Effects of dextran 70 on hemodynamics and lung liquid and protein exchange in awake sheep.

We studied the effect of intravenous dextran 70 infusion on lung liquid and protein exchange to determine whether its effects were due to altered hemodynamics or to altered microvascular permeability. In each of six instrumented awake sheep with chronic lung lymph fistulas, we performed three experiments: 1) control, 2) a 30-minute infusion of 1 l of 6% dextran 70, and 3) an infusion of 1 l of 0.9% NaCl. In addition to pulmonary hemodynamics and lymph dynamics, we measured the plasma-to-lung lymph equilibration rate of [125I] albumin. We followed all the sheep for 10 hours, including a 2-hour baseline period. Dextran was more effective in expanding plasma volume (63 +/- 15% [mean +/- SD]) than saline (11 +/- 6%) at the end of the 30-minute infusion. Pulmonary vascular pressures increased after dextran and remained elevated for 8 hours, whereas after saline the pressures returned to baseline within 1 hour. After dextran, lung lymph flow increased and remained elevated. It was only transiently increased after saline. We confirmed that dextran equilibrated rapidly with lung lymph (half-time, less than 0.6 hour), even though it maintained plasma volume expansion for the whole body (half-time, 11.1 +/- 2.7 hours). The dextran increased both plasma and lymph total macromolecular osmotic pressure but did not increase the plasma-interstitial (lymph) osmotic pressure difference in the lung, except transiently during the infusion. The lymph/plasma protein concentration ratio increased after dextran due mainly to plasma protein dilution. There were no differences in the half-time of tracer albumin equilibration between plasma and lung lymph (control, 2.2 +/- 0.6 hours; saline, 2.0 +/- 0.6 hours; dextran, 2.3 +/- 0.6 hours). Dextran 70 increased liquid filtration mainly by increasing microvascular pressure and possibly filtration surface area. There was no evidence for a change in the leakiness of the lung microvascular barrier to albumin.     

Pulmonary microvascular and alveolar epithelial permeability characteristics in N-nitroso-N-methylurethane-injected dogs

The subcutaneous injection of 5 to 6 mg/kg of body weight of N-nitroso-N-methylurethane (NNNMU) has been reported to cause acute alveolar injury in animals. To determine the permeability characteristics of the alveolar epithelium, we employed the in vivo saline-filled dog lung model and determined the time to 50 percent equilibration in minutes of a specific tracer in the blood and the lung model and determined the time to 50 percent equilibration in minutes of a specific tracer in the blood and the lung liquid (T 1/2) for endogenous serum albumin (MW 69,000 daltons, molecular radius 35 A) and exogenously administered 500,000 MW polydispersed dextrans (molecular radius 200 A). Compared to control animals, T1/2 decreased (permeability increased) in NNNMU-injected dogs from 3,500 +/- 100 to 682 +/- 160 minutes for albumin and from 20,000 +/- 250 to 2,790 +/- 750 minutes for 500,000 MW dextran (P less than 0.001). To determine the permeability characteristics of the pulmonary microvasculature, we employed the right lymph duct cannulation dog model and measured lymph flow/30 minutes, lymph albumin and dextran concentration, and lymph/plasma albumin and dextran ratios in control and NNNMU-injected dogs. Compared to control animals, lymph flow was significantly greater in NNNMU dogs, 2.07 +/- 1.1 vs .71 +/- .50 ml/30 minutes (P less than 0.01), respectively. We conclude that NNNMU injection increases permeability in both the alveolar epithelium and the pulmonary microvasculature.     

