title: Pulmonary blood volume and its effects on pressure/flow relations and flow resistance in isolated lungs of rabbits.
abstract: Quantitative information about the effects of pulmonary blood volume (Qp) on pulmonary haemodynamics is lacking since Qp changes inevitably with flow. To separate flow-dependent from volume-dependent changes in intravascular pressures we imposed changes in Qp (measured continuously) by altering outflow pressure in seven isolated, blood-perfused rabbit lungs and studied the effects of Qp on the relations between arteriovenous pressure gradient (DeltaP) and blood flow (Q.) under two conditions: flow-dependent volume changes were either permitted or compensated. In the latter circumstances, DeltaP changed more for a given change in Q.. The DeltaP/Q. relations were shifted to smaller DeltaP when Qp was increased. Hence, the calculated flow resistance (R = DeltaP/Q.) decreased with increasing Qp at a given Q.. Assuming constant viscosity, changes in R can be predicted from changes in vessel geometry and thus Qp. We found that R increased less than expected (by a factor of 3-7.5 instead of 9) when Qp was reduced to one-third. This discrepancy may be explained by a change in blood distribution within the lung despite constant Qp and by a change in apparent blood viscosity with Q.. Regardless of these speculations we have shown that Qp determines DeltaP at each flow and thus flow resistance.
authors.affiliation: Institut für Experimentelle Anaesthesiologie, Heinrich-Heine-Universität, Moorenstrasse 5, D-40225 Düsseldorf, Germany.
authors.forename: T W
authors.initials: TW
authors.lastname: Scheeren
authors.forename: S A
authors.initials: SA
authors.lastname: Loer
authors.forename: Z P
authors.initials: ZP
authors.lastname: Ding
authors.forename: J O
authors.initials: JO
authors.lastname: Arndt
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity; D001794:Blood Pressure; D001810:Blood Volume; D008168:Lung / Q000098:blood supply*; D011651:Pulmonary Artery / Q000502:physiology; D011817:Rabbits; D014655:Vascular Resistance