Extra-alveolar vessel contribution to hydrostatic pulmonary edema in in situ dog lungs

Gas exchange in the respiratory distress syndromes

This article describes the gas exchange abnormalities occurring in the acute respiratory distress syndrome seen in adults and children and in the respiratory distress syndrome that occurs in neonates. Evidence is presented indicating that the major gas exchange abnormality accounting for the hypoxemia in both conditions is shunt, and that approximately 50% of patients also have lungs regions in which low ventilation-to-perfusion ratios contribute to the venous admixture. The various mechanisms by which hypercarbia may develop and by which positive end-expiratory pressure improves gas exchange are reviewed, as are the effects of vascular tone and airway narrowing. The mechanisms by which surfactant abnormalities occur in the two conditions are described, as are the histological findings that have been associated with shunt and low ventilation-to-perfusion.

Effect of high transcapillary pressures on capillary ultrastructure and permeability coefficients in dog lung

To determine the correlation between ultrastructural and physiological changes in blood-gas barrier function in lungs transiently exposed to very high vascular pressures, we increased capillary transmural pressure (Ptm) of 6 canine isolated perfused left lower lung lobe preparations (high-pressure group) to 80.3 Torr for 3.8 min and then determined the capillary filtration (K(fc)) and osmotic reflection (sigma(d)) coefficients at a Ptm of 19.1 Torr in the ventilated lung lobes. This was followed by perfusion fixation of the lobes at a Ptm of 20.5 Torr for ultrastructural analysis. These data were compared with those obtained in six lobes in which Ptm was not transiently elevated before K(fc), sigma(d), and ultrastructural evaluation. K(fc) was higher [0.249 +/- 0.042 (SE) vs. 0.054 +/- 0.009 g. min(-1). Torr(-1). 100 g(-1); P < 0.01] and sigma(d) was lower (0.52 +/- 0.07 vs. 0.85 +/- 0.08; P < 0.01) in the high-pressure group. In contrast, although endothelial and epithelial breaks were occasionally observed in some experiments, their incidence was not increased in the high-pressure group. These data suggest that the increased transvascular water and protein flux occurred through pathways of a size not resolvable by electron microscopy after vascular perfusion-fixation at a Ptm of 20.5 Torr.

Segmental microvascular permeability in ischemia-reperfusion injury in rat lung

Segmental microvascular permeabilities were measured using pre- and postalveolar vessel capillary filtration coefficient (Kfc) values (ml. min-1. cmH2O-1. 100 g-1) in isolated rat lungs subjected to ischemia-reperfusion (I/R). Total Kfc values measured in flowing and nonflowing lungs were highly correlated (r = 0.98, P < 0.0001). Kfc values were then measured in another group of lungs under no-flow conditions when airway pressure was increased to 20 cmH2O and either the arterial or venous pressure was elevated to 7-8 cmH2O to measure the prealveolar and postalveolar Kfc values. Control total and postalveolar Kfc values were 0.0225 +/- 0.001 and 0.0219 +/- 0.001 ml. min-1. cmH2O-1. 100 g-1, respectively, and the prealveolar permeability was extremely small (0.00003 +/- 0.00005 ml. min-1. cmH2O-1. 100 g-1). Kfc values were again made in nonflowing lungs that had been subjected to 45 min of ischemia followed by 30 min of reperfusion. After I/R, the total membrane Kfc increased 10-fold to 0.2597 +/- 0.006 ml. min-1. cmH2O-1. 100 g-1, the prealveolar Kfc increased to 0.0677 +/- 0.003 ml. min-1. cmH2O-1. 100 g-1, and the postalveolar Kfc increased to 0.1354 +/- 0.008 ml. min-1. cmH2O-1. 100 g-1 (P < 0.05 for all I/R values). These data indicate that normal solvent microvascular permeability was predominantly postalveolar, and after I/R damage, the postalveolar (venular) permeability comprised 52% of the total, whereas the prealveolar and alveolar vessels comprised only 27 and 23%, respectively, of the total Kfc.

