  521  and second leg  522 . 
         [0072]    First leg  521  has a well  551 . A battery block  561 , made as described above, can be inserted into well  551 , according to arrow  553 . In embodiments where the patient&#39;s arms are tied to legs  521 ,  522 , then well  551  can be formed such that its main direction is titled somewhat from the vertical, so that its interior can be accessed the arms of the patient presenting an obstruction. 
         [0073]    In the particular example of  FIG. 5 , CPR system  500  actually has two wells and two battery blocks, optionally symmetrically. In particular, second leg  522  includes an other well  552 , and CPR system  500  further includes an other battery block  562  that has an other battery housing and an other cell within the other battery housing. The other cell can be configured to store energy, of course. The other battery housing of other battery block  562  can be configured to be inserted into other well  552  by the rescuer sliding the other battery housing into other well  552 , for example as per the direction of arrow  554 . Powering the single motor by two battery blocks  561 ,  562  can be coordinated in a number of ways, including optionally using a receiving circuit as described later in this document. 
         [0074]    In some embodiments, the well is in the back plate. Examples are now described. 
         [0075]      FIG. 6  is an elevation diagram of a sample CPR system  600  made according to embodiments. CPR system  600  includes a central member  641 , a first leg  621 , a second leg  622  and a back plate  610 . A compression mechanism  648  can be coupled to central member  641 . Central member  641  can be configured to become coupled to back plate  610  via first leg  621  and second leg  622 . 
         [0076]    Back plate  610  has a well  651 . A battery block  661 , made as described above, can be inserted into well  651 , according to arrow  653 . 
         [0077]    In the particular example of  FIG. 6 , CPR system  600  actually has two wells and two battery blocks, optionally symmetrically. In particular, back plate  610  also has an other well  652 , and CPR system  600  further includes an other battery block  662  that has an other battery housing and an other cell within the other battery housing. The other cell can be configured to store energy. The other battery housing of other battery block  662  can be configured to be inserted into other well  652  by the rescuer sliding the other battery housing into other well  652 , for example as per the direction of arrow  654 . Powering the motor by two battery blocks  661 ,  662  can be coordinated in a number of ways, including optionally using a receiving circuit as described later in this document. 
         [0078]    In embodiments such as those of  FIGS. 5 and 6 , the battery block may be located away from the motor. In such embodiments, the energy may be transferred from the battery block to the motor by wires, as is described later in this document. 
         [0079]    Returning again to  FIGS. 2A &amp; 2B , examples are given for instrument locking component  254  and accessory locking component  264 , for describing how they can lock battery block  261  within well  251 . 
         [0080]      FIG. 7  is a diagram showing a detail of a sample instrument locking component and a complementary sample accessory locking component of a CPR system that are made according to embodiments, and which are shown artificially separated for clarity. In particular, a portion of a retention structure  740  has a well  751 , of which only the left half is shown. The left half of well  751  includes an inner surface  752 . 
         [0081]    Moreover, a battery block  761  according to embodiments has a battery housing  760  with an outer surface  772 . Ordinarily the rescuer slides battery block  761  in well  751  such that outer surface  772  of battery housing  760  moves in parallel with, and very near inner surface  752 . In  FIG. 7 , however, outer surface  772  is shown artificially separated from inner surface  752 , for clarity. 
         [0082]    In the embodiment of  FIG. 7  the instrument locking component of well  751  includes a slot  754  in inner surface  752 . In particular, well  751  has a main depth direction that is downwards in  FIG. 7 , and also in  FIG. 8A . This direction is shown by arrow  891  in  FIG. 8 , and is the direction in which battery block  761  is inserted in well  751 . Slot  754  has a depth in a direction perpendicular to the main depth direction of well  751 . In other words, slot  754  has a depth in a horizontal direction, also shown by arrow  701 . 
         [0083]    In the embodiment of  FIG. 7  the accessory locking component of battery block  761  includes an anchor  764  that is configured to protrude from outer surface  772  of battery housing  760 . In fact, in this embodiment, the accessory locking component further includes an anchor spring  765  that is configured to bias anchor  764  towards thus protruding, as is preferred. 
         [0084]    This way, when anchor  764  protrudes from outer surface  772 , it is configured to become received in slot  754 , as battery housing  760  is thus inserted into well  751  down to the threshold depth. The protruding and the receiving are shown artificially by arrow  701 . 
         [0085]    In embodiments, the receiving of anchor  764  in slot  754  may cause the instrument locking component and the accessory locking component to become thus engaged with each other. This would prevent battery block  761  from accidentally sliding out of well  751 , in a direction upward in  FIG. 7 . 
         [0086]    The aforementioned release handle can be part of either the instrument locking component or the accessory locking component. In the embodiment of  FIG. 7 , it is the accessory locking component that includes a release handle  767 . Actuating release handle  767  can be performed by pushing it to the right, in  FIG. 7 . Actuating release handle  767  may withdraw anchor  764  from thus protruding. The withdrawing, therefore, may cause anchor  764  to no longer be thus received in slot  754 . If, as is preferred, anchor spring  765  is included, thus actuating release handle  767  can be performed by applying force against anchor spring  765 . 
