Patent Publication Number: US-2021162227-A1

Title: Wearable cardioverter defibrillator (wcd) system computing heart rate from noisy ecg signal

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 15/948,884 filed Apr. 9, 2018 (pending), which is a continuation-in-part of U.S. application Ser. No. 15/880,853 filed Jan. 26, 2018 (abandoned). Said application Ser. No. 15/948,884 and said application Ser. No. 15/880,853 both claim the benefit of U.S. Provisional Application No. 62/501,009 filed on May 3, 2017. Said application Ser. No. 15/948,884, said application Ser. No. 15/880,853, and said Application No. 62/501,009 are hereby incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     When people suffer from some types of heart arrhythmias, the result may be that blood flow to various parts of the body is reduced. Some arrhythmias may even result in a Sudden Cardiac Arrest (SCA). SCA can lead to death very quickly, e.g. within 10 minutes, unless treated in the interim. 
     Some people have an increased risk of SCA. People at a higher risk include patients who have had a heart attack, or a prior SCA episode. A frequent recommendation is for these people to receive an Implantable Cardioverter Defibrillator (ICD). The ICD is surgically implanted in the chest, and continuously monitors the patient&#39;s electrocardiogram (ECG). If certain types of heart arrhythmias are detected, then the ICD delivers an electric shock through the heart. 
     After being identified as having an increased risk of an SCA, and before receiving an ICD, these people are sometimes given a Wearable Cardioverter Defibrillator (WCD) system. (Early versions of such systems were called wearable cardiac defibrillator systems.) A WCD system typically includes a harness, vest, or other garment that the patient is to wear. The WCD system further includes electronic components, such as a defibrillator and electrodes, coupled to the harness, vest, or other garment. When the patient wears the WCD system, the external electrodes may then make good electrical contact with the patient&#39;s skin, and therefore can help sense the patient&#39;s ECG. If a shockable heart arrhythmia is detected, then the defibrillator delivers the appropriate electric shock through the patient&#39;s body, and thus through the heart. 
     A challenge in the prior art is that the patient&#39;s ECG signal may be corrupted by electrical noise. As such, it can be hard to interpret the ECG signal. 
     All subject matter discussed in this Background section of this document is not necessarily prior art, and may not be presumed to be prior art simply because it is presented in this Background section. 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 art in any country. Along these lines, any recognition of problems in the prior art discussed in this Background section or associated with such subject matter should not be treated as prior art, unless expressly stated to be prior art. Rather, the discussion of any subject matter in this Background section should be treated as part of the approach taken towards the particular problem by the inventor. This approach in and of itself may also be inventive. 
     BRIEF SUMMARY 
     The present description gives instances of wearable cardioverter defibrillator (WCD) systems, storage media that store programs, and methods, the use of which may help overcome problems and limitations of the prior art. 
     In embodiments, a WCD system includes electrodes with which it senses an ECG signal of the patient. A processor may detect sequential peaks within the ECG signal, measure durations of time intervals between the peaks, including between non-sequential peaks, and identify a representative duration that best meets a plausibility criterion. The plausibility criterion may be that the representative duration is the one that occurs the most often, i.e. is the mode. Then a heart rate can be computed from a duration indicated by the representative duration and, if the heart rate meets a shock condition, the WCD system may deliver a shock to the patient. 
     An advantage can be that the representative duration can be close to a good R-R interval measurement of a patient, notwithstanding noise in the ECG signal that is in the shape of peaks. 
     These and other features and advantages of the claimed invention will become more readily apparent in view of the embodiments described and illustrated in this specification, namely from this written specification and the associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of components of a sample wearable cardioverter defibrillator (WCD) system, made according to embodiments. 
         FIG. 2  is a diagram showing sample components of an external defibrillator, such as the one belonging in the system of  FIG. 1 , and which is made according to embodiments. 
         FIG. 3A  is a conceptual diagram for illustrating how different electrodes may sense ECG signals of the patient along different vectors according to embodiments. 
         FIG. 3B  is a conceptual diagram for illustrating how a first ECG signal may be used for in a heart rate computation while a second sense ECG signal of the patient may be used for a shock decision according to embodiments. 
         FIG. 4  shows time diagrams for illustrating how a patient&#39;s heart rate may be detected from a noise-free ECG signal in the prior art. 
         FIG. 5  is a time diagram for showing how noise in an ECG signal can corrupt the measurements used for the heart rate detection of  FIG. 4 . 
         FIG. 6  is a time diagram for showing how a patient&#39;s heart rate may be detected from a noisy ECG signal according to embodiments. 
         FIG. 7  is a time diagram for showing how a patient&#39;s heart rate may be detected from a noisy ECG signal, according to embodiments where all possible peak pairs are established. 
         FIG. 8  is a bar chart for identifying which one of time durations measured in  FIG. 7  best meets a plausibility criterion, according to embodiments. 
         FIG. 9  is a bar chart of time durations measured in numbers of samples according to embodiments. 
         FIG. 10  is the bar chart of  FIG. 9 , where clusters of time durations have been further discerned, according to embodiments. 
         FIG. 11  is a bar chart of time durations where clusters have been discerned, and further where fractional harmonics have been accounted for, according to embodiments. 
         FIG. 12  is a flowchart for illustrating methods according to embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     As has been mentioned, the present description is about wearable cardioverter defibrillator (WCD) systems, and related storage media, programs and methods. Embodiments are now described in more detail. 
     A wearable cardioverter defibrillator (WCD) system made according to embodiments has a number of components. These components can be provided separately as modules that can be interconnected, or can be combined with other components, etc. 
       FIG. 1  depicts a patient  82 . Patient  82  may also be referred to as a person and/or wearer, since the patient is wearing components of the WCD system. Patient  82  is ambulatory, which means patient  82  can walk around, and is not necessarily bed-ridden. 
       FIG. 1  also depicts components of a WCD system made according to embodiments. One such component is a support structure  170  that is wearable by patient  82 . It will be understood that support structure  170  is shown only generically in  FIG. 1 , and in fact partly conceptually.  FIG. 1  is provided merely to illustrate concepts about support structure  170 , and is not to be construed as limiting how support structure  170  is implemented, or how it is worn. 