PEEP increases non-pulmonary microvascular fluid flux in healthy and septic sheep

The potential for significant interaction between PEEP and the peripheral microcirculations is not as well appreciated as are its central circulatory effects. Therefore, we studied the effects of PEEP, 15 mm Hg, on microvascular fluid flux in the hindlimb of ten mature sheep. Changes in prefemoral lymph flow (QL) and in lymph to plasma [L/P] total protein (TP) ratios were measured following the application of PEEP for 2 h, before and during hyperdynamic sepsis. Sepsis was induced by cecal ligation and perforation (CLP). Although the onset of sepsis was not associated with an increase in prefemoral QL, the [L/P] ratio of iodinated 125I human serum albumin (125I-HSA) was significantly greater 72 h after CLP than during the nonseptic baseline study. Histologic examination of gastrocnemius muscle also demonstrated an increase in protein-rich interstitial edema during the septic studies. During the 2 h of PEEP, prefemoral QL increased equally (p less than 0.05) in three study periods: (1) baseline nonseptic, delta QL = +1.2 +/- 1.4 ml/h; (2) septic period 1, 24 to 48 h after CLP, delta QL = +1.3 +/- 1.2 ml/h; and, (3) septic period 2, 72 h after CLP, delta QL = 1.0 +/- 0.6 ml/h. Calculated microvascular hydrostatic pressures also rose significantly during PEEP therapy in all three study periods. We conclude that PEEP, 15 mm Hg, increased hindlimb microvascular fluid flux and may thereby increase interstitial fluid content in tissues drained by the prefemoral lymph node. These effects of PEEP were not aggravated by hyperdynamic sepsis, despite a presumed increase in systemic microvascular permeability at this time.     

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 times hour) in the base-line condition and did not change significantly over the pressure range studied.     

Plasma-lymph albumin kinetics, total lymph flow, and tissue hematocrit in normally hydrated dog lungs

Lung lymph flow was normalized for lung weight and total lung lymph flows were calculated in five mongrel dogs using a kinetic analysis of albumin distribution between the pulmonary capillaries, interstitial fluid, and pulmonary lymph. Using prenodal tracheobronchial lymph an intravenous bolus of 125I-labeled albumin equilibrated between plasma and lymph with mean T1/2 of 2 hr 22 min. The mean volume of interstitial fluid drained by the cannulated lymphatics was 9.9 ml which corresponded to the extravascular albumin distribution volume of 31% of the total lung weight. Lung tissue hematocrit was determined using 51Cr-labeled red cells and 125I-albumin and averaged 92% of the simultaneous mixed venous hematocrit. The extravascular albumin and 99mTc-DTPA (diethylenetriamine pentacetic acid) spaces in lung were corrected for differences between tissue and mixed venous hematocrit and were 18.5 and 33.0 ml/100 g, respectively. This indicated that albumin distributed in 57% of the interstitial volume at 4 hr after injection. Lung lymph flow normalized to postmortem lung mass during baseline conditions was 0.060 ml/min/100 g after correction for tissue hematocrit differences. Normalized lymph flows are used for quantitative comparisons of lung lymph protein flux data between different types of experiments.     

Combined monitoring of thoracic duct and lung lymph during E. coli sepsis in awake sheep

A thoracic duct lymph fistula in combination with a lung lymph fistula in the awake sheep was used to evaluate effects of thoracic lymph diversion during a septic insult and to monitor systemic and local changes in the lung and gastrointestinal tract. Live Escherichia coli 10(9) kg-1 b.w. were infused in 9 sheep. After sepsis, arterial pressure, cardiac output, partial pressure of oxygen, leukocytes and platelets decreased significantly compared to baseline values. Pulmonary arterial pressure increased significantly throughout the experiment with peak values at 44 +/- 4 mmHg after 15 minutes. Lung lymph flow (QL) (n = 6) increased from 23 +/- 0.5 to 11.2 +/- 2.4 ml/30 minutes after 60 minutes. QL then decreased but remained elevated. Lymph to plasma protein concentration ratio (L/P) in lung lymph decreased from 0.62 +/- 0.02 during baseline to 0.47 +/- 0.04 after 60 minutes. L/P then increased and was, after 150 minutes, no longer different from baseline. These lung lymph data favor increased pulmonary microvascular permeability during sepsis. Lymph flow in the thoracic duct (QT) (n = 9) increased from 34.2 +/- 6 to 58.3 +/- 9 ml/30 minutes during the first 30 minutes after bacterial infusion. QT was, after 90 minutes, back to baseline but then progressively increased. L/P in thoracic lymph steadily increased from 0.56 +/- 0.03 to 0.78 +/- 0.04. Thromboxane B2 and 6-keto PGF1 alpha in thoracic duct and lung lymph increased significantly after bacterial infusion and remained elevated thereafter. Combined monitoring of thoracic duct and lung lymph enabled comparison of systemic and pulmonary reactions in septic sheep.     