         [0087]      FIGS. 8A-8C  are diagrams of successive sample configurations of the components of  FIG. 7 , as they may become engaged and disengaged when operated by a rescuer according to embodiments. Not all reference numerals are repeated from  FIG. 7 , to preserve clarity. 
         [0088]    In  FIG. 8A , the rescuer is inserting battery block  761  into well  751  according to the direction of arrow  891 . Outer surface  772  of battery housing  760  is sliding near inner surface  752 . Anchor  764  is withdrawn within battery housing  760 , and substantially not protruding; actually it may protrude a little within the short space of outer surface  772  and inner surface  752 , but it is still not received within slot  754 . Anchor spring  765  is extended, and biases anchor  764  towards inner surface  752 . 
         [0089]    In  FIG. 8B , battery block  761  has reached the threshold depth within well  751 . Anchor  764  has been aligned with slot  754 , and anchor spring  765  has thus pushed anchor  764  to be received in slot  754  according to an arrow  892 . This locks battery block  761  within well  751 . Anchor spring  765  is no longer extended. 
         [0090]    In  FIG. 8C , release handle  767  is being actuated by being pushed to the right, in the direction of arrow  893 . Anchor spring  765  is again extended, and anchor  764  has been withdrawn from slot  754 . The rescuer can then pull battery block  761  out of well  751  with relatively little force, often less than 50 Nt, in the direction of arrow  894  against retention structure  740 . 
         [0091]    In this embodiment, the rescuer may access release handle  767  by inserting a few fingers via an opening  773  in housing  760 . It will be appreciated that this design, which makes release handle  767  relatively difficult to access, does not permit many scenarios of release handle  767  becoming actuated accidentally, e.g. by being bumped. 
         [0092]    In the example just described, the accessory locking component had the anchor. Equivalently, the anchor can be in the instrument locking component. An example is now described. 
         [0093]      FIG. 9  is a diagram showing a detail of a sample instrument locking component and a complementary sample accessory locking component of a CPR system that are made according to other embodiments, and which are shown artificially separated for clarity. In particular, a portion of a retention structure  940  has a well  951 , of which only the left half is shown. The left half of well  951  includes an inner surface  952 . 
         [0094]    Moreover, a battery block  961  according to embodiments has a battery housing  960  that includes an outer surface  972 . Ordinarily the rescuer slides battery block  961  in well  951  such that outer surface  972  of housing  960  moves in parallel with, and near inner surface  952 . In  FIG. 9 , however, battery housing  960  is shown artificially separated from inner surface  952  for clarity. 
         [0095]    Moreover, the instrument locking component of well  951  includes an anchor  954  that is configured to protrude into well  951  from inner surface  952  of well  951 . In fact, in this embodiment, the instrument locking component further includes an anchor spring  959  that is configured to bias anchor  954  towards thus protruding, as is preferred. 
         [0096]    In the embodiment of  FIG. 9  the accessory locking component of battery block  961  includes a slot  964  in outer surface  972 . This way, when anchor  954  protrudes from outer surface  952 , it is configured to become received in slot  964 , as battery housing  960  is thus inserted into well  951  down to the threshold depth in the direction of arrow  991 . The protruding and the receiving are shown artificially by arrow  901 . 
         [0097]    In embodiments, the receiving of anchor  954  in slot  964  may cause the instrument locking component and the accessory locking component to become thus engaged with each other. This would prevent battery block  961  from accidentally sliding out of well  951  in the direction of arrow  994 . 
         [0098]    The aforementioned release handle can be part of either the instrument locking component or the accessory locking component. In the embodiment of  FIG. 9 , it is the instrument locking component that includes a release handle  967 . Actuating release handle  967  can be performed by pulling it to the right, in  FIG. 9 , for example by inserting a finger through a loop  968  of release handle  967 . Actuating release handle  967  may withdraw anchor  954  from thus protruding. The withdrawing, therefore, may cause anchor  954  to no longer be thus received in slot  964 . If, as is preferred, anchor spring  959  is included, thus actuating release handle  967  can be performed by applying force against anchor spring  959 . 
         [0099]    Other embodiments are also possible. For example, one may consult U.S. Pat. No. 5,741,305 from a different art, and which is incorporated by reference in this document. 
         [0100]    The invention also includes methods.  FIG. 10  shows a flowchart  1000  for describing methods according to embodiments. According to an operation  1010 , a battery housing is inserted into a well of a retention structure by sliding the battery housing by at least 1.5 cm into the well down to a threshold depth. In some embodiments the threshold depth is longer, e.g. 3 cm, 5 cm or even longer. Inserting may thus cause an instrument locking component and an accessory locking component to become engaged with each other. The engagement can be such that the thus inserted battery housing can no longer slide out of the well, even if a force of 50 Nt were to be applied to the battery housing against a retention structure that has the well. 
         [0101]    In embodiments, responsive to operation  1010  a motor becomes able to receive stored energy from a cell in the battery housing, and to drive a compression mechanism while the battery housing has been thus inserted into the well. 
