Gross and subgross anatomy of bronchial circulation in sheep

Lung Circulation

The circulation of the lung is unique both in volume and function. For example, it is the only organ with two circulations: the pulmonary circulation, the main function of which is gas exchange, and the bronchial circulation, a systemic vascular supply that provides oxygenated blood to the walls of the conducting airways, pulmonary arteries and veins. The pulmonary circulation accommodates the entire cardiac output, maintaining high blood flow at low intravascular arterial pressure. As compared with the systemic circulation, pulmonary arteries have thinner walls with much less vascular smooth muscle and a relative lack of basal tone. Factors controlling pulmonary blood flow include vascular structure, gravity, mechanical effects of breathing, and the influence of neural and humoral factors. Pulmonary vascular tone is also altered by hypoxia, which causes pulmonary vasoconstriction. If the hypoxic stimulus persists for a prolonged period, contraction is accompanied by remodeling of the vasculature, resulting in pulmonary hypertension. In addition, genetic and environmental factors can also confer susceptibility to development of pulmonary hypertension. Under normal conditions, the endothelium forms a tight barrier, actively regulating interstitial fluid homeostasis. Infection and inflammation compromise normal barrier homeostasis, resulting in increased permeability and edema formation. This article focuses on reviewing the basics of the lung circulation (pulmonary and bronchial), normal development and transition at birth and vasoregulation. Mechanisms contributing to pathological conditions in the pulmonary circulation, in particular when barrier function is disrupted and during development of pulmonary hypertension, will also be discussed.

Physiological and pathological angiogenesis in the adult pulmonary circulation

Angiogenesis occurs during growth and physiological adaptation in many systemic organs, for example, exercise-induced skeletal and cardiac muscle hypertrophy, ovulation, and tissue repair. Disordered angiogenesis contributes to chronic inflammatory disease processes and to tumor growth and metastasis. Although it was previously thought that the adult pulmonary circulation was incapable of supporting new vessel growth, over that past 10 years new data have shown that angiogenesis within this circulation occurs both during physiological adaptive processes and as part of the pathogenic mechanisms of lung diseases. Here we review the expression of vascular growth factors in the adult lung, their essential role in pulmonary vascular homeostasis and the changes in their expression that occur in response to physiological challenges and in disease. We consider the evidence for adaptive neovascularization in the pulmonary circulation in response to alveolar hypoxia and during lung growth following pneumonectomy in the adult lung. In addition, we review the role of disordered angiogenesis in specific lung diseases including idiopathic pulmonary fibrosis, acute adult distress syndrome and both primary and metastatic tumors of the lung. Finally, we examine recent experimental data showing that therapeutic enhancement of pulmonary angiogenesis has the potential to treat lung diseases characterized by vessel loss.

Sclerosis therapy of bronchial artery attenuates acute lung injury induced by burn and smoke inhalation injury in ovine model

INTRODUCTION

In burned sheep, we showed more than a 10-fold increase in bronchial blood flow following smoke inhalation. It was previously reported that sclerosis of the bronchial artery prior to smoke exposure reduces the pathophysiology of the inhalation insult. We hypothesized that sclerosis of the bronchial artery after insult attenuates smoke/burn-induced acute lung injury.

METHODS

Through an incision at the 4th intercostal space, a catheter was placed via the esophageal artery into the bronchial artery such that the bronchial blood flow remained intact. Acute lung injury was induced by a 40% total body surface area, 3rd degree cutaneous burn and smoke inhalation. Adult female sheep (n=18, 35.6±1.0 kg) were divided into three groups following the injury: (1) sclerosis group: 1h after injury, 4 mL of 70% ethanol was injected into bronchial artery via bronchial catheter, n=6; (2) control group: 1h after injury, an equal dose of saline was injected into bronchial artery via the bronchial catheter, n=6; (3) sham group: no injury and no treatment, n=6. The experiment was conducted in awake animals for 24 h.

RESULTS

Bronchial blood flow, measured by microspheres, was significantly reduced after ethanol injection in the sclerosis group. Pulmonary function, evaluated by measurement of blood gas analysis, pulmonary mechanics, and pulmonary transvascular fluid flux, was severely impaired in the control group. However, pulmonary function was significantly improved by bronchial artery sclerosis.

CONCLUSION

The results of our study clearly demonstrate a crucial role of enhanced bronchial circulation in thermal injury-related morbidity. Decreasing bronchial circulation using pharmacological agents may be an effective strategy in management of burn patients with concomitant smoke inhalation injury.

The bronchial circulation--worth a closer look: a review of the relationship between the bronchial vasculature and airway inflammation

Until recently, the bronchial circulation has been relatively ignored in the research and clinical arenas, perhaps because of its small volume and seeming dispensability relative to the pulmonary circulation. Although the bronchial circulation only receives around 1% of the cardiac output in health, it serves functions that are critical to maintaining airway and lung function. The bronchial circulation also plays an important role in many lung and airway diseases; through its ability to increase in size, the bronchial circulation is able to provide lung parenchymal perfusion when the pulmonary circulation is compromised, and more recently the role of the bronchial circulation in the pathogenesis of inflammatory airway disease has been explored. Due to the anatomic variability and small volume of the bronchial circulation, much of the research to date has necessitated the use of animal models and invasive procedures. More recently, non-invasive techniques for measuring bronchial blood flow in the mucosal microvascular network have been developed and offer a new avenue for the study of this circulation in humans. In conjunction with molecular research, measurement of airway blood flow (Q(aw)) may help elucidate the role of the bronchial circulation in inflammatory airway disease and become a useful tool for monitoring therapy.

Does the bronchial circulation contribute to congestion in heart failure?

Pulmonary congestion is a hallmark feature of heart failure and is a major reason for hospital admissions in this patient population. Heart failure patients often demonstrate restrictive and obstructive pulmonary function abnormalities; however, the mechanisms of these changes remain controversial. It has been suggested that the bronchial circulation may play an important role in the development of these pulmonary abnormalities and in the symptoms associated with pulmonary congestion. Congestion may occur in the bronchial circulation from either a marked increase in flow or an increase in blood volume but with a reduction in flow due to high cardiac filling pressures and high pulmonary vascular pressures (a stasis like condition). Either may lead to thickened bronchial mucosal and submucosal tissues and reduced airway compliance resulting in airway obstruction and restriction and a lack of airway distensibility. These structural changes may contribute to "cardiac asthma" and dyspnea, characteristic features common in HF patients. Thus the bronchial circulation may be a potential target for therapeutic interventions. The aim of this paper is to review factors governing the control of the bronchial circulation, how bronchial vascular conductance may change with HF and to pose arguments, both supporting and in opposition to the bronchial circulation contributing to congestion and altered pulmonary function in HF. We ultimately hypothesize that the engorgement of the bronchial circulatory bed may play a role in pulmonary function abnormalities that occur in HF patients and contribute to symptoms such as orthopnea and exertional dyspnea.

