System and procedure for determining the depth of chest compressions

Abstract

System for determining the depth of compression of a patient's chest (3) receiving chest compressions, the system comprising: a field generator configured to generate a field (5); a field detector (16, 17) comprising at least two coils at a fixed distance (26) from each other, each of the at least two coils having a turn parallel to the turn of the other coil, and each of the at least two coils having a center, wherein the corresponding centers of the at least two coils are aligned along a longitudinal axis (19) perpendicular to a plane (11) of the turns of each of the two coils, wherein the field detector (16, 17) is configured to generate a response signal indicating that any one of the at least two coils is detecting the field (5); and a processor designed to determine position information for the field detector (16, 17) relative to the field generator from the response signal and to determine the chest compression depth from the determined position information; wherein the field generator or field detector (16, 17) is a position sensor (2) configured to move in accordance with the chest while the chest receives the compressions, wherein the other of the field generator and field detector is a reference sensor (4) configured to be stationary relative to the patient (3).

Description

Cross-reference to related registrations

[0001] This disclosure claims priority over preliminary US application No. 61 / 158,002, filed on March 6, 2009, and preliminary US application No. 61 / 235,584, filed on August 20, 2009, the disclosures of which are included here in their entirety by reference. Technical field

[0002] This disclosure relates to systems and methods for determining the depth of chest compressions, e.g., during the application of cardiopulmonary resuscitation (CPR). In particular, this disclosure relates to the determination of chest compression depth using a position sensor and a reference sensor. background

[0003] Currently, there are an estimated 40,000 cases of cardiac arrest in Canada each year, most of which occur outside of hospital settings. The chances of experiencing an out-of-hospital cardiac arrest are currently approximately 5%. In the United States, there are about 164,600 such cases each year, or about 0.55 per 1,000 people. Reducing the number of deaths resulting from these out-of-hospital cardiac arrests may be desirable. Certain locations, such as sports fields, and certain individuals, such as the elderly, are at particular risk, and for these people, an appropriate solution can mean the difference between life and death.

[0004] Cardiopulmonary resuscitation (CPR) has proven to be an effective technique for both medical and non-medical personnel to improve the chances of survival for patients experiencing cardiac arrest. CPR circulates blood through the circulatory system until professional medical help arrives, thereby maintaining oxygen distribution throughout the patient's body. However, the quality of CPR is often poor. Adherence to proper CPR technique and protocol may be inadequate for most individuals, and the anxiety of an emergency situation can confuse and hinder a person from providing appropriate treatment.

[0005] According to the Journal of the American Medical Association (2005), cardiopulmonary resuscitation (CPR) is frequently performed inconsistently and inefficiently, leading to preventable deaths. Months after completing standard CPR training and testing, a person's ability to perform effective chest compressions often deteriorates significantly. This finding has been observed for both untrained individuals and trained professionals such as paramedics, nurses, and even physicians.

[0006] In 2005, the International Liaison Committee for Resuscitation described an effective procedure for applying CPR and the parameters associated with an effective technique. These parameters include the chest compression rate and the chest compression depth. The chest compression rate is defined as the number of compressions delivered per minute. The chest compression depth is defined as the extent to which the patient's sternum is displaced by each compression. An effective compression rate can be 100 chest compressions per minute at a compression depth of approximately 45 cm. According to a 2005 study of actual CPR application at Ulleval University Hospital in Norway, compression rates averaged less than 90 compressions per minute, and the compression depth was too shallow for 37% of compressions.

[0007] Therefore, a system that facilitates the correct delivery of CPR in an emergency can be useful. Furthermore, a system that can also be used for objective training and testing can be helpful for ensuring adherence to the CPR training process and protocol.

[0008] Most existing CPR support technologies use accelerometers to determine compression depth. One such device is disclosed in US Patent US 7,074,199 B2. However, any acceleration data from accelerometers used to measure chest compression depth during CPR is prone to cumulative and drift errors. Consequently, these sensors are not suitable for highly accurate or detailed data acquisition regarding CPR parameters and can only be used to approximate depth values. Furthermore, using an accelerometer in a CPR monitoring device without an external reference is error-prone if the patient or the person administering CPR is mobile. For example, if the patient is moving, the accelerometer's position may be affected.When a patient is being transported medically in an ambulance, helicopter, or on a stretcher, the accelerometer cannot distinguish between external movement of the patient and chest compressions. In any type of non-stationary environment, a device based on an accelerometer can be unreliable and ineffective. Furthermore, using an accelerometer to calculate compression depth relies on complex and error-prone calculations to compensate for the angle and inclination of the compression device. If the accelerometer is not perfectly flat against the patient's chest and its movement is not perfectly vertical, errors can accumulate and must be accounted for by the angle between the two horizontal axes.Furthermore, the absence of any external reference point makes it difficult to know the device's position in space at any given time. All distance measurements are relative, and the origin of the motion during measurements is difficult to ascertain and maintain. This can cause the initiation or starting point of compressions to drift over time, leading to errors in depth measurements. Certain commercial products currently utilize accelerometer technology, such as the AED Plus. ® D-Padz ® Zoll Medical's defibrillator pads have an accelerometer embedded within the pads. Due to the additional circuitry and sensors, these pads are considerably more expensive and must be disposed of after each use. Thus, relatively expensive sensors must be routinely discarded due to the product design.

[0009] US patent application US 2007 / 0276300A1, filed by Kenneth F. Olson et al., discloses a device that uses ultrasound transmission to calculate compression depth. A sound signal is transmitted from a device on the patient's chest to a receiver at another location. This device has several disadvantages. First, the ultrasound signal requires a clear line of sight from the transmitter to the receiver to function. Any obstruction—objects, people, or even the user's hand—in the path of the signal can lead to signal loss or degradation. The transmitter must be pointed toward the receiver, and the relative orientation between the transmitter and receiver is crucial. Second, ultrasound is relatively slow, and the time-of-flight measurement of an ultrasound signal can be subject to significant delay and latency.Third, an ultrasound signal is highly dependent on environmental conditions such as air temperature. If the air temperature fluctuates, the speed of sound also fluctuates, which can lead to inaccuracies. Finally, the calculation of compression depth can be significantly compromised if the plane of chest compression is initially unknown. Ultrasound time-of-flight distance interpolation cannot resolve the receiver's position in six degrees of freedom, and determining downward translational movement can be difficult if the patient, receiver, or transmitter is not level. Even when ultrasound triangulation is used, the latency can be considerable, the resolution can be low, and multiple transmitters and receivers at different locations may be required.

[0010] Existing CPR support devices and systems are relatively ineffective at measuring chest rebound. Chest rebound is the extent to which the chest relaxes after a compression. For a chest compression to be fully effective, the chest must fully relax before the next compression begins. As a compression relaxes, the elastic rebound creates a negative pressure that draws blood into the lungs. Incomplete decompression reduces the amount of blood available to be circulated during the next compression. Accelerometer-based devices are unable to establish a reference point at the top of a compression that can be used for an adequate measurement of rebound.Since there is no external reference, the accelerometer signal can drift over time and the device may be ineffective in determining whether the chest has been fully relaxed.

[0011] A recent study (Resuscitation. Jan. 2009; 80(1):79-82, Epub 25 Oct. 2008: ‘Compression feedback devices over estimate chest compression depth when performed on a bed’) has identified another shortcoming in current CPR support devices. The study indicates that CPR support devices tend to overestimate compression depth when the patient is lying on a mattress. The device tends to incorrectly register the movement of the mattress as part of the chest compression.