         [0102]    According to another, optional operation, prior to operation  1010  a body of a patient can be placed in the retention structure, so that the retention structure retains the body. In such a case, the battery housing can be inserted into the well according to operation  1010  while the retention structure thus retains the body. 
         [0103]    In some embodiments where a CPR system further includes an ejection spring, inserting the battery housing into the well according to operation  1010  requires applying force against the ejection spring. 
         [0104]    In some embodiments, one of the instrument locking component of the well and the accessory locking component of the battery block includes a release handle. In such embodiments, according to another, optional operation  1020 , the release handle is actuated so as to cause the thus engaged instrument locking component and accessory locking component to become disengaged from each other. The disengagement can be such that the battery housing can again slide out of the well if a force of 50 Nt were to be applied to the battery housing against the retention structure. 
         [0105]    In embodiments where an ejection spring is provided, the ejection spring may eject at least partially the battery housing from the well responsive to operation  1020 . 
         [0106]    In some embodiments, one of the instrument locking component and the accessory locking component includes an anchor, a release handle and an anchor spring. In such embodiments, thus actuating the release handle as described in operation  1020  is performed by applying force against the anchor spring. 
         [0107]      FIG. 11  is a partly conceptual diagram of sample components of a CPR system  1100  made according to additional embodiments. CPR system  1100  is usable by a rescuer (not shown) to care for a patient (not shown). 
         [0108]    CPR system  1100  includes a retention structure  1140 . Retention structure  1140  includes a central member  1141 , a leg  1121  and a back plate  1110 . Central member  1141  can be configured to become coupled to back plate  1110  via leg  1121 . Retention structure  1140  can be configured to retain a body of a patient, when central member  1141  is thus coupled to back plate  1110 . 
         [0109]    In some embodiments, retention structure  1140  further optionally includes an other leg  1122 , which can be also called a second leg  1122 . In such embodiments, central member  1141  can be configured to become coupled to back plate  1110  via also second leg  1122 . In such a case, retention structure  1140  can form a closed loop around the chest of the patient, although this is not required. 
         [0110]    As also mentioned above, central member  1141  can be configured to become thus coupled to back plate  1110  in a number of ways. In some embodiments, all components can be wholly separable from each other. In some embodiments, legs  1121  &amp;  1122  can be rotatably coupled with central member  1141 , and wholly separable from back plate  1110 . In some embodiments, central member  1141  can slide down leg  1121  by an adjustable distance, and so on. 
         [0111]    CPR system  1100  also includes a motor  1149  attached to central member  1141 . In some embodiments, central member  1141  outwardly looks like a housing that completely encloses motor  1149 . In addition, CPR system  1100  may also include a compression mechanism  1148  that is attached to central member  1141  and is configured to be driven by motor  1149 . What is written above for motor  249  and compression mechanism  248  may also apply to motor  1149  and compression mechanism  1148 , respectively. 
         [0112]    In embodiments, at least a first battery block  1161  can be configured to be supported by retention structure  1140 . There are a number of different ways for battery block  1161  to be supported by retention structure  1140  that are described later in this document, and any one of them is implied by how battery block  1161  is conceptual depicted in  FIG. 11 . 
         [0113]    Battery block  1161  can be configured to store energy, for delivering to motor  1149 . For this, battery block  1161  can become electrically coupled to motor  1149  as follows: CPR system  1100  also includes a battery wire  1146  having a first end  1191  that is electrically coupled to motor  1149 . Battery wire  1146  also has a second end  1192  opposite first end  1191 . Battery block  1161  can be configured to become electrically coupled to second end  1192  of battery wire  1146  when central member  1141  is thus coupled to back plate  1110 . In such cases, then, motor  1149  can be configured to receive energy from battery block  1161  via battery wire  1146  when central member  1141  is thus coupled. 
         [0114]    Battery wire  1146  further has a length of at least  6  cm between first end  1191  and second end  1192 . In fact, battery wire  1146  could be a lot longer. A supported portion of battery wire  1146  that is least  4  cm long can be supported by leg  1121 . In  FIG. 11 , the supported portion is defined at least between support points  1124 ,  1125 , at which battery wire  1146  is supported by leg  1121 . Points  1124 ,  1125  are at least  4  cm away from each other, and could potentially be a lot farther, even up to the whole length of leg  1121 . The supported portion can be at a surface of leg  1121 , within it, and so on. 
         [0115]    Of course, while only a single battery wire  1146  is being described, this is only for the purpose of simplicity. Another battery wire (not shown) may accommodate the second electrical pole of the cell of battery block  1161 , i.e. the opposite polarity or complementary polarity or reference voltage of the cell. 
         [0116]    In some embodiments, battery wire  1146  may have a flexible portion. An example is now described. 
         [0117]      FIG. 12  is a partly conceptual diagram of sample components of a CPR system made according to embodiments, and in a larger scale than those in  FIG. 11 , so as to show a possible detail according to an embodiment. 