Effect of ablated bronchial blood flow on survival rate and pulmonary function after burn and smoke inhalation in sheep

The bronchial circulation plays a significant role in the pathophysiological changes of burn and smoke-inhalation injury. Bronchial blood flow markedly increases immediately after inhalational injury. This study examines whether the ablation of the bronchial artery attenuates pathophysiological changes and improves survival after burn and smoke-inhalational injury in an ovine model. Acute lung injury was induced by 40% total body surface-area third-degree cutaneous burn and cotton smoke inhalation (48 breaths of cotton smoke, <40 degrees C) under deep anaesthesia. Twelve adult female sheep were divided into two groups: (1) sham (injured, non-ablated bronchial artery, n=6); (2) ablation (injured, ablated bronchial artery, n=6). Ablation of the bronchial artery was performed 72 h before the injury. The experiment was continued for 96 h. Burn and smoke-inhalation injury significantly increased regional blood flow in the bronchi. Ablation of the bronchial artery significantly reduced acute regional blood flow increases in the proximal and distal bronchi. All animals in the ablation group survived to 96 h. Four of these were successfully weaned off the ventilator. Three animals of the sham group met standardised euthanasia criteria at 60 h, while another met the criteria at 78 h. The lung wet-to-dry weight ratio, histology score and myeloperoxidase (MPO) activity were significantly increased by the insult, but ablation of the bronchial artery attenuated these changes. Burn and smoke-inhalation injury induced a significant increase in bronchial blood flow and accelerated airway obstruction, pulmonary vascular changes, pulmonary oedema and pulmonary dysfunction. Ablated bronchial circulation attenuated these pathophysiological changes.

Assessment of vascular permeability in an ovine model of acute lung injury and pneumonia-induced Pseudomonas aeruginosa sepsis

OBJECTIVE

To assess the time changes and mechanism of pulmonary and peripheral vascular permeability in sheep with acute lung injury and sepsis.

DESIGN

Prospective, controlled, randomized trial.

SETTING

University research laboratory.

SUBJECTS

A total of 21 chronically instrumented, adult female sheep.

INTERVENTIONS

Sheep were instrumented with lung and prefemoral lymph fistulas and allocated to either an uninjured control group (n = 5) or sepsis group (n = 5). The sheep in the sepsis group received cotton smoke inhalation injury followed by instillation of Pseudomonas aeruginosa into the lungs. All sheep were mechanically ventilated and fluid resuscitated for the entire duration of the 24-hr experiment. Additional sheep (n = 11) received injury and were killed at different time points for the measurement of vascular endothelial growth factor in lung tissue.

MEASUREMENTS AND MAIN RESULTS

The injury induced a hypotensive-hyperdynamic circulation; increases in pulmonary capillary pressure, net fluid balance, lung and prefemoral lymph flow and protein content, lung water content, abdominal and thoracic fluid and protein content, neutrophil accumulation in the lung, and vascular endothelial growth factor expression in lung tissue; and decreases in PaO2/FiO2 ratio, plasma protein concentration, plasma oncotic pressure, and myocardial contractility.

CONCLUSIONS

Lung edema formation in this model was the result of marked increases in both pulmonary microvascular permeability and pressure. Pulmonary vascular hyperpermeability peaked 12 hrs postinjury and was related to vascular endothelial growth factor overexpression. Early myocardial failure was a potential contributor to the constant increase in pulmonary capillary pressure. The sepsis-induced increase in peripheral microvascular permeability was associated with significant accumulation of fluid and protein in the third space.

Effect of ablated airway blood flow on systemic and pulmonary microvascular permeability after smoke inhalation in sheep

The bronchial circulation plays a significant role in the pathogenesis of smoke inhalation. We investigated the physiological manifestations in both the systemic and the pulmonary circulation after smoke inhalation injury, and determined whether ablation of the bronchial circulation had any effect on these changes. We used a chronically instrumented ovine model with lung and prefemoral lymph fistulae to determine the changes in pulmonary and systemic microvascular permeability. Fourteen animals were divided into two groups. The injection group had bronchial circulation ablation with an ethanol injection into the bronchial artery, whereas it was left intact in the sham group. The sham group showed a four-fold increase in lung lymph flow (l-Q(L)) and a two-fold increase in prefemoral lymph flow (s-Q(L)) 24 h after injury. The increase in s-Q(L) was associated with a decrease in lymph oncotic pressure. Therefore, systemic colloid clearance (s-CC), an indicator of systemic microvascular permeability to protein, was unchanged. The ablated bronchial circulation reversed the pulmonary but not the systemic manifestations after smoke inhalation. In conclusion, the pathophysiological events occurring after smoke inhalation were confined to the lung with increased bronchial blood flow delivering inflammatory mediators directly to the lung parenchyma.

The murine bronchopulmonary microcirculation in hapten-induced inflammation

OBJECTIVE

The clinical observation of central bronchial artery hypertrophy in chronic lung inflammation suggests the possibility that the bronchial circulation may also participate in adaptive responses in peripheral lung inflammation.

METHODS

To investigate the potential role of the bronchial microcirculation in peripheral lung inflammation, we developed a murine model of lung inflammation using the intratracheal instillation of the peptide-hapten trinitrophenol in presensitized mice.

RESULTS

Clinical parameters indicated a peak inflammatory response at 96 hours. Similarly, gross and microscopic evidence of inflammation was observed 96 hours after antigen instillation. Using a forced oscillation technique to probe peripheral lung mechanics at 96 hours, we detected no change in central airway resistance (P > .05), but a significant increase in peripheral tissue resistance (P < .05). The structure of the bronchial circulation was investigated by microsphere occlusion of the pulmonary circulation and corrosion casting of the bronchial circulation. SEM of the bronchial artery casts demonstrated (1) the presence of the peripheral bronchial circulation in mice, (2) interconnections of the two systems in the distal bronchial arteries and at the level of alveolar capillaries, and (3) functional evidence of increased bronchial perfusion of alveolar capillaries during mononuclear inflammation.

CONCLUSION

These results suggest an important adaptive role of the bronchial circulation in pulmonary inflammation.

Injection of prostaglandin F2alpha into the bronchial artery in sheep increases the pulmonary vascular permeability to protein

Lung injury and oedema following smoke inhalation are associated with eicosanoid release and the injury is heavily influenced by the tracheobronchial circulation. We hypothesized that injection of a vasoactive eicosanoid, prostaglandin F2alpha (PGF2alpha), into the tracheobronchial circulation would induce a permeability leak in that circulation as measured in lung lymph flow and protein content. PGF2alpha when injected into the bronchial artery increased lung lymph flow, protein content and lymph protein flux (protein times flow). The increase in lymph to plasma protein concentration after injection of PGF2alpha is consistent with an increase in vascular protein permeability since an increase in pressure alone would cause an increase in fluid flow in excess of protein with a fall in protein concentration. Ligation of the bronchial artery 3min after injection of the PGF2alpha largely prevented the late changes suggesting that the protein leak into the lymph was from the bronchial arteries.

