Working Paper of Public Health Volume 2012 - Azienda Ospedaliera ...

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Azienda Ospedaliera Nazionale“SS. Antonio e Biagio e Cesare Arrigo”Working Paper of Public Healthnr. 10/2012role in treatment of cough ineffective and management of bronchial secretionsreducing respiratory infections.1. INTRODUCTIONRespiratory infections are the most common cause of hospitalization and the most severecomplication of patients with neuromuscular diseases. The most important reasons for thiscondition are the stagnation of deep bronchial secrections and the usual presence of a deficit ofcough. The PCEF (Peak Cough Expiratory Flow), the most important standardized indicator ofefficiency of cough, as a matter of fact, is always reduced. The consequence of this condition is adecreased of the tracheobronchial secretions clearance with a predisposition to infection.Moreover, the reduced physical activity, the high frequency breathing and the low tidal volumegradually lead to an increase of stiffness of the chest wall until sternum chondral joints ankylosis.The reduction of PCEF in neuromuscular diseases is caused by several factors. The most importantare the weakness of respiratory muscles and the reduced compliance of chest wall and lung. Thereduced expansion leads to the formation of pulmonary atelectasis of the lung parenchyma andinfectious episodes. Among the most commonly used spirometric parameters, vital capacity (VC)is reduced, even if, the value must be considered significant when it is equal to or less than 50% ofnormal. The maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP) and thenasal inspiratory pressure (SNIP) are also reduced. The value of PCEF, directly represents theeffectiveness of cough. The value of PCEF considered normal in adults is greater than 360 L / min.Some authors consider worth enough for an effective cough a value of 160 L / min. Other authorssustain that to overcome a bronchopulmonary infection is needed a PCEF value bigger than 270 L/ min (Table 1).2. PHYSIOLOGY OF COUGHThe cough is an automatic mechanism of defence. It however, can be reproduced and partiallycontrolled voluntarily. It is especially useful in cases of increased production of mucus and / orimpairment of muco-ciliary clearance to remove the tracheobronchial secretions. This mechanismis called "cough clearance”. It use the power of a forced expiratory to clean airways from irritantsand secretions. The reflex is triggered by stimulation of receptors placed in the airway: larynx,trachea and bronchial tree. There are also extrapulmonary receptors located in the pleura,esophagus and external ear. The afferent pathways are constituted mainly by the vagus nerve(larynx, trachea, carina, pleura, bronchi), the glossopharyngeal (pharynx) and the intercostal2
Azienda Ospedaliera Nazionale“SS. Antonio e Biagio e Cesare Arrigo”Working Paper of Public Healthnr. 10/2012nerves. The centre of the cough is located close to the breath centre, in the medulla oblongata. Theefferent pathways are represented mainly by the inferior laryngeal nerve (glottis), the phrenicnerve (diaphragm) and spinal nerves (intercostals and abdominal muscles). The cough is the finalphase of a reflex that can be divided in four stages: irritation, inspiration, compression and ejection(Table 2):1. Irritation: stimulation of cough receptors placed in laryngo-tracheal and in bronchial tree.2. Inspiration: it must be rapid and deep to facilitate the return of elastic lung parenchyma,with the aim of producing the maximum expiratory flow possible. High lung volumeoptimizes the voltage-length of the expiratory muscles, allowing to generate high pressuresand high expiratory flow. During this phase, the glottis is open thanks to the abductormuscles of the cartilages aritenoidee. This allows the divergence of the vocal foldsallowing air to enter quickly in the lung.3. Compression: strong expiratory with closed glottis. Its duration is about two seconds.Intrathoracic and abdominal pressure considerably increase due to the contraction ofexpiratory muscles of the chest, abdomen and pelvic floor.4. Expulsion: is the classic cough. Following the sudden opening of the glottis and theconcomitant elevation of the soft palate. This phase is characterized by an explosiverelease of air at high flow and a high-frequency vibration of the bronchial wall. As a resultof the sharp fall in intrathoracic pressure, the diaphragm is passively propelled upward, theair is violently expelled, and the intrapulmonary bronchial material dragged out. Thediaphragm during the third and fourth phase is released and the intra-abdominal pressure istransmitted to the thoracic compartment. In healthy individuals the air intrapulmonaryexpiratory flow reaches more than 6 l / sec. The increased speed of airflow, as determinedby the reduction in size of the airways, allowing contact between air and mucus layer,known as "two-phase flow" (gas and liquid). The posting of secretions is possible due tothe transfer of kinetic energy from molecules of air to those of mucus. The gas-liquidinteraction between the air at high speed and large molecules flow of mucus is themechanism of removal and transport of secretions. The action of coughing is expressed atthe level of airway proximal to the 6 ^ -7 ^ bronchial generations. It represents one of themore effective mechanisms of tracheo-bronchial toilet.3. NEUROMUSCULAR DISEASE: RESPIRATORY FISIOPATOLOGY3
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