Localization of adventitious respiratory sounds

Abstract

In a recent publication by Henry and Royston [J. Acoust. Soc. Am. 142, 1774-1783 (2017)], an algorithm was introduced to calculate the acoustic response to externally introduced and endogenous respiratory sounds within a realistic, patient-specific subglottal airway tree. This work is extended using an efficient numerical boundary element (BE) approach to calculate the resulting radiated sound field from the airway tree into the lung parenchyma taking into account the surrounding chest wall. Within the BE model of the left lung parenchyma, comprised of more than 6000 triangular surface elements, more than 30 000 monopoles are used to approximate complex airway-originated acoustic sources. The chest wall is modeled as a boundary condition on the parenchymal surface. Several cases were simulated, including a bronchoconstricted lung that had an internal acoustic source introduced in a bronchiole, approximating a wheeze. An acoustic source localization algorithm coupled to the BE model estimated the wheeze source location to within a few millimeters based solely on the acoustic field at the surface. Improved noninvasive means of locating adventitious respiratory sounds may enhance an understanding of acoustic changes correlated to pathology, and potentially provide improved noninvasive tools for the diagnosis of pulmonary diseases that uniquely alter acoustics.

FIG. 1.

(Color online) Left lung with 31 429 monopole sources shown as red dots within black parenchymal surface mesh of 6188 BEs. Blue “rods” depict outward normal vectors at BE centroids.

FIG. 2.

(Color online) Thorax geometry: anterior open to depict internal geometry.

FIG. 3.

(Color online) Average monopole strengths for airway segments categorized by Horsfield order from the trachea (order >30) to the smallest modeled bronchioles (order = 8).

FIG. 4.

(Color online) The localization grid including $N_{\theta }=2370$ hypothetical monopole sources, shown in (top) an axial plane, and (bottom) a sagittal plane. Hypothetical monopole sources shown as red dots.

FIG. 5.

(Color online) Normal velocity amplitude at parenchyma surface caused by insonification at 200, 400, and 800 Hz for (a)–(c) healthy and (d)–(f) fibrotic lung cases. Anterior direction to the left, lateral coming out of the page, and cranial at the top of the figure.

FIG. 6.

(Color online) Normal acoustic velocity amplitude at parenchyma surface caused by a wheeze in a lower left lobe bronchiole with system bronchoconstriction at 200 Hz, 400 Hz, and 800 Hz calculated using the BE model (a)–(c) and using incident field assumption (d)–(f). Anterior direction to the left, lateral coming out of the page, and cranial at the top of the figure.

FIG. 7.

(Color online) Source localization for insonified healthy (a)–(c) and fibrotic (d)–(f) lung at 400 Hz. Left lung shown as a light blue (gray) transparent isosurface, with source localizations shown from the thorax front, side, and isometrically. Green (darker gray), yellow (light gray), and red (medium gray) dots represent Bartlett confidence regions in the top 5% (>95%), 85%–95%, and 75%–85%, respectively.

FIG. 8.

(Color online) Bartlett confidence regions of Fig. 7 overlaid with major airway branches with the top 30% of airway wall radial velocity amplitude, colored by magnitude in dB ref 1 m/s. Insonified (a) healthy and (b) fibrotic lung.

FIG. 9.

(Color online) Source localization for a wheeze with bronchoconstriction at 400 Hz. Left lung shown as a light blue (gray) transparent isosurface, with source localizations shown from the thorax front, side, and isometrically. Green (darker gray), yellow (light gray), and red (medium gray) dots represent Bartlett confidence regions in the top 10% (>90%), 80%–90%, and 70%–80%, respectively. Calculated using (a) BE model and (b) incident field assumption, with a 3 × 3 grid of sensors located on the lateral parenchymal surface near the wheeze origination sight.

FIG. 10.

(Color online) Bartlett confidence regions for wheeze case using all BE centroids as sensor locations overlaid with peripheral airway branches within the top 30% of airway wall radial velocity amplitude, colored by magnitude in dB ref 1 m/s. Boxed region of Fig. 9 for BE model case is shown (magnified). The circle denotes the actual wheeze source location, and the × denotes the predicted wheeze source location. Green (darker gray), yellow (light gray), and red (medium gray) dots represent Bartlett confidence regions in the top 10% (>90%), 80%–90%, and 70%–80%, respectively.