Effect of neuropeptide Y on hemodynamics of the rabbit lung

We evaluated the effect of neuropeptide Y (NPY) on the hemodynamics of the isolated rabbit lung perfused at constant flow and outflow pressure. Doses of 10(-8) and 10(-7) M NPY increased pulmonary arterial pressure (Ppa) from 11.5 +/- 1.0 (SE) mmHg to, respectively, 16.4 +/- 1.5 and 26.0 +/- 3.8 mmHg (P < 0.05, n = 5 mmHg lungs), with 78 +/- 4% of the increase at 10(-7) M resulting from an increased arterial resistance. At the latter dose, pulmonary capillary pressure increased from 5.8 +/- 0.9 to 9.4 +/- 1.0 mmHg (P < 0.05). When administered in the presence of norepinephrine, 10(-8) and 10(-7) M NPY (n = 6) produced extreme increases in Ppa to 66.1 +/- 20.5 and 114.7 +/- 25.5 mmHg, respectively, that were due primarily to an increased arterial resistance. To determine the significance of circulating NPY as a pulmonary vasoactive agent, we measured plasma NPY-like immunoreactivity in anesthetized rabbits after massively activating the sympathetic nervous system with veratrine. NPY-like immunoreactivity increased from 74 +/- 10 to 111 +/- 10 (SE) pM (P < 0.05). Thus, although NPY is a potent vasoconstrictor in the rabbit lung, it is not likely that plasma NPY concentrations rise sufficiently, even after massive sympathetic nervous system activation, to produce pulmonary vasoconstriction in the intact rabbit.

Stop-flow studies of distribution of filtration in rat lungs

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.

The influence of circulatory overload on extraalveolar microvessel endothelium of dog lung in vivo

In an earlier study from this laboratory, morphometric evaluations of the alveolar capillary endothelium of the lungs of intact dogs were recorded after periods of sustained increases of pulmonary microvascular pressures (D. O. DeFouw, W. O. Cua, and F. P. Chinard, 1983, Microvasc. Res. 25, 56-67). In the present study ultrastructural characteristics of the extraalveolar microvessel endothelium of these dog lungs were evaluated. Small (25- to 50-microns luminal diameter) nonmuscular vessels, which adjoin the alveolar capillaries, and larger (51-200 microns) partially muscular and muscular microvessels were assessed. After increased microvascular filtration, to be expected from the increased hydrostatic pressures, fluid accumulation was found only in the connective tissue sleeves of the larger microvessels. The endothelium of these partially muscular and muscular vessels was markedly affected by fluid distension of the periendothelial interstitium. The endothelial response included the appearance of basal (abluminal) surface invaginations, de novo plasmalemmal vesicle formation, and increased numbers of cytoplasmic vacuoles. The small nonmuscular microvessels lacked both the fluid cuffs and the alterations of endothelial ultrastructure. This latter observation is consistent with the previous report from this laboratory that indicated an absence of both alveolar septal edema and increased capillary endothelial vesicle densities in these lungs (DeFouw et al., 1983). Thus, it seems likely that the conformational changes of the endothelium of the larger microvessels were related to the formation of the periendothelial fluid cuffs. The mechanisms responsible for this endothelial response have not been determined but can be explained on the basis of the testable hypothesis that they are secondary to an increase of tissue pressure associated with accumulation of tissue fluid. These changes may thus represent a secondary structural adaptation to the increased tissue pressures and may serve as a potential vesicular-vacuolar pathway across the endothelium.

The effects of dobutamine, nitroprusside, or volume expansion on cardiac output and lung water after CPPV

Pulmonary microemboli can create an ARDS-like state in dogs (high pulmonary vascular resistance, pulmonary oedema and arterial hypoxemia). CPPV can correct the hypoxemia of pulmonary microemboli but reduces cardiac output (Q) and tissue oxygenation. This paper compares the effect of improving Q by infusing volume, reducing afterload, or increasing myocardial contractility. Four groups of seven dogs were studied. All had 0.125 g . kg-1 of starch microemboli (63-74 microns) infused and then CPPV at 15 cm H2O applied. The control group had no further treatment applied. In three other groups volume (dextran) or dobutamine or nitroprusside (NTP) was infused to return Q to the level before CPPV was applied. All treatments (volume, dobutamine and NTP) improved Q and O2 transport. Only the volume group had a significant increase in pulmonary microvascular pressure, Pmv = PLA + 0.4 (PPA - PLA) from 2.53 +/- 0.27 to 3.35 +/- 0.13 kPa, p less than 0.05. Only the volume group demonstrated a significant increase in lung water above (double) the control group as measured by a double indicator dilution technique (ETVL) and post mortem lung weights. We conclude volume infusions to improve a CPPV depressed Q may increase lung water and that better treatment would be to infuse NTP or dobutamine, thus maintaining a lower Pmv and therefore lung water. As a corollary the least CPPV should be applied to maintain adequate oxygenation and create the least need for interventions to improve Q.