     Support structure  170  can be implemented in many different ways. For example, it can be implemented in a single component or a combination of multiple components. In embodiments, support structure  170  could include a vest, a half-vest, a garment, etc. In such embodiments such items can be worn similarly to parallel articles of clothing. In embodiments, support structure  170  could include a harness, one or more belts or straps, etc. In such embodiments, such items can be worn by the patient around the torso, hips, over the shoulder, etc. In embodiments, support structure  170  can include a container or housing, which can even be waterproof. In such embodiments, the support structure can be worn by being attached to the patient by adhesive material, for example as shown in U.S. Pat. No. 8,024,037. Support structure  170  can even be implemented as described for the support structure of US Pat. App. No. US2017/0056682, which is incorporated herein by reference. Of course, in such embodiments, the person skilled in the art will recognize that additional components of the WCD system can be in the housing of a support structure instead of being attached externally to the support structure, for example as described in the US2017/0056682 document. There can be other examples. 
     A WCD system according to embodiments is configured to defibrillate a patient who is wearing it, by delivering an electrical charge to the patient&#39;s body in the form of an electric shock delivered in one or more pulses.  FIG. 1  shows a sample external defibrillator  100 , and sample defibrillation electrodes  104 ,  108 , which are coupled to external defibrillator  100  via electrode leads  105 . Defibrillator  100  and defibrillation electrodes  104 ,  108  can be coupled to support structure  170 . As such, many of the components of defibrillator  100  could be therefore coupled to support structure  170 . When defibrillation electrodes  104 ,  108  make good electrical contact with the body of patient  82 , defibrillator  100  can administer, via electrodes  104 ,  108 , a brief, strong electric pulse  111  through the body. Pulse  111  is also known as shock, defibrillation shock, therapy and therapy shock. Pulse  111  is intended to go through and restart heart  85 , in an effort to save the life of patient  82 . Pulse  111  can further include one or more pacing pulses, and so on. 
     A prior art defibrillator typically decides whether to defibrillate or not based on an ECG signal of the patient. However, external defibrillator  100  may initiate defibrillation (or hold-off defibrillation) based on a variety of inputs, with ECG merely being one of them. 
     Accordingly, it will be appreciated that signals such as physiological signals containing physiological data can be obtained from patient  82 . While the patient may be considered also a “user” of the WCD system, this is not a requirement. That is, for example, a user of the wearable cardioverter defibrillator (WCD) may include a clinician such as a doctor, nurse, emergency medical technician (EMT) or other similarly situated individual (or group of individuals). The particular context of these and other related terms within this description should be interpreted accordingly. 
     The WCD system may optionally include an outside monitoring device  180 . Device  180  is called an “outside” device because it could be provided as a standalone device, for example not within the housing of defibrillator  100 . Device  180  can be configured to sense or monitor at least one local parameter. A local parameter can be a parameter of patient  82 , or a parameter of the WCD system, or a parameter of the environment, as will be described later in this document. Device  180  may include one or more transducers or sensors that are configured to render one or more physiological inputs or signals from one or more patient parameters that they sense. 
     Optionally, device  180  is physically coupled to support structure  170 . In addition, device  180  can be communicatively coupled with other components, which are coupled to support structure  170 . Such communication can be implemented by a communication module, as will be deemed applicable by a person skilled in the art in view of this description. 
       FIG. 2  is a diagram showing components of an external defibrillator  200 , made according to embodiments. These components can be, for example, included in external defibrillator  100  of  FIG. 1 . The components shown in  FIG. 2  can be provided in a housing  201 , which may also be referred to as casing  201 . 
     External defibrillator  200  is intended for a patient who would be wearing it, such as patient  82  of  FIG. 1 . Defibrillator  200  may further include a user interface  280  for a user  282 . User  282  can be patient  82 , also known as wearer  82 . Or, user  282  can be a local rescuer at the scene, such as a bystander who might offer assistance, or a trained person. Or, user  282  might be a remotely located trained caregiver in communication with the WCD system. 
     User interface  280  can be made in a number of ways. User interface  280  may include output devices, which can be visual, audible or tactile, for communicating to a user by outputting images, sounds or vibrations. Images, sounds, vibrations, and anything that can be perceived by user  282  can also be called human-perceptible indications. There are many examples of output devices. For example, an output device can be a light, or a screen to display what is sensed, detected and/or measured, and provide visual feedback to rescuer  282  for their resuscitation attempts, and so on. Another output device can be a speaker, which can be configured to issue voice prompts, beeps, loud alarm sounds and/or words to warn bystanders, etc. 
     User interface  280  may further include input devices for receiving inputs from users. Such input devices may additionally include various controls, such as pushbuttons, keyboards, touchscreens, one or more microphones, and so on. An input device can be a cancel switch, which is sometimes called an “I am alive” switch or “live man” switch. In some embodiments, actuating the cancel switch can prevent the impending delivery of a shock. 
     Defibrillator  200  may include an internal monitoring device  281 . Device  281  is called an “internal” device because it is incorporated within housing  201 . Monitoring device  281  can sense or monitor patient parameters such as patient physiological parameters, system parameters and/or environmental parameters, all of which can be called patient data. In other words, internal monitoring device  281  can be complementary or an alternative to outside monitoring device  180  of  FIG. 1 . Allocating which of the parameters are to be monitored by which of monitoring devices  180 ,  281  can be done according to design considerations. Device  281  may include one or more transducers or sensors that are configured to render one or more physiological inputs from one or more patient parameters that it senses. 
