Abstract:
A non-invasive motion and respiration monitor receives impulses from a subject&#39;s movement, heartbeat, and respiration. The raw signal is biased and digitized, and a signal processor applies a Fast Fourier Transform to the signal. The transformed signal is filtered to isolate the component representing heart rate from the component representing respiration. An Inverse Fast Fourier Transform is then applied to the component signals, which are sent to a processor. The processor is programmed to detect irregularities in the respiration and heart rate. If severe irregularities or complete cessation is detected in either signal, a mechanical stimulator is actuated to try to stimulate the subject, and an alarm is sounded to alert a caregiver such as a parent or nurse.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/195,512, filed Oct. 8, 2008, titled “Noninvasive Movement and Respiration Monitor Utilizing Isolated Array, Analysis, and Alarm and Stimulation.” 
     
    
     BACKGROUND 
       [0002]    The invention relates to modular, age-scalable, FPGA-controlled, self-centering biasing signal, monitoring devices of cardiovascular and respiratory rhythms of patients and human subjects in general that is suitable for utilization on or incorporated into beds, lying-pads, furniture, vehicles and clothing. Among other applications, the invention enables what can be termed as smart-beds that will also be of interest to hospitals and emergency response vehicles. The device can be used to detect and monitor medical conditions such as SIDS, epilepsy, seizure, and sleep apnea. The self-centering biasing function of the invention described herein eliminates the need to manually reset the monitoring device. In one specific utilization, this invention can be employed for monitoring the respiratory function of infants in slumber, sleeping individuals and patients in health care facilities. For illustration purposes, the rest of the description contained herein will focus on infants in slumber. 
         [0003]    Sudden Infant Death Syndrome (SIDS) is the leading cause of death among infants who are one month to one year old, and claims the lives of about 2,500 infants each year in the United States alone. The instant invention offers parents around the globe the opportunity to save their child&#39;s life by immediately informing them that a problem exists, as well as triggering an auditory or physical intervention mechanism. Prompt notification reduces response time to seconds; thereby providing parents with the opportunity to take life saving measures. Because of the nature of this invention, this technology is of interest to parents, infant caretakers, health care facilities, retirement homes and medical personnel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a block diagram of an exemplary embodiment of a non-invasive monitoring system; 
           [0005]      FIG. 2  is a block diagram of an exemplary embodiment of a monitor unit for use with a monitoring system; 
           [0006]      FIG. 3  is a block diagram of an exemplary embodiment of a remote unit for use with a monitoring system; 
           [0007]      FIG. 4  is a block diagram of an exemplary embodiment of a sensor array for use with a monitoring system; and 
           [0008]      FIG. 5  is a block flow diagram of an exemplary process for monitoring a subject, carried out by a monitoring system. 
       
    
    
     SUMMARY OF THE INVENTION 
       [0009]    In one aspect, a non-invasive motion and respiration monitoring system receives impulses from a subject&#39;s movement, heartbeat, and respiration. The raw signal is biased and digitized, and a signal processor applies a Fast Fourier Transform to the signal. The transformed signal is filtered to isolate the component representing heart rate from the component representing respiration. An Inverse Fast Fourier Transform is then applied to the component signals, which are sent to a processor. The processor is programmed to detect irregularities in the respiration and heart rate. If severe irregularities or complete cessation is detected in either signal, a mechanical stimulator is actuated to try to stimulate the subject, and an alarm is sounded to alert a caregiver such as a parent or nurse. 
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0010]    A non-invasive motion and respiratory monitoring system monitors cardiovascular and respiratory rhythms of a human subject, for instance, a sleeping or resting child or adult without the use of cumbersome, intrusive or potentially hazardous wires attached to the subject. The respiration may be monitored and analyzed by laying the individual on a mat having transducers disposed thereon. If the breathing patterns and heart beat of the child or adult are detected, a signal indicating the respiratory motion and pulse is wirelessly transmitted through to a receiver. If breathing or the pulse stops or becomes erratic, an audio and/or visual system alerts caretakers or parents of the anomalous situation. The sleeping pad also incorporates a mechanical stimulator, such as a gentle vibration system, within the mat to stimulate the individual if it stops breathing; mimicking a technique utilized by hospital staff in similar situations. Such a monitoring system can therefore be used by parents, infant caretakers, health care facilities, retirement homes and medical personnel to mitigate reduce death or injury from causes such as sudden infant death syndrome (SIDS), sleep apnea, or other similar and possibly-preventable causes. 
