1 Phylogeny and Function   Laryngeal function may be best understood by an appreciation of its origin determined by primitive needs. In this regard Negus' masterful contributions are most illuminating1 (Fig 1-1). FIG 1-1.  Sir Victor Ewings Negus, 1887-1974. Courtesy of the National Portrait Gallery, London. On an evolutionary scale, as animals migrated from an aquatic to a terrestrial existence, a major change in respiratory requirements became necessary. According to Negus, these accomplishmen -- 2 Structure and Function   The upper airway in adult man traverses the digestive tract in the region of the pharynx, complicating its sphincteric protection of the lower airway. By sharing a common passageway with the upper digestive system, the larynx is also compromised in its respiratory performance by resultant ventilatory turbulence and, therefore, resistance. Thus, the anatomical configuration in adult man that benefits phonatory purposes of the larynx simultaneously serves to compromise i -- 3 Innervation of the Larynx   THE AFFERENT SYSTEM Sensory nerve fibers to the larynx are derived from the internal branch of the superior laryngeal nerve, which ipsilaterally innervates the superior mucosal boundary of the larynx to the level of its true vocal cords. Likewise, below the true cords, ipsilateral sensation is mediated by each recurrent laryngeal nerve. Suzuki, however, demonstrates a diamond-shaped area anteriorly in the midline of the subglottic space of the cat that is innervated.

4 Neurophysiology of Protective Function   The most basic function of the larynx is to provide sphincteric protection of the lower airway, most efficiently achieved by simultaneous adduction of both vocal cords. Such action serves to close the glottis by involving the activation of both thyroarytenoid muscles, among other groups of adductors. In fact, it may be the major mechanism of aspiration prevention during the intra-and postdeglutitive periods of swallowing. Reflexive glottic closure is re -- 5 Neurophysiology of Respiratory Function   THE ROLE OF VENTILATORY LOAD ON POSTERIOR CRICOARYTENOID (PCA) ACTIVITY A 78-year-old woman, with known chronic obstructive pulmonary disease and diabetes, was admitted to the hospital febrile and in respiratory distress. Aspiration pneumonia was diagnosed. Steroids, respiratory therapy and antibiotics were initiated.Within several hours, the patient's condition further deteriorated, requiring emergent intubation and ventilator support. Over the next 2 -- 6 Phonatory Function   The phonatory function of the larynx is probably the least well understood of its three basic functions. Due to advances in investigative technique, many established hypotheses based on animal models have been challenged, due in large measure to the advent of advanced technology based on human study.1-3 High-speed cinematography, improved endoscopic techniques with use of laryngeal stroboscope, and direct human electromyographic measurements made possible by hooked wire el.

7 Tracheotomy and Laryngeal Function   THE GLOTTIC CLOSURE RESPONSE A 75-year-old man with a history of severe chronic obstructive pulmonary disease presented to the hospital in respiratory failure, requiring intubation and ventilatory support, following a viral illness. Over the next 3 weeks, despite aggressive pulmonary management, he could not be weaned off the ventilator, eventually requiring tracheotomy and a percutaneous gastrostomy. Following adequate pulmonary recovery, he was transferre -- 8 Laryngeal Paralysis   EFFECTS OF SELECTIVE LARYNGEAL DENERVATION A 56-year-old woman was diagnosed with an extensive squamous cell carcinoma of the right neck. She was taken to the operating room for a right radical neck dissection. Intraoperatively, it was noted that tumor had attached the internal branch of the superior laryngeal nerve, requiring sacrifice to complete the resection. Postoperatively, her laryngoscopic examination was unremarkable with apparent normal voice quality and intact -- Postscript   In summary, as our understanding of laryngeal function grows, one hopes that our management of its dysfunction will be better understood in terms consistent with sound physiologic principles. The impact of Negus' masterful work over 50 years ago establishes the foundation of our present knowledge and provides us with the necessary guidance for future investigation. This textbook is an attempt to provide a selective review of the subject that should be of interest to focused inquiry.