METHODOLOGICAL ASPECTS OF LUNG ACOUSTIC IMPEDANSOMETRY

Abstract

Background. The pandemic caused by a new coronavirus infection has determined the relevance of the development of non-invasive methods for express examination of the function of external respiration in the interests of medical diagnostics and development of personal protective equipment against infectious diseases transmitted by airborne droplets. Purpose. The purpose was to study the possibility of increasing the information content of diagnosing the state of the respiratory system by measuring the acoustic impedance using the modernized two-microphone method. Materials and methods. An experimental study of the impedance and biophysical characteristics of the lungs was carried out on groups of healthy (12 heads) and patients with pneumonia (7 heads) male rabbits weighing 2.5-3 kg. To study the acoustic characteristics of the lungs, a direct method of impedancemetry based on a two-microphone measurement technique was used; the determination of the biophysical parameters of the lungs is based on measuring their weight and volume. Results. The fact of an increase in active energy losses of low-frequency acoustic oscillations during their propagation in the respiratory system has been experimentally established, which makes it possible to create an informative criterion for diagnosing its condition. When examining healthy lungs using acoustic impedancemetry, the active energy loss of acoustic vibrations at low frequencies should not differ significantly from the corresponding values of the energy loss of such vibrations at the resonant frequency. In case of violations of the conductivity of the airways or in the presence of exudate in the lungs, active losses at low frequencies will significantly exceed losses at the resonant frequency: the worse the condition of the lungs, the higher the losses. It has been established that the presence in the lungs of a cavity with its own resonant frequency leads to a decrease in the resistance of the respiratory system at these frequencies. Conclusion. The experimentally recorded fact of a decrease in resistance at frequencies below the resonant frequency of the respiratory system makes it possible to explain the insufficient diagnostic information content of pulsed oscillometry. To increase the sensitivity and specificity of pulsed oscillometry, it is necessary not to limit the determination of acoustic indicators only at frequencies of 5 and 20 Hz, but to determine them in an extended frequency range with a more detailed step.

Keywords

• respiratory system
• respiratory function diagnostics
• respiratory system impedance
• pulse oscillometry
• two-microphone method
• impedance measurement
• resonant characteristics of the respiratory system
• lung biophysics
• acoustic impedancemetry