Patent Publication Number: US-2016242730-A1

Title: Physiological monitoring device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. Provisional Application No. 62/119,732, filed Feb. 23, 2015, the entirety of which is incorporated by reference herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a physiological monitoring device according to an embodiment of the invention. 
       FIG. 2  is a perspective view of a sensor chamber according to an embodiment of the invention. 
       FIG. 3  is a block diagram of a circuit according to an embodiment of the invention. 
       FIG. 4  is an OPAMP circuit diagram according to an embodiment of the invention. 
       FIG. 5  is a microcontroller circuit diagram according to an embodiment of the invention. 
       FIG. 6  is a wireless transmitter circuit diagram according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS 
     Noninvasive, convenient, and low cost systems and methods for acoustic monitoring of fetal and maternal heart beats during pregnancy are described herein. An example monitoring device may use purely passive sensing modalities and, as such, may be completely safe and may be different from various sonar-based fetal monitoring devices. 
     The example system may include one or several acoustic sensor modules containing microphones whose signals may be amplified and conditioned using an electronic network before being sampled by a microcontroller that may subsequently transmit these raw signals over wireless communication channels to a smartphone, tablet device, or other computer which may include special-purpose hardware, firmware, and/or software for subsequent data analysis and algorithms. 
     The sensor modules may contain one or more microphones (e.g., an electret or MEMS microphone) and/or other sensors housed within an enclosure that may be optimized for mechanical amplification of cardiac or abdominal acoustic emissions. During use, this module may be held against the abdomen or upper pubis of the subject. The enclosure may be cylindrical in shape or may assume the shape of a parabolic, elliptical, or cone-shaped acoustic amplifier horn, for example. The surface of the sensor module that is configured to contact the abdomen may be sealed (e.g., with a polymer, rubber, or latex material) to create an airtight chamber within which the microphone is housed. In addition to the microphone, the sensor module may house one or more circuits. For example, the sensor module may house a printed circuit board (PCB) which may include an operational amplifier (OPAMP) or other analog signal conditioning network, a microcontroller unit, a USB or other charging and/or data port, a Bluetooth radio and/or other wireless device, a battery or other power supply, and/or other hardware. The hardware may provide a built-in analog band pass filter to enhance dynamic range, provide desirable performance, and limit requirements for external data acquisition and/or transmission systems. 
     Signal processing hardware, firmware, and/or software may be hosted on a remote device such as a tablet or smartphone running either and Android or iOS operating system, for example. These elements may use algorithms to improve the signal to noise ratio (SNR) of the captured signal, compute maternal and fetal heart rates, isolate maternal and fetal heart sounds, reconstruct acoustic signals of the mother and fetus, and/or provide high quality audio files for recording, playback, and/or sharing via a software application. The signal processing may discriminate and extract fetal heart sound from other sounds such as ambient noise, maternal heartbeat sound, digestive motility sound, peristaltic sound, and/or other sounds. The signal may be extracted even with uncertain sensor coupling, sensor location, and/or signal characteristics. 
     The physical monitoring device may be a hand-held apparatus including one or several sensor modules containing electret or MEMS microphones, a signal conditioning network that performs amplification and anti-aliasing, a microcontroller device that samples the conditioned signal, and/or a Bluetooth radio module that transmits acquired data to a backend smartphone or tablet device. Other components may include a Lithium-ion charger with rubber protective seal, Lithium polymer battery, rubber seal for water resistance, a plastic baseboard to prevent penetration of the neoprene seal, and other electronic components to complete the printed circuit board assembly. Those of ordinary skill in the art will appreciate that other components may be used in other embodiments (e.g., other sensor types, other controllers, other wireless or wired transmitters, other power supplies, other module components, etc.). 
