Monitoring the condition of divers during immersion is essential to ensuring their safety and planning permissible physical activity. Monitoring respiratory rates using a diver's respiratory sounds as parameters might be used for that purpose. This study was conducted with three types of diving apparatuses intended for civilian use: scuba, closed-circuit, and surface-supplied. Respiratory rates were investigated using wearable acoustic sensors installed in diving suit air cavities or remote hydrophones. The respiratory rate monitoring was also possible using a standard underwater voice communication system. Periodic breathing sounds are distinguishable in open-circuit scuba at a distance of 20 m, and a distance of 100–140 m with additional processing using wavelet transforms. The noise of inhalation and exhalation using closed-circuit breathing apparatus was monitored in the vicinity of the diver's respiratory tract. Respiratory sounds were distinguishable while using surface-supplied diving equipment (diver at the bottom, depth 8 m). The mean respiratory rate was 16.4 respiratory cycles per minute. The researchers could assess a diver's respiratory rate without invasive intervention in the breathing apparatus design. The data obtained were helpful for the remote monitoring of divers by the diving supervisor. Additionally, the data could be entered into a personal decompression computer for self-monitoring.

Forced expiratory (FE) noise is a powerful bioacoustic signal containing information on human lung biomechanics. FE noise is attributed to a broadband part and narrowband components—forced expiratory wheezes (FEWs). FE respiratory noise is composed by acoustic and hydrodynamic mechanisms. An origin of the most powerful mid-frequency FEWs (400–600 Hz) is associated with the 0th–3rd levels of bronchial tree in terms of Weibel [(2009). Swiss Med. Wkly. 139(27–28), 375–386], whereas high-frequency FEWs (above 600 Hz) are attributed to the 2nd–6th levels of bronchial tree. The laboratory prototype of the apparatus is developed, which includes the electret microphone sensor with stethoscope head, a laptop with external sound card, and specially developed software. An analysis of signals by the new method, including FE time in the range from 200 to 2000 Hz and band-pass durations and energies in the 200-Hz bands evaluation, is applied instead of FEWs direct measures. It is demonstrated experimentally that developed FE acoustic parameters correspond to basic indices of lung function evaluated by spirometry and body plethysmography and may be even more sensitive to some respiratory deviations. According to preliminary experimental results, the developed technique may be considered as a promising instrument for acoustic monitoring human lung function in extreme conditions, including diving and space flights. The developed technique eliminates the contact of the sensor with the human oral cavity, which is characteristic for spirometry and body plethysmography. It reduces the risk of respiratory cross-contamination, especially during outpatient and field examinations, and may be especially relevant in the context of the COVID-19 pandemic.

The features of respiratory noises and noises of fins for open-circuit scuba divers, indicating a multipole character of noises emission, are specified in cameral conditions. It demonstrates a possibility to detect low-frequency components of noises of fins with pressure gradient sensor in near field. A possibility of estimating the respiratory rate of an open-circuit scuba diver is demonstrated at distances up to 100 m in real sea. It gives an opportunity of estimating the bearing (time delay in a pair of hydrophones) for the open-circuit scuba diver by respiratory noises at distances up to 150 m in real sea. Thus, low-frequency underwater noises of open-circuit scuba divers may be successfully applied to monitor the safety of diving and to prevent waterside intrusion by trespassers.