Functional anatomy of bronchial veins

The amount of bronchial arterial blood that drains into the systemic venous system is not known. Therefore, in this study we further delineated the functional anatomy of the bronchial venous system in six adult, anesthetized, and mechanically ventilated sheep. Through a left thoracotomy, the left azygos vein was dissected and the insertion of the bronchial vein into the azygos vein was identified. A pouch was created by ligating the azygos vein on either side of the insertion of the bronchial vein. A catheter was inserted into this pouch for the measurement of bronchial venous occlusion pressure and bronchial venous blood flow. An ultrasonic flow probe was placed around the common bronchial branch of the bronchoesophageal artery to monitor the bronchial arterial blood flow. Catheters were also placed into the carotid artery and the pulmonary artery. The mean bronchial blood flow was 20.6+/-4.2mlmin(-1) (mean+/-SEM) and, of this, only about 13% of the blood flow drained into the azygos vein. The mean systemic artery pressure was 72.4+/-4.1mmHg whereas the mean bronchial venous occlusion pressure was 38.1+/-2.1mmHg. The mean values for blood gas analysis were as follows: bronchial venous blood pH=7.54+/-0.02, PCO(2)=35+/-2.6, PO(2)=95+/-5.7mmHg; systemic venous blood-pH=7.43+/-0.02, PCO(2)=48+/-3.2, PO(2)=42+/-2.0mmHg; systemic arterial blood-pH=7.51+/-0.03, PCO(2)=39+/-2.1, PO(2)=169+/-9.8mmHg. We conclude that the major portion of the bronchial arterial blood flow normally drains into the pulmonary circulation and only about 13% drains into the bronchial venous system. In addition, the oxygen content of the bronchial venous blood is similar to that in the systemic arterial blood.

Structure and size of bronchopulmonary anastomoses in sheep lung

The distribution and drainage of bronchial arterial blood flow are complex. We used two different methods to study the bronchial-pulmonary anastomoses in sheep lung. Initially, we injected two different sizes of fluorescent microspheres (15 and 100 microm diameter) into the bronchial artery and histologically determined where the different-size microspheres were entrapped in the lung. In a second series of animals, we injected Microfil into the bronchial artery to observe the anastomotic vessels. The microsphere data confirmed the existence of bronchial-to-pulmonary anastomoses. No microspheres were found in the systemic organs (heart and kidney), confirming the absence of large bronchial artery-to-pulmonary vein anastomoses. Unexpectedly, proportionately more large microspheres (100 microm) lodged in the alveolar parenchyma when compared to 15 microm microspheres. This suggests that there are many more small bronchial (< 100 microm) arterioles feeding the airway mucosa than the larger anastomotic vessels feeding into the parenchyma. In the Microfil cast lungs, we observed four types of anastomotic vessels: bronchial arteries/arterioles that anastomose with pulmonary arteries/arterioles that accompany airways; bronchial arterioles that anastomose directly with parenchymal (and eventually alveolar) vessels; bronchial arterioles that anastomose with blood vessels that do not accompany airways; and bronchial arterioles that anastomose with bronchial veins. Based on our in vivo microsphere data, the vessels that do not accompany the airways are most likely bronchial venules, not pulmonary venules.

A fractal analysis of the radial distribution of bronchial capillaries around large airways

We analyzed published measurements of the bronchial circulation and airway wall (Anderson JC, Bernard SL, Luchtel DL, Babb AL, and Hlastala MP. Respir Physiol Neurobiol 132: 329-339, 2002) and determined that the radial distribution of bronchial capillary cross-sectional area was fractal. We limited our analysis to bronchial capillaries, diameter < or =10 mum, that resided between the epithelial basement membrane and adventitia-alveolar boundary, the airway wall tissue. Thirteen different radial distributions of capillary-to-tissue area were constructed simply by changing the number of annuli (i.e., the annular size) used to form each distribution. For the 13 distributions created, these annuli ranged in size from to of the size of the airway wall area. Radial distributions were excluded from the fractal analysis if the sectioning procedure resulted in an annulus with a radial thickness less than the diameter of a capillary. To determine the fractal dimension for a given airway, the coefficient of variation (CV) for each distribution was calculated, and ln(CV) was plotted against the logarithm of the relative piece area. For airways with diameter >2.4 mm, this relationship was linear, which indicated the radial distribution of bronchial capillary cross-sectional area was fractal with an average fractal dimension of 1.27. The radial distribution of bronchial capillary cross-sectional area was not fractal around airways with diameter <1.5 mm. We speculated on how the fractal nature of this circulation impacts the distribution of bronchial blood flow and the efficiency of mass transport during health and disease. A fractal analysis can be used as a tool to quantify and summarize investigations of the bronchial circulation.

Vascular remodeling in the circulations of the lung

The lung is unique in its double sources of perfusion from the pulmonary and systemic circulations. One striking difference between the two circulations is the capacity for angiogenesis. The bronchial circulation has a capacity that seems quite similar to all systemic arteries, whereas the pulmonary circulation seems relatively inert in this regard. Extra-alveolar pulmonary arteries can grow somewhat in length, and septal capillaries seem to have the capability of reforming, but these processes do not seem to occur with nearly the same intensity associated with the bronchial arteries. In this review, we emphasize these differences between the two circulations of the lung, anticipating that future research will allow more focused probing into the molecular signaling that regulates the novel mechanistic and pathological pathways of each.

Soluble gas exchange in the pulmonary airways of sheep

We studied the airway gas exchange properties of five inert gases with different blood solubilities in the lungs of anesthetized sheep. Animals were ventilated through a bifurcated endobronchial tube to allow independent ventilation and collection of exhaled gases from each lung. An aortic pouch at the origin of the bronchial artery was created to control perfusion and enable infusion of a solution of inert gases into the bronchial circulation. Occlusion of the left pulmonary artery prevented pulmonary perfusion of that lung so that gas exchange occurred predominantly via the bronchial circulation. Excretion from the bronchial circulation (defined as the partial pressure of gas in exhaled gas divided by the partial pressure of gas in bronchial arterial blood) increased with increasing gas solubility (ranging from a mean of 4.2 x 10(-5) for SF6 to 4.8 x 10(-2) for ether) and increasing bronchial blood flow. Excretion was inversely affected by molecular weight (MW), demonstrating a dependence on diffusion. Excretions of the higher MW gases, halothane (MW = 194) and SF6 (MW = 146), were depressed relative to excretion of the lower MW gases ethane, cyclopropane, and ether (MW = 30, 42, 74, respectively). All results were consistent with previous studies of gas exchange in the isolated in situ trachea.

