Gas density does not affect pulmonary acoustic transmission in normal men

Abstract

Fremitus, the transmission of sound and vibration from the mouth to the chest wall, has long been used clinically to examine the pulmonary system. Recently, modern technology has become available to measure the acoustic transfer function (TF) and transit times (TT) of the pulmonary system. Because sound speed is inversely proportional to the square root of gas density in free gas, but not in porous media, we measured the effect of air and Heliox (80% He-20% O2) breathing on pulmonary sound transmission in six healthy subjects to investigate the mechanism of sound transmission. Wide-band noise (75-2,000 Hz) was "injected" into the mouth and picked up over the trachea and chest wall. The averaged power spectra, TF, phase, and coherence were calculated using a fast Fourier transform-based algorithm. The phase data were used to calculate TT as a function of frequency. TF was found to consist of a low-pass filter property with essentially flat transmitted energy to 300 Hz and exponential decline to 600 Hz at the anterior right upper lobe (CR) and flat transmission to 100 Hz with exponential decline to 150 Hz at the right posterior base (BR). TF was not affected by breathing Heliox. The average TT values, calculated from the slopes of the averaged phase, were 1.5 +/- 0.5 ms for trachea to CR and 5.2 +/- 0.5 ms for trachea to BR transmission during air breathing. During Heliox breathing, the values of TT were 1.5 +/- 0.5 ms and 4.9 +/- 0.5 ms from the trachea to CR and from the trachea to BR locations, respectively. These results suggest that sound transmission in the respiratory system is dominated by wave propagation through the parenchymal porous structure.

Velocity and attenuation of sound in the isolated fetal lung as it is expanded with air

“…A number of studies have confirmed Rice's findings in lungs inflated in the range from residual volume to total lung capacity (7,8,10,11,17). The upper and lower limits of this range are of particular clinical significance, because compelling evidence shows that injury to the lungs during mechanical ventilation can be attributed to the effects of both overinflation, or volutrauma (5), and underinflation, or atelectrauma (18), in which there is repetitive opening and closing of underexpanded and unstable air spaces.…”

“…A key aspect of our study design was to introduce sound directly to the lung surface, rather than via the airway, the route of entry for sound in most earlier studies using isolated lungs (8,17) or using intact animals (4,15) and humans (1,6,10). Although studies utilizing airway entry of sound report that lung inflation has an effect on the velocity of sound from its point of entry at the airway opening to the surface of the lung or chest wall, interpretation of results requires assumptions about the pathway that sound takes through the respiratory system (1,8).…”

Detection of porcine oleic acid-induced acute lung injury using pulmonary acoustics

“…Studies in healthy humans have established that the mouth-to-chest transit time of an acoustic wave is 1.5-5 ms, corresponding to a velocity of 60-80 m/s, considerably slower than the speed of sound in air, and that the amplitude of sound transfer decreases gradually with increasing frequency (6). Although the exact pathway of sound propagation through the bronchial tree and lung parenchyma is not known, low frequencies are believed to exit the central airways and travel along tissue paths, whereas higher frequencies are transmitted to more peripheral airways (5,14).…”

“…Studies performed in healthy humans and in patients with chronic lung disease indicate that sound energy introduced into the airway can be detected on the surface of the chest and that the transfer of such energy can be quantified in terms of amplitude and wave speed (5,6,15). An experimental study by Donnerberg et al (3) showed that the amplitude of sound transmission through the respiratory system is greater in congested lungs than in normal lungs and that this change is proportional to the lung wet-to-dry weight ratio.…”

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

“…In addition, changes in physical properties of breathing gas mix tures (BGMs) make it possible to clarify some funda mental aspects of the physiology and biomechanics of breathing, in particular, formation of the respiratory noises. Nevertheless, studies of this kind are scanty [1][2][3]. It has been recently demonstrated [4] that an acoustic parameter, namely, the duration of tracheal noises of forced exhalation (FE) has a diagnostic value for detecting adverse changes in the lung function after diving with closed type equipment; these are changes presumably related to hyperbaric hyperoxia [5].…”