         [0118]    In  FIG. 12 , components include a central member  1241  to which a motor  1249  is attached. Leg  1221  is coupled to central member  1241  by using a joint  1281 . Accordingly, leg  1221  can be rotated with respect to central member  1241  around joint  1281 . A battery wire  1246  has a first end  1291  that is electrically coupled to motor  1249 , and has a supported portion that is supported by leg  1221  at a point  1224 . Battery wire  1246  includes a flexible portion  1293  between first end  1291  and point  1224 . Flexible portion  1293  is distinct from the supported portion, and is supported by neither central member  1241  nor leg  1221 . Accordingly, flexible portion  1293  may flex as leg  1221  is rotated with respect to central member  1241 . 
         [0119]    As already mentioned with reference to  FIG. 11 , battery block  1161  can be configured to be supported by any component of retention structure  1140 . Of course, as before, the battery block has a battery housing and a cell within the battery housing that is configured to store the energy. The supporting is done from the battery housing. Different embodiments are now described. 
         [0120]    In some embodiments, the battery block is configured to be supported by a leg of the retention structure, such as the leg. In particular, the battery block has a battery housing that can be configured to be supported by the leg of the retention structure. Examples are now described. 
         [0121]      FIG. 13  is a partly conceptual diagram of sample components of a CPR system  1300  made according to additional embodiments. CPR system  1300  is usable by a rescuer (not shown) to care for a patient (not shown). 
         [0122]    CPR system  1300  includes a retention structure  1340 . Retention structure  1340  includes a central member  1341 , a leg  1321  and a back plate  1310 . Central member  1341  can be configured to become coupled to back plate  1310  via leg  1321 , for example as described above with reference to  FIG. 11 . Retention structure  1340  can be configured to retain a body of a patient, when central member  1341  is thus coupled to back plate  1310 . 
         [0123]    In some embodiments, retention structure  1340  further optionally includes a second leg  1322 . In such embodiments, central member  1341  can be configured to become coupled to back plate  1310  via also second leg  1322 . In such a case, retention structure  1340  can form a closed loop around the chest of the patient, although this is not required. 
         [0124]    CPR system  1300  also includes a motor  1349  attached to central member  1341 . In some embodiments, central member  1341  outwardly looks like a housing that completely encloses motor  1349 . In addition, CPR system  1300  may also include a compression mechanism  1348  that is attached to central member  1341  and is configured to be driven by motor  1349 . What is written above for motor  249  and compression mechanism  248  may also apply to motor  1349  and compression mechanism  1348 , respectively. 
         [0125]    At least a first battery block  1361  can be configured to be supported by leg  1321  of retention structure  1340 , by appropriately shaping the battery housing of battery block  1361  and leg  1321 , for example by making them complementary in form. A battery wire  1346  is similar to what was described for battery wire  1146 . In particular, battery wire  1346  has a first end  1391  that is electrically coupled to motor  1349 , and a second end  1392  that can become electrically coupled to the cell of battery block  1361 . Battery wire  1346  further has a length of at least  6  cm between first end  1391  and second end  1392 , and is potentially a lot longer. A supported portion of battery wire  1346  that is least  4  cm long can be supported by leg  1321 , similarly with what was described in  FIG. 11 . 
         [0126]    Again, while only a single battery wire  1346  is being described, this is only for the purpose of simplicity. Another wire (not shown) may accommodate the second electrical pole of the cell of battery block  1361 . 
         [0127]    The battery housing of battery block  1361  and leg  1321  can be complementarily shaped in a number of ways. For example, leg  1321  may have a small compartment, even with a door, in which battery block  1361  can be placed. For another example, as already described with reference to corresponding elements in  FIG. 5 , leg  1321  can have a well into which the battery housing of battery block  1361  can slide and become secured by an instrument locking component becoming engaged with an accessory locking component, and so on. And, of course, two battery blocks can be supported if two legs are provided, and so on. 
         [0128]    In some embodiments, the battery block is configured to be supported by the back plate of the retention structure. In particular, the battery block has a battery housing that can be configured to be supported by the back plate. Examples of how the battery block can be supported in the back plate have already been described with reference to  FIG. 6 , where the back plate can have a well into which the battery housing of battery block and become secured by an instrument locking component becoming engaged with an accessory locking component, and so on. In other embodiments, the back plate may have a small compartment, even with a door, in which the battery block can be placed. And, of course, two battery blocks can be supported at the two legs, and so on. 
         [0129]    For the electrical contacts, electrical coupling can be made when edges are brought together. Examples are now described. 
         [0130]      FIGS. 14A &amp; 14B  are diagrams of sample mechanical and electrical details of a leg  1421  and a back plate  1410  of a CPR system. In  FIG. 14A  they are apart, for example as seen by their separated edges  1438 ,  1439 , while in  FIG. 14B  leg  1421  and a back plate  1410  have been brought together. When a central member of a CPR system (not shown) becomes coupled to back plate  1410  through leg  1421 , leg  1421  is brought together with a back plate  1410  at edges  1438 ,  1439 . At that time, edges  1438 ,  1439  are brought very close to, or even in contact with each other. 
