Influence of modified gas mixtures on the acoustic parameters of human forced exhalation

It was earlier demonstrated that the duration of tracheal noises of forced exhalation (FE) looks to be promising to determine adverse changes in the lung function after a dive. This study dealt with the parameters of tracheal expiratory noises (FE) as dependent of the composition of breathing gas mixtures. In the first type of experiments, 25 volunteers aged from 22 to 60 years carried out forced exhalation under a normal pressure of air or of an oxygen-helium or oxygen-krypton mixture. In the second type of experiments, six volunteers from 25 to 46 years of age performed forced exhalation with air in an altitude chamber under a normal pressure (0.1 MPa); the same subjects performed FE under an elevated pressure (0.263 MPa) while breathing air or an oxygen-helium mixture. In the first type of experiments, the total duration of tracheal FE noises in the frequency range 200?C2000 Hz and 200-Hz bands FE noises depended directly and linearly on the density of the gas mixture; this was not the case in the high-frequency band from 1400 to 2000 Hz. In the second type of experiments, the high-frequency durations and spectral energies of tracheal FE noises (1600?C2000 Hz) depended inversely and significantly on the adiabatic gas compressibility. In a simulated dive to a depth of 16.3 m (0.263 MPa), individual changes in the total duration of tracheal FE noises exceeded the diagnostic threshold of deterioration of the lung function in divers that was determined earlier under normal pressure.     

Dynamics of the duration of tracheal forced expiratory noises during long-term isolation in the Mars-500 experiment

The dynamics of the duration of tracheal forced expiratory noises in a group of volunteers were studied before, during, and after a 520-day confinement. The duration did not change in most volunteers. Two volunteers exhibited significant changes in the duration of tracheal sounds and some spirometric parameters. The increase in the duration of tracheal forced expiratory noises and the decrease in spirometric parameters reveal ventilation impairment of the obstructive type. Analysis of the duration of tracheal forced expiratory noise dynamics during prolonged confinement has proven to be a sensitive technique to test ventilation function changes.     

Regression simulation of the dependence of forced expiratory tracheal noises duration on human respiratory system biomechanical parameters

BACKGROUND: Estimating the duration of forced exhalation tracheal noises shows promise for recognizing bronchial obstruction. OBJECTIVE: Experimental simulation of an influence of biomechanical parameters on the duration of normal forced exhalation tracheal noises. METHOD AND MATERIALS: Thirty-two healthy non-smoking men aged 16-22 years were examined. The duration of noises, the parameters of computer spirometry, and the maximum static expiratory pressure are recorded. These data were analyzed by means of multiple linear regression simulation for logarithms of the elements of the proportionality relation obtained with the use of a one-component biomechanical model of forced exhalation and a linearized approximation of flow-volume curve. RESULTS: Dependence between duration of the forced expiratory noises recorded on human trachea and the product of forced volume capacity (in power of 1.05 +/- 0.27), maximum static expiratory pressure (in power of 0.46 +/- 0.23), equivalent expiratory resistance in the stage of functional expiratory stenosis (in power of 0.72 +/- 0.15 in healthy is an estimate of the equivalent expiratory resistance of human bronchial tree in the functional expiratory stenosis phase, whereas in patients with bronchial obstruction it is supposed to take into account an excess of noise generation time compared with the time predicted from normal individual value of this resistance.     

Gender-specific characteristics of forced expiratory tracheal noise duration in humans aged 17–25 years

In a sample of 77 men and 53 women aged 17–25 years, it has been shown that the duration of tracheal forced expiratory noises is significantly shorter in women. However, normalizing the duration of tracheal forced expiratory noises to height, body mass, and chest circumference eliminates this difference.     

