Infrasonic stethoscope for monitoring physiological processes
Inventors
Shams, Qamar A. • Zuckerwar, Allan J. • Dimarcantonio, Albert L.
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-10092269-B2
Publication Date
2018-10-09
Expiration Date
2035-03-16
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Abstract
An infrasonic stethoscope for monitoring physiological processes of a patient includes a microphone capable of detecting acoustic signals in the audible frequency bandwidth and in the infrasonic bandwidth (0.03 to 1000 Hertz), a body coupler attached to the body at a first opening in the microphone, a flexible tube attached to the body at a second opening in the microphone, and an earpiece attached to the flexible tube. The body coupler is capable of engagement with a patient to transmit sounds from the person, to the microphone and then to the earpiece.
Core Innovation
The invention provides an infrasonic stethoscope, termed an "infrascope," capable of detecting acoustic signals across a bandwidth that includes both audible frequencies and infrasonic frequencies ranging from 0.03 Hertz to 1000 Hertz. The infrascope comprises a microphone with a body having two spaced apart openings, a body coupler connected to the first opening to engage the patient for transmitting sounds, a flexible tube attached at the second opening, and an earpiece at the tube's end for real-time audio detection. This configuration allows for monitoring physiological processes by capturing acoustic signals including those inaudible to the human ear.
The problem addressed by the invention is the limitation of conventional stethoscopes and microphones which only detect audible frequency bandwidths and are unable to monitor infrasonic frequencies below 20 Hertz, which are valuable in providing physicians with enhanced understanding of heart performance and other physiological conditions. Traditional heart sound monitoring methods, such as phonocardiography, are limited in capturing low frequency, low intensity heart sounds that fall within the infrasonic range and can carry crucial diagnostic information.
The infrasonic stethoscope addresses issues arising from attenuation of acoustic signals in human tissues which particularly affects high-frequency waves, limiting tissue penetration. Since more than 60% of heart signal power spectral density is in the infrasonic band, capturing these low-frequency signals provides valuable insights. The invention also resolves challenges in fetal heart monitoring where conventional ultrasound monitoring suffers from signal attenuation due to absorption and scattering through maternal tissues. By using the infrascope with low attenuation infrasonic signals, better quality and signal-to-noise ratio is achieved.
Claims Coverage
The patent includes two independent claims covering both the microphone for use in an infrascope and methods of using the microphone for physiological monitoring. There are eight main inventive features identified from these claims.
Microphone capable of detecting infrasonic and audible acoustic signals
The microphone is capable of detecting acoustic signals in a frequency range of 0.03 Hertz to 1000 Hertz, covering both audible and infrasonic bandwidths for physiological process monitoring.
Microphone construction with body, capacitive elements, and sealed body coupler
The microphone has a body with proximal and distal ends and an aperture at the distal end sealed by a body coupler that engages the patient. Internally, it includes a conductive backplate and conductive membrane spaced to form a capacitor, a flexible diaphragm in the body coupler spaced from the membrane to transmit acoustic energy, and a preamplifier board connected to measure capacitance changes and convert signals to voltage.
Acoustic damping and airflow design within the microphone
The microphone includes design features such as conductive support plates with apertures for airflow between chambers, holes and slots in the backplate and surrounding parts to provide sufficient acoustic resistance and critical damping of membrane motion, lowering low frequency thresholds and ensuring flat frequency response.
Integration of electrical connections and digitization for wireless signal transmission
The microphone has sealed electrical connections for interfacing with external electronics, including a remote digitizer board that converts voltage signals to digital data and enables wireless or wired transmission to remote workstations for real-time monitoring and analysis.
Methods of positioning and using one or two microphones for physiological signal detection
Methods include positioning a single or two microphones at one or more locations within a patient's body for detecting sound pressure and generating physiological process signals within the infrasonic to audible frequency range for monitoring, with signals transmittable in real time or to remote locations.
Applications in specialized physiological monitoring and identification
The microphone is used in stress phonocardiography tests, fetal heart monitoring during pregnancy and delivery, Doppler phonocardiography, biometric identification via heartbeat signatures, and polygraphs measuring cardiovascular and respiratory responses.
Spectrogram generation and respiratory, cardiac, fetal heart monitoring capabilities
Using the microphone, spectrograms can be generated for visualization and monitoring of respiratory, cardiac, or fetal heart physiological processes, enhancing diagnostic capabilities.
Air passages disposed at different microphone levels for airflow management
The microphone includes air passages at different levels from the distal to proximal ends of the body to control airflow, contributing to acoustic damping and low frequency detection performance.
Together, these inventive features define a microphone and system optimized for sensitive detection of physiological acoustic signals in both audible and infrasonic ranges, with specific structural designs to enhance damping, acoustic resistance, and signal transmission, as well as methods for practical physiological monitoring applications.
Stated Advantages
Enables detection and monitoring of both audible and infrasonic physiological acoustic signals including very low frequency heart sounds not perceptible by human ears.
Provides better tissue penetration and higher signal-to-noise ratio due to low attenuation of infrasonic signals compared to high frequency signals.
Supports multiple applications such as cardiac monitoring, fetal heart monitoring, stress phonocardiography, Doppler phonocardiography, biometric identification, and polygraph testing.
Facilitates real-time wireless transmission of physiological data to remote locations, enabling remote diagnosis and monitoring including in ambulances.
Relatively inexpensive tool for early diagnosis and improved understanding of heart and respiratory conditions.
Documented Applications
Cardiac monitoring including detection of normal and abnormal heart sounds.
External and internal fetal heart monitoring during pregnancy, labor, and delivery.
Stress phonocardiography test for detecting heart problems manifesting during physical activity.
Doppler phonocardiography for measuring blood flow and left ventricular filling pressure non-invasively.
Biometric identification based on heartbeat acoustic signatures.
Use in polygraphs to monitor cardiovascular, electrodermal, and respiratory physiological responses.
Real-time physiological signal monitoring with transmission to remote computers, smartphones, or tablets.
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