Stop-flow studies of distribution of filtration in rat lungs

Abstract

The stop-flow approach was used to investigate where filtration occurs in the pulmonary vasculature after elevation of left atrial pressure and aspiration of HCl. Rat lungs were perfused for 11 min at zero left atrial pressures, and then flow was stopped for 10 min and left atrial pressures were increased to 20 cmH2O. Thereafter, 3HOH was instilled into the air spaces, and the pulmonary vasculature was flushed by perfusing it from the pulmonary artery to left atrium (anterograde flush) or in the opposite direction (retrograde flush). Increases in fluorescein isothiocyanate (FITC)-dextran (molecular weight 2,000,000) indicated filtration, and these preceded increases in 3HOH after anterograde but not retrograde flushes. This suggests that some filtration occurred through vessels that were relatively venous compared with those through which 3HOH exchange had occurred. Filtration increased fivefold after instillation of 0.1 N HCl in isotonic saline into the air spaces before perfusion. Increases in Evans blue-labeled albumin concentrations were < 40% those of FITC-dextran, indicating loss from the vasculature, but increases in unlabeled albumin and FITC-albumin were comparable.

Transvascular fluid flux from the pulmonary vasculature at rest and during exercise in horses

“…Lung lymph flow studies not only measure transpulmonary fluid dynamics but also include lymph flow from non-pulmonary tissues (Demling & Gunther, 1982;Drake et al 1986) and the conducting airways (Wagner et al 1998). Gravimetric lung-fluid dynamic studies only detect variations in total lung water and are unable to account for alterations when changes are to be contributed to the vascular, interstitial and/or cellular compartments in lungs (Lin et al 1998). Methods in the present study provide accurate results acutely in an exercising subject, which can be applied to other animals and humans, in contrast to gravimetric lung studies, which require stagnant experimental conditions, or lymphatic studies, which require extensive surgery and chronic instrumentation.…”

Relationship of Ultrafiltration and Anastomotic Flow in Isolated Rat Lungs

“…Panel C: Some of the concentrated perfusate is lost through defects in the pulmonary exchange vessels. 3 HOH from the airspaces occurred (9). In the earlier experiments, we instilled the 3 HOH at the end of the equal-pressure-flow period and found that increases in concentrations of FITC-dextran appeared in venous outflow samples before 3 HOH was detected.…”

“…The actual causes for small losses of Evans blue from the vasculature in some of these studies remain uncertain. In our previous study, we found that increases in FITC-dextran relative to baseline venous concentrations (rather than arterial concentrations) were similar to increases in concentrations of albumin in the perfusate, suggesting that increases in FITC-dextran concentrations above venous baseline levels can be reliably used to estimate transudation (9). Furthermore, the similarity between the calculated volume of fluid lost by ultrafiltration and the volume of perfusate that entered the vasculature from the arterial and venous reservoirs during the equal-pressure interval suggest that this method of determining transudation is appropriate.…”

“…As an alternative to lung weight, single-pass, and recirculating indicator dilution approaches, we have investigated ultrafiltration and solute exchange with stop-flow studies in isolated rat lungs (6,9). These experiments are analogous to stop-flow experiments in the kidney (11).…”

“…In principle, this approach has two advantages: 1) the volume of fluid from which ultrafiltration occurs is limited to that within the vasculature, thereby magnifying increases in macromolecular concentration, and 2) comparisons of early and later samples collected from the outflow can provide information concerning the site of ultrafiltration in the pulmonary vasculature. Using this approach, we obtained information that suggests that more ultrafiltration occurs at the venous end of exchange vessels than at more arterial sites (9).…”