Acoustical estimation of impact of single dive in closed-type breathing apparatus on human ventilatory lung function

Diving renders negative influence on human respiratory system especially when oxygen breathing apparatus is used. Spirometry indexes, traditionally used to estimate ventilator lung function, have poor sensitivity to toxic effect of hyperbaric hyperoxia. The objective is to study possibility of revealing minimum impairments of lung ventilator function in oxygen divers by analysis of forced expiratory tracheal noise duration. 48 divers were studied before and after single shallow water dive in oxygen closed-type breathing apparatus. A significant drop of FVC, FEV1 over the group as a whole was found after dive however being in the limits of norm. The significant increase of individual forced expiratory tracheal noise duration, exceeding the natural variability limit (19.6%, p < 0.05), was found in 10 subjects (20.8%). Three of them during dive had respiratory symptoms characteristic for initial manifestations of pulmonary oxygen poisoning. The asymptomatic reversible increase of forced expiratory tracheal noise duration in the rest 7 divers was interpreted as a sign of hidden phase of hyperbaric hyperoxia effect.     

The influence of the bronchodilatation test on the duration of forced expiratory tracheal noises in young men

The diagnostic efficiency of estimating the duration of forced expiratory noises under the conditions of bronchial obstruction has been shown. The objective of this study was to analyze the response of the forced expiratory noise duration to the bronchodilatation test with the β₂-agonist in the age- and genderhomogenous group of healthy volunteers and bronchial asthma patients selected as a model of variable bronchial obstruction. Two hundred and sixty young men (16–25 years old) were examined. It was shown that the prevailing type of response in bronchial asthma patients with spirometry confirmed bronchial obstruction was shortened forced expiratory noises. Furthermore, the degree of the shortening considerably depended on the severity of the background bronchial obstruction. The absence of a statistically significant response of the forced expiratory noise duration dominated among healthy volunteers (nonsmokers as well as smokers) and bronchial asthma patients without a spirometry confirmed bronchial obstruction. However, the shortened response occurred much more frequently in bronchial asthma patients than in healthy volunteers. The high specificity (86%) of the response as shortened forced expiratory noises to the β₂-agonist may be useful for diagnostics.     

Forced expiratory tracheal noise time in young men in health and in bronchial obstruction

A group of 270 young men aged 16–25 years including healthy nonsmokers, healthy smokers, and bronchial asthma patients with and without spirometry-confirmed bronchial obstruction was tested. The forced expiratory noise time recorded on the trachea in a frequency band of 200–2000 Hz, the spirometry indices, and the anthropometric parameters were measured. It was shown that the forced expiratory tracheal noise time and its ratios to the squared chest circumference, to the body mass, and to the height reflected bronchial resistance and are promising indices for diagnosing bronchial obstruction.     

Lung hyperinflation in isolated dog lungs during high-frequency oscillation

To study the phenomenon of lung hyperinflation (LHI), i.e., an increase in lung volume without a concomitant rise in airway pressure, we measured lung volume changes in isolated dog lungs during high-frequency oscillation (HFO) with air, He, and SF6 and with mean tracheal pressure controlled at 2.5, 5.0, and 7.5 cmH2O. The tidal volume and frequency used were 1.5 ml/kg body wt and 20 Hz, respectively. LHI was observed during HFO in all cases except for a few trials with He. The degree of LHI was inversely related to mean tracheal pressure and varied directly with gas density. Maximum expiratory flow rate (Vmax) was measured during forced expiration induced by a vacuum source (-150 cmH2O) at the trachea. Vmax was consistently higher than the peak oscillatory flow rate (Vosc) during HFO, demonstrating that overall expiratory flow limitation did not cause LHI in isolated dog lungs. Asymmetry of inspiratory and expiratory impedances seems to be one cause of LHI, although other factors are involved.     

Acoustic and spirometry parameters of forced expiratory sounds during a five-day dry immersion

The dynamic studies of the parameters of forced expiration under the conditions of a five-day dry immersion involved seven healthy male subjects aged 20 to 25 years. During forced expiration, spirometry tests were performed simultaneously with tracheal sounds being recorded by a microphone. A number of parameters, including the acoustic duration of the forced-expiration tracheal sounds, the lungs’ forced vital capacity, the 1-s forced expiration volume, the peak expiratory flow, and time of achieving the peak expiratory flow, were recorded before dry immersion, on days 1 and 4 of immersion, and the next day after the termination of immersion. There was a significant decrease (by 8.4%) in the peak expiratory flow on day 1 of immersion; however, by day 4 of immersion, the peak expiratory flow increased by 8.9%, reaching its baseline values. The lungs’ forced vital capacity and the forced expiration volume during 1 second, on the average, did not change throughout the experiment. There was a significant increase (by 17%) in the duration of the forced expiration tracheal sounds after the immersion, which suggests an increase in respiratory resistance and needs further studies. A moderate negative correlation between the duration of the forced expiration tracheal sounds and Gensler’s index (r = ?0.63) was found, whereas the correlation with other spirometry parameters was weak or absent.     

