Classifacation and mechanism of origin of dry rales
Dry rales, or rhonchi, may be due to various causes. The main one is constriction of the lumen in the bronchi. Constriction may be total (in bronchial asthma), non-uniform (in bronchitis), or focal (in tuberculosis or tumour of the bronchus). Dry rales can be due to (1) spasms of smooth muscles of the bronchi during fits of bronchial asthma; (2) swelling of the bronchial mucosa during its inflammation; (3) accumulation of viscous sputum in the bronchi which adheres to the wall of the bronchus and narrows its lumen; (4) formation of fibrous tissue in the walls of separate bronchi and in the pulmonary tissue with subsequent alteration of their architectonics (bronchiectasis, pneumosclerosis); (5) vibration of viscous sputum in the lumen of large and medium size bronchi during inspiration and expiration: being viscous, the sputum can be drawn (by the air stream) into threads which adhere to the opposite walls of the bronchi and vibrate like strings.
According to the quality and pitch of the sounds produced, dry rales are divided into sibilant (high-pitched and whistling sounds) and sonorous rales (low-pitched and sonoringsounds). High-pitched rales are produced when the lumen of the small bronchi is narrowed, while low-pitched sonorous rales are generated in stenosis of medium calibre and largecalibre bronchi or when viscous sputum is accumulated in their lumen.
Propagation and loudness of dry rales depend on the size of the affected area in the bronchial tree, on the depth of location of the affected bronchi, and the force of the respiratory movements. When the walls of a medium size and large bronchi are affected to a limited extent, rhonchi are insignificant and soft. Diffuse inflammation of the bronchi or bronchospasm arising during attacks of bronchial asthma is attended by both high-pitched sibilant and low-pitched sonorous rales which vary in tone and loudness. These rhonchi can be heard at a distance during expiration.
Classifacation and mechanism of origin of moist rales
Moist rales are generated because of accumulation of liquid secretion (sputum, oedematous fluid, blood) in the bronchi through which air passes. Air bubbles pass through the liquid secretion of the bronchial lumen and collapse to produce the specific cracking sound. This sound can be simulated by bubbling air through water using a fine tube. Moistrales are heard during both the inspiration and expiration, but since the air velocity is higher during inspiration, moist rales will be better heard at this respiratory phase.
Depending on the calibre of bronchi where rales are generated, they are classified as fine, medium and coarse bubbling rales. Fine bubbling rales are generated in fine bronchi and are percepted by the ear as short multiple sounds. Rales originating in the finest bronchi and bronchioles are similar to crepitation from which they should be differentiated. Medium bubbling rales are produced in bronchi of a medium size and coarse bubbling rales in large calibre bronchi, in large bronchiectases, and in pulmonary cavities (abscess, cavern) containing liquid secretions and communicating with the large bronchus. Large bubbling rales are characterized by a lower and louder sound.
Moist rales originating in superficially located large cavities (5-6 cm and over in diameter) may acquire a metallic character. If segmentary bronchiectases or cavities are formed in the lung, rales can usually be heard over a limited area of the chest. Chronic bronchitis or marked congestion in the lungs associated with failure of the left chambers of the heart is as a rule attended by bilateral moist rales of various calibre, which occur at the symmetrical points of the lungs.
Depending on the character of the pathology in the lungs, moist rales are subdivided into consonating or crackling, and non-consonating or bubbling rales. Consonating moistrales are heard in the presence of liquid secretions in the bronchi surrounded by airless (consolidated) pulmonary tissue or in lung cavities with smooth walls surrounded by consolidated pulmonary tissue. The cavity itself acts as a resonator to intensify moist rales. Moist consonating rales are heard as if just outside the ear. Consonating rales in the lower portions of the lungs suggest inflammation of :he pulmonary tissue surrounding the bronchi. Consonating rales heard in the subclavicular or subscapular regions indicatetuberculous infiltration or cavern in the lung.
Non-consonating rales are heard in inflammation of bronchial mucosa (bronchitis) or acute oedema of the lung due to the failure of the left chambers of the heart. The sounds produced by collapsing air bubbles in he bronchi are dampened by the "air cushion" of the lungs as they are conducted to the chest surface.