Effect of heparin on increased pulmonary microvascular permeability after bone marrow embolism in awake sheep

We examined the alterations in pulmonary transvascular fluid and protein exchange after intravenous infusion of fat emboli, i.e., bone marrow suspension (BMS) in awake sheep prepared with chronic lung lymph fistulas and compared these changes with those observed in sheep pretreated with heparin. The BMS injection (0.2 ml/kg) over 15 min caused rapid, but transient, increases (p less than 0.05) in mean pulmonary artery pressure and pulmonary vascular resistance. These increases were accompanied by significant increases in the lymph concentrations of thromboxane B2 and 6-keto-PGF1 alpha. Pulmonary lymph flow increased by 3.9-fold (+/- 0.8) over baseline by 120 min after BMS with no change in the lymph-to-plasma protein concentration ratio (L/P ratio). Heparin pretreatment (700 U/kg) enhanced the BMS-induced increases in pulmonary artery pressure and pulmonary vascular resistance. Thromboxane B2 concentrations in the lymph increased, whereas there was no change in the concentration of 6-keto-PGF1 alpha. Lung lymph flow increased 4-fold (+/- 1.0) over baseline by 120 min after BMS without a change in L/P ratio. Changes in lung vascular permeability were evaluated by elevating pulmonary microvascular pressure (left atrial balloon catheter inflation) at 120 min after BMS. Lung lymph flow increased 7-fold (+/- 1.1) from baseline, whereas the L/P ratio decreased to a mean value of 0.48 +/- 0.03. The protein reflection coefficient (sigma = 1 - L/P ratio) decreased from a control mean of 0.69 +/- 0.02 to 0.52 +/- 0.03 after the BMS challenge.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute effect of paraquat on lung fluid balance and prostanoid production in awake sheep

Paraquat, a widely used herbicide, causes severe lung damage in humans and laboratory animals. Pulmonary edema is a common initial feature of paraquat toxicity, but its pathophysiology is not well understood. The purpose of this investigation was to determine the acute toxic effect of paraquat (30 mg/kg) on pulmonary transvascular protein and fluid fluxes, histologic features, and prostanoid production, using awake sheep with chronic lung lymph fistulas (n = 6). Lung lymph flow increased significantly 3.5 h after intravenous infusion of paraquat and rose to 2.6 times baseline within 8 h (from 4.4 +/- 0.4 to 11.4 +/- 1.5 ml/h, p less than 0.05). Lymph-plasma protein concentration ratio increased during the same time period (from 0.64 +/- 0.05 to 0.75 +/- 0.04, p less than 0.05). Lung lymph protein clearance also increased at 3.5 h and remained elevated throughout the duration of the experiment. Pulmonary arterial and left atrial pressure were only slightly altered. Plasma and lung lymph thromboxane A2 (as TXB2) concentrations were significantly increased at 30 min and continued so thereafter. Plasma and lung lymph prostacyclin (6-keto-PGF1 alpha) concentrations increased significantly at 3 h and were more than 5 times baseline by 7 h. The time course of the increase in 6-keto-PGF1 alpha concentrations seemed similar to that of lung lymph flow. The high flow of protein-rich lymph strongly suggested an increase in pulmonary vascular permeability, which may indicate pulmonary endothelial damage. Histologic studies of the lungs revealed only minor changes in perivascular cuffing, minimal alveolar hemorrhage, and slight neutrophilic alveolar wall infiltration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of dobutamine on lung microvascular fluid flux in sheep with "sepsis syndrome"