         [0131]    Leg  1421  has a leg electrical contact  1426 . A battery wire  1446 , similar to battery wire  1146 , has a first end (not shown) electrically coupled to the motor (not shown) and a second end  1492  that is electrically coupled to leg electrical contact  1426 . In addition, an other battery wire  1447  is used for the opposite polarity. Other battery wire  1447  is electrically coupled between the motor (not shown) and an other leg electrical contact  1427 . In this example, leg electrical contacts  1426 ,  1427  protrude from edge  1438 . 
         [0132]    In  FIGS. 14A &amp; 14B , the battery block is configured to be supported by back plate  1410 . In these partly conceptual diagrams, only the electrical schematic of a cell  1462  of the battery block is shown, to illustrate the electrical connections. In addition, two wires  1448 ,  1449  have first ends that are electrically coupled to the poles of cell  1462 , and second ends that are electrically coupled to intermediate contacts  1458 ,  1459  near edge  1439 . 
         [0133]    Moreover, back plate  1410  has back plate electrical contacts  1416 ,  1417  that correspond to leg electrical contacts  1426 ,  1427 . In this example, back plate electrical contacts  1416 ,  1417  do not protrude from edge  1439 . Back plate electrical contacts  1416 ,  1417  are moveable within their sockets, and can be brought into contact with touch intermediate contacts  1458 ,  1459 . Accordingly, the battery block, i.e. cell  1462 , is configured to become electrically coupled to back plate electrical contacts  1416 ,  1417  when supported in back plate  1410 . 
         [0134]    Referring to  FIG. 14B , when leg  1421  is brought together with a back plate  1410  at edges  1438 ,  1439 , back plate electrical contacts  1416 ,  1417  become electrically coupled with leg electrical contacts  1426 ,  1427 . In addition, at that time back plate electrical contacts  1416 ,  1417  can touch intermediate contacts  1458 ,  1459 , and therefore the power of cell  1462  becomes available to battery wires  1446 ,  1447 . 
         [0135]    In this example, leg electrical contacts  1426 ,  1427  are fixed, while back plate electrical contacts  1416 ,  1417  are moveable. In fact, back plate electrical contacts  1416 ,  1417  are supported by contact springs  1418 . Contact springs  1418  become compressed when leg  1421  and a back plate  1410  are brought together. In an equivalent embodiment, the contact springs could be in the side of the leg, not the back plate. 
         [0136]    In some embodiments where two batteries are used, a receiving circuit may be also used. For such embodiments, it should be remembered that the terms battery and battery block may be used interchangeably in some circumstances, as per the above. Examples are now described. 
         [0137]      FIG. 15  is a partly conceptual diagram of sample components of a CPR system  1500 , which is made according to embodiments that include two batteries  1561 ,  1562  and a receiving circuit  1577 . CPR system  1500  is usable by a rescuer (not shown) to care for a patient (not shown). 
         [0138]    CPR system  1500  includes a retention structure  1540  that is configured to retain a body of a patient. While shown only conceptually in  FIG. 15 , retention structure  1540  may be implemented in a number of ways, for example as described for retention structures earlier in this document. 
         [0139]    CPR system  1500  also includes a motor  1549  that is coupled to retention structure  1540 . In this example, motor  1549  is provided in an optional housing  1541 . CPR system  1500  additionally includes a compression mechanism  1548 . As shown conceptually in  FIG. 15 , compression mechanism  1548  could be a piston such as piston  148  of  FIG. 1A . In the example of  FIG. 15 , at least some of compression mechanism  1548  is shown within optional housing  1541 . 
         [0140]    CPR system  1500  additionally includes a first battery  1561  and a second battery  1562 . Batteries  1561 ,  1562  can be configured to store energy, and to be coupled to retention structure  1540 . Batteries  1561 ,  1562  can be located near motor  1549 , for example within housing  1541  if provided. Or, batteries  1561 ,  1562  can be supported by legs of retention structure  1540 , for example as seen in  FIG. 5  of this document for battery blocks  561 ,  562  being supported by legs  521 ,  522 . Or, batteries  1561 ,  1562  can be supported by a back plate of retention structure  1540 , for example as seen in  FIG. 6  of this document for battery blocks  661 ,  662  being supported by back plate  610 . 
         [0141]    CPR system  1500  moreover includes a receiving circuit  1577  that can be supported on retention structure  1540 , and preferably within optional housing  1541 . Receiving circuit  1577  has a central node  1599 , and possibly also other components. 
         [0142]    Central node  1599  can be electrically coupled to first battery  1561  and second battery  1562 . This electrical coupling can be via optional wires such as battery wires  1546 ,  1536 , plus their respective complementary wires for the opposite polarities. If batteries  1561 ,  1562  are located near motor  1549 , then battery wires  1546 ,  1536  could be very short. If, however, batteries  1561 ,  1562  are located farther away, then battery wires  1546 ,  1536  could be commensurately longer. 
         [0143]    Motor  1549  can be electrically coupled to central node  1599 , for example via a wire  1594 . Depending on embodiments, wire  1594  can be a mere electrical node, i.e. central node  1599 . 