[0012] Other CPR support devices use mechanical force measurements to indicate compression depth. Because of their inability to compensate for varying chest spring effects, these devices can be inaccurate. They tend to rely on the subjective impression of the patient's size to help calibrate the correct force to be applied. Furthermore, a recent study (Resuscitation. July 2008; 78(1):66-70, Epub 18 Apr 2008: ‘Does use of the CPREzy involve more work than CPR without feedback?’) showed that, due to the device's internal mechanism, these devices tend to require more work than CPR without support. The spring in the device can increase the workload of the CPR processes by an additional 20%, causing the user to fatigue more quickly.

[0013] Currently available CPR support devices and systems typically suffer from a major drawback. They tend to measure depth indirectly by first determining acceleration, velocity, or force. Ultimately, compression depth is a measure of position, and determining it from acceleration requires double integration of the received signal to obtain usable data. This integration introduces a significant source of error into the measurement. It may be desirable to establish a method for determining CPR compression depth by measuring position instead of acceleration, velocity, or force. By directly measuring position, no errors related to signal integration or the compliance of the patient's chest are introduced. The positional data can then be used to directly calculate the depth of chest compressions.

[0014] The prior art also includes WO 2010 / 009 531 A1, US 7 402 996 B2 and EP 1 859 770 A1. These relate to a CPR assist device for measuring compression parameters during cardiopulmonary resuscitation, an instrument and method for measuring three-dimensional movements, and a chest compression detector for use in cardiopulmonary resuscitation.

[0015] It may be desirable to create an easy-to-use and inexpensive system for accurately measuring relevant CPR parameters such as compression depth and rate without the problems of the technologies mentioned above. Summary

[0016] The present disclosure relates to a method and a system for determining compression parameters during the application of CPR. The system incorporates the features and methods disclosed in patent applications Nos. 61 / 158,002 and 61 / 235,584 and provides additional processing strategies and hardware components. The aforementioned applications describe the use of a field generator and a field detector. The generator and detector can be used as a reference sensor and a position sensor, respectively. The reference sensor is relatively stationary, while the position sensor is positioned on the patient's chest and moves in accordance with each chest compression. Instead of simply transmitting and receiving a signal, the field generator and field detector specifically generate and detect a field, such as an electromagnetic field.

[0017] In some aspects, a compound field detector is created for determining the depth of compression of the chest of a patient receiving chest compressions, wherein the detector comprises: at least two coils at a fixed distance from each other; wherein the detector is designed to generate a response signal indicating any one of the at least two coils detecting a field.

[0018] In some aspects, a method for determining the depth of chest compression of a patient receiving chest compressions is provided, which uses a system with a field generator and a compound field detector, wherein the compound field detector comprises at least two coils at a fixed and known distance from each other, the method comprising: receiving signals from each of the coils of the compound detector, the signals responding to a field generated by the field generator; determining positional information of each coil; determining an apparent distance between the coils; determining a correction factor based on any differences between the apparent distance and the fixed and known distance between the coils; and determining the chest compression depth using the positional information and the correction factor.

[0019] In some aspects, a system for determining the depth of chest compression of a patient receiving chest compressions is provided, comprising: a field generator designed to generate a field; a composite field detector containing at least two coils at a fixed distance from each other, the field detector being designed to generate a response signal indicating either of the at least two coils that the field detects; and a processor designed to determine position information for the field detector relative to the field generator from the response signal and to determine the chest compression depth from the determined position information;wherein the field generator or field detector is a position sensor designed to move in accordance with the chest while the chest receives the compressions, wherein the other of the field generator and field detector is a reference sensor designed to be stationary relative to the patient.

[0020] Due to the relatively uniform and predictable nature of chest compressions, various computational algorithms can be used to calculate CPR parameters with relative accuracy. Expected sources of error, such as signal jitter and distortion caused by high-ferrous and conductive metals, can be reduced or eliminated by implementing equations and / or filtering techniques tailored to the characteristics of chest compressions.

[0021] Beyond computational algorithms, other techniques can be used to reduce or eliminate errors, noise, and / or distortion in the measured CPR parameters. As with software, the unique characteristics associated with chest compression motion can enable unique hardware designs that result in cleaner, more reliable position and / or depth estimates. More specifically, the field generator and field detector coils can be configured to reduce the effects of metal interference in the operating environment. In some examples, a compound detector can be used, in which two or more detectors are used together in a fixed relationship. The known distance between the centers of these two or more detectors can be used to detect and compensate for distortion in the environment (e.g., due to metal objects).In some examples, adding a second sensing modality can further reduce error by detecting the presence of distorted or otherwise incorrect data. For example, a pressure or force sensor can detect errors originating from sources that do not affect the pressure or force sensor itself, but do affect the field coil (e.g., distortion of metal objects).

[0022] In some aspects, procedures are created that can be used to compensate for or correct potential system error sources or defects resulting from external disturbances to the system. For example, if the reference sensor is moved during the application of the CPR, the system can detect this movement and recalibrate the depth calculation accordingly to compensate for the movement. In some cases, the system can continue to operate during this disturbance. Uninterrupted operation during movement of the reference sensor can be achieved by adding an external sensor, such as a force or pressure sensor, that is unaffected by the movement.

[0023] Furthermore, in some aspects, procedures are created to compensate for unsatisfactory or error-prone environments in which the system can operate. For example, the system can be configured to compensate for a situation where the patient is supported on a non-rigid surface, such as a mattress. A non-rigid surface can exhibit movement or displacement during CPR, which can lead to erroneous measurements if not accounted for. For instance, the mattress under the patient is compressed along with the chest during CPR. This can result in an erroneously large compression depth reading that does not reflect the actual depth to which only the chest is compressed in the absence of the mattress. The use of an additional field detector can overcome this problem.Given that the three components of a first detector, a second detector, and a generator are predetermined, one component can be designed to move in accordance with the non-rigid surface (e.g., positioned on the mattress beneath the patient), a second component can be designed to move in accordance with the patient's rib cage (e.g., positioned on the patient's rib cage), and the third component can be designed to remain stationary relative to the patient. The actual depth of the compressions can then be determined by calculating the relative motion between the component (e.g., the first detector) moving with the non-rigid surface and the component (e.g., the second detector) moving with the patient's rib cage, for example, by subtracting the position of one from the position of the other.

[0024] In some examples, the system can be adapted to the specific emergency situation. For instance, the position sensor can be detachably housed in a cover or receptacle. The cover can protect the user's hands while providing additional support. In some examples, the cover can be removed from the position sensor when the system is used to perform CPR on a child. Removing the cover can transform the position sensor from an adult-sized pillow to a child-sized pillow. In some examples, the position sensor can be attached to or receptacled within a number of items found in an emergency scene. For example, the generator and / or detector can be attached to a patient's backboard, embedded in the electrodes of a defibrillator, or mounted on a stretcher or hospital bed. Brief description of the drawing

