HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



duct lymph arising from the heart is constant, and 

 variation in output reflects conditions in the lungs." 



A second variable is introduced by the occasional 

 occurrence of anastomotic connections with the 

 thoracic duct and thus free flow between the two ducts. 

 Freeman (76) found anastomotic connections in 1 2 

 out of 25 carefully injected and examined animals. 

 In the living animal, the presence of anastomotic 

 connections is obvious if right duct lymph is milky 

 rather than clear or becomes milky and increases in 

 rate of flow after pressure upon the abdomen, a 

 maneuver which is very effective in increasing flow 

 from the thoracic duct but not from the right duct. 

 Drinker (60) also suggested that shifting from natural 

 breathing to artificial respiration through a tracheal 

 cannula was a useful test, since artificial respiration 

 increases right duct flow but reduces thoracic duct flow. 

 Further tests can be made by introducing T-1824 dye 

 into one of the lungs via a long catheter or by injecting 

 the dye into the paw or a leg lymphatic. The former 

 procedure results in coloring only right duct lvmph 

 if no anastomotic connections are present; the second 

 procedure results in coloring only thoracic duct 

 lymph. Using these tests, our experience has been that 

 fewer than 20 per cent of dogs show functional anas- 

 tomotic connections. 



It is interesting that, in spite of the difficulties 

 described as inherent in the study of right duct lymph, 

 estimations of its flow and protein concentration are 

 not too different from those originally reported by 

 Warren and Drinker for lymph collected from the 

 mediastinal lymph duct, and the protein concentra- 

 tions are similar to those found in leg and cervical 

 lymph. Thus Courtice (47) found that the average 

 flow from the right lymph ducts of dogs was 2.3 ml 

 per hour and the average protein concentration was 

 3.7 per cent, levels similar to those found in our labo- 

 ratory (197). As Yoffey & Courtice (234) point out 

 this would amount to about 2 g of protein daily or 3.6 

 per cent of the total circulating plasma proteins. The 

 lymph flow is small in terms of the rich blood supply 

 of the lungs. It should be borne in mind, however, 

 that these experiments were done on anesthetized dogs 

 in the supine position and levels of flow and concentra- 

 tion may only at best reflect minimum values. 



The pulmonary circulation is a low pressure system 

 and pulmonary capillary pressure is ordinarily less 

 than plasma colloid osmotic pressure, a situation con- 

 ducive to "dry" lungs. According to the Starling 

 principle, edema would be expected to occur either 

 when capillary filtration pressure was high or protein 

 concentration reduced. Paine et al. (163), using the 



heart-lung preparation, showed this to be true in ex- 

 periments in which a) they lowered the plasma pro- 

 teins by plasmapheresis or by replacement with 

 Locke's solution, and b) they elevated hydrostatic 

 pressures by imposing a left ventricular overload. The 

 onset and progression of pulmonary edema were al- 

 ways attended by an increase in the flow of lymph 

 from the right thoracic duct. They conclude that 

 measurement of an increased pulmonary lymph flow 

 is a reliable indicator of the presence of pulmonary 

 edema. Uhley et al. (210) and Rabin & Meyer (176) 

 also studied the relationship between pulmonary 

 hypertension, lymph flow, and edema. The former 

 investigators devised a technique to collect pulmonary 

 lymph flow more completely. Instead of cannulating 

 the right lymphatic duct, they create a chamber 

 within the right external jugular vein which traps 

 lymph between the outside of a tube secured in the 

 vein and the vein wall. Lymph is removed from the 

 chamber by a polyethylene catheter. In 13 anesthe- 

 tized, open-chest dogs under artificial respiration they 

 found average lymph flow to be 0.3 ml per hour. 

 This value is considerably less than that found by 

 others, as indicated above. Elevation of pulmonary- 

 venous pressure to 30 mm Hg by introduction of a 

 balloon into the left atrium resulted in an increase in 

 lymph flow to an average of 1 . 14 ml per hour, the rise 

 occurring about 15 min after inflation of the balloon. 

 After maintenance of elevated pulmonary venous 

 pressure and progressive increase of lymphatic flow 

 for approximately 30 min, critical pulmonary edema 

 ensued. The protein content of lymph paralleled 

 lymph flow. Both increased lymph flow and pulmo- 

 nary edema were generally promptly decreased with 

 relief of the high pulmonary venous pressures. The 

 authors conclude that the small absolute increase in 

 right duct lymph suggests that lymphatics were 

 unable to function significantly to relieve the acute 

 pulmonary edema. Rabin and Meyer raised left 

 atrial pressures by means of previously appropriately 

 placed snares and found that, with this method, an 

 acute elevation of left atrial pressure could be precisely 

 controlled at any desired level up to a mean of 60 mm 

 Hg in dogs with an intact thorax. Right lymphatic 

 duct flow did not increase at acutely elevated left 

 atrial mean pressures below 25 mm Hg, whereas flow 

 increased 3- to 4-fold at mean pressures above 25 mm 

 Hg. The total amount of lymph at maximum flow, 

 however, was only 0.3 ml per min. Lymph flow re- 

 mained elevated for as long as 1 hour after left atrial 

 pressure was restored to normal. Pulmonary edema 

 did not occur readily when left atrial mean pressure 