     Patient parameters may include patient physiological parameters. Patient physiological parameters may include, for example and without limitation, those physiological parameters that can be of any help in detecting by the wearable defibrillation system whether the patient is in need of a shock, plus optionally their medical history and/or event history. Examples of such parameters include the patient&#39;s ECG, blood oxygen level, blood flow, blood pressure, blood perfusion, pulsatile change in light transmission or reflection properties of perfused tissue, heart sounds, heart wall motion, breathing sounds and pulse. Accordingly, monitoring devices  180 ,  281  may include one or more sensors configured to acquire patient physiological signals. Examples of such sensors or transducers include electrodes to detect ECG data, a perfusion sensor, a pulse oximeter, a device for detecting blood flow (e.g. a Doppler device), a sensor for detecting blood pressure (e.g. a cuff), an optical sensor, illumination detectors and sensors perhaps working together with light sources for detecting color change in tissue, a motion sensor, a device that can detect heart wall movement, a sound sensor, a device with a microphone, an SpO 2  sensor, and so on. In view of this disclosure, it will be appreciated that such sensors can help detect the patient&#39;s pulse, and can therefore also be called pulse detection sensors, pulse sensors, and pulse rate sensors. Pulse detection is also taught at least in Physio-Control&#39;s U.S. Pat. No. 8,135,462, which is hereby incorporated by reference in its entirety. In addition, a person skilled in the art may implement other ways of performing pulse detection. In such cases, the transducer includes an appropriate sensor, and the physiological input is a measurement by the sensor of that patient parameter. For example, the appropriate sensor for a heart sound may include a microphone, etc. 
     In some embodiments, the local parameter is a trend that can be detected in a monitored physiological parameter of patient  282 . A trend can be detected by comparing values of parameters at different times. Parameters whose detected trends can particularly help a cardiac rehabilitation program include: a) cardiac function (e.g. ejection fraction, stroke volume, cardiac output, etc.); b) heart rate variability at rest or during exercise; c) heart rate profile during exercise and measurement of activity vigor, such as from the profile of an accelerometer signal and informed from adaptive rate pacemaker technology; d) heart rate trending; e) perfusion, such as from SpO 2  or CO 2 ; f) respiratory function, respiratory rate, etc.; g) motion, level of activity; and so on. Once a trend is detected, it can be stored and/or reported via a communication link, along perhaps with a warning. From the report, a physician monitoring the progress of patient  282  will know about a condition that is either not improving or deteriorating. 
     Patient state parameters include recorded aspects of patient  282 , such as motion, posture, whether they have spoken recently plus maybe also what they said, and so on, plus optionally the history of these parameters. Or, one of these monitoring devices could include a location sensor such as a Global Positioning System (GPS) location sensor. Such a sensor can detect the location, plus a speed can be detected as a rate of change of location over time. Many motion detectors output a motion signal that is indicative of the motion of the detector, and thus of the patient&#39;s body. Patient state parameters can be very helpful in narrowing down the determination of whether SCA is indeed taking place. 
     A WCD system made according to embodiments may include a motion detector. In embodiments, a motion detector can be implemented within monitoring device  180  or monitoring device  281 . Such a motion detector can be made in many ways as is known in the art, for example by using an accelerometer. In this example, a motion detector  287  is implemented within monitoring device  281 . 
     A motion detector of a WCD system according to embodiments can be configured to detect a motion event. In response, the motion detector may render or generate, from the detected motion event or motion, a motion detection input that can be received by a subsequent device or functionality. A motion event can be defined as is convenient, for example a change in motion from a baseline motion or rest, etc. In such cases, a sensed patient parameter is motion. 
     System parameters of a WCD system can include system identification, battery status, system date and time, reports of self-testing, records of data entered, records of episodes and intervention, and so on. 
     Environmental parameters can include ambient temperature and pressure. Moreover, a humidity sensor may provide information as to whether it is likely raining. Presumed patient location could also be considered an environmental parameter. The patient location could be presumed, if monitoring device  180  or  281  includes a GPS location sensor as per the above, and if it is presumed that the patient is wearing the WCD system. 
     Defibrillator  200  typically includes a defibrillation port  210 , such as a socket in housing  201 . Defibrillation port  210  includes electrical nodes  214 ,  218 . Leads of defibrillation electrodes  204 ,  208 , such as leads  105  of  FIG. 1 , can be plugged into defibrillation port  210 , so as to make electrical contact with nodes  214 ,  218 , respectively. It is also possible that defibrillation electrodes  204 ,  208  are connected continuously to defibrillation port  210 , instead. Either way, defibrillation port  210  can be used for guiding, via electrodes, to the wearer the electrical charge that has been stored in an energy storage module  250  that is described more fully later in this document. The electric charge will be the shock for defibrillation, pacing, and so on. 
     Defibrillator  200  may optionally also have a sensor port  219  in housing  201 , which is also sometimes known as an ECG port. Sensor port  219  can be adapted for plugging in sensing electrodes  209 , which are also known as ECG electrodes and ECG leads. It is also possible that sensing electrodes  209  can be connected continuously to sensor port  219 , instead. Sensing electrodes  209  are types of transducers that can help sense an ECG signal, e.g. a 12-lead signal, or a signal from a different number of leads, especially if they make good electrical contact with the body of the patient and in particular with the skin of the patient. Sensing electrodes  209  can be attached to the inside of support structure  170  for making good electrical contact with the patient, similarly with defibrillation electrodes  204 ,  208 . 
     Optionally a WCD system according to embodiments also includes a fluid that it can deploy automatically between the electrodes and the patient&#39;s skin. The fluid can be conductive, such as by including an electrolyte, for establishing a better electrical contact between the electrode and the skin. Electrically speaking, when the fluid is deployed, the electrical impedance between the electrode and the skin is reduced. Mechanically speaking, the fluid may be in the form of a low-viscosity gel, so that it does not flow away from the electrode, after it has been deployed. The fluid can be used for both defibrillation electrodes  204 ,  208 , and for sensing electrodes  209 . 
     The fluid may be initially stored in a fluid reservoir, not shown in  FIG. 2 , which can be coupled to the support structure. In addition, a WCD system according to embodiments further includes a fluid deploying mechanism  274 . Fluid deploying mechanism  274  can be configured to cause at least some of the fluid to be released from the reservoir, and be deployed near one or both of the patient locations, to which the electrodes are configured to be attached to the patient. In some embodiments, fluid deploying mechanism  274  is activated prior to the electrical discharge responsive to receiving activation signal AS from a processor  230 , which is described more fully later in this document. 