Effect of bronchial artery blood flow on cardiopulmonary bypass-induced lung injury

Cardiovascular surgery requiring cardiopulmonary bypass (CPB) is frequently complicated by postoperative lung injury. Bronchial artery (BA) blood flow has been hypothesized to attenuate this injury. The purpose of the present study was to determine the effect of BA blood flow on CPB-induced lung injury in anesthetized pigs. In eight pigs (BA ligated) the BA was ligated, whereas in six pigs (BA patent) the BA was identified but left intact. Warm (37°C) CPB was then performed in all pigs with complete occlusion of the pulmonary artery and deflated lungs to maximize lung injury. BA ligation significantly exacerbated nearly all aspects of pulmonary function beginning at 5 min post-CPB. At 25 min, BA-ligated pigs had a lower arterial Po2at a fraction of inspired oxygen of 1.0 (52 ± 5 vs. 312 ± 58 mmHg) and greater peak tracheal pressure (39 ± 6 vs. 15 ± 4 mmHg), pulmonary vascular resistance (11 ± 1 vs. 6 ± 1 mmHg·l–1·min), plasma TNF-α (1.2 ± 0.60 vs. 0.59 ± 0.092 ng/ml), extravascular lung water (11.7 ± 1.2 vs. 7.7 ± 0.5 ml/g blood-free dry weight), and pulmonary vascular protein permeability, as assessed by a decreased reflection coefficient for albumin (σalb; 0.53 ± 0.1 vs. 0.82 ± 0.05). There was a negative correlation ( R = 0.95, P < 0.001) between σalband the 25-min plasma TNF-α concentration. These results suggest that a severe decrease in BA blood flow during and after warm CPB causes increased pulmonary vascular permeability, edema formation, cytokine production, and severe arterial hypoxemia secondary to intrapulmonary shunt.

Methods to track leukocyte and erythrocyte transit through the bronchial vasculature in sheep

Study of the underlying mechanisms of leukocyte recruitment in the airway circulation is a crucial aspect of understanding the pathology of inflammatory airways disease. However, few in vivo studies have focused on leukocyte kinetics through the systemic airway vasculature. Because the bronchial vasculature of the sheep shows anatomical similarity to that of the human as well as being easily accessible for perfusion, we developed methods to study leukocyte transit through the sheep bronchial circulation. Leukocytes were isolated from whole blood after hypotonic lysis of red cells and labeled with 5-(and 6) carboxyfluorescein succinimidylester (CFSE; 0.1 microM), a green fluorescent dye. Red blood cells were labeled using PKH26-GL Red Fluorescent Cell Linker and served as a marker for blood flow and volume. Labeled leukocytes were tested for activation during the labeling process by monitoring surface levels of leukocyte adhesion molecules CD11b and L-selectin. When activated with phorbol myristate acetate (10 ng/ml), sheep leukocytes showed a marked increase in CD11b expression and a decrease in L-selectin. However, sheep leukocytes labeled with CFSE showed no significant increase of CD11b or shedding of L-selectin, suggesting that the labeling process did not significantly activate the adhesion properties of the cells. Aliquots containing both labeled erythrocytes and leukocytes were infused into the bronchial vasculature of the sheep through the cannulated bronchial artery at normal bronchial flow (0.6 ml/kg). Serial blood samples were withdrawn from the outflow of the bronchial vasculature (the left atrium) and analyzed using conventional flow cytometry. Retention of leukocytes and transit relative to red cell transit could then be evaluated with this technique. In addition, since cells are stably labeled, airway tissue samples can be removed and analyzed histologically to determine sites of extravasation. These methods offer an approach for examining leukocyte kinetics in situ in the airways of a relevant animal model.

Axial and radial distribution of the bronchial vasculature in sheep

A morphometric analysis was made on the bronchial vasculature of intrapulmonary airways in sheep lungs. This study provides the parameters to calculate the quantity of soluble gas diffusion between the vasculature and airways for use in a mathematical model describing heat and mass exchange in the lungs. To achieve these results, the lungs of four adult sheep (30-36 kg.) were excised, fixed, dissected and microtomed to obtain airway cross-sections for measurement. Blood vessel size and airway proximity was measured using a microscope interfaced with a computer. Distance from airway lumen to most airway vessels ranged from 30 to 270 microm. It was found that the bronchial vessels surrounding intraparenchymal airways can be described by a right-skewed distribution. Most importantly, a practical description of the bronchial capillary size and airway proximity as a function of airway diameter was found using a weighed average. This analysis facilitates calculation of soluble gas flux from the bronchial vasculature to the airway for use in a mathematical model.

Responses of the bronchial and pulmonary circulations to short-term nitric oxide inhalation before and after endotoxaemia in the pig

The physiological responses of the bronchial circulation to acute lung injury and endotoxin shock are largely unexplored territory. This study was carried out to study the responsiveness of the bronchial circulation to nitric oxide (NO) inhalation before and after endotoxaemia, in comparison with the pulmonary circulation, as well as to study changes in bronchial blood flow during endotoxaemia. Six anaesthetized pigs (pre-treated with the cortisol-synthesis inhibitor metyrapone) received an infusion of 10 microg/kg endotoxin during 2 h. Absolute bronchial blood flow was measured via an ultrasonic flow probe around the bronchial artery. The pigs received increasing doses of inhaled NO over 5 min each (0, 0.2, 2 and 20 ppm) before and after 4 h of endotoxaemia. The increase in bronchial vascular conductance during 5 min of inhalation of 20 ppm NO before endotoxin shock was significantly higher (area under curve (AUC) 474.2 +/- 84.5% change) than after endotoxin shock (AUC 118.2 +/- 40.4%, P < 0.05 Mann-Whitney U-test). The reduction of the pulmonary arterial pressure by 20 ppm NO was not different. A short rebound effect of the pulmonary arterial pressure occurred after discontinuation of inhaled NO before endotoxaemia (AUC values above baseline 54.4 +/- 19.7% change), and was virtually abolished after endotoxaemia (AUC 6.1 +/- 4.0%, P = 0.052, Mann-Whitney U-test). Our results indicate that the responsiveness of the bronchial circulation to inhalation of increasing doses of inhaled NO during endotoxin shock clearly differ from the responsiveness of the pulmonary circulation. The reduced responsiveness of the bronchial circulation is probably related to decreased driving pressure for the bronchial blood flow. The absence of the short rebound effect on pulmonary arterial pressure (PAP) after induction of shock could be related to maximum constriction of the pulmonary vessels at 4 h.

Heterogeneous distribution of thrombomodulin and von Willebrand factor in endothelial cells in the human pulmonary microvessels

Laser scanning confocal fluorescence microscopy techniques were used to study the localization of von Willebrand factor (vWf; Factor VIII-related antigen) and thrombomodulin (transmembrane receptor for thrombin) in the microvascular endothelial cells in the normal human lung. Tissues were obtained from lobectomy specimens resected for solitary nodules (7 adenocarcinomas and 4 hamartomas) from 11 patients. The plasma membranes of the capillary endothelial cells in the alveolar zones (A-zones) showed red linear fluorescence for thrombomodulin. However, their cytoplasm was mostly unreactive for vWf. The microvessels which were located in the connective tissue (C-zones), including peribronchial, and subpleural areas and large vascular walls, consistently demonstrated band-like green fluorescence for vWf in their cytoplasm, and their plasma membranes usually lacked reactivity for thrombomodulin. Only a limited number of peribronchial capillaries measuring <10 microm in diameter showed a mosaic-like appearance, in which red fluorescence along the plasma membranes was found together with green fluorescence in the subjacent cytoplasm. In the juxtaalveolar (J-zones) microvessels located along the borders between A- and C-zones, and measuring up to 40 microm in diameter, the endothelial cells showed a mosaic-like pattern of distribution of the two antigens. However, the localization of thrombomodulin in the J-zone microvessels was separate and independent from that of vWf. The thrombomodulin-reactive cells were directly connected to the alveolar capillary endothelial cells. Heterogeneous patterns of distribution of thrombomodulin and vWf suggest that topographic differences of endothelial function occur to maintain a balance of coagulation and anticoagulation in the normal human lung.

