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PubMed2004

Fluid balance.

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Blood Volume↗
PubMed1979

Lung fluid balance in awake newborn lambs with pulmonary edema from rapid intravenous infusion of isotonic saline.

To study pulmonary transvascular filtration of fluid and the normal adaptive response of newborn animals to excessive water in the lungs, we measured lung lymph flow, pulmonary vascular pressures, and the concentration of protein in lymph and plasma of nine unanesthetized 1- to 3-wk-old lambs, before, during, and after a rapid iv infusion of isotonic saline, 130-250 ml/kg.hr for 3-4 hr. During infusions, lung vascular pressures increased, the transvascular gradient of protein osmotic pressure decreased, and there was a 2- to 5-fold increase of lung lymph flow. When infusions stopped, lymph flow decreased, as the concentration of protein in plasma increased and pulmonary vascular pressures decreased to new steady-state levels. The concentration of protein in lymph did not change for several hours after the infusions. Body weight increased by 28% and extravascular lung water content was 19% above normal after saline; these changes were associated with mild tachypnea, hypercarbia, and hypoxemia. Sections of lung from these lambs had prominent cuffs of fluid surrounding large blood vessels.

Animals↗
PubMed1986

Mechanics of lung fluid balance.

Recent research in pulmonary physiology, anatomy, and mechanics have clarified our general understanding of liquid and solute transport through the lung. Fluid crosses the microvascular endothelial membrane at a rate that depends on gradients in the transmembrane hydrostatic and osmotic pressures and the conductance of the permeable membrane. Under normal conditions, the filtered fluid is removed by an efficient lymphatic pump. Edema accumulates in the lung when an increased flux due to an elevated vascular pressure or to a more permeable membrane is not matched by an adequate lymph clearance rate. Initially a favorable hydrostatic pressure gradient drives the excess fluid into interstitial spaces surrounding large blood vessels and airways away from filtration sites near capillaries and thereby ensures efficient gas exchange. Further edema formation reduces the pressure gradient, eventually leading to the flooding of alveolar air spaces and impaired gas exchange. I will focus on the role of the above forces in the regulation of extravascular lung water. It will become clear that many details of the general scheme are not known, and our conceptual understanding of the relevant mechanisms involved is often rudimentary and incomplete. Some of the more important questions pertain to the interstitial pressure around capillaries, the resistance and compliance of the interstitial matrix, and the role of the lymphatics in regulating interstitial fluid volume and interstitial pressure.

Animals↗
PubMed1982

Effect of ADP-induced platelet aggregation on lung fluid balance in sheep.

The effects of platelet aggregation (PA), induced by an intravenous injection of adenosine 5'-diphosphate (ADP), on pulmonary fluid and protein exchange and on arterial blood gases were determined in artificially ventilated sheep prepared with lung lymph fistulas. ADP injection produced small increases (P less than 0.01) in pulmonary lymph flow (Qlym) and transvascular protein clearance (Qlym X lymph-to-plasma protein concentration ratio). These changes were not associated with significant increases in pulmonary arterial and left atrial pressures, pulmonary blood flow, or pulmonary vascular resistance. ADP-induced PA did not increase the pulmonary endothelial permeability to proteins, because an elevation of pulmonary microvascular pressure (Pmv), induced by inflation of a left atrial balloon catheter, produced the same increases in Qlym and protein clearance as in normal sheep after comparable increases in Pmv. The increases in Qlym and protein clearance can be explained by an increase in pulmonary vascular surface area. ADP-induced PA decreased the arterial oxygen tension, which was sustained for the 3 h duration of the study; the arterial carbon dioxide tension did not change and the arterial pH decreased (P less than 0.05) after PA. Chronic depletion of platelets with antiplatelet serum prevented the increases in Qlym and protein clearance and the arterial hypoxemia, indicating that these changes were the direct result of PA. Thus ADP-induced PA in sheep increased pulmonary fluid filtration and protein clearance by an increase in the vascular surface area. Also PA produced a rapid and prolonged arterial hypoxemia, which may result from the release of vasoactive and bronchoactive factors causing a maldistribution of ventilation and perfusion.