The effect on pulmonary fluid balance of adrenergic receptor agonist agents commonly employed in clinical sepsis has not been well characterized. Therefore, we tested the hypothesis that dobutamine would increase pulmonary microvasular fluid flux in experimental sepsis-induced lung injury. To define the effects of this synthetic catecholamine on pulmonary lymph flow (QL), we infused dobutamine in sheep at two doses in sequence (5 micrograms/kg/min and 10 micrograms/kg/min) before and after the induction of intraperitoneal sepsis which resulted in the development of lung microvascular injury. In the nonseptic state, cardiac output increased at both 5 micrograms/kg/min and 10 micrograms/kg/min (22 and 36 percent, respectively), while QL was unchanged from baseline (for 5 micrograms, delta QL = +0.44 +/- 1.35 ml/15 min; not significant) (for 10 micrograms, delta QL = -0.20 +/- 1.0 ml/15 min; not significant). Values for the ratio of lymph/plasma total protein levels [( L/P]TP) fell modestly in the nonseptic study at both doses (p less than 0.05). With established sepsis syndrome, QL increased from the nonseptic baseline study (2.99 +/- 1.8 to 7.01 +/- 3.95 ml/15 min; p less than 0.05), without change in [L/P]TP ratios or the calculated microvascular hydrostatic pressure. (Pmv) During sepsis, dobutamine infusion was again associated with an increase in cardiac output at both the 5 micrograms/kg/min (+29 percent) and 10 micrograms/kg/min (+33 percent) doses, while QL increased modestly only with the lower dose of dobutamine infused (5 micrograms/kg/min, delta QL = 1.80 +/- 2.2 ml/15 min; p less than 0.05). In this model of sepsis-induced lung injury, dobutamine increased systemic flow without substantially augmenting QL.     

Tissue to plasma capillary permeability of 131I-albumin in the perfused rabbit ear

The tissue to plasma transfer of 131I-albumin was recorded in perfused rabbit ears (n = 6) following equilibration for 24 hr. 125I-fibrinogen served as the plasma marker, and was introduced intravenously 15 min before clamping. The ears were rollerpump perfused with isotonic diluted plasma at a constant rate of (mean +/- SD) 5.1 +/- 1.5 ml (min.100 g)-1. The mean extravascular albumin distribution volume was 12.4 +/- 1.1 ml.100 g-1, and the fibrinogen volume (plasma volume in tissue) was 3.1 +/- 0.4 ml.100 g-1 as determined from biopsies of the contralateral ear. The initial transfer of albumin was marked, and occurred at rates corresponding to a unidirectional clearance (Cl(0)) of 0.068 +/- 0.012 ml (min.100 g)-1. However, with a reduction of mean interstitial albumin tracer content of no more than 4%, net transport decreased to reach slowly declining levels 5 to 10 times lower within 10 min of continued perfusion. The decrease was considered due to rapid exhaustion of a small interstitial pool of tracer immediately adjacent to the exchange vessel membrane, followed by an increasingly retarded outwash from more distant areas. The results suggest a bimodal structural resistance to albumin movement: a relatively low resistance in the capillary membrane, and a considerable restriction to albumin transport located within the interstitial space.     

Lung edema caused by high peak inspiratory pressures in dogs. Role of increased microvascular filtration pressure and permeability