       FIG. 3A  is a conceptual diagram for illustrating how electrodes of a WCD system may sense or capture ECG signals along different vectors according to embodiments. A section of a patient  382  having a heart  385  is shown. There are four electrodes  304 ,  306 ,  307 ,  308 , attached to the torso of patient  382 , each with a wire lead  305 . Any pair of these electrodes defines a vector, across which an ECG signal may be measured. These vectors are also known as channels and ECG channels. The four electrodes  304 ,  306 ,  307 ,  308  therefore can define six vectors, across which six respective ECG signals  311 ,  312 ,  313 ,  314 ,  315 ,  316  can be sensed.  FIG. 3A  thus illustrates a multi-vector situation. In  FIG. 3A  it will be understood that electrodes  304 ,  306 ,  307 ,  308  are drawn on the same plane for simplicity, while that is not necessarily the case. Accordingly, the vectors of ECG signals  311 - 316  are not necessarily on the same plane, either. 
     Any one of ECG signals  311 - 316  might provide sufficient data for making a shock/no shock determination. The effort is to shock when needed, and not shock when not needed. The problem is that, at any given point in time, some of these ECG signals may include noise, while others not. The noise may be due to patient movement or how well the electrodes contact the skin. The noise problem for a WCD may be further exacerbated by the desire to use dry, non-adhesive monitoring electrodes. Dry, non-adhesive electrodes are thought to be more comfortable for the patient to wear in the long term, but may produce more noise than a conventional ECG monitoring electrode that includes adhesive to hold the electrode in place and an electrolyte gel to reduce the impedance of the electrode-skin interface. 
       FIG. 3A  also shows a measurement circuit  320  and a processor  330 , which can be made as described for measurement circuit  220  and processor  230  later in this document. Processor  330  may further compute a heart rate  333  according to embodiments, as described in more detail further in this document. 
     Returning to  FIG. 2 , defibrillator  200  also includes a measurement circuit  220 , as one or more of its sensors or transducers. Measurement circuit  220  senses one or more electrical physiological signals of the patient from sensor port  219 , if provided. Even if defibrillator  200  lacks sensor port  219 , measurement circuit  220  may optionally obtain physiological signals through nodes  214 ,  218  instead, when defibrillation electrodes  204 ,  208  are attached to the patient. In these cases, the physiological input reflects an ECG measurement. The patient parameter can be an ECG, which can be sensed as a voltage difference between electrodes  204 ,  208 . In addition the patient parameter can be an impedance, which can be sensed between electrodes  204 ,  208  and/or the connections of sensor port  219 . Sensing the impedance can be useful for detecting, among other things, whether these electrodes  204 ,  208  and/or sensing electrodes  209  are not making good electrical contact with the patient&#39;s body. These patient physiological signals can be sensed, when available. Measurement circuit  220  can then render or generate information about them as physiological inputs, data, other signals, etc. More strictly speaking, the information rendered by measurement circuit  220  is output from it, but this information can be called an input because it is received by a subsequent device or functionality as an input. 
     Defibrillator  200  also includes a processor  230 . Processor  230  may be implemented in a number of ways. Such ways include, by way of example and not of limitation, digital and/or analog processors such as microprocessors and Digital Signal Processors (DSPs); controllers such as microcontrollers; software running in a machine; programmable circuits such as Field Programmable Gate Arrays (FPGAs), Field-Programmable Analog Arrays (FPAAs), Programmable Logic Devices (PLDs), Application Specific Integrated Circuits (ASICs), any combination of one or more of these, and so on. 
     Processor  230  may include, or have access to, a non-transitory storage medium, such as memory  238  that is described more fully later in this document. Such a memory can have a non-volatile component for storage of machine-readable and machine-executable instructions. A set of such instructions can also be called a program. The instructions, which may also be referred to as “software,” generally provide functionality by performing methods as may be disclosed herein or understood by one skilled in the art in view of the disclosed embodiments. In some embodiments, and as a matter of convention used herein, instances of the software may be referred to as a “module” and by other similar terms. Generally, a module includes a set of the instructions so as to offer or fulfill a particular functionality. Embodiments of modules and the functionality delivered are not limited by the embodiments described in this document. 
     Processor  230  can be considered to have a number of modules. One such module can be a detection module  232 . Detection module  232  can include a Ventricular Fibrillation (VF) detector. The patient&#39;s sensed ECG from measurement circuit  220 , which can be available as physiological inputs, data, or other signals, may be used by the VF detector to determine whether the patient is experiencing VF. Detecting VF is useful, because VF typically results in SCA. Detection module  232  can also include a Ventricular Tachycardia (VT) detector, and so on. 
     Another such module in processor  230  can be an advice module  234 , which generates advice for what to do. The advice can be based on outputs of detection module  232 . There can be many types of advice according to embodiments. In some embodiments, the advice is a shock/no shock determination that processor  230  can make, for example via advice module  234 . The shock/no shock determination can be made by executing a stored Shock Advisory Algorithm. A Shock Advisory Algorithm can make a shock/no shock determination from one or more ECG signals that are sensed or captured according to embodiments, and determining whether a shock criterion is met. The determination can be made from a rhythm analysis of the sensed or captured ECG signal or otherwise. 
     In some embodiments, when the determination is to shock, an electrical charge is delivered to the patient. Delivering the electrical charge is also known as discharging. Shocking can be for defibrillation, pacing, and so on. 
     Processor  230  can include additional modules, such as other module  236 , for other functions. In addition, if internal monitoring device  281  is indeed provided, it may be operated in part by processor  230 , etc. 
