DYNAMICS OF PULMONARY CIRCULATION 



l69c 



tracer into the left atrium. By these techniques, the 

 pulmonary blood volume is of the order of 10 per 

 cent of the total circulating blood volume (106, 246, 



293)- 



It is surprising how closely the latter indicator-dilu- 

 tion value of 10 per cent in intact man corresponds to 

 the more direct measurements in animals, i.e., dog, 

 rabbit, and rat (293). The indicator-dilution value of 

 10 per cent also coincides with estimates based on 

 pulmonary vascular dimensions in the dog (169). 



Variations in Pulmonary Blood Volume 



The pulmonary blood volume increases under a 

 heterogenous group of conditions (fig. 28) : a) an in- 

 crease in pulmonary blood flow (224, 250); b) infla- 

 tion of an antigravity suit (33); c) negative (pleural) 

 pressure breathing (397) ; d) the assumption of the 

 supine position (381); e) systemic vasoconstriction 

 from a variety of causes (64, 154, 186, 372); /) im- 

 mersion in water (188); g) clamping of the pul- 

 monary veins (114); and h) left ventricular failure 

 and mitral stenosis (238). 



Conversely, a decrease in pulmonary blood volume 

 occurs during venesection and reduced cardiac output 

 (184), positive pressure breathing and the Valsalva 

 maneuver (44), systemic vasodilatation from warming 

 (369, 381) and the assumption of the upright posture 

 (247,381). 



Partition of Pulmonary Blood I 'olume 



One particularly hazy aspect of the pulmonary cir- 

 culation is the pattern in which the pulmonary 



arteries, capillaries, and veins share the pulmonary 

 blood volume under natural conditions, and the wax- 

 in which this pattern is modified either by physiologi- 

 cal stimuli or by disease. A few beginnings have been 

 made: anatomical measurements in the dog suggest 

 that the capacity of the pre- and postcapillary pul- 

 monary vascular segments is approximately the same 

 (169); observations on the isolated lung, while failing 

 to define precise anatomical boundaries, have suc- 

 ceeded in disclosing how the pulmonary blood volume 

 may be reapportioned in response to mechanical in- 

 fluences (124, 315, 317, 324) and to special stimuli 

 (116, 305). However, there is no obvious way to ap- 

 ply these experimental observations to the arrange- 

 ment of the pulmonary blood volume in life. 



HEMODYNAMIC INTERRELATIONS 



Distensibility and Resistance 



In previous sections, pulmonary blood flow, vol- 

 ume and pressures were considered separately. The 

 analysis of their interplay is a much more complicated 

 matter. Generally speaking, the aim of such an 

 analysis is to relate the static and dynamic properties 

 of the pulmonary vascular tree to its architecture and 

 to the structure of its walls. Until recently, investiga- 

 tors were preoccupied with the model of the pul- 

 monary circulation which pictured it as the 

 hemodynamic analog of an electrical d-c circuit and 

 which viewed the pulmonary blood flow as though it 

 were continuous and steady (169); for testing this con- 

 ceptual model, the isolated lung seemed ideal on the 



mm 

 Hg 

 2 



UP 

 t 



LEG RAISING 

 mmHg MI H 



DOWN 80_ 



'■^ ih^^h ^ Mm^^^ 



SUPINE EXERCISE 

 80- 



UP DOWN 



1, * bdfi^^ttlKittAfttaM a 



^^fmMW0^ 



0-. 



fig. 28. Effects of leg raising and supine exercise on pulmonary arterial blood pressure. Leg raising. 

 In the normal subject (upper left), leg raising is without appreciable effect on the pulmonary arterial 

 pressure ; in the patient with tight mitral stenosis (upper right), leg raising elicits a considerable in- 

 crease in pressure. Supine exercise. In normal subject (lower left), exercise increases pulmonary arterial 

 pressure by a few mm Hg; in the patient with tight mitral stenosis (lower right), the increase in pressure 

 is much more striking. [After Turino & Fishman (406).] 



