DYNAMICS OF PULMONARY CIRCULATION 



1725 



(225). However, the gradual progression from angios- 

 tomy cannulae (187) to combined right and left 

 heart catheterization (92) has made it feasible to 

 record simultaneously the blood pressures at both 

 ends of the pulmonary circulation as well as the blood 

 pressure in a systemic artery in the intact, unanesthe- 

 tized animal and man. 



Predominantly Passive Effects 



Certain familiar drugs seem to affect the pulmo- 

 nary circulation of the intact animal or man pre- 

 dominantly by way of the systemic circulation. 

 Cardinal examples are the effects of digitalis and 

 quinidine in subjects with left heart failure: digitalis 

 reduces the pulmonary hypertension of left heart 

 failure by improving myocardial performance; quini- 



30--" 



20-- 



10 - 



15 

 10 

 5 



.16-- 

 .08-- 



fig. 47. Comparison of the effects of acute hypoxia and of 

 infusing norepinephrine on pulmonary vascular pressures and 

 resistance. PA = mean pulmonary arterial pressure; 

 P "WEDGE" = mean pulmonary arterial wedge pressure; 

 Rp = mean pulmonary vascular resistance. The solid circles 

 represent the average values for the group of 13 normal sub- 

 jects; the vertical bars represent the range. During hypoxia, the 

 increase in pulmonary arterial pressure was not associated with 

 an increase in "wedge" pressure; during norepinephrine infu- 

 sion, an increase in pulmonary arterial pressure was invariably 

 associated with an increase in "wedge" pressure. Accordingly, 

 calculated resistance increased during hypoxia and decreased 

 during norepinephrine infusion. [After Goldring et at. (163).] 



dine, on the other hand, improves the emptying of 

 the left heart by decreasing systemic vascular resist- 

 ance rather than by a direct action on the myocard- 

 ium (87, 129). 



The effects of epinephrine on the pulmonary circu- 

 lation have long been disputed, primarily because of 

 the occurrence of simultaneous changes in both the 

 systemic and pulmonary circulations (97, 187, 436). 

 However, granting that a direct pulmonary vasocon- 

 stricting effect can be demonstrated in special prep- 

 arations (355), in the intact animal the increase in 

 pulmonarv arterial pressure evoked by epinephrine 

 is almost exclusively a consequence of passive back 

 pressure from the left heart and systemic circulation 

 (187). Indeed, in the dog, excessively large doses of 

 epinephrine reproduce the sequence elicited by the 

 intracisternal implantation of fibrin (64, 372), in- 

 cluding pulmonary hypertension and pulmonary 

 edema from left heart failure. And, consistent with 

 the prepotent effects of epinephrine on the systemic 

 circulation in the dog, is the observation that in the 

 turtle (single ventricle), intravenous epinephrine in- 

 creases systemic vascular resistance without affecting 

 pulmonary vascular resistance (443). 



Levarterenol (/-norepinephrine) also elicits an in- 

 crease in pulmonary arterial pressure. As in the case of 

 epinephrine, the capacity for pulmonary vasoconstric- 

 tion can be demonstrated by special techniques (355)- 

 However, in intact man, the increase in pulmonary 

 arterial pressure elicited by levarterenol is predomi- 

 nantly, if not exclusively, passive, i.e., secondary to an 

 increase in left atrial pressure (fig. 47) (163). 



Histamine elicits a complex series of ventilatory and 

 circulatorv effects. In the isolated lung, it elicits 

 vasoconstriction (442); the intensity of this response 

 varies with the species, dose, and preparation. In 

 intact man, tolerable doses, which are sufficient to 

 elicit systemic hypotension, are without discernible 

 effect on pulmonary hemodynamics; whether tolera- 

 ble doses are inadequate to provoke pulmonary vaso- 

 constriction, or whether vasoconstriction does occur 

 and is neutralized by some concomitant passive 

 effects, remains unsettled (4). Finally, the induction of 

 severe systemic hypotension in the dog by large 

 quantities of histamine is associated with passive 

 pulmonary hypotension (100). 



Pulmonary I asoconstrictors 



The systemic circulation is far more sensitive to the 

 usual vasoconstrictor agents than is the pulmonary 

 circulation. However, a host of apparently unrelated 