         [0144]    Embodiments of receiving circuit  1577  can be such that motor  1549  can be configured to receive energy via central node  1599  from first battery  1561 , or second battery  1562 , or both first battery  1561  and second battery  1562 . Examples are now described. 
         [0145]    In some embodiments, receiving circuit  1577  is only central node  1599 , as shown in  FIG. 15 . In such embodiments, motor  1549  can be receiving from both batteries  1561  &amp;  1562 . A person skilled in the art will recognize, however, that in this embodiment, if batteries  1561 ,  1562  are not equally charged, then the stronger battery could be also charging the weaker one through central node  1599 . 
         [0146]      FIG. 16  is a block diagram of sample components for implementing a receiving circuit  1677 . Receiving circuit  1677  includes a central node  1699  that is coupled to motor  1649  via a wire  1694 . Moreover, receiving circuit  1677  includes stopping circuits  1651 ,  1652  so as to prevent the stronger one of batteries  1661 ,  1662  from charging the weaker one via central node  1699 . In particular, central node  1699  is electrically coupled to a first battery  1661  via a battery wire  1646  and a first stopping circuit  1651 . Central node  1699  is also electrically coupled to a second battery  1662  via a battery wire  1636  and a second stopping circuit  1652 . 
         [0147]    Each of stopping circuits  1651 ,  1652  can be configured to prevent one of first battery  1651  and second battery  1652  from adding charge to the other via central node  1699 . Stopping circuits  1651 ,  1652  could be made of diodes. A challenge with diodes, however, is that they render the charge they pass through at a lower voltage than they receive it. 
         [0148]    Returning to  FIG. 15 , in some embodiments, receiving circuit  1577  is configured to select one of first battery  1561  and second battery  1562  over the other. This selection is also known as arbitration. In such embodiments, receiving circuit  1577  can be configured to permit motor  1549  to thus receive energy from the selected one of first battery  1561  and second battery  1562  preferentially over the other. 
         [0149]    In some embodiments, receiving circuit  1577  is configured to thus permit motor  1549  to receive energy from the selected one of first battery  1561  and second battery  1562 , by prohibiting motor  1549  from receiving energy from the one of first battery  1561  and second battery  1562  that was not selected. This prohibiting may be implemented in a number of ways. For example, is some embodiments, receiving circuit  1577  also includes a switching circuit that is configured to disconnect from central node  1599  the one of first battery  1561  and second battery  1562  that was not selected. Such switching circuits are described later in this document. 
         [0150]    In some embodiments, CPR system  1500  further includes a user interface  1578 . User interface  1578  can be configured to output a human-perceptible indication, such as a sound or an image or a light. The human-perceptible indication may indicate which one of first battery  1561  and second battery  1562  is thus selected. 
         [0151]    Receiving circuit  1577  may select one batteries  1561 ,  1562  over the other in a number of ways. Examples are now described. 
         [0152]    In some embodiments, CPR system  1500  further includes a clock. A sample clock  1898  is shown in  FIG. 18  within choice controller  1819 . However implemented, the clock can be configured to generate time inputs. In such embodiments, receiving circuit  1577  can be configured to thus select one of first battery  1561  and second battery  1562  according to the time inputs. 
         [0153]    In some embodiments, receiving circuit  1577  is configured to monitor a first voltage V 1  of first battery  1561 , and a second voltage V 2  of second battery  1562 . Sample first and second voltages V 1 , V 2  are shown in  FIG. 18 . In  FIG. 15 , where battery wires  1546 ,  1536  are indeed provided, first and second voltages V 1 , V 2  can be monitored from these battery wires  1546 ,  1536 , if they are permitted to be different by including more components in receiving circuit  1577  than central node  1599 . 
         [0154]    In such embodiments, receiving circuit  1577  can be configured to thus select one of first battery  1561  and second battery  1562  according to the monitored first voltage V 1  and the monitored second voltage V 2 . If user interface  1578  is indeed provided, it can be configured to further output a human-perceptible indication representing at least one or both of the monitored first voltage V 1  and the monitored second voltage V 2 . This would further help the rescuer in choosing to replace the battery desired at the time, which would often be the more depleted battery. 
         [0155]    In some embodiments, CPR system  1500  further includes a communications module  1579 , which can be adapted for wireless or wired communication. Communications module  1579  can be configured to output data that encodes at least one or both of the monitored first voltage V 1  and the monitored second voltage V 2 . This data can then be received by a device of the rescuer such as a mobile device, a tablet Personal Computer (PC), or a remote server. 
         [0156]    In some embodiments, receiving circuit  1577  selects one of batteries  1561 ,  1562 , so as to preferentially draw from the battery that is already the least charged. By selecting this way, receiving circuit  1577  preserves the battery that is the best charged for when the rescuer will be replacing the battery with the least charge. Examples are now described. 