Under normal conditions, breathing is reflexive, so it provides the necessary content of oxygen and carbon dioxide to the human body. However, elevated levels of partial oxygen, carbon dioxide and nitrogen pressure during underwater diving (considering the depth of diving, physical activity load, respiratory delays and changes in the inhaled gas density), require a conscious breathing control from the diver. Loss of breathing control can cause panic and/or loss of consciousness under water. The purpose of the paper is to study the possibility to control diver’s physiological state under water by in-situ breathing noises. Materials and Methods. The authors developed a method to record underwater breathing noises of a scuba diver. The method ensures the determination of the breathing rhythm without violating the integrity of the respiratory apparatus tract. They also proposed a method to separate the inspiration and expiration sounds, which allowed them to control the duration of respiratory phase ratio. Methods of analyzing heart rate variability were used to assess respiration rhythms. Results. During field experiments, it was shown that in case of a regular diving, the average respiratory rhythm of a diver was 9.3 respiratory movements per minute; inhalation/exhalation ratio was 1:2.5; mean square deviation – 1.4 s. In the case of an emergency, the average respiratory rhythm of a diver was 18 respiratory cycles per minute; the ratio of respiration phases was 1:1.3; variability – 1 s. Thus, in an emergency situation, the diver’s breathing was 2 times faster, exhalation shortened in regard to inspiration, and the breathing rhythm became less variable. Consequently, the acoustical physiological parameters of the respiratory rhythm, namely, its variability, inspiration/expiration ratio can indicate the diver’s state. Conclusion. The developed method allowed us to measure underwater parameters of the diver’s breathing rhythm and inspiration/expiration ratio without violating the integrity of the respiratory apparatus tract. Indication of the physiological respiration parameters can be implemented in the decompression computer of an underwater swimmer. Keywords: diver, monitoring, breathing noises, breathing rhythm, respiratory cycle, variability, voice recorder. В нормальных условиях дыхание осуществляется рефлекторно, обеспечивая необходимое содержание кислорода и двуокиси углерода в организме человека. Однако повышенные уровни парциального давления кислорода, двуокиси углерода и азота при подводном погружении с учетом глубины погружения, уровня физической нагрузки, наличия задержек дыхания и изменения плотности вдыхаемого газа требуют от водолаза сознательного контроля над дыханием. Утрата контроля над дыханием может стать причиной панических состояний и/или потери сознания под водой. Цель работы – исследование возможности контроля физиологического состояния водолаза под водой по шумам дыхания in situ. Материалы и методы. Разработан метод регистрации шумов дыхания водолаза-аквалангиста под водой, обеспечивающий определение ритма дыхания без нарушения целостности трактов дыхательного аппарата. Предложен способ разделения шумов вдоха и выдоха, который позволяет контролировать соотношение продолжительностей фаз дыхания. При оценке ритма дыхания применены методы анализа вариабельности частоты сердечных сокращений. Результаты. В ходе натурных экспериментов показано, что при штатном погружении водолаза средний дыхательный ритм составил 9,3 дыхательного движения в минуту; отношение продолжительностей вдоха и выдоха – 1:2,5; вариабельность по среднеквадратическому отклонению – 1,4 с. В случае нахождения водолаза в нештатной ситуации средний дыхательный ритм составил 18 дыхательных циклов в минуту; соотношение продолжительностей фаз дыхания – 1:1,3; вариабельность – 1 с. Таким образом, у водолаза в нештатной ситуации дыхание участилось в 2 раза, выдох укоротился по отношению к вдоху, а ритм дыхания стал менее вариабельным. Следовательно, получаемые акустически физиологические параметры ритма дыхания, его вариабельности, соотношения фаз вдоха и выдоха могут служить индикаторами состояния водолаза. Выводы. Разработанный метод позволяет, не нарушая целостности трактов дыхательного аппарата, измерить под водой параметры ритма дыхания водолаза и соотношение продолжительностей фаз вдоха и выдоха. Индикация физиологических параметров дыхания может быть реализована в декомпрессионном компьютере подводного пловца. Ключевые слова: водолаз, мониторинг, шумы дыхания, ритм дыхания, дыхательный цикл, вариабельность, диктофон.

Acoustic sensors for recording lung sounds at the chest surface should meet some basic requirements—(a) achievement the acceptable sensitivity or sensitivity threshold to the useful signal, (b) a linearity of frequency response, and (c) sufficient noise immunity. Specific condition of recording acoustic wave propagating through human thorax is its registering on the border of the body with air medium which can be regarded as an acoustically soft one. Existing types of acoustic sensors usually used may be divided into contact and non-contact receivers. Non-contact receivers are still exotic to some extent. Currently, three types of acoustic receivers mounted in contact with the chest surface are used. They are accelerometer sensor, stethoscope sensor with microphone, and so called “contact” sensor. Any acoustic sensor having a mass when placed on a layer of soft tissues having hardness should inevitably have an eigenfrequency of suspending. According to ratio of working frequency range and the frequency of suspending all mentioned sensors are modeled as the receivers of oscillatory acceleration, velocity, displacement or dynamic force. Experimental study and theoretical estimates indicate that there is no one optimal sensor meeting all basic requirements for all scenarios of acoustic study of lungs. Hence a passive recording of lung sounds is more frequently performed with a stethoscope or with “contact” sensor, whereas active transmission sounding is performed with an accelerometer or “contact” sensor. However even these sensors are frequently used in non-optimal modes. New studies are welcome to design more optimal sensors.

