Norman C. Staub

Beta-adrenergic agonists increase lung liquid clearance in anesthetized sheep.

We did experiments to determine whether beta-adrenergic agonists increase lung liquid clearance in anesthetized ventilated adult sheep and, if so, whether the increase is mediated by beta receptors and what mechanism is involved. We instilled 100 ml of autologous serum either alone or with a beta-adrenergic agonist (terbutaline, 10(-5) M, or epinephrine, 5.5 X 10(-6) M) into one lower lobe. After 4 h both terbutaline and epinephrine increased lung liquid clearance. The increase in lung liquid clearance was inhibited when propranolol (a beta blocker) or amiloride (a sodium channel blocker) was added to the terbutaline. Increased clearance was not explained by changes in pulmonary hemodynamics, pulmonary blood flow, or lung lymph flow. We conclude that beta-adrenergic agonists increase lung liquid clearance in anesthetized intact adult sheep. This increase is mediated through beta receptors and probably depends on increased active transport of sodium across the alveolar barrier.

Increased Sheep Lung Vascular Permeability Caused by Pseudomonas Bacteremia

In awake sheep, we compared the responses of lung lymph flow and lymph and plasma protein concentrations to steady state elevations of pulmonary vascular pressures made by inflating a left atrial balloon with those after an intravenous infusion of 10(5)-10(10)Pseudomonas aeruginosa. Lymph flow increased when pressure was increased, but lymph-plasma protein concentration ratios always fell and lymph protein flow (lymph flow x lymph protein concentration) increased only slightly. After Pseudomonas, sheep had transient chills, fever, leukopenia, hypoxemia, increased pulmonary artery pressure and lymph flow and decreased left atrial pressure and lymph protein concentration, 3-5 h after Pseudomonas, when vascular pressures and lymph protein concentrations had returned to near base line, lymph flow increased further to 3-10 times base line and remained at a steady level for many hours. During this steady state period, lymph-plasma protein concentration ratios were similar to base line and lymph protein flow was higher than in the increased pressure studies. Two sheep died of pulmonary edema 7 and 9 h after Pseudomonas, but in 16 studies, five other sheep appeared well during the period of highest lymph flow and all variables returned to base line in 24-72 h. Six serial indicator dilution lung water studies in five sheep changed insignificantly from base line after Pseudomonas. Postmortem lung water was high in the two sheep dead of pulmonary edema and one other, but six sheep killed 1-6 h after Pseudomonas had normal lung water. Because of the clear difference between the effects of increased pressure and Pseudomonas on lymphplasma protein concentration ratios and lymph protein flow, we conclude that Pseudomonas causes a prolonged increase in lung vessel permeability to protein. Because we saw lung lymph flow as high as 10 times base line without pulmonary edema, we conclude that lung lymphatics are a sensitive high-capacity mechanism for removing excess filtered fluid. An equivalent pore model of sheep lung vessels suggests that the changes we saw after Pseudomonas could result from small changes in the structure of exchanging vessel walls.

Preparation of chronic lung lymph fistulas in sheep.

Abstract The majority of lung lymph in the sheep drains through a large caudal mediastinal lymph node. At a preliminary operation, we remove the systemic lymph contamination. We obtain lung lymph by cannulating the efferent duct of the node. We use a physiologic test in which we elevate systemic and pulmonary venous pressures separately to show that the origin of the lymph is from the lung. The overall success rate in obtaining lung lymph flow for periods longer than 1 week is less than 50%. Successful animals are excellent models in which to study net lung fluid and protein flow.

Effect of increased vascular pressure on lung fluid balance in unanesthetized sheep.

In 20 unanesthetized sheep, we measured lung lymph flow and lymph and plasma protein concentrations during steady-state base-line conditions and during steady-state elevations of pulmonary microvascular hydrostatic pressure (range 3 to 23 cm H2O). In every sheep there was a base-line lung lymph flow (average 5.7 ± 2.5 (SD) ml/hour), demonstrating that net fluid filtration occurred. The base-line lymph-plasma total protein ratio averaged 0.69 ± 0.05, indicating a high protein osmotic pressure in the interstitial fluid at the filtration site. Lymph flow increased and lymph protein concentration decreased approximately linearly whenever hydrostatic pressure rose. A new steady-state condition was reached in 1–2 hours. The difference in plasma-to-lymph protein osmotic pressure increased by half the hydrostatic pressure increment (50% negative feedback regulation). Extravascular lung water content, measured post-mortem, did not change significantly until microvascular hydrostatic pressure more than doubled, indicating a large safety factor that protects the lungs against fluid accumulation normally. The major contributions to the safety factor appeared to be a sensitive and efficient lymph pump coupled to a washout of interstitial protein. The fluid filtration coefficient, whose calculation required many assumptions, averaged 1.64 ± 2.65 ml/(cm H2O x hour) in the base-line condition and did not change significantly over the pressure range studied.