Ligation of the bronchial artery in sheep attenuates early pulmonary changes following exposure to smoke

Smoke inhalation can produce acute pulmonary edema. Previous studies have shown that the bronchial arteries are important in acute pulmonary edema occurring after inhalation of a synthetic smoke containing acrolein, a common smoke toxin. We hypothesized that inhalation of smoke from burning cotton, known to contain acrolein, would produce in sheep acute pulmonary edema that was mediated by the bronchial circulation. We reasoned that occluding the bronchial arteries would eliminate smoke-induced pulmonary edema, whereas occlusion of the pulmonary artery would not. Smoke inhalation increased lung lymph flow from baseline from 2.4 +/- 0.7 to 5.6 +/- 1.2 ml/0.5 h at 30 min (P < 0.05) to 9.1 +/- 1 ml/0.5 h at 4 h (P < 0.05). Bronchial artery ligation diminished and delayed the rise in lymph flow with baseline at 2.8 +/- 0.7 ml/0.5 h rising to 3.1 +/- 0. 8 ml/0.5 h at 30 min to 6.5 +/- 1.5 ml/0.5 h at 240 min (P < 0.05). Wet-to-dry ratio was 4.1 +/- 0.2 in control, 5.1 +/- 0.3 in smoke inhalation (P < 0.05), and 4.4 +/- 0.4 in bronchial artery ligation plus smoke-inhalation group. Smoke inhalation after occlusion of the right pulmonary artery resulted in a wet-to-dry ratio after 4 h in the right lung of 5.5 +/- 0.8 (P < 0.05 vs. control) and in the left nonoccluded lung of 5.01 +/- 0.7 (P < 0.05). Thus the bronchial arteries may be major contributors to acute pulmonary and airway edema following smoke inhalation because the edema occurs in the lung with the pulmonary artery occluded but not in the lungs with bronchial arteries ligated.

Mosaic-like distribution of endothelial cell antigens in capillaries and juxta-alveolar microvessels in the normal human lung

The distribution patterns of endothelial cell antigens, including thrombomodulin and von Willebrand factor (vWf), were studied in normal lung tissues obtained from distant areas of solitary nodules (seven adenocarcinomas and four hamartomas). By single immunoalkaline phosphatase and dual immunofluorescence stainings, the plasma membranes of alveolar capillary endothelium showed linear distribution of thrombomodulin, but their cytoplasm was rarely reactive for vWf (thrombomodulin-dominant pattern). Microvessels with a diameter larger than 10 microm located in the connective tissue zones demonstrated band-like reaction for vWf in their cytoplasm, and their plasma membranes often lacked reactivity for thrombomodulin (vWf-dominant pattern). The juxta-alveolar microvessels located along the borders between the alveolar- and connective-tissue zones showed mosaic-like pattern of distribution for these antigens. The pulmonary venules and peribronchial microvessels measuring up to 40 microm in diameter, demonstrated the expression of thrombomodulin along the plasma membrane, and that of vWf in the cytoplasm. Capillaries of the bronchial circulation were also characterized by mosaic-like pattern of distribution. Both antigens were often expressed in a single cytoplasmic segment. The heterogeneous distribution pattern of these antigens suggests topographic difference in endothelial cell function to maintain coagulatory and anticoagulatory balance in the normal human lung.

Effect of aerosolized acetylcholine on bronchial blood flow

We studied the effects of aerosolized as well as intravenous infusion of acetylcholine on bronchial blood flow in six anesthetized sheep. Intravenous infusion of acetylcholine, at a dose of 2 microg/kg, increased bronchial blood flow from 45 +/- 15 (SE) to 74 +/- 30 ml/min, and vascular conductance increased by 76 +/- 22%. In contrast, aerosolized acetylcholine at doses of 2 and 20 microg/kg decreased bronchial vascular conductance by approximately 10%. At an aerosolized dose of 200 microg/kg, the bronchial vascular conductance increased by approximately 15%, and there was no further increase in conductance when the aerosolized dose was increased to 2,000 microg/kg. Pretreatment of animals with a nitric oxide synthase inhibitor, Nomega-nitro-L-arginine methyl ester hydrochloride, partially blocked the vasodilatory effects of intravenous acetylcholine and completely blocked the vasodilatory effects of high-dose aerosolized acetylcholine. These data suggest that aerosolized acetylcholine does not readily penetrate the vascular wall of bronchial circulatory system and, therefore, has minimal vasodilatory effects on the bronchial vasculature.

Effect of prostaglandin E2 on the tracheobronchial distribution of lung preservation perfusate

Complete lung preservation requires the perfusate to reach the cell it intends to protect; this is directly related to the distribution of the preserving solution throughout the lung vasculature. Several prostanoids are clinically used to enhance lung preservation. We evaluated the effect of prostaglandin E2 (PGE2) on the distribution of lung perfusate throughout tracheobronchial tissue. Fourteen pulmonary blocks were procured from an equal number of dogs and divided according to whether or not they had previously received a PGE2 infusion. All lung blocks were perfused with a glucose-insulin-potassium solution, and distribution within the lung parenchyma and tracheobronchial tissue was measured using the flow reference technique and gadolinium-153-labeled microspheres. Once perfusion had taken place, samples of lung parenchyma, tracheobronchial tissue, and flow reference were measured for radioactivity, and flow was calculated per 100 g tissue. Animals receiving PGE2 had an expected 38% decrease in systemic arterial pressure; the duration of infusion of lung perfusate during procurement was shorter in those animals receiving PGE2 (5.75 +/- 0.3 min, vs. no PGE2 8.9 +/- 1.2 min; p < .05). Perfusate flow of bronchial mucosa and cartilage increased by two to three times with the infusion of PGE2 (p < .01). Perfusate flow to lobar bronchus or lung parenchyma was similar in both groups. Flow within the lung parenchyma did not differ statistically when compared to its lobar distribution. In conclusion, PGE2-treated animals had a two- to threefold increase in perfusate flow to mainstem bronchi (including mucosa); these findings to some extent support the rationale for utilizing prostanoids in order to enhance lung preservation in clinical lung transplantation.

