Lung sounds: Relative sites of origin and comparative amplitudes in normal subjects

Abstract

Little is known about the comparative amplitude of the vesicular lung sounds heard over the lung apices and bases. Neither is the site of origin of these sounds known. Recent studies suggest that differences in amplitude between the left and right sides of the chest may be considerable. In order to better assess these differences, and to determine the relative sites of origin of these sounds, a new computerized lung sound measurement technique was employed to study the lung sound amplitude and phase relationships over the left and right posterior lung bases and anterior apices in 9 healthy volunteers. Twenty-four inspiratory breath sounds were recorded simultaneously using 2 microphones at 8 different intermicrophone separations (1 to 8 cm) at those locations. The mean amplitude of the lung sounds so recorded at each location was determined by automated flow-gated measurement at an inspiratory air flow rate of 1.3 l/s. Simultaneously, the degree of similarity of phase between the sounds from both microphones (Subtraction intensity index — SII) was determined. In addition, 3 inspirations were recorded simultaneously by 1 microphone on either side of the sternum in the second intercostal space in order to assess the phase similarity of the lung sounds at these positions. The results showed that the sound intensity at one base (left or right) was significantly greater than at the opposite base in 7 of the 9 subjects. The sound intensity at the left apex was always louder than or equal to that at the right. The subtraction patterns suggested that the sound sources at the apex were more central than at the bases but that additional phase shifting may have occurred during transmission to the chest wall. The sounds recorded from opposite sides of the sternum showed little or no similarity indicating that the sound at this location, though bronchial in character, was not transmitted from the trachea. It is concluded that significant inequality in lung sound amplitude between homologous areas on opposite sides of the chest is a common finding and that the vesicular sounds over the lung apices are possibly produced more centrally than those at the bases but that the trachea is not the source of these sounds.