5,6 Often, fine crackles are repetitive, originate in the basal part of the lung, and are altered by changes in body habitus, but not by coughing they are not transmitted to the mouth. Crackles are generally differentiated into two categories, one being “fine,” having a short duration (∼5 ms) and a higher pitch, with frequency content dominant on the order of 600–700 Hz, but ranging up to 2 kHz. Fredberg and Holford 6 suggested that the cross-section of the airways that are subjected to the sudden closing and opening is one of the possible factors affecting the spectral-temporal character of crackling sounds. 5 The sudden opening of an obstructed airway causes an immediate re-equilibration of the pressures on both sides creating vibrations in the airway walls. 1–4 Crackles are generated when airways that were abnormally closed (due to accumulation of secretions or to airway collapse) open in the inspiration phase or, to a lesser extent, close during the expiration phase. 2 They are correlated to numerous pathologies, including bronchiectasis, chronic obstructive pulmonary disease (COPD), edema, and fibrosis. Common adventitious respiratory soundsĬrackles, also known as crepitations and rales, correspond to short, discontinuous, and non-stationary sounds. I, followed by a summary of the objectives of the present study and the structure of the remainder of this article.ġ. Conventional classifications of some of the more common adventitious sounds, their multiple pathological connections, and prior strategies to identify their spatial location are reviewed in Sec. Different types of adventitious sounds correlate with different pathologies. Adventitious respiratory sounds have been classified into several different types, depending on their spectral-temporal characteristics and their location. 1 The absence or deficiency of normal breath sounds or the manifestation of adventitious sounds may be an indicator of a pulmonary disease. These sounds are generally subdivided into tracheobronchial and vesicular the former originate in the trachea and larger bronchial airways, and the latter may originate in small branches of the airway tree further from the trachea or from other mechanisms at distal regions of the lung parenchyma. Normal respiratory sounds are generated in healthy airways by physiological unforced breathing. Respiratory sounds are categorized as normal and abnormal ( adventitious). 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. 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. Several cases were simulated, including a bronchoconstricted lung that had an internal acoustic source introduced in a bronchiole, approximating a wheeze. The chest wall is modeled as a boundary condition on the parenchymal surface. 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. 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. In a recent publication by Henry and Royston, an algorithm was introduced to calculate the acoustic response to externally introduced and endogenous respiratory sounds within a realistic, patient-specific subglottal airway tree.
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