Adenosine Diphosphate↗
PubMed1981

Effects of epinephrine and norepinephrine infusion on lung fluid balance in sheep.

The effect of an intravenous infusion of epinephrine or norepinephrine (45 microgram.kg-1.min-1) on the transcapillary exchange of fluid and protein were studied in anesthetized sheep prepared with lung lymph fistulas. After infusion of epinephrine, pulmonary lymph flow (Qlym) and the ratio of lymph to plasma protein concentration (L/P) did not change significantly from base line despite an increase in mean pulmonary arterial pressure (Ppa) from 17.3 +/- 0.8 to 22.6 +/- 0.09 Torr, In contrast, Qlym increased (p less than 0.05) from 9.24 +/- 1.53 to 11.46 +/- 1.97 ml/h and L/P decreased (p less than 0.05) from 0.78 +/- 0.03 to 0.74 +/- 0.04 after infusion of norepinephrine; these changes were associated with an increase in Ppa from 16.5 +/- 1.5 to 21.6 +/- 1.8 Torr. Pulmonary vascular resistance (PVR) increased from 5.90 +/- 0.83 to 12.12 +/- 1.23 Torr. 1-1 min (p less than 0-.01) after epinephrine and from 6.52 +/- 0.82 to 9.26 +/- 1.74 Torr.1-1 min (p less than 0.05) after norepinephrine. Left atrial hypertension, induced in four sheep infused with norepinephrine and in five sheep infused with epinephrine by inflating a left atrial balloon, increased Qlym and decreased L/P in all animals. Thus the infusions of epinephrine or norepinephrine did not increase lung vascular permeability to proteins. Epinephrine infusion also did not increase fluid filtration despite increases in Ppa and PVR, suggesting that pulmonary microvascular pressure did not increase significantly due to greater constriction of precapillary than postcapillary vessels. However, norepinephrine infusion increased filtration, suggesting that microvascular pressure was increased due to a greater constriction of postcapillary than precapillary vessels.

Animals↗
PubMed2004

Spectrum of ion channels in alveolar epithelial cells: implications for alveolar fluid balance.

The efficient transition from placental to atmospheric delivery of oxygen at birth is critically dependent on rapid reabsorption of fetal lung fluid. In the perinatal period, this process is driven by active transepithelial sodium transport and is almost exclusively dependent on expression and modulation of the amiloride-sensitive epithelial sodium channel (ENaC). However, later in development, the amiloride sensitivity of the reabsorptive response, which must be sustained to keep the lungs effectively dry, wanes as a function of postnatal age. This Featured Topic (Experimental Biology Meeting, Washington, DC, April, 2004) presented exciting new evidence to demonstrate that, in addition to ENaC, the adult alveolar epithelium expresses a plethora of amiloride-insensitive ion channels, including cystic fibrosis transmembrane conductance regulator, proton channels, voltage-dependent potassium channels, and cyclic nucleotide-gated cation channels. Furthermore, important evidence for selective modulation of ENaC subunits in the lung in response to cardiovascular disease was demonstrated. Finally, it is clear that newly emerging models of human alveolar epithelium in combination with the novel lung slice electrophysiological preparation will ensure that the ascription of function to specific ion channels in the in situ human lung will soon be a real possibility.

Animals↗
PubMed1980

Lung fluid balance in hypoxic, awake newborn lambs and mature sheep.

To study the pulmonary vascular response to hypoxia and associated transvascular flow of fluid into the lungs of newborn lambs and mature sheep, we collected lung lymph and measured pulmonary vascular pressures and blood flow in 14 unanesthetized lambs and 9 sheep breathing 10-12% oxygen for 3-6 h after a 2-hour control period in air. In both groups of animals, pulmonary arterial pressure, blood flow, and lung vascular resistance increased with hypoxia, but only in lambs did the flow of lymph increase and th concentration of protein in lymph decrease with hypoxia. These results suggest that hypoxia increased transvascular filtration of fluid into the lungs of the lambs by increasing hydraulic pressure in the pulmonary microcirculation. In sheep, the vascular response to hypoxia did not increase lung fluid filtration. Hypoxia had no effect on microvascular permeability to protein in the lungs of either group of animals.

Age Factors↗