Mechanical ventilation with high peak airway pressures (Paw) has been shown to induce pulmonary edema in animal experiments, but the relative contributions of transvascular filtration pressure and microvascular permeability are unclear. Therefore, we examined the effects of positive-pressure ventilation on two groups of open-chest dogs ventilated for 30 min with a peak Paw of 21.8 +/- 2.3 cm H2O (Low Paw) or 64.3 +/- 3.5 cm H2O (High Paw). No hemodynamic changes were observed in the Low Paw group during ventilation, but mean pulmonary artery pressure (Ppa) increased by 9.9 cm H2O, peak inspiratory Ppa by 24.6 cm H2O, and estimated mean microvascular pressure by 12.5 cm H2O during High Paw ventilation. During the same period, lung lymph flow increased by 435% in the High Paw and 35% in the Low Paw groups, and the terminal extravascular lung water/blood-free dry weight ratios were 5.65 +/- 0.27 and 4.43 +/- 0.13 g/g, respectively, for the two groups. Lung lymph protein clearances and minimal lymph/plasma ratios of total protein were significantly higher (p less than 0.05) after 2 h of increased left atrial pressure (PLA) in the High Paw group versus the Low Paw group, which indicates a significant increase in microvascular permeability. Lymph prostacyclin concentration in pulmonary lymph, measured as the stable metabolite 6-0-PGF1 alpha, was increased significantly by 70 to 150% from baseline (p less than 0.05) in both groups during the periods of increased Paw and increased PLA, but it was not significantly different between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of naloxone on the pulmonary vascular responses to graded levels of intracranial hypertension in anesthetized sheep

We increased intracranial pressure (ICP) in anesthetized sheep for 3 h by connecting the cisterna magna to an elevated reservoir of buffered saline. We monitored systemic and pulmonary vascular pressures, pulmonary blood flow, and the flow of lymph from the lungs. The volume and protein concentration of the lymph were used to assess changes in lung vascular permeability-surface area. Extravascular lung water was measured postmortem, and in vivo indicator dilution studies were used to measure permeability-surface area product (PS urea) of the lung circulation for a small hydrophillic molecule (14C-urea) and extravascular water volume (VH2O). These studies were done in 16 sheep with ICP raised to 0, 60, or 100 mmHg. Thirteen other sheep received naloxone before and during elevation of ICP to 0, 60, or 100 mmHg. Elevation of ICP increased pulmonary artery pressure (Control: 16 +/- 3 cmH2O; ICP: 60 mmHg = 16 +/- 2 cmH2O; ICP: 100 mmHg = 23 +/- 2 cmH2O), cardiac output (Control: 2.7 +/- 0.1 L/min; ICP: 60 mmHg = 3.3 +/- 0.05, p less than 0.05; ICP: 100 mmHg = 5.3 +/- 1.0, p less than 0.05), lung lymph flow (Control: 94 +/- 8% baseline; ICP: 60 mmHg = 193 +/- 25% baseline, p less than 0.05; ICP: 100 mmHg = 285 +/- 38% baseline, p less than 0.05), PS urea (Control: 7.0 +/- 0.5 ml/s; ICP: 60 mmHg = 11.0 +/- 3.7 ml/s; ICP: 100 mmHg = 12.4 +/- 1.3 ml/s, p less than 0.05), and VH2O (Control: 93 +/- 8% baseline; ICP: 60 mmHg = 112 +/- 6% of baseline; ICP: 100 mmHg = 129 +/- 13% of baseline, p less than 0.05) proportional to the level of ICP. Sheep with ICP raised to 100 mmHg had modestly increased lung water (pulmonary edema).(ABSTRACT TRUNCATED AT 250 WORDS)     

Thromboxane A2 mediates increased pulmonary microvascular permeability following limb ischemia