Acoustic estimation of the impact of a single dive using a closed-type breathing apparatus on the ventilatory function of the human lungs

Diving negatively affects the human respiratory system, especially if an oxygen breathing apparatus is used. The spirometry indices generally used to estimate the ventilatory function of the lung have a poor sensitivity to the toxic effect of hyperbaric hyperoxia. The goal of this study was to estimate the possibilities of using the forced expiratory (FE) tracheal noise duration. The study was done on 48 divers who had been tested before and after a single dive.     

Sound transmission between 50 and 600 Hz in excised pig lungs filled with air and helium.

This study measured transit time (TT) and attenuation of sound transmitted through six pairs of excised pig lungs. Single-frequency sounds (50-600 Hz) were applied to the tracheal lumen, and the transmitted signals were monitored on the tracheal and lung surface using microphones. The effect of varying intrapulmonary pressure (Pip) between 5 and 25 cmH(2)O on TT and sound attenuation was studied using both air and helium (He) to inflate the lungs. From 50 to approximately 200 Hz, TT decreased from 4.5 ms at 50 Hz to 1 ms at 200 Hz (at 25 cmH(2)O). Between approximately 200 and 600 Hz, TT was relatively constant (1.1 ms at upper and 1.5 ms at lower sites). Gas density had very little effect on TT (air-to-He ratio of approximately 1.2 at upper sites and approximately 1 at lower sites at 25 cmH(2)O). Pip had marked effects (depending on gas and site) on TT between 50 and 200 Hz but no effect at higher frequencies. Attenuation was frequency dependent between 50 and 600 Hz, varying between -10 and -35 dB with air and -2 and -28 dB with He. Pip also had strong influence on attenuation, with a maximum sensitivity of 1.14 (air) and 0.64 dB/cmH(2)O (He) at 200 Hz. At 25 cmH(2)O and 200 Hz, attenuation with air was about three times higher than with He. This suggests that sound transmission through lungs may not be dominated by parenchyma but by the airways. The linear relationship between increasing Pip and increasing attenuation, which was found to be between 50 and approximately 100 Hz, was inverted above approximately 100 Hz. We suggest that this change is due to the transition of the parenchymal model from open to closed cell. These results indicate that acoustic propagation characteristics are a function of the density of the transmission media and, hence, may be used to locate collapsed lung tissue noninvasively.     

Acoustic biomechanical relationships of human forced exhalation in bronchial obstruction

A statistically significant bidirectional influence of the incidence and degree of bronchial obstruction on the acoustic parameters of forced expiration and the spirometry/body plethysmography indicators of lung function has been revealed by means of nonparametric analysis of variance in a sample of 218 subjects. It has been shown that the acoustic band pass times and energies of forced expiratory tracheal noises coordinate with both tidal resistance and residual volume.     

Modeling expiratory flow from excised tracheal tube laws.

Flow limitation during forced exhalation and gas trapping during high-frequency ventilation are affected by upstream viscous losses and by the relationship between transmural pressure (Ptm) and cross-sectional area (A(tr)) of the airways, i.e., tube law (TL). Our objective was to test the validity of a simple lumped-parameter model of expiratory flow limitation, including the measured TL, static pressure recovery, and upstream viscous losses. To accomplish this objective, we assessed the TLs of various excised animal tracheae in controlled conditions of quasi-static (no flow) and steady forced expiratory flow. A(tr) was measured from digitized images of inner tracheal walls delineated by transillumination at an axial location defining the minimal area during forced expiratory flow. Tracheal TLs followed closely the exponential form proposed by Shapiro (A. H. Shapiro. J. Biomech. Eng. 99: 126-147, 1977) for elastic tubes: Ptm = K(p) [(A(tr)/A(tr0))(-n) - 1], where A(tr0) is A(tr) at Ptm = 0 and K(p) is a parametric factor related to the stiffness of the tube wall. Using these TLs, we found that the simple model of expiratory flow limitation described well the experimental data. Independent of upstream resistance, all tracheae with an exponent n < 2 experienced flow limitation, whereas a trachea with n > 2 did not. Upstream viscous losses, as expected, reduced maximal expiratory flow. The TL measured under steady-flow conditions was stiffer than that measured under expiratory no-flow conditions, only if a significant static pressure recovery from the choke point to atmosphere was assumed in the measurement.     

