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HANDEOOK OF PHYSIOLOGY 



CIRCULATION II 



"Bronchomotor Tone" 



Mechanical Compression (Atelectasis) 



Hypertonic Solutions 

 Pulmonary Vasomotor Activity 



Respiratory Gases 



Acute Hypoxia 



Chronic Hypoxia 



Acute Hyperoxia 



Acute Hypercapnia 



Acute Acidosis 



Alveolar Hypoventilation 



Pulmonary Vasomotor Reflexes 



Pulmonary Vasomotor Waves 

 Effect of Drugs 



Predominantly Passive Effects 



Pulmonary Vasoconstrictors 



Pulmonary Vasodilators 

 Cardiopulmonary Disorders 



Pulmonary Arterial Hypertension 

 Restricted vascular bed 

 Increase in pulmonary blood flow 

 Increase in pulmonary venous pressure 

 Pulmonary arterial vasoconstriction 



Cor Pulmonale 



Pulmonary Edema 



Pulmonary Hypotension 



Pulmonary Arteriovenous Fistula 



Pulmonic Stenosis 



Pulmonic Valvular Insufficiency 



(242). By this arrangement, the lung is equipped to 

 operate efficiently over a wide range of metabolic ac- 

 tivities: the enormous expanse of alveolar-capillary 

 surface is capable of increasing during activity (346) 

 and the geometric distribution of airways and blood 

 vessels favors the continued balance of alveolar venti- 

 lation and pulmonary capillary perfusion even during 

 strenuous exertion (7). Finally, governing the coordi- 

 nated performance of this respiratory apparatus is a 

 complicated system of ventilatory and circulatory 

 controls; these succeed, despite the phasic and 

 asynchronous nature of the ventilation and circula- 

 tion, in stabilizing the gaseous composition of the 

 alveolar gas and in ensuring adequate perfusion of 

 the gas-exchanging surfaces. 



In addition to participating in external respiration, 

 the pulmonary circulation also performs several me- 

 chanical functions as a consequence of its architecture 

 and location. Thus, as the bridge between the two 

 sides of the heart, it is in a position to serve as a 

 reservoir of blood for the left ventricle and to control 

 left ventricular output by varying the pulmonary 

 venous return (183). .Similarly, as a consequence of 

 their position at the outlet of the right ventricle, the 

 smaller pulmonary vessels constitute a filter for sys- 

 temic venous particles of all kinds, including the 

 normal formed elements of the blood (1). 



the pulmonary circulation is part of an elaborate 

 tonometric system for external respiration; it exists 

 for the perfusion of the lungs rather than for their nu- 

 trition. And, as a consequence of its anatomical dispo- 

 sition with respect to the pulmonary airways and air 

 spaces, the lung operates as a respiratory organ 

 rather than as an air sac. 



The lung appeared in the vertebrate phylum. In 

 principle, it is designed to bring a thin stream of 

 venous blood into gaseous equilibrium with a large 

 volume of alveolar gas; however, in construction and 

 in efficiency, it varies from class to class. Thus, in the 

 amphibia — vertebrates which bridge the gap between 

 the water and the land — the lung resembles a large 

 bulla (fig. 1 ) ; this inefficient construction apparently 

 suffices for the low metabolic requirements of the 

 amphibia for oxygen. At the other extreme is the 

 complex lung of the large and vigorous terrestrial 

 vertebrates; in such a lung, septation and alveolation 

 have created a porous structure, composed mainly of 

 myriads of microscopic air spaces; suspended in the 

 walls of these tiny air spaces are the pulmonary capil- 

 laries to which the pulmonary arterial tree delivers 

 the entire right ventricular output for arterialization 



fig. 1. Alveolar structure of the frog lung. Each lung con- 

 sists of a large central cavity surrounded by numerous small 

 chambers of varying size. The alveolar walls are outlined by 

 the vessels which they contain. (Prepared in collaboration with 

 H. O. Heinemann.) 