The short- and long-term postural effects on the forced expiratory tracheal noise time were studied in a sample of 12 subjects. In contrast to the spirometric parameters, the tracheal forced expiratory noise time does not respond to a short-term change in the body posture from sitting and standing positions to the lying position, as well as to 14-day-long orthostatic hypokinesia in a lying position with a body angle of +9.6°. However, significant multidirectional individual dynamics of the tracheal forced expiratory noise time was observed in all subjects during long-term orthostatic hypokinesia, whereas the spirometric parameters had a dominant growth response. It is assumed that the estimation of the forced expiratory tracheal noise time during long-term orthostatic hypokinesia in lunar gravity simulation may provide useful data in addition to spirometry when assessing the individual lung function dynamics. The dynamics of acoustic parameters, as well as spirometric parameters, during long-term postural effects can be considered as adaptive changes.

Passive acoustic monitoring of scuba divers is a promising way to ensure the safety of recreational divers and prevent waterside intrusion by terrorists. It is shown experimentally that the low-frequency underwater respiratory-associated noise of an open-circuit scuba diver can be used successfully to monitor the respiratory rate at distances of up to 100 m. Respiratory-associated noise in the frequency band of 30-1200 Hz provides the possibility of localizing an open-circuit scuba diver in a noisy shallow-water area by using two pairs of hydrophones at distances of up to 220 m and with a predominant discrepancy of no more than 10 m in comparison with Global Positioning System data.

The possibility of decomposition of received signals into high-speed (150–1000 m/s) and low-speed components (50–150 m/s) previously revealed is verified in independent sample. Four types of the ratio between the amplitudes of high- and low-speed arrivals and their changes depending on air-filling of lungs (inspiration/exhalation) are found. Only one of these types, representing predominance of amplitudes of high-speed arrivals, both during inspiration and exhalation is found in one elderly patient with a long-term course of hormone-dependent asthma, but not in 3 other young healthy volunteers. For medium frequency 15 kHz of the range low-speed arrivals velocities result in wavelengths between 0.33 and 1 cm. Such small wavelengths may provide the spatial resolution in lung parenchyma about the first centimeters. Thus transmission sounding of lungs in the range of 10–19 kHz seems promising to provide high-resolution acoustic imaging or may be even transmission tomography of pulmonary parenchyma.

Some types of human professional activities are associated with the influence of adverse environmental factors, therefore, the study of the human body response both in acute situations and in case of prolonged exposure to such factors is necessary to identify early signs of functional distress and prevent the disease development. The purpose of the paper is to assess the ability to control changes in the human lungs ventilation function under extreme physical loads and a bronchodilation test using the developed acoustic parameters of forced expiratory tracheal noise. Materials and Methods. The authors examined three groups of volunteers: professional divers (n=25) before and after scuba diving, testers (n=11) while modeling the physiological effects of prolonged null-gravity condition, and healthy persons (n=29) during bronchodilation test. Results. The authors revealed significant individual dynamics of tracheal noise duration of forced expiration after diving in modern respiratory equipment of closed type in 28 % (7/25) of divers. They also found multidirectional correlations between the dynamics of the duration of forced expiratory tracheal noises under specific diving and the dynamics of spirometric indicators reflecting the state of the ventilation function in divers. It was found that the specific band energies of forced expiratory noise were characterized by multidirectional sensitivity to the extreme effects under study: postural simulations of null-gravity condition for 3 days revealed a decrease in specific energy in 800–1000 Hz and an increase in 1400–1600, 1600–1800 Hz; during bronchodilation test, an increase in specific energy was found in 1600–1800 Hz, and in case of diving, a decrease in energy in 1400–1600 Hz. Conclusion. Monitoring of changes in the lungs ventilation function using the acoustic parameters of forced expiratory noise seems promising for individual monitoring of a human state under extreme conditions. Keywords: ventilation function, forced expiration, tracheal noises, extreme effects, signal processing. Некоторые виды профессиональной деятельности человека связаны с воздействием неблагоприятных факторов внешней среды, поэтому изучение ответных реакций организма как в острых ситуациях, так и при длительном воздействии необходимо для выявления ранних признаков функционального неблагополучия и профилактики развития заболеваний. Цель исследования. Оценить возможности контроля изменений вентиляционной функции легких человека при экстремальных физических воздействиях и бронходилятационной пробе с помощью разработанных акустических параметров трахеальных шумов форсированного выдоха (ФВ). Материалы и методы. Обследовано 3 группы добровольцев: профессиональные водолазы (n=25) до и после подводного погружения, испытатели (n=11) при моделировании физиологических эффектов длительной невесомости и здоровые лица (n=29) при проведении бронходилятационной пробы. Результаты. Выявлена значимая индивидуальная динамика продолжительности трахеальных шумов форсированного выдоха после погружения в современном дыхательном снаряжении замкнутого типа у 28 % (7/25) водолазов. Обнаружены разнонаправленные корреляционные взаимосвязи между динамикой продолжительности трахеальных шумов форсированного выдоха со специфическими факторами погружения и динамикой спирометрических показателей, отражающих состояние вентиляционной функции у водолазов. Установлено, что удельные полосовые энергии шумов форсированного выдоха характеризуются разнонаправленной чувствительностью к исследуемым экстремальным воздействиям: при постуральном моделировании невесомости в течение 3 сут выявлено снижение удельной энергии в полосе частот 800–1000 Гц и рост – в полосах 1400–1600, 1600–1800 Гц; при бронходилятационной пробе обнаружен рост удельной энергии в полосе частот 1600–1800 Гц, а при водолазном погружении – снижение энергии в полосе частот 1400–1600 Гц. Выводы. Мониторинг изменений вентиляционной функции легких с помощью акустических параметров шумов форсированного выдоха представляется перспективным для индивидуального контроля состояния человека при экстремальных воздействиях. Ключевые слова: вентиляционная функция, форсированный выдох, трахеальные шумы, экстремальные воздействия, обработка сигналов.