Lower torso ischemia and reperfusion lead to respiratory dysfunction characterized by pulmonary hypertension and increased lung microvascular permeability. This is associated with lung leukosequestration and thromboxane (TX) generation. This study tests the role of elevated TX levels following muscle ischemia in mediating remote lung injury. Anesthetized sheep prepared with chronic lung lymph fistulae underwent 2 hours of bilateral hind limb tourniquet ischemia. In untreated controls (n = 7), 1 minute after reperfusion there was a transient increase in plasma immunoreactive (i)-TXB2 levels from 211 to 735 pg/ml (p less than 0.05), and at 30 minutes, lung lymph i-TXB2 levels rose from 400 to 1,005 pg/ml (p less than 0.05). At 1 minute, the mean pulmonary arterial pressure (MPAP) increased from 13 to 38 mm Hg (p less than 0.05) and pulmonary microvascular pressure (Pmv) from 7 to 18 mm Hg (p less than 0.05). Lung lymph flow (QL) rose from 4.3 to 8.3 ml/30 min (p less than 0.05), the lymph/plasma (L/P) protein ratio was unchanged from 0.6, and the lymph protein clearance increased from 2.6 to 4.6 ml/30 min (p less than 0.05). Two hours after reperfusion, neutrophils were observed sequestered in lung capillaries and proteinaceous exudates were found in alveoli in contrast to sham-operated animals (n = 3). To maximize lung vascular surface area and achieve a pressure independent L/P protein ratio a left atrial balloon was inflated during one group of ischemia-reperfusion experiments (n = 5). This resulted in a baseline rise in MPAP to 20 mm Hg (p less than 0.05); a 4.3-fold increase in QL (p less than 0.05), a decrease in the L/P ratio from 0.70 to 0.28 (p less than 0.05) and a protein reflection coefficient (sigma d) of 0.72. During reperfusion the L/P ratio rose to 0.49 (p less than 0.05) and the sigma d decreased to 0.51 (p less than 0.05), documenting an increase in lung microvascular permeability. In contrast to untreated ischemic controls, inhibition of TX synthetase with OKY 046 (n = 6) reduced plasma i-TXB2 levels to 85 pg/ml (p less than 0.05) but also increased i-6-keto-PGF1 alpha levels to 78 pg/ml relative to 15 pg/ml in untreated controls (p less than 0.05). OKY 046 prevented the increase in MPAP, Pmv, QL, and lymph protein clearance (p less than 0.05). Lung histology was normal in distinction to the leukosequestration in untreated ischemic controls.(ABSTRACT TRUNCATED AT 400 WORDS)     

Pulmonary fibrin deposition and increased microvascular permeability to protein following fibrin microembolism in dogs: a structure-function relationship

The effects of fibrin microembolism were examined using an infusion of a prothrombin activator (Echis carinatus venom, ECV; 30 min, 0.5 NIH thrombin equivalent units/kg) in acute mongrel dogs prepared with a pulmonary lymph cannula (n = 6, 12.3-21.5 kg). Lymph flow increased approximately 2.5-fold after 1-1.5 hr of elevated left atrial pressure (Pla = 20 cm H2O; 26 +/- 7 to 63 +/- 16 microliter/min, P less than 0.01) and the plasma to lymph protein concentration ratio (CP/CL) declined from 0.66 +/- .04 to 0.54 +/- .16 (P less than 0.01, x +/- SE). After Pla was reduced to control levels, the initiation of fibrin microembolism was associated with an approximate 2.7-fold elevation of lymph flow (62 +/- 8 microliters/min, P less than 0.01) and the CP/CL was not changed (0.56 +/- 0.04, P = ns). When Pla was increased following microembolism, lymph flow more than doubled to 117 +/- 24 microliter/min (P less than 0.01) and the CP/CL remained unaltered (0.56 +/- 0.03, P = ns). These changes were associated with afibrinogenemia and the appearance of fibrin degradation products (FDP) in plasma (150 +/- 50 micrograms/ml) and lymph (80 micrograms/ml) in three of the animals tested. No consistent pattern was seen in the CL/CP of separate endogenous plasma proteins after each intervention. These data support the view that pulmonary fibrin microembolism without inhibition of the fibrinolytic system was associated with an early increased pulmonary microvascular permeability to protein. In a separate group of similarly prepared animals (n = 8, 13-21.5 kg) without a lymph catheter, scanning electron microscopic observations showed branching fibrin microemboli to partially occlude some pulmonary arterioles. Mixed thrombus formations in larger precapillary blood vessels were also seen. Ultrastructural observations revealed the deposition of fibrin strands (periodicity = 220-230 A) within the pulmonary capillaries. Some of these deposits were overlaid by lamellar pseudopodia from endothelial cells and the fibrin appeared to be within these cells. Although plasmalemmal vesicles seemed to be more numerous in the endothelial cells with adjacent fibrin deposits, no gaps or breaks were seen in the densely stained interendothelial cell junctions and/or the endothelial cell membrane of the affected lung capillaries. Activated neutrophils and platelets were more numerous in the pulmonary capillaries following EVC. These data suggest that the presence of FDP and/or fibrin deposits within the pulmonary microvasculature may influence the early functional integrity of pulmonary endothelial cells at sites of fibrin accumulation.     