[0025] In the following, aspects of the present revelation will be discussed in more detail with reference to the drawing in which: Fig. 1 a representation of a CPR support system in accordance with an embodiment of the present disclosure; Fig. 2 is a top view showing a field detector of a CPR support system in a cushion on the patient's chest; Fig. 3 is a representation of a field that can be generated by an exemplary field generator and detected by an exemplary field detector suitable for an exemplary embodiment of the CPR support system; Fig. 4 is a flowchart that shows an exemplary algorithm for calculating the position; Fig. 5 is a representation that shows an exemplary procedure for calculating the chest compression depth by first forming a plane in space; Fig. 6 is a diagram showing a normal vector parallel to the path of a chest compression and its corresponding plane in space; Fig. 7 is a representation showing an exemplary pillow in which an exemplary position sensor is included, and the plane that bisects the pillow; Fig. 8 is a representation of an exemplary cushion in which an exemplary position sensor is included, in which the coordinate axes on the cushion are labelled; Fig. 9 is a representation showing an exemplary embodiment of the CPR support system in which a second field detector is arranged in a fixed position in the environment; Fig. 10 is a representation showing two exemplary position sensors arranged in a fixed relationship to each other in a composite detector; Fig. 11 is a diagram that shows the normal vector which is the center of the position sensors in the configuration of Fig. 10 connects, shows; Fig. 12 is a representation that shows the movement of each field detector in the configuration of Fig. 10 shows; Fig. 13 is a representation showing two exemplary detectors arranged in a further exemplary composite detector; Fig. 14 is a representation of another exemplary composite detector in which each of the detectors shares one or more common coils; Fig. 15 is a representation of an exemplary composite detector in which the detectors do not share any common coils; Fig. 16 is a representation showing a composite detector moving between two quadrants in space; Fig. 17 is an exemplary exploded view of an exemplary composite detector with an exemplary force sensor; Fig. 18 is a representation showing an exemplary basic unit comprising an exemplary reference sensor mounted in a holder on the wall of a hospital and an exemplary position sensor on the chest of a patient; Fig. Figure 19 shows an example of a basic unit with an example detachable position sensor in its off configuration; Fig. 20 is a representation of an exemplary basic unit with an exemplary detachable position sensor, which is detached from the unit and ready for use; Fig. 21 is a representation showing an exemplary field generator detached from its base unit and placed under the patient, and an exemplary field detector placed on the patient's chest; Fig. 22 is a representation showing an exemplary field generator in a basic unit and two exemplary field detectors, one being positioned under the patient and the other on the patient's chest; Fig. 23 is a representation showing an exemplary reference sensor located under the patient and an exemplary position sensor located on the patient's chest, with feedback provided at an exemplary position sensor; Fig. 24 is a representation showing an exemplary patient backboard with an exemplary reference sensor embedded in the backboard; Fig. 25 is a diagram showing the rotation angles of an exemplary pillow image of an exemplary orientation sensor; Fig. 26 is a representation of a user performing a CPR in an example of the correct form; Fig. 27 is a representation showing an exemplary wearable embodiment of the CPR support system; Fig. 28 is a representation showing an exemplary reference sensor position on or adjacent to a pulse oximetry device; Fig. 29 is a representation showing a chest impedance measurement between the cushions of a defibrillator with an exemplary position sensor embedded in one of the cushions; Fig. 30 is a representation showing an exemplary resolvable recording for an exemplary position sensor; Fig. 31 is a representation showing an exemplary position sensor with feedback provided on the position sensor; and Fig. 32 is a representation that shows an exemplary basic unit that indicates an exemplary feedback request. Detailed description

[0026] The present disclosure relates to a method and a system for determining and calculating chest compression parameters, such as chest compression depth, during the application of cardiopulmonary resuscitation (CPR). The system can also be referred to as a CPR support system.

[0027] The system comprises a field generator and a field detector. In some embodiments, the field detector is a position sensor and the field generator is a reference sensor. The position sensor can be located at a position corresponding to the movement of the patient's chest, while the reference sensor can be located at a relatively fixed position. The reference sensor generates signals, e.g., electromagnetic fields, which are detected by the position sensor. In other embodiments, the field detector is the reference sensor and the field generator is the position sensor, in which case signals, which may be fields, are generated by the position sensor and detected by the reference sensor. It is clear to those skilled in the art that the position sensor and the reference sensor are interchangeable. A processor in the system determines the position of the position sensor relative to the reference sensor based on the signal.Based on the determined position, the processor determines the chest compression parameters, including chest compression depth, during the application of CPR.

[0028] It will now be on Fig. 1 and Fig. 2. In this example, the CPR support system can include a relatively stationary base unit 1, which may contain a reference sensor 4 in the vicinity of an emergency and a position sensor 2 that can move relative to the reference sensor 4 in accordance with chest movement of the patient, thus tracking the movement of the patient's chest 3 during CPR. In this example, the reference sensor 4 is the field generator and the position sensor 2 is the field detector. The reference sensor 4 can generate a signal, such as a field 5, which is detected by the position sensor 2. In this example, the position sensor 2 is provided in a structure placed on the patient's chest, such as a block, a pillow 6, or another suitable structure, and is connected to the base unit 1 by a cable 8.The person administering CPR or the user 9 can directly compress the patient's chest by placing their hands 7 on the cushion 6. The base unit 1 is positioned here on the floor 10, which is relatively stable relative to the patient. Although the base unit 1 is shown, in some examples the system does not include a base unit.

[0029] As in Fig. As shown in Figure 3, the field detector (e.g., the position sensor in the example above) is configured to detect the field generated by the field generator (e.g., the reference sensor in the example above). The field detector can then generate a response signal. A processor uses this response signal to determine the position of the position sensor, e.g., its three-dimensional position coordinates, relative to the reference sensor. The processor can be integrated with the reference sensor in the base unit, attached to the position sensor, or be a separate component. The processor can receive information from the position sensor via wired or wireless communication. For example, the position sensor can include a wire for coupling to the reference sensor and / or the processor, or it can include a wireless transmitter for wireless coupling to the reference sensor and / or the processor.Similarly, the reference sensor can communicate with the processor via wired or wireless communication.

[0030] The position sensor's coordinates can be determined by measuring the strength of the detected field from the field generator. The processor can use this position information to determine a chest compression parameter, such as compression depth. This chest compression parameter (e.g., compression depth) can be provided to the user via a feedback component, such as audible, visual, and / or tactile feedback. Compression depth can be calculated from the position information by determining and subtracting the initial and final positions, corresponding to the beginning and end of a single compression. Other common calculations can also be used to determine compression depth.

[0031] Possible hardware and software that can be used to calculate the coordinate position information of three degrees of freedom are disclosed in US patent application No. 12 / 354,913, the disclosure of which is included here in its entirety by reference. This application discloses methods for demodulating and filtering the response signal to generate a 3 × 3 signal matrix representing the nine generator-detector couplings. The position calculation can be performed using methods similar to those disclosed in US patent US 4,314,251 A, the disclosure of which is included here in its entirety by reference. One method for calculating the position uses a three-axis field detector. The three-axis sensor determines the complete signal vector generated by each excitation vector of the field generator at the location of the position sensor.Initially, the orientation of the position sensor relative to the reference sensor is unknown. Therefore, the position can be determined from signal parameters that are unaffected by the unknown sensor orientation. Solutions for the unknown position of the sensor can be formulated in terms of the squared magnitudes and the scalar products of the sensor output vectors. These two quantities are invariant under sensor rotation.

[0032] For example, the magnitudes of the three position coordinates of the sensor can be determined by a system of equations based on the outputs of a three-axis position sensor generated by all three excitation vectors. Trigonometric relationships and position frame sensor output vectors corresponding to the excitation vectors can be used to determine relationships between the squared vector magnitudes and the x, y, and z coordinates.

[0033] Once the x, y, and z values ​​have been determined, the coordinates can be denormalized if appropriate. The signs of the x, y, and z coordinates are determined by the dot products of the sensor output vectors. The process for calculating x, y, and z can be modified for sensors and sources with fewer or more than three axes. An example procedure for calculating the position of the orientation sensor is described in Fig. 4 shown.

[0034] After obtaining the x, y, and z coordinates for the sensor's position, the compression depth and other parameters can be calculated. Several methods can be used to calculate the chest compression depth. For example, where the field generator provides the reference frame for the system, the chest compression depth can be calculated by forming an imaginary plane 11 in space, as shown in Fig. As shown in Figure 5, the plane 11 is essentially parallel to the patient's rib cage. This plane 11 forms a reference point for the start of a chest compression, with the chest compression depth being calculated as a distance from the plane. The equation of the plane can be calculated by forming an initial vector 12 along the downward movement of the first compression.