         [0157]      FIG. 17  is a sample decision diagram  1700  for the selections of receiving circuit of  FIG. 15  according to an embodiment. Decision diagram  1700  shows domains of possible voltages (V 1 , V 2 ), and indicates selections made for points in those domains. In decision diagram  1700 , a diagonal line  1711  helps by separating the domains in values where V 1 &gt;V 2  (lower right) from values where V 2 &gt;V 1  (upper left). 
         [0158]    For one example, as illustrated by point  1701  in decision diagram  1700 , the receiving circuit can be configured to select the first battery (B 1 ) over the second battery (B 2 ) if first voltage V 1  is less than second voltage V 2 . Point  1702  in decision diagram  1700  illustrates the inverse decision. 
         [0159]    For another example, as again illustrated by point  1701  in decision diagram  1700 , the receiving circuit can be configured to select the first battery (B 1 ) over the second battery (B 2 ) if first voltage V 1  is less than second voltage V 2 , as long as first voltage V 1  is higher than a threshold voltage VT. This is also illustrated by point  1703 , in which first voltage V 1  is again less than second voltage V 2 , but first voltage V 1  is less than threshold voltage VT, in which case the second battery (B 2 ) is selected. 
         [0160]    Of course, once a selection is made, as time goes one the point may shift, given that the batteries may be drained. Where the selected battery is being drained preferentially over the unselected battery, the operative point (V 1 ,V 2 ), may migrate enough to where it enters a different domain, and the selected battery changes. For example, rules such as the above could create a space H in decision diagram  1700 , whose selection could be made by hysteresis, i.e. the previous selection still holds. This can be the case for point  1704 , for example, whose selection can be either the first battery B 1  or the second B 2 , depending on which battery was being drawn from at the time domain H was entered. 
         [0161]    Threshold voltage VT can be very small, and could be zero. In fact, the receiving circuit could be configured to select the first battery over the second battery if second voltage V 2  is zero. Second voltage V 2  could indeed be zero while the second battery is being replaced. 
         [0162]    A receiving circuit can be made in a number of ways. One such way is described in U.S. Pat. No. 5,640,078 from a different art, and which is incorporated herein by reference. Another such way is now described. 
         [0163]      FIG. 18  is a block diagram of sample components for implementing a receiving circuit  1877 . Receiving circuit  1877  is electrically coupled with a first battery  1861  via a battery wire  1846 , with a second battery  1862  via a battery wire  1836 , and with a motor  1849  via a wire  1894  that includes a node  1899 . 
         [0164]    Receiving circuit  1877  also includes a first switching circuit  1811  that is electrically coupled to first battery  1861 , and a second switching circuit  1812  that is electrically coupled to second battery  1862 . Switching circuits  1811   1812  can be made using electrical components like transistors, Field Effect Transistors, etc. 
         [0165]    Receiving circuit  1877  also includes a first battery voltage monitor  1881  configured to monitor first voltage V 1 , and a second battery voltage monitor  1882  configured to monitor second voltage V 2 . Battery voltage monitors  1881 ,  1882  are preferably implemented with a high input impedance. 
         [0166]    Receiving circuit  1877  includes a choice controller  1819 , which may optionally have a clock  1898 . Choice controller  1819  may be implemented by a logic device such as a microprocessor, a programmable logic device, etc. Choice controller  1819  can be configured to receive inputs about monitored first voltage V 1  and monitored second voltage V 2  from battery voltage monitors  1881 ,  1882 . In that case, battery voltage monitors  1881 ,  1882  could have an A/D converter, or could include a comparator for the threshold voltage VT of  FIG. 17 , and so on. 
         [0167]    Choice controller  1819  can be configured to control first switching circuit  1811  and second switching circuit  1812  responsive to monitored first voltage V 1  and monitored second voltage V 2 . Such controlling can be so as to enable one of first battery  1861  and second battery  1862  to provide power to motor  1849  preferentially over the other. Choice controller  1819  thus selects one of first battery  1861  and second battery  1862  preferentially over the other. 
         [0168]    In some of these embodiments, first battery voltage monitor  1881  is configured to set a replace flag, responsive to sensing that monitored first voltage V 1  is below a replace threshold. In such embodiments, a user interface such as user interface  1578  can be configured to output a human-perceptible indication responsive to the replace flag being set. This way the rescuer would know to replace first battery  1861  with a freshly charged one. 
         [0169]    Embodiments of methods for a Cardio-Pulmonary Resuscitation (CPR) system are now described. Such a CPR system may include a retention structure, a compression mechanism, a motor, a first battery storing energy, a second battery storing energy, and a receiving circuit electrically coupled to the motor, to the first battery and to the second battery. Such a method comprises selecting, by the receiving circuit, one of the first battery and the second battery over the other; and permitting, by the receiving circuit, the motor to receive energy from the one of the first battery and the second battery that has been thus selected preferentially over the other, so as to drive the compression mechanism. 
         [0170]    In some versions, in the method of the previous paragraph the CPR system is used for caring for a patient, the retention structure retains a body of the patient, and the compression mechanism, when thus driven, performs automatically CPR compressions alternating with releases to a chest of the patient, the CPR compressions thus causing the chest to become compressed by at least 2.5 cm. 
