1 694 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



qualitative measure of the state of the pulmonary 

 blood volume: an increase in pulmonary interstitial 

 fluid during acute pulmonary venous hypertension 

 may be indistinguishable from associated increase in 

 pulmonary blood volume (378); the discrepancies 

 between esophageal pressure and pleural pressure 

 are exaggerated in the supine position since medi- 

 astinal contents compress the esophagus to yield 

 artificially high values for pleural pressures; changes 

 in the lung volume may, per se, affect apparent pul- 

 monary distensibility (287). 



Despite the limitations of methodology and the un- 

 certain distinction between an expanded pulmonary 

 blood volume on the one hand and its consequences 

 on the other, pulmonary mechanics in pulmonary con- 

 gestion continues to attract attention on several physio- 

 logical accounts. For example, mechanical work and 

 energy cost of moving congested lungs has proved to 

 be abnormally high; moreover, in some obscure way, 

 stiff lungs seem to set the characteristic breathing pat- 

 tern (rapid frequency, small tidal volume) of pulmo- 

 nary congestion (177, 406). 



radioactive tracers. Change in the radioactivity 

 of a portion of the lung field after the intravenous 

 administration of a radioactive tracer has been used 

 as a measure of the change in pulmonary blood vol- 

 ume under various experimental conditions (271, 

 425). The validity of this approach rests heavily on 

 the assumption that the external detector continues 

 to survey an unchanged geometry throughout the 



control and test periods. It is difficult to prove that 

 this assumption is fulfilled in experiments which in- 

 volve either respiratory maneuvers or changes in body 

 position (425). 



miscellaneous. Some experiments require only the 

 recognition of a change in thoracic (instead of pul- 

 monary) blood volume. For such experiments, the 

 critically balanced teeter board has served as a useful 

 device to detect a shift in the center of gravity of the 

 body as blood is displaced from one end of the body 

 to the other (fig. 27) (86, 154, 395). Also, the "cardio- 

 pneumogram'' has provided an approach to the 

 changes in thoracic blood volume during each cardiac 

 cycle (185). 



Normal Values for Pulmonary Blood J'olume 



It is meaningless to use the central blood volume — 

 with its vague boundaries and its potential for internal 

 rearrangement — as a measure of the pulmonary blood 

 volume as long as the test substance is injected into a 

 peripheral vein (184, 307). The first step to narrow 

 the boundaries of the central blood volume was the 

 pulmonary arterial injection of the test substance 

 (coupled with peripheral arterial sampling) ; under 

 these conditions, the central blood volume approxi- 

 mates 20 to 25 per cent of the total circulating blood 

 volume (224, 249, 250). The second step was to couple 

 the pulmonary arterial injection either with sampling 

 from the left atrium or with the injection of a second 



Fig. 27. The teeter board for detect- 

 ing shifts in regional blood volumes. 

 The records show that during acute hy- 

 poxia (.4) the position of the center of 

 gravity of the body remains unchanged; 

 on the other hand, during the infusion 

 of noradrenaline (B), the center of 

 gravity shifts cephalad. CAL = cali- 

 bration by placing a 200-gram weight at 

 the angle of Louis. [After Fritts el al. 

 (■54)-] 



DASH-POT 

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START 

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