[0035] An initial, reference, or "output" coordinate 13 and one or more further coordinates 14 together with the length of the compression can be defined as in Fig. The coordinates shown in Figure 6 are determined and stored in memory. Using these coordinates, the normal vector 12 for the plane can be calculated. The equation of the plane is Ax + By + Cz + D = 0, where (A, B, C) is the vector normal to the plane. The value of D can be calculated by substituting the "initial" coordinates into the plane equation and solving. The calculated plane represents the highest depth level that the position sensor can reach during chest compression. As shown in Figure 6, the normal vector 12 for the plane can be calculated. The equation of the plane is Ax + By + Cz + D = 0, where (A, B, C) is the vector normal to the plane. The value of D can be calculated by substituting the "initial" coordinates into the plane equation and solving. The calculated plane represents the highest depth level that the position sensor can reach during chest compression. Fig. As shown in Figure 7, the plane can be, for example, essentially parallel to the patient's rib cage and essentially parallel to the upper surface of the cushion 6 in which the position sensor 2 is embedded. The compression depth can then be calculated as the distance of the current coordinate from this plane. The distance from any current coordinates (x, y, z) to the plane is calculated as: d=Ax+By+Cz+DA2+B2+C2.

[0036] The sign of d can be used to determine whether the current compression coordinate is above or below the initial position of the chest compression. Any value indicating a compression position above the plane is likely erroneous or may represent movement of the cushion that is not part of the chest compression. Furthermore, adequate chest rebound can be calculated by ensuring that the user sufficiently relaxes the patient's chest so that the sensor returns to its position in the initial plane.

[0037] Another exemplary method for determining the depth of chest compressions is to use the position sensor to provide the reference frame for the calculations. If the position sensor is the reference frame, rotations of the position sensor do not affect its x, y, and z coordinates. Thus, the initial rotation of the position sensor is irrelevant to its current x, y, and z position as it moves within its own reference frame. The calculations can be transferred from the reference sensor's frame of reference to the position sensor's frame of reference by simple rotations known to those skilled in the art. The initial configuration (i.e., orientation) of the position sensor may be known relative to the patient's chest. For example, in a CPR support system, the cushion 6, in which the position sensor is housed, may be, as in Fig. Figure 8 shows lines 15 indicating where the cushion should be positioned on the patient's chest. The cushion can be positioned, for example, between the patient's nipples and on the sternum. Since the position sensor's reference system is the reference system, all movements of the position sensor occur relative to its own current position and configuration. Thus, the coordinate positions calculated during chest compression can be used to directly determine the compression depth. To determine the current compression depth, the actual x, y, z trajectory of the position sensor in three-dimensional space can be tracked while the compression is applied, or the distance between the initial coordinate of the compression and any current coordinate can be calculated.

[0038] By tracking coordinates in space, rather than directly calculating the distance between points, alternative algorithms can be developed that account for the lateral displacement of the system and / or other movements not part of the chest compression. For example, lateral movement of position sensor 2 might be misinterpreted as part of the vertical movement of the compression. By monitoring the three-dimensional trajectory of the position sensor as it moves within the chest compression, errors resulting from these erroneous movements can be reduced or eliminated. Lateral, non-compression components of the movement can be removed from the calculated depth. This can be an advantage of directly measuring the x, y, z position of the position sensor over conventional systems that use accelerometers and force sensors, which cannot easily distinguish such erroneous movements.

[0039] In another exemplary method for calculating compression depth, the field generator is designed to move in accordance with the patient's rib cage (e.g., within a cushion placed on the rib cage), and the field detector is designed to remain stationary relative to the patient. Since the field generator is the reference system, all positional data in the system of the cushion on the patient's rib cage are constant. Thus, the cushion can be marked with symbols or reference points, as described above, to ensure correct alignment on the rib cage. The known configuration of the cushion relative to the rib cage allows for relatively accurate monitoring of the current position and depth of chest compression. Unlike the previous method, this technique does not require rotating the coordinates in the position sensor system, as the field generator itself is the position sensor, and all measurements are taken relative to it.

[0040] As previously described, either the field detector or the field generator can be used as the position sensor, while the other of the pair can be used as the reference sensor. Multiple reference and / or position sensors can be used, which can further improve the accuracy of the position and orientation information. As described in Fig. As shown in Figure 9, for example, in an environment with a significant noise or interference source (where, for example, if the system uses electromagnetic fields as signals, a noisy environment may be one containing significant metal sources), a second field detector 16 can be arranged in the vicinity of the first field detector 17, the first field detector being used as a position sensor and the reference sensor being a field generator. This second field detector can be in a relatively fixed position and used to calibrate the system's measurements by determining the environmental disturbance in the environment. For example, in a hospital, an existing field detector can be mounted in the environment and measure the environmental distortion present there.

[0041] Electromagnetic tracking systems, such as that described in US Patent 4,313,251 A, the full disclosure of which is included here by reference, can suffer from a major limitation. The electromagnetic signals generated by these systems are typically susceptible to distortion caused by the presence of metal objects. The primary sources of distortion are mainly large, conductive metal objects. There are two properties of a metal that determine the extent to which it distorts an electromagnetic field. The first property is the metal's conductivity. Variable fields, such as sinusoidal electromagnetic fields, induce eddy currents in conductive materials. The extent to which eddy currents are induced depends on the size and conductivity of the material.Highly conductive metals, such as copper, pose a greater threat to the field than less conductive metals, such as stainless steel. The second property is the metal's permeability. Materials that are highly permeable at the frequency of the generated field can make the detected field asymmetrical.

[0042] Current electromagnetic tracking systems allow for precautionary measures to reduce metal interference. For example, the distance between the field generator or field detector and any large metal object can be increased until the effect is negligible. Alternatively, the distance between the field generator and the field detector can be minimized, thereby reducing distortion caused by any nearby metal. Additionally, all sources of metal in the environment can be mapped before data collection. However, these and other existing distortion compensation methods may not be practical in a number of operational situations. For instance, in a real-world environment, it is often difficult and cumbersome to ensure that all metal sources have been completely removed.Furthermore, identifying and mapping all metal sources before system operation is often difficult and time-consuming. In applications where metal may be present, but fast and reliable operation is required, mapping is frequently not a practical option.

[0043] Certain tracking applications require only relative position measurements and involve a relatively predictable motion trajectory. For example, the application may require tracking along a simple, linear path, such as the path traveled by a patient's chest during CPR. During CPR, the vector along which the chest moves is essentially known (i.e., the chest is compressed along an essentially straight, downward path toward the spine). The properties of this linear motion, together with an essentially known vector, can be used to improve data accuracy while reducing or eliminating distortion from metal noise and / or other interference from other electrical devices.

[0044] Reducing the effects of metal distortion while improving accuracy in an electromagnetic system where the tracked object (as in CPR) moves along a known vector path can be achieved, for example, using a compound detector having at least two coils at a fixed distance from each other. The compound detector behaves similarly to a simple (i.e., non-compound) detector, except that response signals from the compound detector can be generated by one or both coils. As in Fig. As shown in Figure 10, for example, a second field detector 16 can be mounted directly below the first field detector 17, with both moving together as a single unit, also referred to as a "stacked detector" or composite detector 18. In the exemplary composite detector 18, there are at least two coil assemblies (in this case, the field detectors 16 and 17) with windings that are substantially parallel to each other and spaced apart at a fixed and known distance. Although the composite detector 18 is described as having two or more detectors, it can, of course, have two or more spaced-apart coils or coil assemblies instead of detectors. The known distance is substantially parallel in one direction to the direction of the expected motion (in this case, perpendicular to the parallel windings).In the example shown, the two detectors 16, 17 can be arranged directly above one another, such that the corresponding coils are parallel to each other and the center of one detector 16 lies directly above the center of the other detector 17. As in . Fig. As shown in Figure 11, a longitudinal axis 19, perpendicular to the planes defined by each of the coils and connecting the centers of each field detector 16, 17, can run essentially directly along or parallel to the expected path of motion to be measured (i.e., the path of chest compression). Since the two detectors 16, 17 are stacked and attached to one another, the distance between the centers of the two field detectors 16, 17 is a known and fixed constant value.