     Defibrillator  200  optionally further includes a memory  238 , which can work together with processor  230 . Memory  238  may be implemented in a number of ways. Such ways include, by way of example and not of limitation, volatile memories, Nonvolatile Memories (NVM), Read-Only Memories (ROM), Random Access Memories (RAM), magnetic disk storage media, optical storage media, smart cards, flash memory devices, any combination of these, and so on. Memory  238  is thus a non-transitory storage medium. Memory  238 , if provided, can include programs for processor  230 , which processor  230  may be able to read and execute. More particularly, the programs can include sets of instructions in the form of code, which processor  230  may be able to execute upon reading. Executing is performed by physical manipulations of physical quantities, and may result in functions, operations, processes, actions and/or methods to be performed, and/or the processor to cause other devices or components or blocks to perform such functions, operations, processes, actions and/or methods. The programs can be operational for the inherent needs of processor  230 , and can also include protocols and ways that decisions can be made by advice module  234 . In addition, memory  238  can store prompts for user  282 , if this user is a local rescuer. Moreover, memory  238  can store data. This data can include patient data, system data and environmental data, for example as learned by internal monitoring device  281  and outside monitoring device  180 . The data can be stored in memory  238  before it is transmitted out of defibrillator  200 , or stored there after it is received by defibrillator  200 . 
     Defibrillator  200  may also include a power source  240 . To enable portability of defibrillator  200 , power source  240  typically includes a battery. Such a battery is typically implemented as a battery pack, which can be rechargeable or not. Sometimes a combination is used of rechargeable and non-rechargeable battery packs. Other embodiments of power source  240  can include an AC power override, for where AC power will be available, an energy-storing capacitor, and so on. In some embodiments, power source  240  is controlled by processor  230 . Appropriate components may be included to provide for charging or replacing power source  240 . 
     Defibrillator  200  may additionally include an energy storage module  250 . Energy storage module  250  can be coupled to the support structure of the WCD system, for example either directly or via the electrodes and their leads. Module  250  is where some electrical energy can be stored temporarily in the form of an electrical charge, when preparing it for discharge to administer a shock. In embodiments, module  250  can be charged from power source  240  to the desired amount of energy, as controlled by processor  230 . In typical implementations, module  250  includes a capacitor  252 , which can be a single capacitor or a system of capacitors, and so on. In some embodiments, energy storage module  250  includes a device that exhibits high power density, such as an ultracapacitor. As described above, capacitor  252  can store the energy in the form of an electrical charge, for delivering to the patient. 
     Defibrillator  200  moreover includes a discharge circuit  255 . When the decision is to shock, processor  230  can be configured to control discharge circuit  255  to discharge through the patient the electrical charge stored in energy storage module  250 . When so controlled, circuit  255  can permit the energy stored in module  250  to be discharged to nodes  214 ,  218 , and from there also to defibrillation electrodes  204 ,  208 , so as to cause a shock to be delivered to the patient. Circuit  255  can include one or more switches  257 . Switches  257  can be made in a number of ways, such as by an H-bridge, and so on. Circuit  255  can also be controlled via user interface  280 . 
     Defibrillator  200  can optionally include a communication module  290 , for establishing one or more wired or wireless communication links with other devices of other entities, such as a remote assistance center, Emergency Medical Services (EMS), and so on. The data can include patient data, event information, therapy attempted, CPR performance, system data, environmental data, and so on. For example, communication module  290  may transmit wirelessly, e.g., on a daily basis, heart rate, respiratory rate, and other vital signs data to a server accessible over the internet, for instance as described in US 20140043149. This data can be analyzed directly by the patient&#39;s physician and can also be analyzed automatically by algorithms designed to detect a developing illness and then notify medical personnel via text, email, phone, etc. Module  290  may also include such interconnected sub-components as may be deemed necessary by a person skilled in the art, for example an antenna, portions of a processor, supporting electronics, outlet for a telephone or a network cable, etc. This way, data, commands, etc. can be communicated. 
     Defibrillator  200  can optionally include other components. 
     Returning to  FIG. 1 , in embodiments, one or more of the components of the shown WCD system have been customized for patient  82 . This customization may include a number of aspects. For instance, support structure  170  can be fitted to the body of patient  82 . For another instance, baseline physiological parameters of patient  82  can be measured, such as the heart rate of patient  82  while resting, while walking, motion detector outputs while walking, etc. Such baseline physiological parameters can be used to customize the WCD system, in order to make its diagnoses more accurate, since the patients&#39; bodies differ from one another. Of course, such parameters can be stored in a memory of the WCD system, and so on. 
     A programming interface can be made according to embodiments, which receives such measured baseline physiological parameters. Such a programming interface may input automatically in the WCD system the baseline physiological parameters, along with other data. 
     Detection of the heart rate from the ECG signal is now described in more detail. 
       FIG. 3B  is a conceptual diagram that includes a time axis  348 . A first sample ECG signal  317  and a second sample ECG signal  318  of the patient are shown with reference to time axis  348 . Second ECG signal  318  has been sensed after sensing first ECG signal  317 . It will be recognized that sample ECG signals  317 ,  318  indicate VT, but that is only for example. Either one of ECG signals  317 ,  318  may be sensed from any of the ECG channels or vectors of  FIG. 3A , regardless of the fact that they are shown against the same time axis  348 . 
     First ECG signal  317  may result in computing heart rate  333  according to embodiments. The computing heart rate  333  may be stored in memory  238 , which is repeated in  FIG. 3B . The heart rate stored in memory  238  may then be downloaded later, transmitted wirelessly via communication module  290 , displayed by a screen of user interface  280 , and so on. 
     Second ECG signal  318  may be used to determine whether or not a shock criterion is met, for example by advice module  234 . Second ECG signal  318  may or may not have been used to compute the heart rate according to embodiments. 
     If so, processor  230  may control, responsive to the shock criterion being met, discharge circuit  255  to discharge through patient  82  electrical charge that is stored in energy storage module  250 , while support structure  170  is worn by patient  82  so as to deliver a shock  111  to  82  patient. 
       FIG. 4  shows an ECG signal in a time diagram  409 . Diagram  409  has an ECG amplitude axis  407  and a time axis  408 . Diagram  409  depicts a somewhat-idealized, noise-free ECG signal of patient  82 , as it might be sensed from a single channel  311 . The ECG signal of diagram  409  hovers around a horizontal baseline value BL. Baseline value BL can be considered to be zero, or it might be changing value due to noise, as described later in this document. 