Objective: The time signature of tracheal noise in the 200–2000 Hz frequency band recorded during a forced expiratory manoeuvre (FETa) is a promising tool for diagnosis of bronchial obstructions. FETa is typically registered using a microphone with a stethoscope head placed on the neck over the trachea (stethoscope sensor). We studied basic time and spectral parameters of forced expiratory tracheal noises with a microphone placed near the mouth (lapel microphone, outside the flow of exhaled air) and compared these with measurements via stethoscope sensor, with the aim of providing patient home monitoring via standard personal computer facilities. Approach: FETa, 200 Hz band pass times, and frequency responses of signals recorded simultaneously with both sensors were analysed in a sample of 24 healthy volunteers. Main results: Averaged real transfer function of signals from a stethoscope sensor and a lapel microphone in the frequency range 200–1800 Hz was characterized by a slope of  −7.2 dB/octave. This is near the slope of  −6 dB/octave predicted via theoretical models of both sensors. The lapel microphone and stethoscope sensor were not interchangeable regarding spectral characteristics of forced expiratory tracheal noises. However, FETa measurements in healthy volunteers via stethoscope sensor and lapel microphone showed no significant differences according to U-Mann–Whitney test for independent samples. Significance: The ability to measure FETa successfully with a lapel microphone placed near the mouth was experimentally demonstrated in healthy volunteers. Additional studies are needed to verify whether FETa measured near the mouth is acceptable for monitoring pulmonary status in patients with asthma or chronic obstructive pulmonary disease.

Forced expiratory (FE) noise is powerful bioacoustic signal, carrying information on human lung function. FE noise differs from sounds of quiet breathing by increasing an intensity of the broadband component and by appearance of narrowband components. When recording FE respiratory noise with a sensor on the neck, above trachea, there are two mechanisms of origin of recorded signal. The first one “acoustic” is determined by superposition of acoustic noises emitted through airway lumen, and assumes sound propagation from distant sources located inside the bronchial tree. The second one “hydrodynamic” is due to the pseudo-sound effect of turbulent pressure pulsations in the vortex flow on the inner wall of trachea. Estimates of Reynolds numbers in the average model of bronchial tree for healthy adults indicate that the developed turbulence is achieved in trachea lumen, thus an existence of the second mechanism is unquestionable. As for the first mechanism, a turbulent flow (broadband component), shedding of vortices or self-oscillatory effects (narrowband components) may be involved to form sources of powerful sound emission inside airway lumen. Approximate estimates show that these effects can be observed no further than in the 10-th level of bronchial tree branching. A variety of identified sound and pseudo-sound FE effects opens new opportunities for diagnostic applications. The method of medical diagnosis of human lung function is developed. Forced expiratory noise time (FETa) in the frequency band 200-2000 Hz is justified as the acoustic predictor. The correlation between FETa and aerodynamic resistance of the respiratory tract is found experimentally. A sufficiently high sensitivity and specificity of the method (near 90%) and an ability to detect hidden bronchial obstruction not revealed by spirometry as well as possibilities to monitor lung function under diving and simulation weightlessness are demonstrated.

