A close relationship between pulmonary ventilation and blood flow exists in the normal functioning of the lungs. Thus, primary alterations in one of these processes are difficult to distinguish from secondary changes in the other. In order to study these two functions in the intact animal, we have separated them by utilizing a technique which allows us to induce alterations in pulmonary blood flow while keeping ventilation constant in rate and tidal volume. This report describes changes observed in the pulmonary circulation and respiratory gas exchange of dogs in whom blood flow was decreased by hemorrhage and then restored by blood replacement.Studies on experimental animals and human subjects have indicated that all pulmonary vessels are not open at the same time (1), and that the pulmonary circulation is able to accommodate a marked increase in blood flow with little rise in the pulmonary arterial blood pressure (2-7). An increase in blood flow, then, must be accompanied by a decrease in vascular resistance, presumably due to expansion of the pulmonary bed. However, the mechanisms by which such accommodation occurs have not been fully elucidated, and questions remain as to the relative importance of physical forces, the effectiveness of vasomotor control and the significance of local pressor and chemo-reflexes. Moreover, only fragmentary
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.
Laryngcal activity during normal and labored breathing i n anesthetized dogs. Fed. Proc., 22, 2 (Abstracts).Acta oto-laryng. 67 Acta Otolaryngol Downloaded from informahealthcare.com by University of Otago on 07/13/15For personal use only.
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.
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