Pulmonary microvascular changes during hyperdynamic sepsis in an ovine model

Hyperdynamic sepsis (increased cardiac output and reduced peripheral vascular resistance) was created in sheep with chronic lung lymph fistulae (n = 8) by giving them a 30-min infusion of 1.5 micrograms/kg of endotoxin (LPS) iv. Four hours after LPS the cardiac output (CO) was reduced (6.56 +/- 0.43 to 4.96 +/- 0.33 liters/min) and lymph flow was increased (5.4 +/- 1.0 to 18.6 +/- 3.1 ml/h). Nine hours after LPS the CO output was increased (8.42 +/- 0.60 liters/min). Early cardiopulmonary changes were associated with a fall in neutrophils (PMNs) (2,667 +/- 748 to 450 +/- 90 cells/microliter) and an elevation of their chemiluminescence (CL), an indication of increased O2 free-radical formation in the blood (1,250 +/- 160 to 3,340 +/- 744 units/1,000 leukocytes). The granulocytic enzyme, aryl sulfatase, was increased in the lymph (0.19 +/- 0.03 to 0.37 +/- 0.05 microgram/h/mg protein) indicating degranulation (activation) of PMNs. When CO was increased (9 h after LPS), blood CL rose even higher (5,330 +/- 173 units/1,000 leukocytes) and CL in the lung lymph decreased (1,160 +/- 220 units/1,000 leukocytes). At this time, lymphatic aryl sulfatase had returned to baseline levels (0.25 +/- 0.02 microgram/h/mg protein). These data suggest that pulmonary microcirculatory injury produced by LPS may be the result of margination of PMNs in the lung and their release of permeability-inducing mediators. Later, as the CO increases, the PMNs or their lesion-producing mediators may be washed from the lung and the lung injury thus may be made less severe.     

Pulmonary oxygen toxicity: increased microvascular permeability to protein in unanesthetized lambs

To study transvascular filtration of fluid and microvascular permeability to protein in the lung during prolonged hyperoxia, we measured lung lymph flow, protein transport, and simultaneous pulmonary vascular pressures of six lambs breathing 100 percent O2 for five days. Lymph flow doubled, protein flow increased by 131 percent, and radioactive tracer studies demonstrated a clearcut increase in pulmonary microvascular permeability to protein after five days of continuous O2 breathing.     

Lung fluid and protein flux during postoperative sepsis

Pulmonary microvascular injury during sepsis after injury appears to be amplified with plasma fibronectin deficiency, but the degree of injury relative to the extent of sepsis has not been defined. We evaluated pulmonary vascular permeability in sheep as influenced by various levels of postoperative Pseudomonas sepsis during a period of plasma fibronectin deficiency. The hemodynamic response to Pseudomonas was very similar regardless of the intensity of septic challenge and characterized by systemic arterial hypotension, decreased cardiac output, and pulmonary arterial hypertension. In contrast, increased pulmonary microvascular permeability was observed with increments in the bacterial challenge. Thus, lung protein clearance (LPC) or so called pulmonary transvascular protein clearance (TPC) used as an index of lung vascular permeability was 9.1 +/- 1.9 ml/hr, 15.1 +/- 1.7 ml/hr, and 19.3 +/- 3.0 ml/hr 2 hr after low (3 X 10(9) i.v.; 1 X 10(10) i.p.), medium (3 X 10(9) i.v.; 3 X 10(10) i.p.), and high (5 X 10(9) i.v.; 5 X 10(10) i.p.) dose Pseudomonas challenges, respectively. Thus, the extent of the altered pulmonary microvascular integrity in sheep during sepsis after surgery in the presence of fibronectin deficiency is dependent on the degree of bacterial sepsis. In addition, infusion of cryoprecipitate was an effective means of reversing the plasma fibronectin deficiency. Accordingly, this may be used as a model to investigate the mechanism of altered lung fluid balance during postoperative septic shock and the effect of fibronectin on this response.     