Monitoring health condition of a scuba diver and his displacement within the exploited water area is necessary to ensure the safety of diving. Respiratory noises, emitted by the diver into water, may be used for this purpose. In the hydroacoustic basin, powerful signals, having repetition frequency of about 0.12 Hz are found, which correspond to diver’s respiratory rate. The main broadband signal of exhalation is concentrated in the frequency band of 150–1150 Hz. The high-frequency signal in the frequency band of 3.5–4.7 kHz is associated with inspiration. Thus, acoustic estimating the respiratory rate and the ratio of the inspiration/expiration durations are possible, which are important physiological parameters to assess a health condition of the diver. When registering in sea respiratory noises of scuba diver against the background noise, it is possible to trace the acoustic signs of respiratory maneuvers associated with the noise of floating bubbles in the spectrograms at distances up to 100–200 m. The same acoustic signs provide monitoring the displacement of a scuba diver by determining the delays of the maxima of the cross-correlation function at 2 hydrophones. Trails of the delays in correlograms are traced at distances up to 300 m.

Estimating the effect of microgravity/hypogravity on pulmonary ventilation function remains topical. Recently developed acoustic techniques based on the evaluation of the forced expiratory noise time (FETa) were hypothesized to be a promising tool for this aim. The aim of the protocol is to study the effect of two different modalities of bed rest space simulations (microgravity and lunar gravity) on FETa and spirometric indices. The FETa in the frequency band of 200-2000 Hz, recorded above human trachea, was evaluated. The 21st-day exposure to 6 degree head-down tilt (HDT) bed rest, simulating microgravity, and 9.6 degree head-up tilt (HUT) bed rest with head-zero tilt (HZT) rest intervals (HUT + HZT), simulating lunar gravity, in statistically identical subgroups of five and six healthy male volunteers, was studied. In the course of HDT bed rest, a significant elongation of FETa was found in relation to background measurements in "sitting" position (p = 0.016). The effect corresponded to a significant decrease of basic spirometric indices (p < 0.02). Moreover, FETa provided reliable discrimination of HDT and HUT + HZT bed rest tests (p = 0.018), while spirometric indices did not (p > 0.05). Based on previously found correlations (Korenbaum and Pochekutova, 2008; Malaeva et al., 2017), a FETa elongation in response to HDT bed rest was attributed to an increase of aerodynamic resistance of the respiratory tract. The technique seems promising to monitor human pulmonary ventilation dynamics in long-term space missions; however, new studies are welcome to verify it in real spaceflight.

The unexpected phenomenon of sound transmission through human lungs at frequencies above 10 kHz with a speed of about 1000 m/s was revealed by Rueter et al., 2010. The objective is a study of characteristics of sound transmission in human lungs in the frequency range of 10–19 kHz using signal compression technique. The 14-channel receiving apparatus was used. Chirp signals 10–19 kHz (6 min) were emitted into human thorax by small shaker. Sound propagation in human lungs was studied in paths with opposite chest positions of shaker and sensors in 4 volunteers. An existence of low-speed arrivals with propagation velocities of 150–50 m/s, which amplitude and/or velocity is inversely dependent on the air-filling of lungs (inspiration/exhalation) has been revealed. These arrivals may be treated as a result of sound propagation mainly through the lung parenchyma. On the contrary, the amplitudes of high-speed arrivals with velocities of 150–1000 m/s are enhanced with a decrease in air-filling of lungs. They may be connected to the sound propagation mainly through high-density tissues of thorax. The results are promising for medical acoustic visualization of local reduction in air-filling/ventilation of lung parenchyma. [This study was supported by the RFBR grant 16-08-00075.]

The correlations between acoustic characteristics and lung function parameters measured by body plethysmography were revealed when analyzing the sample of 230 subjects consisting of subgroups of healthy subjects, subjects with risk factors, and patients with obstructive lung diseases. Multidirectional character of the correlations between acoustic characteristics of forced expiratory tracheal sounds and parameters measured by body plethysmography/spirometry was established in subgroups of healthy subjects, asthma patients with spirometrically confirmed and unconfirmed obstructive changes, and patients with chronic pulmonary disease.

Technical solutions for the construction of inertial-type pressure-gradient receivers were developed. The manufactured laboratory prototypes with dimensions of 110 × ∅32 mm and 112 × ∅80 mm have acoustic-pressure sensitivities of 70–80 and 500 μV/Pa, respectively, in a plane wave at a frequency of 100 Hz. The performance characteristics of the hydroacoustic pressure-gradient receivers, which are used in oceanological investigations at frequencies that are substantially lower than 1 kHz, were improved.