         [0171]      FIG. 19  shows a flowchart  1900  for describing methods according to embodiments. These methods maybe implemented by what is described above. 
         [0172]    According to an operation  1910 , one of a first battery and a second battery of a CPR system is selected over the other by a receiving circuit. In some embodiments, time inputs are further generated by a clock, and the selecting of operation  1910  is performed according to the time inputs. In some embodiments, a first voltage V 1  of the first battery is monitored, a second voltage V 2  of the second battery is monitored, and the selecting of operation  1910  is performed according to the monitored first voltage V 1  and the monitored second voltage V 2 . The selection can be according to rules described above. 
         [0173]    According to another operation  1920 , a motor of the CPR system is permitted, by the receiving circuit, to receive energy from the selected one of the first battery and the second battery preferentially over the other. Such receiving of energy enables driving a compression mechanism to perform automatically CPR compressions alternating with releases to a chest of the body, the CPR compressions thus causing the chest to become compressed by at least 2.5 cm. 
         [0174]    According to another, optional operation  1930 , a human-perceptible indication may be output. The human-perceptible indication may indicate which one of the first battery and the second battery was selected at operation  1910 . Or it may indicate that a replace flag is set, which may happen if the monitored first voltage is below a replace threshold. 
         [0175]    In the methods described above, each operation can be performed as an affirmative step of doing, or causing to happen, what is written that can take place. Such doing or causing to happen can be by the whole system or device, or just one or more components of it. It will be recognized that the methods and the operations may be implemented in a number of ways, including using systems, devices and implementations described above. In addition, the order of operations is not constrained to what is shown, and different orders may be possible according to different embodiments. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Moreover, in certain embodiments, new operations may be added, or individual operations may be modified or deleted. The added operations can be, for example, from what is mentioned while primarily describing a different system, apparatus, device or method. 
         [0176]    A person skilled in the art will be able to practice the present invention in view of this description, which is to be taken as a whole. Details have been included to provide a thorough understanding. In other instances, well-known aspects have not been described, in order to not obscure unnecessarily this description. Plus, any reference to any prior art in this description is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms parts of the common general knowledge in any country or any art. 
         [0177]    This description includes one or more examples, but this fact does not limit how the invention may be practiced. Indeed, examples, instances, versions or embodiments of the invention may be practiced according to what is described, or yet differently, and also in conjunction with other present or future technologies. Other such embodiments include combinations and sub-combinations of features described herein, including for example, embodiments that are equivalent to the following: providing or applying a feature in a different order than in a described embodiment; 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 features incorporated in such combinations and sub-combinations. 
         [0178]    In general, the present disclosure reflects preferred embodiments of the invention. The attentive reader will note, however, that some aspects of the disclosed embodiments extend beyond the scope of the claims. To the respect that the disclosed embodiments indeed extend beyond the scope of the claims, the disclosed embodiments are to be considered supplementary background information and do not constitute definitions of the claimed invention. 
         [0179]    In this document, the phrases “constructed to” and/or “configured to” denote one or more actual states of construction and/or configuration that is fundamentally tied to physical characteristics of the element or feature preceding these phrases and, as such, reach well beyond merely describing an intended use. Any such elements or features can be implemented in a number of ways, as will be apparent to a person skilled in the art after reviewing the present disclosure, beyond any examples shown in this document. 
         [0180]    Any and all parent, grandparent, great-grandparent, etc. patent applications, whether mentioned in this document or in an Application Data Sheet (“ADS”) of this patent application, are hereby incorporated by reference herein as originally disclosed, including any priority claims made in those applications and any material incorporated by reference, to the extent such subject matter is not inconsistent herewith. This disclosure, which may be referenced elsewhere as “3358”, is meant to be illustrative and not limiting on the scope of the following claims. 
         [0181]    In this description a single reference numeral may be used consistently to denote a single item, aspect, component, or process. Moreover, a further effort may have been made in the drafting of this description to use similar though not identical reference numerals to denote other versions or embodiments of an item, aspect, component or process that are identical or at least similar or related. Where made, such a further effort was not required, but was nevertheless made gratuitously so as to accelerate comprehension by the reader. Even where made in this document, such a further effort might not have been made completely consistently for all of the versions or embodiments that are made possible by this description. Accordingly, the description controls in defining an item, aspect, component or process, rather than its reference numeral. Any similarity in reference numerals may be used to infer a similarity in the text, but not to confuse aspects where the text or other context indicates otherwise. 
         [0182]    The claims of this document define certain combinations and subcombinations of elements, features and steps or operations, which are regarded as novel and non-obvious. Additional claims for other such combinations and subcombinations may be presented in this or a related document. These claims are intended to encompass within their scope all changes and modifications that are within the true spirit and scope of the subject matter described herein. The terms used herein, including in the claims, are generally intended as “open” terms. For example, the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” etc. If a specific number is ascribed to a claim recitation, this number is a minimum but not a maximum unless stated otherwise. For example, where a claim recites “a” component or “an” item, it means that it can have one or more of this component or item.