Viscoelasticity of the trachea and its effects on flow limitation.

To test the hypothesis that peak expiratory flow is determined by the wave-speed-limiting mechanism, we studied the time dependency of the trachea and its effects on flow limitation. For this purpose, we assessed the relationship between transmural pressure and cross-sectional area [the tube law (TL)] of six excised human tracheae under controlled conditions of static (no flow) and forced expiratory flow. We found that TLs of isolated human tracheae followed quite well the mathematical representation proposed by Shapiro (Shapiro AH. J Biomech Eng 99: 126-147, 1977) for elastic tubes. Furthermore, we found that the TL measured at the onset of forced expiratory flow was significantly stiffer than the static TL. As a result, the stiffer TL measured at the onset of forced expiratory flow predicted theoretical maximal expiratory flows far greater than those predicted by the more compliant static TL, which in all cases studied failed to explain peak expiratory flows measured at the onset of forced expiration. We conclude that the observed viscoelasticity of the tracheal walls can account for the measured differences between maximal and "supramaximal" expiratory flows seen at the onset of forced expiration.     

Airflow and pressure during canary song: direct evidence for mini-breaths

Summary Male canaries (Serinus canaria) produce songs of long duration compared to the normal respiratory cycle. Each phrase in a song contains repetitions of a particular song syllable, with repetition rates for different syllables ranging from 3 to 35 notes/s. We measured tracheal airflow and air sac pressure in order to investigate respiratory dynamics during song.Song syllables (11–280 ms) are always accompanied by expiratory tracheal airflow. The silent intervals (15–90 ms) between successive syllables are accompanied by inspiration, except for a few phrases where airflow ceases instead of reversing. Thus, the mini-breath respiratory pattern is used most often by the five birds studied and pulsatile expiration is used only occasionally.Songs and phrases accompanied by minibreaths were of longer duration than those accompanied by pulsatile expiration, presumably because the animal's finite vital capacity is not a limiting factor when the volume of air expired for one note is replaced by inspiration prior to the next. Pulsatile expiration was used for only a few syllable types from one bird that were produced at higher repetition rates than syllables accompanied by mini-breaths. We suggest that male canaries switch to pulsatile expiration only when the syllable repetition rate is too high (greater than about 30 Hz) for them to achieve mini-breaths.Changes in syringeal configuration that may accompany song are discussed, based on the assumption that changes in the ratio of subsyringeal (air sac) pressure to tracheal flow rate reflect changes in syringeal resistance.     

Duration of tracheal sound recorded during forced expiration: From a model to establishing standards

Analysis of the duration of tracheal sound recorded during forced expiration (TSFE) was performed to detect bronchial conductance disorders and to develop a method for establishing individually tailored standards. A standard individual duration of the TSFE served as an estimate of the relevant expiratory resistance of the bronchial tree in healthy subjects and showed the extent to which sound duration exceeded that predicted from the normal individual resistance in flow-limited subjects.     

Spectral content of forced expiratory wheezes during air, He, and SF6 breathing in normal humans.

The effect of gas density on the spectral content of forced expiratory wheezes was studied in the search for additional information on the mechanism of generation of respiratory wheezes. Five normal adults performed forced vital capacity maneuvers through four or five orifice resistors (0.4-1.92 cm ID) after breathing air, 80% He-20% O2, or 80% SF6-20% O2. Tracheal lung sounds, flow, volume, and airway opening (Pao) and esophageal (Pes) pressures were measured during duplicate runs for each orifice and gas. Wheezes were detected in running spectra of lung sounds by use of a frequency domain peak detection algorithm. The wheeze spectrograms were presented along side expiratory flow rate and transpulmonary pressure (Ptp = Pao - Pes) as function of volume. The frequencies and patterns of wheeze spectrograms were evaluated for gas density effects. We found that air, He, and SF6 had similar wheeze spectrograms. Both wheeze frequency and patterns (as function of volume) did not exhibit consistent changes with gas density. Speech tone, however, was substantially affected in the usual pattern. These observations support the hypothesis that airway wall vibratory motion, rather than gas phase oscillations, is the source of acoustic energy of wheezes.     