     The ECG signal of diagram  409  includes three full heartbeats. In particular, three peaks  421 ,  422 ,  423  are shown, which occur sequentially. It will be recognized that peaks  421 ,  422 ,  423  are due to QRS complexes, each of which is followed by a T-wave of lesser amplitude. In this somewhat-idealized signal, a P-wave before the QRS complex and a U-wave after the QRS complex are not shown at all. The ECG signal of diagram  409  is further idealized in that the QRS complexes are shown as peaks, or spikes; in fact, some heart rhythms have QRS complexes that don&#39;t look like spikes. 
     Peaks  421 ,  422 ,  423  are typically used for detecting the heart rate, because their large amplitude relative to the remainder of the ECG signal makes them easier to identify and/or detect. In particular,  FIG. 4  also shows another time axis  448 . Time axis  448  indicates only the time occurrences  441 ,  442 ,  443  of peaks  421 ,  422 ,  423 , respectively. Moreover, the successive peaks are considered in pairs to define time intervals. In particular, the pair of peaks  421  and  422  defines a time interval  451  from time occurrences  441 ,  442 , while the pair of peaks  422  and  423  defines a time interval  452  from time occurrences  442 ,  443 . Time intervals  451 ,  452  are sometimes called R-R intervals of the ECG signal. The durations of time intervals  451 ,  452  are measured, and heart rate  333  of the patient is thus computed from them. 
     It will be recognized that this process of computing heart rate  333  from peaks  421 ,  422 ,  423  in the ECG signal is the same regardless of how these peaks  421 ,  422 ,  423  are detected. Medical devices sometimes measure the ECG signal electronically and focus on these peaks to detect the R-R interval, for example as per the above. Other times, peaks  421 ,  422 ,  423  correspond with peaks in the patient&#39;s blood pressure, which can be sensed by someone placing their hand against the neck or a wrist of a patient. 
     It is more difficult, however, to measure the patient&#39;s heart rate from these peaks in the presence of noise in the ECG signal. An example is now described. 
       FIG. 5  shows an ECG signal in a time diagram  529 . Diagram  529  has an ECG peaks axis  527  and a time axis  528 . Diagram  529  depicts only peaks  521 ,  522 ,  523 ,  524 ,  525  of an ECG signal, with all other values of the ECG signal being shown as zero for simplification. This simplification is acceptable in this instance, as  FIG. 5  is used for discussing only the detection of the heart rate, and only by the peaks of the ECG signal. 
       FIG. 5  also shows a time diagram  539  to depict sample noise that could be added to the ECG of diagram  529 . Diagram  539  has a Noise peaks axis  537  and a time axis  538 . Diagram  539  depicts only peaks  531 ,  532  of noise, with all other values of the sample noise being shown as zero for simplification. In addition, noise peaks  531 ,  532  may have unequal amplitudes. 
       FIG. 5  further shows another time axis  548 . Time axis  548  indicates only the time occurrences  541 ,  542 ,  543 ,  544 ,  545 ,  546 ,  547  of peaks  521 - 525  and also of peaks  531 ,  532 . Time intervals  551 ,  552 ,  553 ,  554 ,  555 ,  556  can be used to compute a heart rate  533 . It is clear, however, that these time intervals  551 - 556  are no longer true R-R intervals, as they were in the idealized noise-free case of  FIG. 4 , because of the noise in the ECG signal. As such, computed heart rate  533  may not be the true heart rate  333 . Rather, in the situation of  FIG. 5 , the patient may be misdiagnosed with tachycardia due to noise peaks  531 ,  532 . 
     In embodiments, however, the true heart rate  333  is measured, even in the presence of noise. Examples are now described. 
     Referring now to  FIG. 6 , a time diagram  609  has an ECG amplitude axis  607  and a time axis  608 . Diagram  609  depicts an actual ECG signal of a patient. This ECG signal hovers around a horizontal baseline value BL. The units of time axis shows the ordinal number of a sample, i.e. 200 th , 400 th , etc. 
     In embodiments, peaks are detected, which occur sequentially within a sensed ECG signal. In the example of  FIG. 6 , peaks  621 ,  622 ,  623 ,  624 ,  625 ,  626 ,  627 ,  628 ,  629  are detected, which occur sequentially. These peaks are detected in an effort to identify QRS complexes such as those of  FIG. 4 , with the apprehension that some of these peaks may be due to noise as seen in  FIG. 5 . 
     For purposes of detection, a number of criteria can be advantageously applied. For example, all peaks could have the same polarity, as QRS complexes do. Peaks of the opposite polarity can be ignored. In this example the polarity is positive, but it could equivalently be negative. Moreover, a peak can be deemed detected if it meets certain criteria, such as amplitude (e.g., relatively large rise over previous values, and relatively large fall back to about the same values), sharpness (e.g., relatively steep rise and relatively steep fall), and width (e.g., not wider beyond a threshold at mid-amplitude). 
       FIG. 6  also shows another time axis  648 . Time axis  648  indicates only the time occurrences  641 ,  642 ,  643 ,  644 ,  645 ,  646 ,  647  of detected peaks  621 ,  622 ,  623 ,  624 ,  625 ,  626 ,  627  respectively. 
     In embodiments, pairs of the detected peaks can be established, where at least one of the pairs is established by peaks that do not occur sequentially. Such pairs may thus define time intervals. Then durations of the time intervals can be measured. In the example of  FIG. 6 , a pair of peaks  621  &amp;  622  defines a time interval  651  between time occurrences  641  &amp;  642 . The same is true for time intervals  652  and  654 , and so on. 
     It will be noted that a pair of peaks  621  &amp;  623  define a time interval  653  between time occurrences  641  &amp;  643 . In this case, however, peaks  621  &amp;  623  do not occur sequentially; rather, peak  622  occurs after peak  621  and before peak  623 . And it will be recognized that, absent any noise and assuming perfect detection, time interval  653  will be a lot larger than either time interval  651  or  652 . In fact, the duration of time interval  653  would be the sum of the durations of time intervals  651  and  652 . Similarly, a pair of peaks  621  &amp;  624 , which do not occur sequentially, define a time interval  655  between time occurrences  641  &amp;  644 , and so on. More durations could be shown in  FIG. 6 . 