[0045] To obtain more precise positional information, the original data from each of the two field detectors can be correlated in the composite detector 18. The known spacing can be used to detect distortion and / or noise sources in the environment and can be used to correct for distortion and / or other noise sources. Although two field detectors are shown in the composite detector, more than two field detectors can be used, provided that the distances between the field detectors are all known and fixed. Where the composite detector contains more than two detectors, the field detectors can all be spaced apart along the same direction (e.g., parallel to the expected compression direction) or along different directions.Where the field detectors are spaced apart in different directions, this configuration can be used to determine and correct distortions in multiple directions.

[0046] There are several ways in which the coils in the compound detector can be used to compensate for metallic objects in the vicinity. For example, if conductive or ferrous metal is located near the detector or generator, the measured absolute position from the source to each of the field detectors will be distorted. This distortion causes the known and fixed distance between the two field detectors to be perceived as either smaller or larger, depending on the nature of the distortion. This discrepancy between the known actual fixed distance and the measured apparent distance indicates the type and magnitude of the distortion present along the path of motion. This information can be used to calculate the effect of the distortion on the detector as it moves along the vector connecting the centers of the detector coils.Since the vector connecting the centers of the two detectors is essentially aligned with or parallel to the axis of motion, the distortion can be determined along this vector and thus along the length of the motion.

[0047] For example, if the actual distance between the detector coils in the composite detector configuration is five millimeters and the measured apparent distance is ten millimeters, a scaling factor of two can be used in the motion measured over the distance separating the coils. Thus, if the detector has a measured apparent motion of four millimeters, its actual motion can be corrected to an actual two millimeters. Although the distortion over the vector path separating the detectors may cause a nonlinear effect, the approximation can still help improve the position estimate. Additional such correction factors can be used. For example, scaling or correction factors can be collected and combined (e.g., averaged) over a time period or a number of compressions to correct for any measurement distortions.

[0048] Another exemplary approach to distortion compensation using the composite detector is to map a new coordinate system along the path of movement. As long as the detector movement occurs substantially along or parallel to the path connecting the detectors, and the distance between them is sufficiently small, one of the two detectors will move through the initial position of the other. When the position of the first detector moves to the position previously occupied by the second detector, the measured coordinates of the first detector should be equal to, or very similar to, the coordinates of the second detector when it was in the same position. Even if a metal distortion factor is present in the vicinity, the coordinates of the first detector will be distorted in the same way that the coordinates of the second detector were distorted in the same position. Thus, the second detector can be measured as in Fig. Figure 12 shows how to map a new, distorted coordinate system for the first detector along the path of motion.

[0049] For example, if chest position is measured during CPR, the composite detector can be positioned on the patient's chest such that the vector connecting the centers of the detectors is substantially perpendicular to the chest surface and substantially aligned with, or parallel to, the direction of movement (e.g., substantially straight down toward the spine). The distance between the detectors can be small compared to the total distance traveled. In the case of CPR, an average chest compression might be five centimeters, and thus an approximate distance of, for example, 10% of the total compression, or five millimeters, could be used. A smaller distance can ensure improved positional resolution.

[0050] At the start of chest compressions, the initial position of the second detector is measured and defined. 20. As the first detector moves downwards towards the second detector during chest compressions, its position is measured. 21. When the position of the first detector is approximately aligned with the initial position of the second detector, 22 it can be assumed that the first detector has moved the five-millimeter distance. At this point, the system can again measure and define a new initial position for the second detector, and the process can be repeated. Even if a source of distortion is present in the environment, the distortion should affect both detectors equally in the same position in space. Consequently, distortion errors can be mitigated, reduced, or eliminated.While the chest compression reaches its lowest point 23 and begins to move upwards again 24, the position of the first detector can be used to map the coordinate positions.

[0051] Once the coordinates along the path of motion have been mapped, position measurements from only one detector may be necessary. However, it can be useful to perform the process of mapping the coordinates along the path of motion regularly or repeatedly (e.g., at fixed time intervals or upon triggering events such as the beginning of a compression) to account for any new distortions that have entered the environment and were not considered during the initial mapping process.

[0052] An exemplary method for measuring chest compression depth is now described. In particular, this method may be suitable for use with a system that includes a combined field detector and field generator as described above.

[0053] The positions of at least two coils (e.g., the coils of the composite detector) designed to move in accordance with the patient's chest (e.g., positioned on the chest) are determined. As described above, this can be achieved by the processor processing response signals received from each coil in response to a detected field from the field generator. The response signals can represent information (e.g., positional information) that can be processed by the processor.

[0054] The apparent distance between the coils is estimated. For example, the processor can determine the apparent distance between the centers of the coils based on the response signals received from each coil.

[0055] A correction factor is estimated based on any differences between the apparent distance and the known, fixed distance between the coils. For example, the processor's memory may store the actual, fixed distance between the coils of the composite detector. This actual distance is compared with the calculated apparent distance, and a correction factor is calculated accordingly.

[0056] The chest compression depth is determined based on the specified positions and the correction factor. For example, the processor can determine the position of the composite detector (e.g., by averaging the positional information from the coils of the composite detector), calculate the apparent chest compression depth using known methods, and apply the correction factor to obtain the actual chest compression depth.

[0057] The apparent distance between the coils can be determined from the position information of each coil at a given time (e.g., as described above) or from the distance as one coil moves from its own initial position to the initial position of the other coil (e.g., as described above).

[0058] The two field detectors or coil arrays in the compound detector configuration can be arranged such that their centers are not aligned along the vector path of chest compression. For example, in Fig. As shown in Figure 13, the detectors can, for example, be spaced apart not only spatially in a direction parallel to the expected direction of motion, but also laterally. This can allow the detectors in the composite detector to have a smaller distance in the direction of motion. This can also allow the composite detector to be more compact. As shown in Fig. As shown in Figure 13, the centers of the field detectors in this case can maintain a fixed and known distance 25 along the compression vector path, but also have a fixed and known lateral distance 26 that must be compensated. Although the positional information can be improved by reducing the distance, the lateral distance introduces a vector component into the distance between the detectors that does not lie along the path of motion. This additional vector can complicate the mathematical compensation of the distortion in the environment.

[0059] As in Fig. As shown in Figure 14, the configuration of the composite detector can also include two detectors or coil arrangements in which each of the two detectors can share one or more common perpendicular coils. For example, the first detector and the second detector can each consist of a Z-axis coil 27, but share the same X-axis coil 28 and Y-axis coil 29. Calculations can take into account that the centers of the Z-axis coils and the X- and Y-axis coils do not coincide. Despite the increased mathematical complexity, this configuration allows the use of fewer coils, which can reduce costs and / or manufacturing complexity. For example, in a system as shown in Figure 14, the following configurations can be used: Fig. 15 showed six coils 30 might have required, now four are sufficient.

[0060] A composite detector configuration can allow the system to exhibit lower sensitivity to the absolute tolerance of the individual detector arrays. Instead, the relative tolerance of the two detectors can be the more important parameter. For example, if the second detector of the composite measures coordinates along the path of the first detector, the more similar the two detectors are to each other when they are in the same position in space, the more similar the two detectors are. Thus, the two coil arrays in the composite detector can be wound such that their number of turns, inductance, resistance, area, and other parameters are relatively closely matched.