Inspiratory muscle activity during bird song

The apparently continuous flow of bird song is in reality punctuated by brief periods of silence during which there are short inspirations called minibreaths. To determine whether these minibreaths are accompanied, and thus perhaps caused, by activity in inspiratory muscles, electromyographic (EMG) activity was recorded in M. scalenus in zebra finches and in M. scalenus and Mm. levatores costarum in cowbirds, together with EMGs from the abdominal expiratory muscles, air sac pressure and tracheal airflow. EMG activity in Mm. scalenus and levatores costarum consistently preceded the onset of negative air sac pressure by ∼11 ms during both quiet respiration and singing in both species. The electrical activity of these two muscles was very similar. Compared with during quiet respiration, the amplitude of inspiratory muscle EMG during singing was increased between five- and 12-fold and its duration was decreased from >200 ms to on average 41 ms during minibreaths, again for both species, but inspiratory muscle activity did not overlap with that of the expiratory muscles. Thus, there was no indication that the inspiratory muscles acted either to shorten the duration of expiration or to reduce the expiratory effort as might occur if both expiratory and inspiratory muscles were simultaneously active. Inspiratory and expiratory muscle activities were highly stereotyped during song to the extent that together, they defined the temporal pattern of the songs and song types of individual birds. © 1998 John Wiley & Sons, Inc. J Neurobiol 36: 441–453, 1998     

The influence of body size on the diving behaviour and physiology of the bimodally respiring turtle, Elseya albagula

In aquatic vertebrates that acquire oxygen aerially dive duration scales positively with body mass, i.e. larger animals can dive for longer periods, however in bimodally respiring animals the relationship between dive duration and body mass is unclear. In this study we investigated the relationships between body size, aquatic respiration, and dive duration in the bimodally respiring turtle, Elseya albagula. Under normoxic conditions, dive duration was found to be independent of body mass. The dive durations of smaller turtles were equivalent to that of larger individuals despite their relatively smaller oxygen stores and higher mass specific metabolic rates. Smaller turtles were able to increase their dive duration through the use of aquatic respiration. Smaller turtles had a relatively higher cloacal bursae surface area than larger turtles, which allowed them to extract a relatively larger amount of oxygen from the water. By removing the ability to respire aquatically (hypoxic conditions), the dive duration of the smaller turtles significantly decreased restoring the normal positive relationship between body size and dive duration that is seen in other air-breathing vertebrates.     

High density respiratory syndrome: I. Oscillations of flow-volume curves during forced respiration in dense gas media]

33 divers exposed to high pressure have been examined in three series. The dynamics of the forced breathing parameters has been studied: I--helio or neon-oxygen medium under pressure of 1.078-3.53 MPa (11-36 kg/m2) with density to 32.7 kg/m3; II--nitrogen-oxygen medium under 0.274-0.882 MPa (2.8-9.0 kg/m2) with density of 11.7 kg/m3; III--under the same conditions, as II, but using bronchospasmolytics (stimulators of 2-adrenoreceptors: astompent, salbutamol, berotec) under hyperbaria. A new phenomenon: high-density breathing syndrome is revealed. It includes appearance of oscillations of respiratory flows against the background of a decrease of forced breathing rate in dense gas medium and has a common mechanism of appearance both during inhale and exhale. High hydrostatic pressure and narcotic qualities of inert gases can have a modulating effect. Evidences are obtained that tremor phenomena observed during high pressure nervous syndrome can influence the biomechanics of forced breathing at hyperbaria. A high correlation between amplitude modulation of electromyograms of breathing muscles and pneumotachogram oscillations within the range, corresponding to the frequency of physiological tremor, allowed assuming that tremor of breathing muscles induced by high-density gas medium action is one of factors responsible for appearance of respiratory flows oscillations.