         [0011]    In an exemplary embodiment, a monitor unit includes a sensor pad that can be placed on a mattress where a subject, such as a baby, is to sleep. The sensor pad may, for example, be placed beneath a fitted sheet, which will keep the sensor in placed and not substantially impair its sensitivity. A parent can then place the baby on the mattress for a nap and turn on both the monitor and a remote unit. Under normal conditions, the baby&#39;s normal respiration and heart beat patterns will be detected by the sensor pad, and the monitor will send an “OK” signal to the remote receiver unit. But if normal respiration or heart beat stops for a specified time, such as two seconds, the monitor will send an “ALERT” signal to the remote unit. The monitor may also actuate a stimulation aid, such as a gentle agitator or shrill alarm, intended to startle the baby awake and restart natural respiration and heart beat. The ALERT signal will also cause a shrill alarm to sound on the remote unit, alerting the parent to a problem. This gives the parent an opportunity to try to wake the baby and stimulate activity. In some embodiments, the remote unit may also enter an ALERT state if no OK signal is received from the monitor for a specified time period, such as 20 seconds. 
         [0012]    A non-invasive motion and respiration monitor will now be described with more particular reference to the attached drawings. Hereafter, details are set forth by way of example to facilitate discussion of the disclosed subject matter. It should be apparent to a person of ordinary skill in the field, however, that the disclosed embodiments are exemplary and not exhaustive of all possible embodiments. Throughout this disclosure, a hyphenated form of a reference numeral refers to a specific instance or example of an element and the un-hyphenated form of the reference numeral refers to the element generically or collectively. Thus, for example,  102 - 1  may refer to a “pen,” which may be an instance or example of the class of “writing implements.” Writing implements may be referred to collectively as “writing implements  102 ” and any one may be referred to generically as a “writing implement  102 .” 
         [0013]      FIG. 1  discloses a block diagram of an exemplary embodiment of a non-invasive monitoring system  100 . Monitoring system  100  includes a monitor unit  110  and a remote unit  130  that may be communicatively coupled, for example via wireless link  140 . Wireless link  140  may employ any of a number of protocols known in the art, such as radio frequency (RF), WiFi, microwave, or infrared (IR), by way of non-limiting example. Monitor Unit  110  interfaces with a monitoring point such as bed  120 . The disclosed configuration enables monitor unit  110  to monitor activity on bed  120  and communicate with remote unit  130  to indicate either normal respiration and heart activity (an OK condition), or an ALERT condition. 
         [0014]      FIG. 2  discloses a block diagram of an exemplary embodiment of monitor unit  110 . This embodiment includes a sensor array  210 , which may include, for example, an array of piezoelectric sensors such as the array disclosed in  FIG. 4 , or any other suitable impulse-sensitive transducer. Sensor array  210  provides sensitivity over a large surface area. In some embodiments, sensor array  210  may be provided as a single prepared pad constructed of a material selected to not substantially inhibit the sensitivity of the sensors, such as a plastic film. In other embodiments, sensor array  210  may include a pouch filled with a non-conductive fluid, which may translate motion to multiple individual sensors. 
         [0015]    Sensor array  210  provides time-domain analog signals to analog-to-digital converter (ADC)  220 , which may be one of many such devices known in the art. The purpose of ADC  220  is to receive an analog input signal and to provide a digital output signal. The output from ADC  220  is provided to signal processor  230 . In one embodiment, signal processor  230  is a field-programmable gate array (FPGA) programmed to provide suitable functions, such as the process described in  FIG. 5 . In other embodiments, signal processor  230  may be a processing device such as a microprocessor, microcontroller, digital signal processor, programmable logic array, or similar. Signal processor  230  is also communicatively coupled to a memory  270 , which may be a low-latency data medium such as cache or dynamic random access memory (DRAM), or a combination thereof. In some embodiments, memory  270  may be a volatile storage medium, in contrast to storage  260 , which may be a similar, but generally higher-latency non-volatile storage medium. 
         [0016]    Signal processor  230  is also connected to a mechanical stimulator  250 . Mechanical stimulator  250  may be configured, for example, to gently shake the subject being monitored, which may wake the subject or cause him or her to move, thus restarting the respiratory or heartbeat processes. In particular, if the subject is a baby or is prone to apnea, it&#39;s possible that he or she may have breathing blocked by a pillow, blanket, or other obstruction. The stimulator may awaken the subject and cause him or her to move away from the obstruction. 
         [0017]    Signal processor  230  is also connected to a transceiver  240 , which communicatively couples monitor unit  110  to remote unit  130 . Transceiver  240  contains the necessary hardware and software functions to implement wireless link  140 , thus enabling signal processor  230  to send signals such as OK or ALERT to remote unit  130 . In embodiments where auxiliary equipment is provided, transceiver  240  may also provide additional data, such as streamed audio or video data. 
