Behavior of Normal Pulmonary Circulation during Changes of Total Blood Volume in Man*

Pulmonary vascular distensibility and lung compliance as modified by dextran infusion and subsequent atropine injection in normal subjects.

“…Even the widely held concept that the pulmonary vascular bed is a highly distensible system (48,49) does not seem consistent with these findings and probably requires limitation under several circumstances. The present data are substantially in agreement with the observations of Doyle, Lee, and Kelly (50), De Freitas and associates (44), and Varnauskas and co-workers (46), who infused saline, polyvinylpyrrolidone, and rheomacrodex solutions, respectively, measured central (50) and pulmonary (44,46) blood volumes, and concluded that the pulmonary circulation behaves, under these circumstances, as a bed of low distensibility. However, the appreciable rise of PBV observed in this study, in comparison with the lack of a significant rise reported by the latter two groups (44,46), suggests the possibility that the rate and the amount of the infusion overcome, to some extent, the mechanism that prevents any increase of PBV during acute hypervolemia.…”

“…It appears likely that this difference in the behavior of PBV is real and depends on the duration and modality of the infusion, which differ in the two series. This interpretation is in keeping with the behavior of the pulmonary vascular resistances, which tend to rise + 17% and to fall -12%o in the subjects of De Freitas and associates (44) and in our subjects (Figure 2), respectively. Similar considerations seeim also to apply to the findings of Varnauskas, Korsgren, Houk, and Prerovsky (46), who recently reported no systematic increase of PBV with some elevation of PVR after the infusion of 500 ml of rheomacrodex given at a rate of 10 to 20 ml per minute, which is much lower than our mean infusion rate for macrodex of 54 ml per minute.…”

“…Increase of the blood volume from inferior vena cava to left atrium in man has recently been reported by De Freitas. and associates after infusion of 1,000 ml of polyvinylpyrrolidone (44). These authors, however, found that most of the increase occurs upstream to the pulmonic valve, whereas PBV, as determined from the difference in mean transit times of the left atrial and pulmonary arterial dilution curves, increases only 3%.…”

“…The increase in cardiac output after infusions has been attributed to the anemia produced thereby (41), but this interpretation has been questioned (43). Probably, the variations of the total effective blood volume (44) and of the extracellular volume (43) may also influence the cardiac output. As to the effect of dextran infusion, previous findings show a variable increase of cardiac output probably depending on the rate of infusion and the amount given (35)(36)(37); our results are in general agreement with these reports.…”

Effect of Portal Venous Blood Flow Diversion on Portal Pressure

“…Lesser slopes result from its activity. The failure of the portal pressure-shunted portal flow slope to be altered by changing blood volume, portal pressure, and presumably cardiac output (27) points to a splanchnic rather than systemic origin ofthe proposed mechanism. The small portal pressure-shunted portal flow slopes recorded in control subjects may reflect both low and variable hepatic resistance to flow (28,29).…”