Effect of reduced bronchial circulation on lung fluid flux after smoke inhalation in sheep

We determined the effect of reduced bronchial blood flow on lung fluid flux through changes in lung lymph flow, lung wet weight-to-dry weight (wet/dry) ratios, and pulmonary microvascular reflection coefficient (sigma). In the first of two surgical procedures, Merino ewes (n = 21) were surgically prepared for chronic study. Five to seven days later, in a second operation, the bronchial artery of the injection group (n = 7) was ligated, and 4 ml of 70% ethanol were injected into the bronchial artery to cause sclerosis of the airway circulation. In the ligation group (n = 7), only the bronchial artery was ligated. In the sham group (n = 7), the bronchial artery was surgically exposed but left intact without ligation or ethanol injection. One day after these operations the animals received a tracheotomy and 48 breaths of cotton smoke. The value of sigma was determined at two points: 24 h before the second surgical procedure and 24 h after smoke inhalation. Lung lymph flow, blood-gas parameters, and hemodynamic data were measured every 4 h after injury. At the end of investigation, samples of lung were taken for determination of blood-free wet/dry ratio. In the sham group, inhalation injury induced a gradual increase in pulmonary vascular resistance and lung lymph flow, which was associated with deterioration of oxygenation. Reduction of the bronchial blood flow attenuated these pathophysiological changes, and the degree of this attenuation was greater in the injection group than in the ligation group. The value of sigma was significantly higher after smoke inhalation in the injection group compared with the sham group (0.77 +/- 0.04 vs. 0.61 +/- 0.03, means +/- SE) at 24 h. The mean wet/dry ratio value of the injection group animals was 30% less than that of the sham group. Our data show that the bronchial circulation contributes to edema formation in the lung occurring after acute lung injury with smoke inhalation.

Non-cAMP-mediated bronchial arterial vasodilation in response to inhaled beta-agonists

We studied the dose-dependent effects of inhaled isoetharine HCl, a beta-adrenergic bronchodilator (2.5, 5.0, 10.0, and 20.0 mg), on bronchial blood flow (Qbr) in anesthetized sheep. Isoetharine resulted in a dose-dependent increase in Qbr. With a total dose of 17.5 mg, Qbr increased from baseline values of 22 +/- 3.4 (SE) to 60 +/- 16 ml/min (P < 0.001), an effect independent of changes in cardiac output and systemic arterial pressure. To further study whether synthesis of endogenous nitric oxide (NO) affects beta-agonist-induced increases in Qbr, we administered isoetharine (20 mg) by inhalation before and after the NO-synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME). Intravenous L-NAME (30 mg/kg) rapidly decreased Qbr by approximately 80% of baseline, whereas L-NAME via inhalation (10 mg/kg) resulted in a delayed and smaller (approximately 22%) decrease. Pretreatment with L-NAME via both routes of administration attenuated bronchial arterial vasodilation after subsequent challenge with isoetharine. We conclude that isoetharine via inhalation increases Qbr in a dose-dependent manner and that beta-agonist-induced relaxation of vascular smooth muscle in the bronchial vasculature is partially mediated via synthesis of NO.

Nitric oxide and beta-adrenergic agonist-induced bronchial arterial vasodilation

In anesthetized sheep, we measured bronchial blood flow (Qbr) by an ultrasonic flow probe to investigate the interaction between inhaled nitric oxide (NO; 100 parts/million) given for 5 min and 5 ml of aerosolized isoetharine (1.49 x 10(-2) M concentration). NO and isoetharine increased Qbr from 26.5 +/- 6.5 to 39.1 (SE) +/- 10.6 and 39.7 +/- 10.7 ml/min, respectively (n = 5). Administration of NO immediately after isoetharine further increased Qbr to 57.3 +/- 15.1 ml/min. NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME; 30 mg/kg, in 20 ml saline given i.v.) decreased Qbr to 14.6 +/- 2.6 ml/min. NO given three times alternately with isoetharine progressively increased Qbr from 14.6 +/- 2.6 to 74.3 +/- 17.0 ml/min, suggesting that NO and isoetharine potentiate vasodilator effects of each other. In three other sheep, after L-NAME three sequential doses of isoetharine increased Qbr from 10.2 +/- 3.4 to 11.5 +/- 5.7, 11.7 +/- 4.7, and 13.3 +/- 5.7 ml/min, respectively, indicating that effects of isoetharine are predominantly mediated through synthesis of NO. When this was followed by three sequential administrations of NO, Qbr increased by 146, 172, and 185%, respectively. Thus in the bronchial circulation, there seems to be a close interaction between adenosine 3',5'-cyclic monophosphate- and guanosine 3',5'-cyclic monophosphate-mediated vasodilation.

Angiogenesis in bronchial circulatory system after unilateral pulmonary artery obstruction

We studied the effects of left pulmonary artery (LPA) ligation on the bronchial circulatory system (BCS) by using a sheep model. LPA was ligated in the newborn lambs soon after birth (n = 8), and when the sheep were approximately 3 yr of age anatomic studies revealed marked angiogenesis in BCS. Bronchial blood flow and cardiac output were studied by placing flow probes around the bronchial and pulmonary arteries in four adult sheep. After LPA ligation, bronchial blood flow increased from 35 +/- 6 to 134 +/- 42 ml/min in approximately 3 wk (P < 0.05). We also studied gas-exchange functions of BCS approximately 3 yr after the ligation of LPA in newborn lambs (n = 4) and used a control group (n = 12) in which LPA was ligated acutely. In the left lung, O2 uptake after acute ligation was 16 +/- 3 ml/min and was similar to the chronic model, whereas CO2 output in the control group was 27 +/- 3 ml/min compared with 79 +/- 12 ml/min in the chronic preparation (P < 0.05). We conclude that LPA ligation causes marked angiogenesis in BCS that is capable of performing some gas-exchange functions.

Importance of airway blood flow on particle clearance from the lung

The role of the airway circulation in supporting mucociliary function has been essentially unstudied. We evaluated the airway clearance of inert, insoluble particles in anesthetized ventilated sheep (n = 8), in which bronchial perfusion was controlled, to determine whether airway mucosal blood flow is essential for maintaining surface transport of particles through airways. The bronchial branch of the bronchoesophageal artery was cannulated and perfused with autologous blood at control flow (0.6 ml.min-1.kg-1) or perfusion was stopped. With the sheep in a supine position and after a steady-state 133Xe ventilation scan for designation of lung zones of interest, an inert 99mTc-labeled sulfur colloid aerosol (2.1-microns diameter) was deposited in the lung. The clearance kinetics of the radiolabeled particles were determined from the activity-time data obtained for right and left lung zones. At 60 min postdeposition of aerosol, average airway particle retention for control bronchial blood flow conditions was 57 +/- 7 (SE)% for the right and 53 +/- 8% for the left lung zones. Clearance of particles was significantly impaired when bronchial blood flow was stopped, e.g., right and left lung zones averaged 77 +/- 6 and 76 +/- 7% at 60 min, respectively (P < 0.05). These data demonstrate a significant influence of the bronchial circulation on mucociliary transport of insoluble particles. Potential mechanisms that may account for these results include the importance of the bronchial circulation for nutrient flow, maintenance of airway wall temperature and humidity, and release of mediators and sequelae associated with tissue ischemia.