[0061] Electromagnetic systems inherently suffer from hemispheric or quadrant ambiguity. Depending on the number of coils in each detector and generator configuration, the received signals may be the same in opposite quadrants or opposite hemispheres. Certain quadrant ambiguities can be resolved by determining the phase of the detected signals. However, it may be impossible to determine the operating quadrant if only two detector or generator coils are used instead of three. If three detector and three generator coils are used, it may be possible to determine the operating quadrant but not the hemisphere. The use of a composite detector configuration may allow the resolution of certain hemispheric ambiguities.

[0062] For example, in the case of CPR, a change of quadrant while the detector is being moved over chest compressions can cause an unexpected change in position. As in Fig. As shown in Figure 16, an axis 31 can be crossed and a new quadrant 32 entered if the compression occurs along the Z-axis of the detector coil and the generator is arranged such that the detector can move from above the generator to below the generator. In this case, the first detector of the composite detector crosses the axis before the second detector of the composite detector. Once the first detector has crossed the axis, its Z-coordinate value may begin to increase, while the Z-coordinate value of the second detector continues to decrease. This difference in the direction of motion of each of the detectors can indicate that the composite detector is crossing an axis, and the appropriate signs can be assigned to the measured coordinates.

[0063] Providing a composite detector with two detectors whose centers are aligned along the path of chest compression at a known distance can offer a further advantage. The two detectors can enable the relatively accurate calculation of a plane perpendicular to the chest compression motion. Calculating the normal vector for this plane can be relatively simple, as two points along the vector are available: the centers of each of the two field detectors in the composite detector. The normal vector formed by each of the field detector centers can be used to calculate, relatively efficiently and accurately, a plane representing the onset of compression. As previously described, this plane can then be used to calculate the compression depth.

[0064] Although the composite detector was described above as containing two spaced-apart detectors or coil assemblies, the composite detector can, of course, generally contain more than two spaced-apart detectors or coil assemblies. Although the detectors or coil assemblies in the composite detector are shown to be relatively similar, they may also differ in terms of dimensions, number of turns, inductance, resistance, etc.

[0065] As in Fig. As shown in Figure 17, in a further embodiment, a sensor 33 or material is provided in the field sensor, e.g., between each of the field generator detectors in a composite two-detector system, which can measure force, pressure, or contact. As described above, the two field detectors can be used to compensate for distortion and improve the accuracy of the system. The force, pressure, or contact sensor is used to measure the force or contact exerted by the user on the patient's chest during compression. In the case of a force and / or pressure sensor, the force signal can be used to further improve the measured position data. For example, a force or pressure signal can be correlated with the position signal to filter out noisy data and signal distortion.

[0066] Furthermore, the force, pressure, and / or contact sensor can be used to achieve a more accurate measurement of chest rebound. The sensor can be used to detect when the chest has fully relaxed after compression has been applied. Field data alone can be used to measure adequate chest rebound by measuring the extent to which a chest compression returns to its initial or resting position. However, the chest may lose its springiness over time, and the resting position may change. In this case, a pressure sensor can help provide a more accurate determination of chest rebound.

[0067] The positional data from the field detectors can also be used to measure the spring action of the patient's chest. By measuring the total force applied by the user to compress the patient's chest over a specific distance (as measured by the field detector / generator), a compliance constant can be determined that correlates the force signal with the chest compression depth for that specific patient. This compliance constant can have a number of uses. For example, if the system determines that its power level is below a given threshold (where the system is powered by a battery, for instance), the system can enter an operating mode in which positional and / or depth information is based solely on the force data.For example, the first compression of each thirty-cycle can be used to calculate a compliance constant, which is used to convert all subsequent force measurement results into positional data.

[0068] Beyond the benefits of power savings, this design strategy also allows the system to operate with relatively few or no side effects in a highly noisy or distorted environment. Furthermore, the force sensor enables the system to continue operating even if the reference sensor is moved during chest compressions. For example, if the reference sensor is accidentally disturbed while CPR is being performed, the detected sudden movement can trigger the system to automatically switch to determining position information using data from the force sensor until it is determined that the reference sensor is relatively stationary again. This can prevent an interruption in determining compression depth and / or delivering depth feedback to the user.Such sudden movements of the base can be determined by comparing the force data from the force sensor with the position data from the position sensors. Any significant discrepancies between the two data sets can indicate a sudden shift in the position of the reference sensor. Furthermore, discrepancies between the force and position sensors can indicate the presence of other noise or distortion sources in the operating environment.

[0069] Another exemplary benefit of integrating a force sensor into or onto the position sensor is the resolution of hemispheric ambiguity. Typically, the quadrant and hemisphere of the operation can be resolved using scalar products calculated from the position vectors in the 3 × 3 signal matrix. However, resolving ambiguity using scalar products does not eliminate ambiguity across hemispheric boundaries. Nevertheless, a force or pressure sensor can be used to detect the crossing of a hemispheric boundary of the system. When a hemispheric boundary is crossed, the positional coordinates may have the wrong sign. This can lead to an incorrect compression depth; it may appear as if the compression is upward instead of downward.By monitoring the direction of movement with the force sensor, the signs of the coordinates in each hemisphere can be corrected and the direction of movement can be determined.

[0070] Although the preceding description, which integrates a force, pressure, or contact sensor into the field detector assembly, refers to an exemplary embodiment in which the force sensor is located between the two field detectors of a composite detector, other embodiments are possible. For example, instead of a composite detector, there may be only one field detector, with the force, pressure, or contact sensor located either on the front surface of the field detector (e.g., opposite the user's palm) or on the rear surface of the field detector (e.g., opposite the patient's chest).

[0071] A major source of positional error in an electromagnetic tracking system is distortion resulting from the presence of metallic objects in the tracking environment. In particular, highly conductive metals are especially problematic because they generate eddy currents. These eddy currents produce an electromagnetic field that opposes the magnetic field emitted by the field generator. Using two field detectors at a fixed location relative to each other in a composite detector can reduce the distortion effect described above. However, in environments known to be filled with or encapsulated by large amounts of metal, other distortion compensation methods may be employed. For example, CPR is frequently performed inside an ambulance.The ambulance frame may be made of aluminum sheets, which can generate large eddy currents that can be detected by the field detector, leading to distorted data. In a known and stable environment, such as an ambulance, these field distortions can be mapped for future reference by the system.

[0072] For example, field distortion can be empirically measured at any point in the operating environment, and a lookup table or compensation equation (e.g., a polynomial fit) representing the measured distortion can be stored in the system's processor memory. When a particular distortion is measured and fitted to a known distortion stored in memory, the processor uses the corresponding distortion map to correct this known distortion. For example, the correct position for the data can be determined from the lookup table or using the distortion compensation equation. The use of the distortion map can be initiated automatically by the processor (e.g., in response to the detection of the known distortion) or in response to a user selection. When the processor detects a known distortion, it can prompt the user (e.g.,(using a dialog box provided via the feedback component) to confirm whether the known distortion should be corrected before using the distortion map.

[0073] Since, for example, most ambulances have a similar structure and metal composition, it may be possible to integrate a general "ambulance operating mode" into the system. In this mode, the system uses the stored distortion map to correct any distortion arising from the known environment and can be activated when CPR is performed in an ambulance. Furthermore, it may be possible to automatically detect the presence of distortion caused by the ambulance's frame. The system can recognize the distortion signature caused by the typical structure and characteristics of an ambulance's body. Upon detecting the distortion signature, the system can automatically begin operating in a distortion compensation mode using the predefined distortion map that corresponds to the detected distortion signature.

[0074] For example, in Fig. As shown in Figure 18, the system can also have an automatic calibration mode in which the system is positioned at a specific location (e.g., defibrillator holder 34 in an ambulance) and the environment is measured for distortion. This type of distortion compensation may not be as effective as mapping the environment in advance, but it does not require any previously stored information.