     Each microphone may be contained in an airtight enclosure optimized for mechanical amplification of acoustic and pressure signatures associated with fetal and maternal heart activity. For example,  FIG. 1  is a cross-sectional view of a physiological monitoring device  100  according to an embodiment of the invention. The device  100  may include a nearly airtight sensor chamber  110  defined by a membrane  101 , walls  102 , and an electronic printed circuit board (PCB)  104 . The membrane  101  may be made of elastomer material in some embodiments, and the walls  102  may be plastic in some embodiments, but other materials may be used. PCB  104  may be impermeable to air except for a small hole  105  (which may be approximately 0.6 mm in diameter in some embodiments, for example) which may allow for venting of pressure from the chamber  110 . The sensor chamber  110  may be entirely airtight except for this feature. The hole  105  may allow for venting of low-frequency pressure changes due to modulation of application pressure or other disturbances. This may reduce the gain of the system at low frequencies that may not contain fetal heartbeat sounds without affecting the sensitivity of the system at higher frequencies. Accordingly, the sensor chamber  110  may serve as a mechanical high pass filter removing inputs with frequencies lower than approximately 20 Hz, for example. 
     A microphone  106  may be mounted on the top of the PCB  104  aiming downward towards the sensor chamber  110 , and a hole in the PCB  104  covered by the microphone  106  may allow acoustic energy to pass through to the microphone  106 . The interface between the microphone  106  and the PCB  104  may be formed by a two-sided adhesive and may be airtight. Similarly, the PCB  104  may be attached to the walls  102  in an airtight fashion using a two-sided adhesive. Other adhesives, such as epoxy or cyanoacrylate, may be used in some embodiments. 
     A protective grid  103  may be provided to protect the membrane  101  from excessive deflection as well as to prevent the user from contacting any electronic elements as a safety feature. The grid  103  may be made from the same material as the walls  102  in some embodiments (e.g., ABS or other plastic). The grid  103  may be curved inward in some embodiments as shown in  FIG. 1 . This may allow the membrane  101  to deform inward when pressed against a user&#39;s skin to prevent or reduce user discomfort. 
     The sensor chamber  110  may be mounted inside an exterior chamber  107 . This chamber  107  may include one or more vents  108  and is thereby not airtight, allowing for pressure vented from the sensor chamber  110  to escape the device  100  and thereby equilibrate quickly. However, even if a user accidentally covers these vents, the larger volume of the exterior chamber  107  relative to the sensor chamber  110  may allow for effective venting of pressure from the sensor chamber  110  until the vents  108  are uncovered by the user. 
       FIG. 2  is a perspective view of a sensor chamber  110  according to an embodiment of the invention. For example, the sensor chamber  110  may be a plastic cylindrical tube with internal diameter of approximately 32 mm and height of approximately 22 mm, although other enclosures having different internal volumes may be used in some embodiments. The shape of the enclosure may be chosen to minimize ambient noise registered by the microphone while maximizing amplification of the microphone. 
     The membrane  101  may be made of a latex or other elastomer material such as neoprene with an elastomer coating, for example. Other example materials may include santoprene or silicone. Neoprene, santoprene, or silicone may provide a flexible enclosure, and the elastomer coating may strengthen the neoprene, santoprene, or silicone and provide a shiny surface for the enclosure. The latex or other elastomer material may be designed to provide improved impedance matching with human tissue and may be flexible enough to conform to the contours of the user&#39;s skin, thereby enhancing transfer of acoustic signals into the sensor chamber  110 . 
       FIG. 3  is a block diagram of a circuit  200  according to an embodiment of the invention. The circuit  200  may be formed entirely, or in part, on the PCB  104 . The circuit  200  may include the microphone  106 , an OPAMP  210 , a microcontroller unit  202 , a USB or other charging and/or data port  203 , a Bluetooth radio and/or other wireless transmitter or transceiver  204 , a battery or other power supply  205 , and/or other hardware. The circuit  200  may perform processing associated with capturing signals from the microphone  106  and sending data to a remote device (e.g., via the data port  203  and/or wireless transmitter  204 ). 
     For example, because the acoustic emissions associated with fetal heart events are characterized by very low amplitude, signals captured by the microphone  106  may be amplified and/or conditioned. To this end, the OPAMP  210  may be used to provide gain and anti-aliasing capabilities. To avoid saturation, a relatively low gain (e.g., 20 dB) may be used. The OPAMP  210  used may be chosen to optimize other amplifier parameters such as high-pass and anti-alias filters.  FIG. 4  is an OPAMP circuit  300  diagram according to an embodiment of the invention, including the OPAMP  210  and related circuit elements. The OPAMP circuit  300  may include a multi-stage analog amplifier with band pass filtering. The OPAMP circuit  300  may reach an overall gain of about 20 dB at around 40 Hz, resulting in the amplification of input heart beat signal. The frequency response may be such that the signal rolls off on the low end (˜15 Hz), followed by a sharp increase in gain peaking at about 40 Hz. As the frequency of input signal increases, the OPAMP circuit  300  may filter off higher frequencies to dampen signals to about 40 dB below the peak gain value, producing a narrow frequency response that may condition fetal heart beat signals and reject other frequencies/noises. 