Effects of vagal stimulation on slowly adapting pulmonary stretch receptors and lung mechanics in anesthetized rabbits

An in vivo preparation was designed to investigate the effect of vagus nerve stimulation-induced bronchoconstriction on the relationship of slowly adapting pulmonary stretch receptor (SAR) activity and lung mechanics. SAR activities were recorded from the left vagus nerve. The responses of SARs, total lung resistance (RL), and dynamic lung compliance (Cdyn) to electrical stimulation of the peripheral end of the cut right vagus nerve (10-15 V, 5-30 Hz, 0.2 ms) were examined before atropine and 5 and 10 min after atropine (2 mg/kg) in anesthetized, artificially ventilated, bilaterally vagotomized rabbits. In the time course profile during vagal stimulation, an increase in RL and a decrease in Cdyn occurred simultaneously, and these opposite changes were frequency dependent. The average responses of SAR activity, RL, and Cdyn to vagal stimulation became more pronounced as the frequencies of the stimulation were increased. The responses obtained during vagal stimulation (5-30 Hz) were blocked or diminished greatly by the administration of atropine. Repeated vagus nerve stimulation in the presence of atropine did not show any significant change in SAR activity and lung mechanics. These results suggest that changes of SAR activity, RL, and Cdyn induced by vagal stimulation occur as a result of smooth muscle contraction in the airways, which is mediated mainly by muscarinic receptor activation and which is not involved in the release of neurotransmitters to relax airway smooth muscle.

Three-dimensional structure of the bronchial microcirculation in sheep

BACKGROUND

The bronchial circulation affects both pulmonary vascular and airway activity. Fundamental to understanding the role of the bronchial microcirculation in health and disease is understanding its anatomy. This study sought to identify specific structural elements that might contribute to the drop that occurs between the systemic blood pressure of the bronchial artery and the low pressure of the pulmonary bed into which the bronchial circulation flows and to better describe the connections of the bronchial and pulmonary circulations.

METHODS

To do this, the lungs of five sheep were cast by injecting a resin through bronchial and pulmonary arteries. After taking samples for light microscopy, the tissue was digested and the casts were viewed with a scanning electron microscope.

RESULTS

Casts of extrapulmonary bronchial arteries were structurally similar to other systemic arteries. Tortuous ones spiraled around bronchi and large blood vessels. Intrapulmonary bronchial arteries, about 100-300 microns in diameter, had sharp branching and deep focal constrictions with great rugosity that completely shut off the flow of the resin. These vessels correspond to the Sperrarterien described by von Hayek (and could cause the resistance associated with the pressure drop). Vasa vasorum ran in the walls of intrapulmonary pulmonary arteries for a variable distance before they entered the lumens of the pulmonary arteries. The smallest blood vessel found that was supplied with vasa vasorum was a bronchial artery 42 microns in diameter. Capillary-like networks with large luminal diameters were found on the pleural surface.

CONCLUSIONS

Scanning electron microscopy of microvascular casts provides a fresh description of the bronchial circulation, further delineates the communications of these two circulations, and may structurally account for some pressure drop between the bronchial and pulmonary circulations.

Smoke inhalation causes a delayed increase in airway blood flow to primarily uninjured lung areas

OBJECTIVE

Single lung inhalation injury causes tissue damage to the contralateral lung. We therefore examined airway blood flow after smoke inhalation in chronic instrumented sheep to get further information about the underlying pathophysiology.

DESIGN/PATIENTS

The right lung and lower trachea of 5 animals were smoke-exposed, while their left lung was air-insufflated using a split ventilation technique. Three animals, where both lungs were only air-insufflated, served as controls. Blood flow to the airway was measured using a labeled microsphere technique. All animals were studied for 24 h following smoke inhalation. Then they were sacrificed and their tissues harvested.

RESULTS

The airway blood flow to the smoke-exposed lung was elevated 11-fold immediately after inhalation injury. The bronchial blood flow to the air insufflated lung became significantly elevated 24 h post-smoke, although to a lesser extent. The control animals did not show any changes of bronchial blood flow during the observation time.

CONCLUSIONS

Damage to one lung can lead to pathophysiologic changes in the contralateral lung. This response appears to be mediated by hematogenous factors.

Development of the pharyngeal arch system related to the pulmonary and bronchial vessels in the avian embryo. With a concept on systemic-pulmonary collateral artery formation

BACKGROUND

The literature is ambiguous as to the question of the developmental background of systemic-pulmonary collateral arteries. These are found in combination with various congenital heart malformations such as pulmonary atresia. From a clinical point of view, it is of interest to know whether we are dealing with the persistence of transient embryological vessels such as ventral segmental arteries or parts of pharyngeal arch arteries or with the prenatal or postnatal recruitment of the bronchial vasculature that normally supplies the lung. This study of the embryology of the extrapulmonary and intrapulmonary vasculature aims at a better understanding of the variations in origin, course, branching pattern, and histology of collateral arteries.

METHODS AND RESULTS

Serial sections of quail embryos ranging between stage HH11 and stage HH28 were incubated with a monoclonal antibody (alpha MB1) against endothelial cells and their precursors. Additional series of chick embryos were injected with india ink to study the lumenized vascular patterns. A splanchnic plexus consisting of endothelial cells and precursors is present around the foregut before the lung buds develop. This plexus expands and gives rise to the pharyngeal arch arteries, the ventral pharyngeal veins, the pulmonary vessels, and the bronchial vessels, including the intrapulmonary vessel network. During two subsequent periods, the splanchnic plexus is transiently connected to the systemic arteries and veins. The bronchial arteries and veins develop in the second period from these transient vessels. The expansion and extension of the splanchnic plexus to many organs during the formation of the bronchial vessels explains the varying course and branching pattern of the bronchial vasculature.

CONCLUSIONS

These results show that we are not dealing with two or more individual vascular systems that contribute to the developing vessels of the lungs but with one vascular plexus that normally gives rise to the pulmonary and bronchial vasculature but has the potential to give rise to other systemic-pulmonary connections.

Cardiopulmonary bypass and pulmonary thromboxane generation

Sporadic cases of inexplicable noncardiogenic pulmonary edema occur after operations requiring total cardiopulmonary bypass (CPB). Prostaglandins, such as thromboxane (Tx) A2, have been implicated in this form of pulmonary pathology in many clinical and experimental settings. Because Tx generation has been demonstrated in association with ischemia of solid organs, we postulated that total CPB, which decreases pulmonary tissue perfusion and oxygenation, would stimulate local Tx synthesis. Total CPB was examined in 7 sheep. The level of TxB2 (a stable metabolite of the active, unstable A2) was measured in the left and right atria before, during, and after 105 minutes of total CPB. Significant increases in TxB2 concentrations occurred in the left atrium compared with the right (p < 0.05) during CPB. Immediately after reperfusion, both the left atrial and right atrial TxB2 concentrations increased significantly over the baseline values (p < 0.05), but this increase and the atrial gradient were rapidly abolished with continued pulmonary perfusion. To determine the effect of extracorporeal circulation without significant (< 30%) alteration in pulmonary perfusion, we evaluated the effect of partial CPB in 5 sheep. Increased TxB2 concentrations were noted at 15 and 30 minutes after the onset of partial CPB (left atrium increased significantly over baseline; p < 0.05), but this elevation spontaneously diminished to insignificance after 15 and 30 additional minutes of extracorporeal circulation. These data establish that total CPB stimulates Tx generation in the lung, and although the effect of partial CPB is transient, that of total CPB is progressive and abolished by reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Lymph and blood flow responses in central airways

