key: cord-0034980-sv886qku authors: Tomori, Zoltan; Donic, Viliam title: High-Risk Infections: Influence of Down-Regulation and Up-Regulation of Cough Using Airway Reflexes and Breathing Maneuvers date: 2013-05-29 journal: Noninvasive Ventilation in High-Risk Infections and Mass Casualty Events DOI: 10.1007/978-3-7091-1496-4_1 sha: 774f9937102125a25dbfa163e1d26b9f88d00f2e doc_id: 34980 cord_uid: sv886qku Coughing is a watchdog of the lungs. It represents the most important airway defensive reflex and one of the main symptoms of respiratory disease. During coughing and sneezing, particles of mucus can be expelled for a distance of up to 9 m [1]. Various pathogens, if present, may therefore, infect nearby people and animals, contributing to massive dissemination of airborne infections. In addition to using various protective measures, down-regulation of coughing plays a substantial role in preventing dissemination of respiratory infections. For example, about 80 % of passengers on a 3-h airplane trip may be infected by the cough of an individual carrying the flu virus. These newly infected passengers then disseminate the viral infection at their destinations worldwide. During the breathing cycle, the lung volume at the moment determines the actions of two alternating tendencies-inspiration and expiration-mediated by two distinct ventilatory refl exes. The refl exes are induced by stimulation of the airway and lung receptors, again depending on the lung volume and local pressure at the moment. At the early phase of inspiration, the lung volume is very low, just starting to increase gradually from its functional residual capacity (FRC). There is a strong general tendency to inspire at this point [ 5 ] . Inspiratory efforts can be provoked by various methods for stimulating airway rapidly adapting receptors (RARs). In cats, rapid inspiratory efforts can be evoked by nasopharyngeal stimulation, manifesting as the sniff-and gasp-like aspiration refl ex (AspR) [ 1 , 6 -8 ] and by rapid lung infl ation [ 5 ] , which decreases the frequency and intensity of the subsequent expiratory efforts of cough and postpones them [ 9 ] . During gastroesophageal refl ux or inhalation of irritant substances to the larynx, there is a strong "urge to cough" that can be voluntarily suppressed. To prevent aspiration of irritant substances into the lower airways, the necessary effort of coughing may be postponed by a previous, very slow voluntary inspiration followed by breathholding and swallowing of the bolus to the esophagus. Only then can the effort to cough be initiated for expulsion of irritants from the airways [ 10 -12 ] . Similar voluntary cough suppression commonly decreases the disturbing effect of coughing during a concert. It can similarly strongly inhibit dissemination of airborne infections due to coughing. Such ventilatory maneuvers might be usefully applied to the fi ght against fl u pandemics and other widespread respiratory infection outbreaks. On the other hand, the increasing lung volume at and above the tidal volume ( V T ) stimulates the slowly adapting receptors (SARs). Also, because of the Hering Breuer inspiration inhibiting refl ex (HBIIR), after inspiratory "switch-off" the V T induces the expiratory phase. The tendency to expire is strong at the end of tidal inspiration [ 5 ] . Therefore, stimulation of laryngeal RARs interrupts the inspiration and evokes laryngoconstriction and the expiration refl ex (ExpR) [ 1 , 7 , 8 ] . Additionally, an inspired or infl ated volume above the normal V T or blockade of lung defl ation at the beginning of expiration by positive pressure can adequately speed up and increase the intensity of the subsequent expiratory effort. It is caused by stimulation of airway receptors and manifests as the Hering Breuer expiration facilitating refl ex (HBEFR) [ 5 ] . Hyperinfl ation or occlusion of airways and hindering lung defl ation by a ventilator or a pressure pulse provokes the ExpR and the cough refl ex (CR). Such rapid expiratory efforts might promote expulsion of infected mucus, preventing its protrusion from the larynx to the lungs and preclude, or at least postpone, the development of dangerous aspiration pneumonia [ 13 ] . A proposed voluntary breathing maneuver consists of several rapid sniffs with a closed mouth of 0.5 s duration, each followed by forced expiration lasting about 3 s. Such a maneuver might save many lives and improve the quality of life of millions of people worldwide during imminent fl u pandemics or other widespread respiratory infections. The early inspiratory sniffs and other spasmodic inspirations, including provocation of the AspR, result in down-regulation of coughing and may substantially retard a fl u or other respiratory infection pandemic. Rapid refl ex or voluntary hyperinfl ation or occluded lung defl ation-started at the early expiratory phase by pressure pulses-may result in refl ex up-regulation of cough due to stimulation of airway receptors and mediated by HBEFR [ 5 ] . Such up-regulation may prevent, or at least postpone, the development of mostly fatal aspiration pneumonia. The sniff-and gasp-like AspR provoked by nasopharyngeal stimulation in anesthetized cats decreased the number and intensity of cough efforts provoked in the tracheobronchial region [ 9 ] . Similarly, the urge to cough may be suppressed, and even the motor act of coughing might be inhibited or at least postponed by voluntary action, helping to decrease the dissemination of airborne infections [ 11 , 12 ] . Rapid, deep breaths through the nose, but not through the mouth, have bronchoprotective and bronchospasmolytic effects in probands and patients with mild bronchial asthma. This bronchoprotective effect in humans requires rapid inspiratory airfl ow [ 14 , 15 ] . The sniff-like voluntary inspiration decreases the bronchoconstriction detected by one-second forced expiratory volume (FEV 1 ), induced by metacholine inhalation in adult asthmatics [ 16 ] and decreased the number of coughs provoked by capsaicin inhalation in young asthmatics [ 17 ] . These results indicate a refl ex origin of the bronchodilator effect of nasopharyngeal stimulation, which decreases in parallel with bronchodilation and bronchoconstrictor-triggered coughing [ 18 ] . Taking advantage of voluntary airway refl exes and ventilatory maneuvers have many important practical applications [ 19 ] . They include detection of preparatory movement activity in the premotor area in persons in a vegetative state [ 20 , 21 ] . The control of wheelchairs by trained paraplegics [ 22 ] can be reproduced by voluntary performance of aspiration and expiration refl exes, representing binary signals [ 19 ] . Gasping respiration developing in animals can provide autoresuscitation for few minutes even during cardiac arrest [ 23 ] . Therefore, provocation of the gasp-like AspR persisting even in agonal state or voluntary sniffs, might provide autoresuscitation in emergency situations [ 7 , 19 ] . 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