Leukocytes are required for increased lung microvascular permeability after microembolization in sheep.

We studied the effects of uneven pulmonary artery obstruction by microemboli on steady state transvascular fluid and protein exchange in normal and leukopenic sheep. We measured pulmo- nary artery and left atrial pressures, cardiac output, lung lymph flow, and lymph plasma protein concentrations. Sheep were made profoundly leukopenic by administration of intra-arterial mechlor- ethamine hydrochloride (0.4 mg/kg, two doses) and colchicine (0.1-0.2 mg/kg, anesthetized sheep only). In anesthetized sheep, we injected glass beads 200 jum in diameter via the right atrium to raise pulmonary vascular resistance to 2-3 times baseline values. With normal levels of circulating leuko- cytes, sheep developed an increased protein-rich lymph flow from the lung characteristic of increased permeability edema. Leukopenic sheep had a significantly attenuated response after embolization for equivalent degrees of vascular obstruction. In unanesthetized sheep, we continuously infused air bubbles 1 mm in diameter via the right atrium to raise pulmonary vascular resistance to about 2 times baseline values. Each sheep served as its own control. With normal circulating leukocyte levels, there was an increase in protein-rich lymph flow from the lung during embolization. When the air infusion ended, the sheep recovered to the baseline condition in 24 hours. We induced emboli with the same amount of air when the sheep were profoundly leukopenic; lymph and protein flow from the lung were significantly less for equivalent degrees of obstruction. We conclude that circulating leukocytes are essential for the microvascular injury that results in increased permeability in the lungs of sheep after microembolization. Circ Res 48: 344-351, 1981

Response of Small Pulmonary Arteries to Unilobar Hypoxia and Hypercapnia

We measured the internal diameters of small muscular pulmonary arteries in the right and left lower lobes of lungs rapidly frozen in the anesthetized, open-thorax cat. In every cat the right lower lobe was ventilated with the test gas and all other lobes were ventilated with O2. In 4 cats, the test gas supplied to the right lower lobe was also O2 (control experiments); in 6, it was 100% N2 and in 6 it was 90% N2–10% CO2. In the 4 controls, there was no difference between the internal diameters of corresponding arteries in the right and left lower lobes. In the other 12 cats, there was a highly significant decrease in the diameter of arteries in the right lower lobe that correlated well with a large decrease in blood flow to that lobe, calculated using a shunt equation. Ventilation of the right lower lobe with 10% CO2 in air (4 cats) did not affect the diameter of arteries and ligation of the pulmonary artery to the right lower lobe resulted in only a slight decrease in arterial dimensions in 3 of 4 cats. These data show that in regional alveolar hypoxia without systemic hypoxia the muscular pulmonary arteries of the terminal respiratory units in the hypoxic region actively constrict. The constriction occurs with or without alveolar hypercapnia.

Lung fluid exchange after uneven pulmonary artery obstruction in sheep.

We studied steady state transvascular fluid and protein exchange after uneven obstruction of the pulmonary arteries. In anesthetized sheep, ventilated by positive pressure, we measured pulmonary artery and left atrial pressures, cardiac output, lung lymph flow, and lymph/plasma protein ratios. We calculated pulmonary vascular resistance. In 16 sheep we obstructed the pulmonary arteries with various microemboli or balloons in lobar arteries until pulmonary vascular resistance was 2-3 times baseline. In every experiment, lung lymph flow increased as pulmonary vascular resistance increased. The lymph/plasma protein ratio did not change. In four sheep, we increased left atrial pressure by balloon obstruction of the mitral orifice. Pulmonary artery pressure increased as much as in the embolization experiments and lymph flow increased but the lymph/plasma protein ratio decreased, meaning that the increased fluid and protein flux after embolization cannot be due to high pulmonary artery or pulmonary venous outflow pressures alone. In four sheep we compared obstruction of the lower lobe pulmonary arteries by balloons with that of upper lobe pulmonary arteries. Lower lobe arterial obstruction caused the lymph flow which drains predominantly from the lower lobes to decrease whereas upper lobe artery obstruction increased lymph flow. This means that the increased fluid and protein flux occurred mainly in the open, perfused portion of the microvascular bed. The mechanism of the increased fluid filtration and protein permeability may be related to high vascular pressure and high linear blood flow velocity through a markedly restricted microvascular bed, although release of substances that affect endothelial permeability is not ruled out.