     In embodiments, these durations  651 ,  652 ,  653 ,  654 ,  655  can be used to compute heart rate  333  as further described later in this document. 
     In some embodiments, pairs are established among only some of the detected peaks. This can be implemented from the beginning, for example by not establishing all the possible pairs in  FIG. 6 . This can be implemented after some of the processing described later where all the possible pairs are established. At that time which a recognition value may be computed. Then a peak may be rejected, at least tentatively, for example according to a recognition criterion. It may turn out that rejecting the peak improves the recognition value, and detection of heart rate  333  becomes more robust. 
     In some embodiments, all possible pairs of the detected peaks are established. An example is now described. 
       FIG. 7  shows a time axis  748 . Time axis  748  indicates only the time occurrences  741 ,  742 ,  743 ,  744 ,  745 ,  746  of peaks detected as described elsewhere in this document. For this discussion, pairs of peaks may be referred to by the time durations they define. For example, peaks at  741  &amp;  742  define a time duration  751 . In turn, time duration  751  has a duration indicated by arrow  761 . In this example, time duration  751  has a measured duration of 5. Of course, this value of 5 can be in relative terms for this example. 
     It will be recognized that the peak at  741  defines a group  771  of time occurrences with each of the remaining considered peaks. Similarly, the peak at  742  defines a group  772  of time occurrences with each of the remaining considered peaks, and so on with groups  773 ,  774 , and single time occurrence  755 . As such, group  777  is a group of all possible pairs of peaks  741 ,  742 ,  743 ,  744 ,  745 ,  746 . Each pair is shown by an arrow, with its measured duration as a number within the arrow. 
     In some embodiments, it can be identified which one of the measured durations occurs the most often. The heart rate of the patient can be computed from the identified duration. An example is now described. 
       FIG. 8  is a bar chart  806 . Its horizontal axis  802  shows possible values for the measured durations of time intervals. Its vertical axis  804  shows numbers for how often a measured interval had the duration of horizontal axis  802 . As such, bar chart  806  is not a time diagram. 
     Time durations  777  have been plotted in bar chart  806 . As such, the time intervals defined by the peak pairs have been classified by their durations. 
     A salient feature of bar chart  806  is bar  881 , which is the tallest. As such, it can be identified that the measured duration that occurs the most often has a duration of 5. Other features are bars  882 ,  883 ,  884 , which occur at durations of 10, 15 and 20, and are the 2 nd , 3 rd , and 4 th  harmonics of bar  881 . 
     Bars  889  show some entries, which are presumed to be due to noise. In addition, some durations like  4  and  6 , indicated by arrow  880 , have no occurrences. This may be a result of the time durations having discrete enough values for this example or, equivalently, the bins of the bar chart time durations being wide enough. 
     As seen above, in some embodiments the ECG signal is sensed in samples, and the time durations are measured in numbers of samples. Again, if the bins of the bar chart are wide enough, they can produce a bar chart like bar chart  806 , which is easy to work with even by having empty bins. 
     In some embodiments, from the measured durations, a representative duration can be identified that best meets a plausibility criterion. Such a plausibility criterion can be implemented in a number of ways. For example, as seen above, the plausibility criterion may include that the representative duration is the one that occurs the most often among the measured durations. Additional ways are described later in this document. In such embodiments, a heart rate of the patient can be computed from a duration indicated by the representative duration. Then it can be determined from the computed heart rate whether or not a shock criterion is met. Discharge circuit  255  can be controlled, responsive to the shock criterion being met, to discharge the stored electrical charge through patient  82  while support structure  170  is worn by patient  82 , so as to deliver a shock to patient  82 . 
     In embodiments, it is desired to add to these measurements&#39; durations of time intervals from additional channels. For example, in some embodiments the electrodes are further configured to sense another ECG signal, and the processor is further configured to: detect other peaks occurring sequentially within the sensed other ECG signal, establish other pairs of the detected other peaks, at least one of the other pairs being established by other peaks not occurring sequentially within the sensed other ECG signal, and measure other durations of time intervals defined by the established other pairs. In such embodiments, the representative duration can be identified from both the measured durations and the measured other durations, thus providing more data points. Examples are now described. 
       FIG. 9  is a bar chart  906 . Its horizontal axis  902  shows possible values for the measured durations of time intervals. These values are in numbers of samples, for example as seen in axis  608  above. The vertical axis  904  of bar chart  906  shows numbers for how often a measured interval had the duration of horizontal axis  902 . Intervals in this dataset range from 75-1000 samples, which could give a heart rate anywhere from 30-400 bpm (beats per minute). It will be observed that the most frequent occurrence is 3 for bar  981 , which occurs at a value between 300 and 350, perhaps at 335 samples. 
     In some embodiments the heart rate can be computed from the representative duration. For example, if at  FIG. 9  the representative duration is taken to be at 335 samples, the heart rate can be computed from that value, factoring in also the frequency with which the ECG signal is sampled. 
     In  FIG. 9  it will be observed that the durations are measured in samples much more discretely than in  FIG. 8 , and so there are very few times when there is an occurrence of more than 1. To overcome this, in some embodiments processor  230  is further configured to discern clusters of the measured durations. In such embodiments, the representative duration is identified from the cluster that best meets a plausibility criterion. An example is now described. 
       FIG. 10  repeats bar chart  906  of  FIG. 9 . In addition,  FIG. 10  adds a computed line  1007  that identifies clusters of the bar charts, according to grouping of the values of the horizontal axis  902 . Line  1007  shows a cluster with a maximum at point  1081 , which corresponds to 331 samples. Line  1007  also shows clusters at a second harmonic  1082  (662 samples), and at a third harmonic  1083  (993 samples). As such, the cluster that best meets a plausibility criterion is at point  1081 . Accordingly, the representative duration is identified at 331 samples, and as occurring about 7 times after the grouping. This representative duration corresponds to a heart rate of 90.6 bpm, which seems plausible. 