Increased sheep lung vascular permeability caused by Escherichia coli endotoxin.

We infused Escherichia coli endotoxin, 0.07-1.33 microgram/kg, intravenously into chronically instrumented unanesthetized sheep and measured pulmonary arterial and left atrial pressures, lung lymph flow, lymph and blood plasma protein concentrations, and arterial blood gases. Endotoxin caused a biphasic reaction: an early phase of pulmonary hypertension and a long late phase of steady state increased pulmonary vascular permeability during which pulmonary arterial and left atrial pressures were not increased significantly and lung lymph flow was 5 times the baseline value. Lymph: plasma total protein concentration ratio during the late phase (0.76 +/- 0.04) was significantly (P less than 0.05) higher than during baseline (0.66 +/- 0.03). The lymph response was reproducible. Lung lymph clearance of endogenous proteins with molecular radii (r) 35.5 to 96 A was increased during the steady state late phase of the reaction, but, as during baseline, clearance decreased as r increased. The endotoxin reaction was similar to the reaction to infusing whole Pseudomonas bacteria, except that endotoxin had less effect on pressures during the steady state response and caused a relatively larger increase in lymph clearance of large proteins. We conclude that E. coli endotoxin in sheep causes a long period of increased lung vascular permeability and may have a greater effect on large solute pathways across microvessels than do Pseudomonas bacteria.     

Effects of plasmapheresis and of hypoproteinemia on lung liquid conductance in awake sheep

The Starling equation, which describes net transvascular liquid flow, does not include the possibility that a reduction in plasma protein concentration may have a direct effect on lung liquid conductance or microvascular protein permeability. Nevertheless, both effects have been reported. Since these results were not predictable, we wondered whether the changes were due to the decrease in plasma protein concentration or to the process by which protein depletion was accomplished (batch plasmapheresis which involves considerable handling of blood). To separate these factors, we did control (sham) and protein removal plasmapheresis in awake sheep by two plasmapheresis methods (batch and continuous-flow). We monitored pulmonary hemodynamics, measured lung lymph flow, and determined protein concentrations in lymph and plasma. We calculated or measured the protein osmotic pressures of plasma and lymph. After control plasmapheresis, lymph flow increased and lymph:plasma protein concentration decreased but had returned to baseline levels by 4 hours. After protein removal plasmapheresis, the changes persisted for 24 hours. However, lung microvascular conductance (filtration coefficient) was not increased, except during the first 4-hour period. The changes in lymph flow and protein concentration ratio are explained using a simple two-pore model. We conclude that, over the range studied, hypoproteinemia does not increase lung microvascular liquid conductance or protein permeability.     

Effect of exercise on lung lymph flow in unanesthetized sheep with increased pulmonary vascular permeability

To investigate the effect of increased cardiac output on lung water and solute movement in abnormally permeable lungs, experiments were performed in sheep with chronic vascular catheters and lung lymph fistulas. Pulmonary permeability was increased by infusing air microemboli intravenously for 3 h. Once stable lymph flow was observed after stopping the air embolization sheep were either exercised on a treadmill to increase cardiac output (n = 10) or merely continuously monitored (control experiments, n = 6). In control experiments, lung lymph flow remained at markedly elevated but stable values. Sheep exercised for a median time of 45 min. Cardiac output increased 85%, whereas lung lymph flow, in terms of baseline flow rates, increased 296%. The lymph to plasma concentration ratio for total protein was unchanged, and left atrial pressure remained stable and normal during exercise. During exercise, pulmonary arterial pressure increased by 3 mm Hg. The data, when compared with previous observations in normal sheep, demonstrate that exercise-induced increases in cardiac output result in disproportionate increases in lung lymph flow when pulmonary vascular permeability is increased.