         [0018]    In some embodiments, monitor unit  120  may also include auxiliary devices  290  such as a video camera or microphone configured to provide additional information, such as providing an audio or video feed to an observer operating remote unit  130 . In such cases, additional equipment for interfacing with auxiliary equipment, such as additional ADCs, signal processing functions, and compression algorithms may also be provided as necessary. As an additional convenience, a pressure switch  280  may also be provided. Pressure switch  280  may for example be configured to close when an infant is placed on the mattress, but not when lighter items such as bedding or stuff animals are present. When pressure switch  280  is open, signal processor  230  may enter an inactive state where it ceases to monitor for life signs, thus preventing false positives. For example, it may be annoying if a mother is required to turn monitoring system  100  off within two seconds each time she lifts the baby from its bed, or risk being annoyed by a shrill alarm. Similarly, if the mother must remember to activate monitoring system  100  each time she puts the baby down for a nap, she may occasionally forget, thus limiting the effectiveness of the system. With pressure switch  280 , the process of enabling and disabling active monitoring can be automated so that the human error element is mitigated. 
         [0019]      FIG. 3  is a block diagram of an exemplary embodiment of remote unit  130 . Remote unit  130  includes a transceiver  340  configured to communicatively couple remote unit  130  to monitor unit  110 . Processor  310  receives data from transceiver  340 , including, for example, OK and/or ALERT signals. Processor  310  is also communicatively coupled to a memory  320  and storage  340 . These are functionally similar to memory  270  and storage  260  of  FIG. 2 . Also note that many divisions of processing tasks between processor  310  and signal processor  230  ( FIG. 2 ) are possible without departing from the spirit or scope of the present invention. For example, signal processor  230  may be limited to filtering and transforming digital signals, which may then be sent to processor  310 , which in this example would be responsible for providing algorithms to detect irregularities and making decisions on whether to operate in the OK state or ALERT state. In other embodiments, such decision-making algorithms could be provided locally on signal processor  230 , which would then be responsible for sending data packets including OK and/or ALERT signals to remote unit  130 . In this example, processor  310  of remote unit  130  would simply act on the signal received from signal processor  230  of remote unit  120 . For example, processor  310  would take no further action as long as OK signals are regularly received. But in the event that an ALERT signal is received, or that an OK signal is not received for a particular time span, which may for example vary in the range from 5 to 30 seconds, and which may preferably be one of 5, 10, 15, 20, 25, or 30 seconds, then processor  310  may default to an ALERT state. When an ALERT state is entered, processor  310  may activate elements of display  360 , such as an audio or video feed, warning LEDs, or other indicators. Processor  310  may also activate alarm  370 , which may be a shrill alarm, similar to a fire alarm, configured to command immediate attention. 
         [0020]    In the exemplary embodiment, as long as remote unit  130  is operating in the OK state, either no action is taken, or auxiliary actions such as providing an audio or video stream to a display  360  may be performed. 
         [0021]      FIG. 4  is a diagrammatic drawing of sensor array  210 . In this exemplary embodiment, sensors  410  may be, for example, piezoelectric sensors such as APS4812B-LW100-R piezoelectric transducers produced by PUI Audio (a division of Products Unlimited). Those having skill in the art will recognize that other impulse-sensitive transducers could also be used. In the disclosed embodiment, sensors  410  are arranged in an array and connected in series, with a total voltage drop of 3.3V across the array. A probe point  480  is also connected between sensor  410 - 4  and sensor  410 - 6 . This probe point is biased to a self-centering voltage of approximately 1.65V by a voltage divider formed by resistors  440 - 1  and  440 - 2 , which in the preferred embodiment are both selected to be 3.7 MΩ. 
         [0022]      FIG. 5  is a block diagram of an exemplary process for filtering and detecting a heart rate and respiratory rate. For purposes of discussion, the following description will assume that the process is performed entirely on signal processor  230 . But note that the process of  FIG. 5  may be performed by signal processor  230  of monitor unit  110 , processor  310  of remote unit  130 , or tasks may be divided between the two devices without affecting the viability of the process. In the exemplary embodiment, ADC  220  receives a time-domain analog signal from sensor array  210  in block  510 . In block  520 , ADC  220  converts the analog signal to a time-domain digital waveform, which it provides to signal processor  230 . Signal processor  230  performs a Fast Fourier Transform (FFT) on the digitized signal in block  530  to provide a frequency-domain signal, and in block  540  runs the frequency-domain signal through a pair of bandpass filters. In block  550 , the first bandpass filter passes frequencies in the range of 0.4 Hz to 0.98 Hz to isolate the portion of the signal representing a respiratory pattern. In block  560 , the second bandpass filter passes frequencies in the range from 0.98 Hz to 2.54 Hz to isolate the portion of the signal representing a heart rate. In blocks  570 - 1  and  570 - 2 , an inverse Fast Fourier Transform (IFFT) is performed on each frequency-domain signal, resulting in two separate time-domain signals, one representing respiration in block  580 , and one representing heart rate in  590 . 
