1054 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



limit, hereby producing an irreversible damage to the 

 capillary wall. It is assumed that in the extravasation 

 stage following acute radiation damage, the elasticity 

 and the stretchability of these processes are greatly 

 reduced." 



It should be obvious from the brief review given 

 that, in discussing the pathogenesis of pulmonary 

 edema, we are concerned with a syndrome, like cir- 

 culatory shock, in which many factors may be opera- 

 tive. In an individual case, a single factor may produce 

 indeterminable effects unless it is very powerful. On 

 the other hand, several factors may combine to pro- 

 duce the syndrome at a threshold lower than that 

 necessary for each to act singly. In the final analysis 

 we must assume that in the healthy animal, fluid and 

 proteins which leak from the capillaries are drained 

 off as an equal amount of lymph. Pulmonary edema 

 arises when capillary filtration exceeds the point 

 where the lymphatic drainage is adequate to main- 

 tain the relatively "dry" state of pulmonary tissue. 

 This concept, that pulmonary edema results from a 

 relative deficiency in lymph drainage is further 

 supported by the experiments of Foldi and his col- 

 laborators (75). They studied dogs in which they had 

 experimentally produced mitral insufficiency, mitral 

 stenosis, or bilateral vagal section and ligated the right 

 and thoracic lymph ducts and lymph nodes of the 

 anterior mediastinum. Only tying off the lymphatic 

 supply failed to produce edema as did each experi- 

 mental procedure under control conditions. When the 

 procedure was combined with lymphatic ligation, 

 however, edema ensued in most animals. Failure to 

 occur under the combined procedure was correlated 

 with lack of lymph congestion presumably to incom- 

 plete cutting off of lymph drainage. 



Cardiac 



The lymphatic supply of the myocardium was first 

 described by Rudbeck in 1653 and has been debated 

 ever since, particularly as to whether myocardial 

 lymphatic capillaries exist. Patek (167) described 

 three plexuses, subendocardial, myocardial, and sub- 

 epicardial. The subendocardial vessels comprise capil- 

 laries in a single plane which drain into the myocardial 

 plexus, a profuse system of interconnected capillaries. 

 According to Patek, there were no efferent lymphatics 

 but only anastomoses with the subepicardial system. 

 Rusznyak et al. (188), however, review more recent 

 work of Zhemcherzhnikova and Zhdanov showing 

 that "the musculature of the ventricles in man con- 

 tains reticularly arranged true lymphatic capillaries. 



The loops of these capillaries are situated along the 

 fasciculated muscles." According to these workers, the 

 lymphatic system of the epicardium consists of a dou- 

 ble, intercommunicating deep and superficial plexus. 

 The efferent lymphatics are chiefly situated subepi- 

 cardially, i.e., on the surface, and follow the branches 

 of the coronary artery. The lymphatic trunks of the 

 anterior surfaces of the two ventricles unite to form two 

 lymphatics which run in the anterior longitudinal 

 sulcus from the apex to the base of the heart. The 

 lymphatic which unites the lymph vessels of the 

 posterior surface of the left ventricle runs in the 

 posterior longitudinal sulcus and reaches the anterior 

 surface of the heart in the coronary sulcus. Uniting 

 below the left auricle, these lymphatics form the 

 heart's main collecting lymph vessel which drains into 

 a bifurcation or laterotracheal lymph node. The 

 lymphatics of the posterior and part of the anterior 

 aspect of the right ventricle unite in the right efferent 

 main lymphatic trunk which starts in the posterior 

 longitudinal sulcus, passes over to the anterior surface 

 of the aorta and runs along the surface of the right 

 auricle to the cranial mediastinal lymph node which 

 usually lies on the aortic arch at the origin of the left 

 common carotid artery. 



Miller et al. (146) have recently raised the question 

 as to whether lymphatic vessels exist in the heart valves 

 of the dog. They examined mitral valves in three 

 groups of dogs: /) stock dogs killed during the course 

 of other laboratory experiments, 2) "sham"-operated 

 dogs, and 3) dogs in which surgical obstruction of 

 cardiac lymphatic drainage was produced and which 

 were then killed at varying periods of time after 

 surgery. Only an occasional thin-walled channel 

 was found on histological study in the first two groups. 

 However, numerous channels, presumed to be lym- 

 phatics, appeared in animals with obstructed lymph 

 flow. The authors believe that interference with lymph 

 flow may play a direct role in heart valve scarring and 

 may provide an additional clue to the mechanism of 

 progressive valvular fibrosis in the years following an 

 inflammatory insult (such as rheumatic valvulitis). 

 These authors also reported ventricular endomyo- 

 cardial pathology produced by chronic cardiac lym- 

 phatic obstruction in the dog (145). Their results are 

 similar to those previously described by Rusznyak 

 (187) who reported many variations in the anatomy of 

 the cardiac lymphatic system. They did not, however, 

 find cardiac lymphatics entering the thoracic duct as 

 Rusznyak reported. They found interstitial edema 

 most often with dilatation of lymph capillaries. Dis- 

 seminated focal necrosis in the myocardium was pres- 