Micropuncture measurement of lung microvascular pressure profile during hypoxia in cats.

To determine the lung microvascular pressure profile during hypoxia, we micro-punctured the subpleural microtirculation of isolated perfused cat lungs. Our procedures involvedexsanguinating a cat, then cannulating its pulmonary artery, left atrium, and trachea. Using thecats own blood, we perfused the lungs at pulmonary artery and left atrial pressures of 18 and 9cm water, respectively, to obtain lung blood flow of 81 ± 29 ml/(kg body weight ± min), whichwe held constant throughout the experiment. We stabilized the lung surface with a vacuum ringand micropunctured 30- to 50-μm arterioles and venules to measure microvascular pressure bythe servo-null method. During micropuncture, we held the lungs at constant inflation usingairway pressure of 8 cm water. We varied the oxygen concentration of the inflation gas from 30%during baseline to 2% during hypoxia. We studied groups with high (±7.5) or normal pH. Duringnormoxia, 27, 44, and 29% of the pressure drop occurred in the arterial, capillary and venoussegments, respectively. During hypoxia, the increase in pulmonary vascular resistance, which wasmarked in both groups, was significantly greater in the normal pH group. All segmental pressuredrops increased significantly during hypoxia. However, the predominant increase occurred in thearteries where segmental pressure drop increased by 148% and 210%, respectively, in the highand normal pH groups. We conclude that the major site of hypoxic vasoconstriction is in thepulmonary arteries.

Relationship of pleural effusions to increased permeability pulmonary edema in anesthetized sheep.

Abstract We studied anesthetized sheep to determine the relationship between increased permeability pulmonary edema and the development and mechanism of pleural effusion formation. In 12 sheep with intact, closed thoraces, we studied the time course of pleural liquid formation after 0.12 ml/kg i.v. oleic acid. After 1 h, there were no pleural effusions, even though extravascular lung water increased 50% to 6.0 +/- 0.7 g/g dry lung. By 3 h pleural effusions had formed, they reached a maximum at 5 h (48.5 +/- 16.9 ml/thorax), and at 8 h there was no additional accumulation of pleural liquid (45.5 +/- 16.9 ml). Morphologic studies by light and electron microscopy demonstrated subpleural edema but no detectable injury to the visceral pleura, suggesting that the pleural liquid originated from the lung and not the pleura. In nine sheep, we quantified the rate of formation of pleural liquid by enclosing one lung in a plastic bag. By comparing in the same sheep the volume of pleural liquid collected from the enclosed lung to the volume found in the opposite intact chest, we estimated the rate of liquid absorption from the intact chest to be 0.32 ml/(kg.h); we had previously reported a liquid absorption rate of 0.28 ml/(kg.h) in normal sheep. These studies also supported the conclusion that the majority of the pleural liquid originated from the lung because we could account for all of the pleural liquid that was formed and cleared. The volume of pleural liquid collected from the enclosed lungs was equal to 21% of the excess lung liquid that formed after oleic acid-induced lung injury. Thus, the pleural space and parietal pleural lymphatic pathways are important pathways for the clearance of pulmonary edema liquid after experimentally induced increased permeability pulmonary edema.

Pulmonary capillary length in dog, cat and rabbit

Abstract We perfused isolated, air-filled lungs of dog, cat and rabbit via the pulmonary artery with whole blood followed by olive oil stained black. The oil did not pass into the capillary bed so that the arteries were black and the veins red. We rapidly froze the lungs and on random samples we measured the average minimal capillary path between arterioles (less than 60 μ diameter) and venules (less than 60 μ diameter) both on the lung surface and in the interior in different planes. The average length of pulmonary capillaries is 600–800 μ in dog and cat and 550–650 μ in rabbit. On the average each capillary is continued over 5 to 7 different alveoli. Using available data on red cell velocity in capillaries at the pleural surface in closed-thorax, anesthetized animals we calculated the average transit time (contact time) of red cells with alveolar gas to be 0.35 to 1.7 sec (average 0.8 sec). This is essentially the same as determined by the indirect measurement of pulmonary capillary blood volume by carbon monoxide methods. There is thus adequate time of oxygen diffusion and reaction with hemoglobin to reach completion.