     While the chosen heart rate is 331 samples, it is possible that there was no duration measured with that exact value. It is further possible that the chosen heart rate does not correspond with the heart rate calculated for any given channel, which may raise questions. A WCD system incorporating this method may also have logic for deciding when to use the heart rate mode and when to use a simpler method. The mode tends to be beneficial when there is a substantial disagreement in the heart rate between channels and there is not an obvious reason for disqualifying one or more channels (like a dislodged ECG lead). 
     In some embodiments, the clusters are identified by filtering the measured durations. For example, in such embodiments, computed line  1007  can be generated by running a grouping kernel to identify the true R-R interval. Discreet time, digital implementations are preferred. The grouping kernel can be implemented as a boxcar Finite Impulse Response (FIR) filter with numerator coefficients of 1. This, effectively, counts up the intervals that are within the filter length. In addition, a standard FIR filter can be run, possibly in both directions, to smooth the result. This method is particularly attractive in a multichannel system because it is helpful to have numerically enough R-R intervals to work with. In a single channel system, the mode may still stand out, but it may not stand out as much because there are fewer intervals altogether. Other methods of identifying clusters (or groups) may produce similar results. 
     In some embodiments, the plausibility criterion includes that a fraction of the identified representative duration occurs less often than an occurrence threshold. That fraction could be a half-, a third-, a quarter-harmonic and so on. For example, while the representative duration has a value of D and occurs M times, the plausibility criterion may include that a duration having a value of D/N occurs less often than M/N times, where N takes one of the values of 2, 3, 4 and 5. This helps mitigate against the possibility that an interval that is 2× the true interval may show up with the highest count, which can cause the heart rate to read half the actual value. If the patient&#39;s rhythm is non-shockable, then there is not much harm in this, but if the patient has a shockable rhythm, then such undercounting might cause a false no-shock decision. An example is now described. 
       FIG. 11  is a bar chart  1106 . Its horizontal axis  1102  shows possible values for the measured durations of time intervals, in numbers of samples. Its vertical axis  1104  shows numbers for how often a measured interval had the duration of horizontal axis  1102 . 
     In addition,  FIG. 11  adds a computed line  1107  that identifies clusters of the bar charts, according to grouping. Line  1107  shows a cluster with a maximum at point  1181 , which corresponds to 98 samples, and occurs 13.57 times. Line  1107  also shows clusters at a second harmonic  1182 , at a third harmonic  1183 , at a fourth harmonic  1184 , and at a fifth harmonic  1185 . 
     It should be noted that the highest occurrence is at peak  1182 . However, the half-harmonic of peak  1182  would be peak  1181 , which does not occur less often than an occurrence threshold. 
     More particularly, in this example, the peak R-R interval would be at peak  1182 , which occurs M=16 times, and is at 194 samples. The more advanced plausibility criterion included that a duration having a value of D/N, i.e. 194/2=97 samples occur less often than 16/2=8 times. Here, however, peak  1181  occurs 13.57 times at 98 samples, which is more than 8, and therefore peak  1182  is rejected as the representative duration. Accordingly, another representative duration is considered, which could be ½ or ⅓ the peak R-R interval. Here, peak  1181  is chosen, which passes the advanced plausibility criterion, even though it is shorter. 
     The devices and/or systems mentioned in this document perform functions, processes and/or methods. These functions, processes and/or methods may be implemented by one or more devices that include logic circuitry. Such a device can be alternately called a computer, and so on. It may be a standalone device or computer, such as a general purpose computer, or part of a device that has one or more additional functions. The logic circuitry may include a processor and non-transitory computer-readable storage media, such as memories, of the type described elsewhere in this document. Often, for the sake of convenience only, it is preferred to implement and describe a program as various interconnected distinct software modules or features. These, along with data are individually and also collectively known as software. In some instances, software is combined with hardware, in a mix called firmware. 
     Moreover, methods and algorithms are described below. These methods and algorithms are not necessarily inherently associated with any particular logic device or other apparatus. Rather, they are advantageously implemented by programs for use by a computing machine, such as a general-purpose computer, a special purpose computer, a microprocessor, a processor such as described elsewhere in this document, and so on. 
     This detailed description includes flowcharts, display images, algorithms, and symbolic representations of program operations within at least one computer readable medium. An economy is achieved in that a single set of flowcharts is used to describe both programs, and also methods. So, while flowcharts described methods in terms of boxes, they also concurrently describe programs. 
     Methods are now described. 
       FIG. 12  shows a flowchart  1200  for describing methods according to embodiments. According to an operation  1210 , a first ECG signal of the patient may be sensed, such as ECG signal  317 . Sensing can be by the electrodes. 
     According to another operation  1220 , peaks occurring sequentially within the first ECG signal may be detected. 
     According to another operation  1230 , pairs of the detected peaks may be established. At least one of the pairs may be established by peaks not occurring sequentially. 
     According to another operation  1240 , durations of time intervals defined by the established pairs may be measured. 
     According to another operation  1250 , a representative duration may be identified, which best meets a plausibility criterion. The representative duration may be identified from the measured durations. 
     According to another operation  1260 , a heart rate of the patient may be computed. Computing may be from a duration indicated by the representative duration. According to another operation  1261 , the computed heart rate of the patient may be stored in a memory. Computing may be from a duration indicated by the representative duration. According to another, optional operation  1262 , the computed heart rate may be transmitted wirelessly, for example by a communication module. According to another, optional operation  1264 , the computed heart rate may be displayed on a screen. 
     According to an operation  1268 , a second ECG signal of the patient may be sensed, such as ECG signal  318 . According to one more operation  1270 , it may be determined whether or not a shock criterion is met. The determination may be from the second ECG signal of operation  1268 . If at operation  1270  the answer is “no”, indicated by a cross-out, then execution may return to a previous operation, such as operation  1210 . 
     If at operation  1270  the answer is “yes”, indicated by a checkmark, then according to another operation  1280 , responsive to the shock criterion being met the discharge circuit may be controlled to discharge the stored electrical charge through the patient. Discharging may be while the support structure is worn by the ambulatory patient, so as to deliver a shock to the patient. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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.