[0075] A specific distortion operating mode can also utilize a force or pressure sensor embedded in the field detector. For example, in such an operating mode, the system can rely more heavily on the force sensor to help remove distortion from the signal. If the patient is moved from a non-distorted environment (e.g., from a roadway) to a distorted environment (e.g., into an ambulance), the system can use force sensor calibration constants calculated in the non-distorted environment for proper operation in the distorted environment.

[0076] Metal objects are a potential source of error and distortion for the system. Another source of error includes phase-shift movement between the field detector and the field generator. Since all measurements are relative to the reference sensor, any movement of the reference sensor during the application of the CPR is a potential source of error. The system can be configured to detect any movement of the reference sensor. This movement is usually large and sudden and can be easily filtered out using various signal processing techniques. Movement of the reference sensor can also be determined by placing a motion detection sensor, such as an accelerometer, next to or inside the reference sensor. The accelerometer can be used to warn the processor that the reference sensor (e.g., the field generator) is not stationary.If the reference sensor is moved, the system can temporarily stop sending position and / or depth feedback to the user. Once the reference sensor movement has stopped, the system can recalibrate an initial position for calculating compression depth and resume determining position information and delivering feedback. If a force or pressure sensor is embedded in the position sensor, calibration can be performed by determining when the rib cage has fully relaxed (i.e., when the force applied to the rib cage is minimal). At this point, the system can determine that compression is at its initial point. Furthermore, a force or pressure sensor can allow the system to continue operating while the reference sensor is moving. For example, if the system...If the sensor detects that the reference sensor is moving, the position data can temporarily be based on force data instead of data from the field detector / generator. As described previously, the force sensor can initially be calibrated using the position data acquired by the field detector / generator.

[0077] When an accelerometer is positioned near the reference sensor, the movement of the reference sensor can be determined and extracted from the position data. For example, a three-axis accelerometer can determine the movement of the reference sensor along the x, y, and z axes, and this movement can be subtracted from the movement detected along the three axes by the position sensor.

[0078] CPR is often performed on a patient supported by a non-rigid surface, such as a mattress. When chest compressions are delivered to a patient on a mattress or other flexible material, the chest undergoes two distinct movements. The first movement is that of the rib cage being compressed inward by the user's hands. The second movement is that of the torso moving into the soft surface of the non-rigid material. Only the movement of the compression itself is used to propel blood through the patient's circulatory system. However, a typical CPR support system may not be able to distinguish between these two movements and could measure a greater compression depth than may have actually been delivered.Thus, the system can indicate to the user that each chest compression is deeper than it is, resulting in shallower compressions.

[0079] Several potential methods can be used to address this situation. For example, if the three components of a first detector, a second detector, and a generator are given, one component can be designed to move in accordance with the non-flat surface (e.g., positioned on the mattress beneath the patient), a second component can be designed to move in accordance with the patient's rib cage (e.g., positioned on the patient's rib cage), and the third component can be designed to be stationary relative to the patient. The actual depth of compression can then be determined by measuring the relative motion between the component (e.g., the first detector) moving with the non-rigid surface and the component (e.g., the second detector) moving with the patient's rib cage.can be determined by subtracting the position of one from the position of the other.

[0080] As in Fig. 19 and Fig. As shown in Figure 20, in an exemplary embodiment the field generator can be detachable from the base unit of the system. If the base unit is, for example, a defibrillator, the field generator can be detachable from the defibrillator. The field generator can be, as shown in Fig. The field generator (21) is shown positioned on the mattress (35) beneath the patient, either adhering to the patient's back or lying between the mattress and the patient's back. The field detector (2) can be positioned on the patient's sternum. During chest compression, the field generator may move with the mattress, while the field detector may move with the combined movement of the mattress and the patient's chest. The position of the field detector is measured relative to the field generator, effectively eliminating mattress movement since the field generator and field detector are both subject to the same movement.

[0081] As in Fig. As shown in Figure 22, in another exemplary embodiment there can be two field detectors and a field generator. The field generator can be located in the base, and one of the field detectors can be positioned on the patient's chest. The second field detector 36 can be positioned on the mattress under the patient, attached to the patient's back, or located between the mattress and the patient's back. Thus, the second field detector can move with the mattress and therefore determine the amount of movement the mattress experiences during chest compression. The first field detector 37 can detect the combined movement of the chest compression and the mattress. Thus, the processor can subtract the movement of the second field detector from the movement of the first field detector, thereby eliminating the movement of the mattress from the chest compression depth measurement.

[0082] In another exemplary embodiment, there may be no base unit. The system may comprise a field generator and a field detector, wherein, as in Fig. As shown in Figure 23, the field generator is positioned under the patient and the field detector is positioned on the patient's chest. As described in the preceding embodiments, the movement of the mattress can easily be subtracted from the compression depth calculation. Further embodiments in which the arrangement of the field generator and the field detector are reversed are also possible.

[0083] Other possible situations may require compensatory mechanisms. For example, the patient's chest may lose compliance over time. During CPR, the chest may collapse, and the internal structures may become less elastic. This can lead to a drift in the actual starting position of the chest compressions over time. The system can compensate for a loss of chest compliance and a change in the starting position of the compressions by recalibrating the starting position (e.g., the top of the chest compression) before each cycle of chest compressions. For example, if each CPR cycle consists of thirty compressions and two rescue breaths, the system can recalibrate the initial compression position during the delivery of the two breaths.If continuous compressions are delivered without any interruptions, the system can calibrate itself using a force or pressure sensor. The system can determine the initial position of a compression by detecting the point at which the user applies the minimum force to the chest.

[0084] Often, CPR must be performed in a moving environment. For example, CPR is regularly administered in a moving ambulance or medical helicopter. Furthermore, CPR may be performed in larger vehicles such as trains, airplanes, or large ships. Current compression depth methods that utilize accelerometers can register the external movements of these vehicles as part of the chest compressions. The accelerometer measures acceleration relative to the ground, and it can be relatively difficult for the accelerometer to separate the compression motion from that of the vehicle. Using an external reference sensor can easily eliminate the motion caused by a vehicle. For example, the reference sensor can be located inside the vehicle or in the moving environment, and all measurements can be taken by the position sensors relative to the reference sensor.Thus, any movement detected by both the reference sensor and the position sensors can be effectively ignored or taken into account by the system.

[0085] Beyond transporting a patient by vehicle, other mobile environments are possible. For example, a patient can be transported on a stretcher, a gurney, or a backboard. As in Fig. As shown in Figure 24, the reference sensor can be arranged on or in the back panel 38. The position sensor can be connected to the back panel via a connector 39, and the feedback 40 can be supplied to the position sensor's cushion mount.

[0086] The orientation of the position sensor can be determined using calculations disclosed in US patent US 4,314,251 A, the disclosure of which is included here in its entirety by reference. As in Fig. As shown in Figure 25, the roll 41, pitch 42, and yaw 43 can be used to determine the three-dimensional configuration of the position sensor. During CPR, the initial configuration and orientation of the position sensor relative to the patient's chest can be known. If the position sensor is mounted in a disc or cushion 6 placed on the patient's chest, the axes 15 or other markings on the position sensor mount can indicate the correct orientation of the system. The inclination of the position sensor can then be calculated and included in the depth calculation. If the position sensor is unevenly positioned on the chest, the orientation angles can be used to correct the depth calculation. Furthermore, the calculated angles can be used to rotate the reference system for the position sensor.For example, the position information can be rotated into the reference system of the position sensor to simplify calculations and improve accuracy.