         [0023]    With the signals thus isolated, problems can be detected in as little as two seconds. For example, if the heart rate signal goes flat for two full seconds, this may represent between two and five heart beats missed completely. As missing two to five heart beats can be considered anomalous, monitoring system  100  can enter an ALERT state after  2  seconds with a reduced probability of a false positive. Similarly, if the respiratory signal is flat for a full two seconds, this may represent between one and two breath cycles completely missed. As a normally sleeping baby will not hold its breath for one to two full breathing cycles, this can also be considered an anomalous result, causing monitoring system  100  to enter an ALERT state. Furthermore, if the heart rate or respiration pattern becomes excessively fast and/or shallow, the signal will not pass bandpass filter  540 , so that the anomalous result will still be detected. 
         [0024]    The occurrence of false positives will vary inversely with the time span selected to represent an anomalous condition. For example, if signal processor  230  waits for five seconds before entering an ALERT state, this may represent between 5 and 13 missed heart beats and between 2 and 5 missed breaths, or alternatively five seconds of irregularly fast respiration and/or heart rate. This is more likely to be an anomalous condition than at two seconds, but also spends an additional three seconds of precious response time. Similarly, at intervals of 10, 15, and 20 seconds, the likelihood of a false positive drops dramatically with the increased time, but time for a parent or care giver to appropriately respond and render aid is increasingly impinged on. In an alternative embodiment, responses to timer intervals can be gradated, so that an increased response can be provided in response to an increased likelihood of a problem. In this embodiment, monitoring system  100  will provide more than just a binary OK/ALERT state. Instead, the OK state may be followed by a number of ALERT grades, such as ALERT 0 , ALERT 1 , ALERT 2 , etc. For example, the ALERT 0  stage may be triggered after two seconds. In response to ALERT 0 , signal processor  230  may gently actuate mechanical stimulator  250  to try to agitate the subject just enough to get a response. If the signal remains flat for an additional 3 seconds, monitoring system may enter ALERT 1  state, and in response more aggressively actuate mechanical stimulator  250 , as well as light an indicator such as an LED on display  360  of remote unit  130 . If no response is received for an additional 2 to 5 seconds, monitoring system  100  may enter an ALERT 2  state, and in response continue to aggressively actuate mechanical stimulator  250 , as well as sound a shrill audible alarm such as alarm  370 . 
         [0025]    In use, the mat containing sensor array  210  monitoring system  100  is placed on a sleeping surface such as bed  120 , e.g., a foam mat or mattress, and the mat is covered with either a sheet or additional foam material for comfort. Alternatively, however, sensor array  210  can be integrated into a mattress of bed  120 . The electronics are preferably placed outside of the sleeping area, and all wires connecting the transducer electronics and power supplies are secured via e.g., Velcro, to a surface out of the reach of the child/adult to avoid any strangulation risks. 
         [0026]    Once sensor array  210  and necessary electronics are in place, a child or adult lays on bed  120  and monitoring system  100  either is automatically powered on, or is turned on by a caregiver. 
         [0027]    While the child or adult is lying on bed  120 , the monitoring device of the instant invention is constantly monitoring the heart beat and respiratory rate of the child or adult. If the respiratory rate or hear beat becomes erratic or stops, remote unit  130  issues an audio and/or visual alarm to the caregiver so that life saving measures can be administered to the child or adult. 
         [0028]    As one skilled in the art will appreciate, several modifications can be made to the above embodiment and such modifications are included within the scope of this disclosure. For example, transceiver  240  of monitor unit  110  could be a one-directional transmitter, while transceiver  340  or remote unit  130  could be a one-directional receiver. With bi-directional communication, however, additional features can be provided, such as allowing a care giver to request an audio or video feed, or manually control mechanical stimulator  250  in the case of SIDS. Remote unit  130  could also receive telemetric data such power status for the transducer array. Additionally, the memory  270  may store multiple life signals for a particular child or adult for wired or wireless upload to a physician computer or hospital network. Also, signal processor  230  and processor  310  may be capable of being reprogrammed or written with multiple programs that a user can toggle between depending upon application. In other words, the monitoring device could be capable of monitoring SIDs, seizure activity and apnea. Furthermore, while heart rate and respiration are disclosed as exemplary embodiments of possible bio-indicators to monitor, those having skill in the art will recognize that other pass bands could be used to isolate and monitor additional bio-indicators. 
         [0029]    While the subject of this specification has been described in connection with one or more exemplary embodiments, it is not intended to limit the claims to the particular forms set forth. On the contrary, the appended claims are intended to cover such alternatives, modifications and equivalents as may be included within their spirit and scope.