The physiological derangements during and following the administration of higher oxides of nitrogen have been studied in dogs anaesthetized with pentobarbitone. The dogs were exposed to concentrations of nitric oxide or nitrogen dioxide between 0.1 and 2.0 per cent over periods between 5 and 136 minutes. Despite the inhalation of 98 per cent oxygen, death was always associated with a critical reduction in arterial oxygen content. This was caused by one or more of the following three factors: methaemoglobinaemia, low arterial Po 2 , and acidaemia which caused a shift of the oxyhaemoglobin dissociation curve. The reduction of arterial Po 2 was caused by an outpouring of fluid into the alveoli
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.
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