     The amplified and conditioned analog signal may be sampled by the microcontroller  202  through the microcontroller&#39;s onboard analog to digital converter (ADC) capabilities. For example, the microcontroller  202  may be an MSP43012021 from Texas Instruments or a RFDUINO (nRF51822) from Nordic Semiconductor. In some cases, the microcontroller  202  may include a wireless transmitter  204 . For example, the nRF51822 features a 32-bit ARM Cortex M0 core integrated with a Bluetooth Smart® radio device (i.e., wireless transmitter  204 ). In other cases (e.g., when the MSP43012021 is used), the wireless transmitter  204  may be a standalone element, such as an LBCA2HNZYZ certified BLE radio module from Murata Electronics.  FIG. 5  is a microcontroller circuit  202  diagram according to an embodiment of the invention, illustrating how an MSP43012021 may be configured to function within the circuit  200 .  FIG. 6  is a wireless transmitter  204  circuit diagram according to an embodiment of the invention, illustrating how an LBCA2HNZYZ may be configured to function within the circuit  200 . 
     The microcontroller  202  may sample the amplified microphone signal (e.g., at a rate of 1-2 kHz) and temporarily store data in buffers before transmitting it at time intervals (e.g., roughly 50 mS) via the wireless transmitter  204 . This relatively low sample rate may be capable of accurately capturing heart sounds, which are characterized by low frequencies typically below 200 Hz. Other microcontrollers  202  may be used in other embodiments and may perform similar functions. 
     The microcontroller  202  may perform housekeeping tasks, such as continuously monitoring or periodically checking inputs and performing appropriate operations in response to user inputs. The microcontroller  202  may be able to detect when a USB is plugged in for battery recharging purposes. The microcontroller  202  may also measure system battery health and communicate battery health data to a remote device via the wireless transmitter  204 , for example. Via the separate OPAMP analog measurement circuit  300  and a built-in ADC, the microcontroller  202  may determine the system battery status and communicate the system battery status to a remote device via wireless transmitter  204 . Other power management circuitry may include LDO voltage regulators to regulate system power and an analog comparator/PFET circuit that may cut off the main power to the system when a low battery is detected. A push button controller circuit may enable system activation and shutdown when a button press is detected for at least a pre-determined amount of time. A suitable battery charger IC may be used to charge the on board battery at a pre-determined rate upon plugging the device into a USB power source. 
     The wireless transmitter  204  may transmit this data to a remote processing device such as a such as a tablet or smartphone running an Android, iOS or other operating system. Known or proprietary signal processing algorithms may be hosted on the remote device. The algorithms may improve the signal to noise ratio (SNR) of the captured signal, compute maternal and fetal heart rates, isolate maternal and fetal heart sounds, reconstruct acoustic signals of the mother and fetus, and/or provide high quality audio files for recording, playback, and sharing via the software application. 
     While various embodiments have been described above, it should be understood that they have been presented by way of example and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope. In fact, after reading the above description, it will be apparent to one skilled in the relevant art(s) how to implement alternative embodiments. 
     In addition, it should be understood that any figures that highlight the functionality and advantages are presented for example purposes only. The disclosed methodologies and systems are each sufficiently flexible and configurable such that they may be utilized in ways other than that shown. 
     Although the term “at least one” may often be used in the specification, claims and drawings, the terms “a”, “an”, “the”, “said”, etc. also signify “at least one” or “the at least one” in the specification, claims, and drawings. 
     Finally, it is the applicant&#39;s intent that only claims that include the express language “means for” or “step for” be interpreted under 35 U.S.C. 112(f). Claims that do not expressly include the phrase “means for” or “step for” are not to be interpreted under 35 U.S.C. 112(f).