[0087] CPR is physically demanding, and fatigue often sets in soon after chest compressions begin. Inefficient technique and improper physical condition can lead to faster onset of fatigue and pain associated with prolonged CPR. When delivering compressions, the user should be positioned as described in... Fig. 26 showed his shoulders 44 positioned directly above the patient's body, with his arms 45 extended, straight and perpendicular to the patient's ribcage. As in Fig. As shown in Figure 27, the system can be used to monitor the angle 46 of chest compressions by incorporating the position sensor into a wearable embodiment of the system. The position sensor can, for example, be incorporated into a wristband or glove that positions the sensor on the user's wrist. The roll, pitch, and yaw angles can be used to determine the relative orientation of the user's arm. The user can then be prompted to adjust their arm angle 46 to maximize force transmission during CPR and reduce user fatigue. To reduce distortion and error in angle measurement, the wearable system can include a curved sensor 47 that changes its resistance with the degree of bending. The sensor can be used to measure the flexion of the user's wrist.This data can be correlated with field data to improve accuracy. The curved sensor serves a similar function for angle as the force or pressure sensor does for depth.

[0088] To improve positional accuracy and correct distortion and / or noise, various methods can be used to combine different sensors with the field detector and field generator. The system can also be combined with other sensors. As previously described, accelerometers can be used to detect external motion, such as the movement of the base unit or reference sensor during CPR. An accelerometer can also be used to verify the data acquired by the field detectors and eliminate sources of metal distortion. Additionally, the system can be combined with pulse oximetry to monitor blood flow through the patient and correlate this blood flow with field data for increased accuracy. For example, the reference sensor can be used as described in Fig. 28 shown to be integrated into a pulse oximetry unit 48 on the finger or forehead of the patient.

[0089] Furthermore, the system can include chest impedance measurements. Chest impedance 49 can be used to measure the impedance between two electrodes, such as those in Fig. The defibrillator pads shown in Figure 29 are designed to detect movement of the patient's chest. The chest impedance measurements can serve a similar function to the force sensor measurements in the present system. The chest impedance measurements can be correlated with field data to improve accuracy and eliminate sources of distortion from the measurements. Furthermore, the field data can be used to calculate calibration constants for the chest impedance measurements, correlating chest impedance with compression depth. In this way, chest impedance can be used for depth data if the reference sensor moves during the application of chest compressions or if the system is used in a highly distorted environment.Since many defibrillators already have integrated chest impedance measurements, the field data can be easily adjusted to transform the impedance data into more useful and accurate parameters.

[0090] The system disclosed herein can be adapted for different patients. Since the position sensor, which is positioned on the patient's chest, can be manufactured to be very small and lightweight, it can be designed for use on a child or an adult. For example, the position sensor can be incorporated into a detachable mount 51 for adult CPR, as described in Fig. The 30 shown are arranged as shown. The mount can provide a larger surface area and be configured for two-handed CPR. If the orientation sensor is removed, it can be smaller and better suited for two-finger CPR on a child.

[0091] The system disclosed herein can be implemented in a number of embodiments, and feedback can be transmitted to the user in various forms via a feedback component (e.g., screen, speaker, light, buzzer, etc.). The feedback can be, for example, audible, visual, or both. The feedback can be displayed on an LCD in the base unit. As in Fig. As shown in Figure 31, the feedback can also be integrated into the position sensor cushion 6 itself. The feedback on the cushion can be a display or can take the form of an LED graphic 52. The audio feedback can be provided via a speaker in the base or in the position sensor cushion. The audio feedback can take the form of voice prompts and / or a pacemaker metronome.

[0092] Beyond the CPR prompt, further information can be transmitted to the user. For example, the system can detect that the distance between the position sensor and the reference sensor is outside the operating range. As in Fig. As shown in Figure 32, in this scenario the system can prompt the user 53 to move the base unit containing the reference sensor closer to the position sensor.

[0093] The embodiments described above in this disclosure are intended to be examples only. The disclosure may be amended, modified, and altered without deviating from its intended scope. In particular, selected features from one or more of the embodiments described above may be combined to create alternative embodiments not explicitly described. All values ​​and sub-areas within disclosed areas are also disclosed. The subject matter described herein is intended to encompass and include all suitable modifications of the technology. All references cited are included here in their entirety.

Claims

[1] System for determining the depth of compression of a patient's chest (3) receiving chest compressions, the system comprising: a field generator configured to generate a field (5); a field detector (16, 17) comprising at least two coils at a fixed distance (26) from each other, each of the at least two coils having a turn parallel to the turn of the other coil, and each of the at least two coils having a center, wherein the corresponding centers of the at least two coils are aligned along a longitudinal axis (19) perpendicular to a plane (11) of the turns of each of the two coils, wherein the field detector (16, 17) is configured to generate a response signal indicating that any one of the at least two coils is detecting the field (5); and a processor designed to determine position information for the field detector (16, 17) relative to the field generator from the response signal and to determine the chest compression depth from the determined position information; wherein the field generator or field detector (16, 17) is a position sensor (2) configured to move in accordance with the chest while the chest receives the compressions, wherein the other of the field generator and field detector is a reference sensor (4) configured to be stationary relative to the patient (3). [2] System according to claim 1, wherein the longitudinal axis (19) is substantially parallel to one direction of the chest compressions. [3] System according to claim 1, wherein the field generator is coupled to the field detector (16, 17) via a wire. [4] System according to claim 1, wherein the field generator is wirelessly coupled to the field detector (16, 17). [5] System according to claim 1, wherein the chest compression depth is calculated by forming a plane (11) in space which is substantially perpendicular to a direction of the chest compression depth. [6] System according to claim 1, wherein the field detector (16, 17) is the position sensor (2) and the field generator is the reference sensor (4). [7] System according to claim 1, wherein the position sensor (2) is portable. [8] System according to claim 1, further comprising an accelerometer provided at the reference sensor (4). [9] System according to claim 1, wherein coordinates of the position information are manipulated with respect to a reference system of the position sensor (2). [10] System according to claim 9, wherein the chest compression depth is calculated by determining the distance (26) from an initial position coordinate of the chest compression to an end position coordinate of the chest compression, wherein the end position coordinate corresponds to an end depth of the chest compression. [11] System according to claim 1, wherein the field generator is configured to be arranged on the chest of the patient (3) and the field detector (16, 17) is configured to be stationary relative to the patient (3). [12] System according to claim 11, wherein the position information is in a reference system of the field generator and the chest compression depth is calculated by determining the distance (26) from an initial position coordinate of the chest compression to an end position coordinate of the chest compression, wherein the end position coordinate corresponds to an end depth of the chest compression. [13] System according to claim 1, further comprising a receptacle in which the position sensor (2) is detachably contained. [14] System according to claim 13, wherein the releasable receptacle is releasable to perform CPR on a child. [15] System according to claim 1, wherein the system comprises a feedback component for providing feedback to a CPR administrator based on the specified position information and / or the specified chest compression depth. [16] System according to claim 15, wherein the feedback includes at least visible, audible and tactile prompts. [17] Field detector (16, 17) for determining the depth of compression of the chest of a patient (3) receiving chest compressions, the detector comprising: at least two coils at a fixed distance (26) from each other; each of the at least two coils includes a turn which is substantially parallel to the turn of the other of the at least two coils and each of the at least two coils has a center, wherein the corresponding centers of the at least two coils are aligned along a longitudinal axis (19) which is perpendicular to a plane (11) of the turns of each of the two coils;wherein the detector is configured to generate a response signal indicating position information of any one of the at least two coils detecting a field (5) generated remotely from the detector, and wherein the detector is further configured to determine the compression depth of the patient's chest (3) based at least partially on the position information. [18] Detector according to claim 17, wherein the longitudinal axis (19) is substantially parallel to one direction of the chest compressions. [19] Detector according to claim 17, further comprising a wire for coupling to a field generator. [20] Detector according to claim 17, wherein the detector is further configured for wireless coupling with a field generator.

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