Auscultatory characteristics of pleural friction sound
Pleural friction sound is a peculiar adventitious noise generated by friction of visceral and parietal layers of the pleura during breathing. Fibrin is deposited in inflamed pleura to make its surface rugh; moreover, cicatrices, commissures, and bands are formed between pleural layers at the focus of inflammation. Tuberculosis or cancer are also responsible for the friction sounds.
Pleural friction sounds are heard during both inspiration and expiration. The sounds are differentiated by intensity, or loudness, length and localisation. During early dry pleurisy the sounds are soft and can be imitated by rubbing silk or fingers in the close vicinity of the hair. The character of pleural friction sound is altered during the active course of dry pleurisy. It can resemble crepitation or fine bubbling rales sometimes crackling of snow). In pleurisy with effusion, during the period of rapid resorption of exudate, the friction sound becomes coarser due to massive deposits on the pleural surfaces. This friction (to be more exact, brations of the chest) can be even identified by palpation of the chest.
The time during which pleural friction sound can be heard varies with causes. For example, in rheumatic pleurisy pleural friction is only heard during a few hours; after a period of quiescence it reappears. Pleural friction persists for a week and over in dry pleurisy of tuberculous aetiology id pleurisy with effusion at the stage of resorption. Pleural friction sounds can be heard in some patients for years after pleurisy because of rge cicatrices and roughness of the pleural surfaces.
The point over which pleural friction can be heard depends on the focus of inflammation. Most frequently it is heard in the inferolateral parts of e chest, where the lungs are most mobile during respiration. In rare cases is sound can be heard over the lung apices, when they are affected by berculosis with involvement of the pleural membranes.
This is the voice conduction by the larynx to the chest, as determined by auscultation. But as distinct from vocal fremitus, the words containing sounds 'r' or 'ch' are whispered during auscultation. In physiological conditions, voice conducted to the outer surface of the chest is hardly audible on either side of the chest in symmetrical points. Exaggeratedbronchophony (like exaggerated vocal fremitus) suggests consolidation of the pulmonary tissue (which better conducts sound waves) and also cavities in the lungs which act as resonators to intensify the sounds. Bronchophony is more useful than vocal fremitus in revealing consolidation foci in the lungs of a patient with soft and high voice
Date: 2015-02-03; view: 1051