Opening and closing mechanisms of the larynx.

Opening and closing of the larynx are determined by the intrinsic and extrinsic muscles acting on the elastic forces in the tongue, pharynx, larynx, and trachea. The pharynx is opened or closed by two mechanisms: (1) Contractions of the cricothyroid and of the intrinsic muscles of the larynx open and close the vocal cords. (2) The false cords, ventricle, and true cords accordion open or close in a bellows mechanism. We conclude that the posterior cricoarytenoid opens the laryngeal airway. The cricothyroid together with the posterior cricoarytenoid accentuates this opening. The larynx is also opened by the geniohyoid, mylohyoid, sternothyroid, and middle constrictor. The thyrohyoid, cricothyroid, sternohyoid, and inferior constrictor close the laryngeal airway. Abnormalities in the soft tissues of the neck or of the innervation of the larynx, pharynx, and neck muscles may severely interfere with patency of the laryngeal airway. This occurs in such conditions as vocal cord paralysis, sleep apnea, multiple sclerosis, amyotrophic lateral sclerosis, spastic dysphonia, mandibular fractures or hypodevelopment, and cerebrovascular disease.

Prolonged oro- or nasotracheal intubation.

From July 1975 to September 1979, 6 patients were treated with truly prolonged endotracheal intubation; the duration ranged from 55--155 days. Only patients who survived after extubation and were discharged from the hospital were included in this study. Of the 6 patients, 4 were still alive as of November 1980, 23 patients died from causes not related to the intubation. The most common complication was hoarseness, which occurred in 4 patients. During the time of the study, 3 patients who were intubated in excess of 50 days did not survive. In none of these cases was the patient's death related to the intubation. The authors believe that the risk of long-term intubation has been reduced significantly by the use of nasotracheal tubes and to the newer tube materials, which are completely biocompatible, and to improved techniques of cuff inflation. Complications to tracheostomy are less frequent, but often more serious, than complications of long-term nasotracheal intubation.

Local control of pulmonary resistance and lung compliance in the canine lung.

Local control of pulmonary resistance and lung compliance was studied in the in situ left lower lobe of the canine lung. Recirculation of blood through the lobe while the Pco2 of the ventilatory gas was varied resulted in an increase in resistance and a decrease in compliance only when the pulmonary venous pH was greater than 7.42. Alternating sodium bicarbonate and lactic acid infusion while alveolar Pco2 was maintained below 5 mmHg demonstrated the dependence of the hypocapnic response on the acid-base status of the blood perfusing the respiratory airways. The increase in resistance and decrease in compliance observed at a pulmonary venous pH of 7.64 was comparable to that observed after lobar pulmonary artery occlusion. Varying degrees of hypoxia did not significantly affect bronchomotor tone, nor was the bronchoconstriction following lobar pulmonary artery occlusion affected by the hypoxia. Vagal stimulation superimposed on a stepwise increase in pulmonary venous pH from 7.32 to 7.62 resulted in an increase in resistance which paralleled the increase in resistance when pulmonary venous pH alone was increased. Compliance was not significantly affected by vagal stimulation at any level of pulmonary venous pH.