The lymphatic drainage of the lung has been used as a quantitation of pulmonary microvascular fluid flux in normal animals and after various forms of injury. This review supports the importance of the bronchial microvasculature in the formation of lung lymph. Proof that the lymph drainage of the lung comes from the pulmonary circuit has been based on the finding of an elevation of lymph flow when the pulmonary venous pressure is elevated. This proof is wanting since recent work demonstrates that the venous drainage of the intrapulmonary bronchi flows into the pulmonary vascular system at the precapillary level. The administration of endotoxin induces an elevation of lung lymph. The bronchial circuit may play a role in this response since it is likewise exposed to the high pulmonary pressures induced by endotoxin, and there is evidence that ischemia/reperfusion injury to the airway occurs with endotoxin administration. After acute lung injury from smoke inhalation, lung lymph flow is markedly elevated. The lymph drainage from the airway may play an important role in this response. Bronchial blood flow is markedly increased after inhalation injury and there is airway edema. The increases in lung lymph flow and extravascular lung water are markedly reduced by occlusion of the bronchial artery. These data support the need for additional study of the role of the bronchial circulation in the formation of lung lymph.

Airway obstruction and bronchial hyperresponsiveness in left ventricular failure and mitral stenosis

Small and large airways narrow in LVF and the term cardiac asthma is often used. However, current usage of this term is inconsistent and its meaning is therefore ambiguous. The term is better avoided despite several emerging similarities with bronchial asthma. Airway narrowing may be precipitated by acute elevation of pulmonary or bronchial vascular pressures. This appears to be mainly due to reflex bronchoconstriction. The afferents of this reflex are C-fibers with their endings in the lung parenchyma, bronchi, and pulmonary blood vessels and RAR in the larger airways, and they run in the vagus nerves, as do the efferent bronchoconstrictor fibers. Chronic elevation of pulmonary vascular pressures, as in mitral stenosis, are also associated with airway narrowing. Pulmonary edema (in the absence of vascular hypertension) also causes reflex bronchoconstriction. Bronchial responsiveness to bronchoconstrictor drugs is increased in LVF, partly, at least, due to reflex mechanisms. Bronchial mucosal swelling may also contribute. Narrowing by nonreflex mechanisms definitely occurs and there is direct evidence that decreased lung volume caused by pulmonary edema may cause this. There is little evidence for bronchial narrowing due to the mechanical effect of peribronchial edema, or by swelling of the bronchial mucosa. However, edema foam may terminally cause grave obstruction. Patients with LVF are commonly treated with bronchodilator drugs, but the basis for this approach needs further clarification.

Morphometry of the subepithelial circulation in sheep airways. Effect of vascular congestion

In order to quantitate the subepithelial microvascular volume and its relation to the airway lumen, we conducted a morphometric analysis of the vascular compartment in the wall of the trachea (within a 55-microns depth from the epithelial basement membrane) and of 1.0 and 0.5-mm bronchioles of sheep. The lungs were fixed by bronchial and pulmonary artery perfusion with glutaraldehyde under three experimental conditions: (1) bronchial artery pressure, 100 mm Hg pulmonary artery pressure, 20 mm Hg (control); (2) bronchial artery pressure, 100 mm Hg, pulmonary artery pressure, 40 mm Hg (pulmonary hypertension, PH); (3) bronchial artery pressure, 100 mm Hg, pulmonary artery pressure, 40 mm Hg (pharmacologic vasodilation with sodium nitroprusside, PH + V). Venous pressures were atmospheric. Under control conditions, the microvascular volume fraction comprised 12, 16, and 15% of the subepithelial tissue in the trachea and 1-mm and 0.5-mm bronchioles, respectively. PH increased the microvascular volume fraction in the bronchioles (p less than 0.05), but it had no effect on the microvasculature in the trachea. PH + V approximately doubled the microvascular volume fraction in the trachea and the bronchioles. PH increased the mean wall thickness, and PH and PH + V decreased the airway cross-sectional area in the 1-mm bronchioles. These observations demonstrate that the microvasculature constitutes a considerable volume fraction of the subepithelial airway tissue and that vascular congestion can narrow the bronchiolar lumen.

The effect of bronchial venous pressure on pulmonary edema in the dog

We examined the effect of elevating systemic venous pressure on the rate of edema formation in the left lower lobes (LLL) of anesthetized, open-chested dogs. The pulmonary circulation of the LLL was isolated using cannulae in the artery and vein which were attached to blood-filled reservoirs. The LLL was distended to an alveolar pressure of 25 cm H2O with 5% CO2 and air, and suspended from a strain gauge which allowed continuous weight recording. The pulmonary vascular pressures were raised so all of the LLL was in zone III. The rate of weight change occurring over the last 4 minutes of a 6 minute period of this pulmonary vascular pressure rise was taken to represent the control transvascular fluid flux. The rate of weight gain of the LLL was then determined with the same pulmonary vascular pressure elevation only when downstream bronchial venous pressure alone, downstream lymphatic pressure alone, or when both downstream lymphatic and bronchial venous pressures were elevated. The transvascular fluid flux was increased when downstream bronchial venous pressure was elevated. When only downstream lymphatic pressure was elevated there was no augmentation of transvascular fluid flux. These findings suggest that when a lung is already subjected to raised pulmonary vascular pressure sufficient to cause edema, acute elevation of bronchial systemic venous pressure augments the net rate of outward fluid flux, while downstream lymphatic pressure elevation does not.

Pulmonary artery infusion of prostacyclin increases lobar bronchial blood flow

Intrapulmonary systemic to pulmonary bronchial blood flow [Qbr (s-p)] decreases with administration of cyclooxygenase inhibitors. This effect may be due to a decrease in the production of vasodilating prostaglandins and reflect either a decrease in the total intrapulmonary bronchial blood flow (Qbr), or a redistribution of the intrapulmonary systemic venous return. In nine open chested dogs the left lower lobe (LLL) was isolated and perfused in situ. Blood flow to the extrapulmonary airways (Qep), and Qbr were measured by the reference flow technique. Qbr (s-p) was measured as the overflow from the closed LLL perfusion circuit. After ibuprofen, PG-I2 was infused into the LLL PA and the Qbr (s-p) was continuously monitored. Qbr, and Qep were measured before and after ibuprofen, and during and after the PG-I2 infusion. The upstream pressure for Qbr (s-p) was estimated with and without PG-I2 infusion. After ibuprofen the Qep, Qbr, and Qbr (s-p) fell to 45, 22, and 17%, respectively, of the pre-ibuprofen values (P less than 0.05). PG-I2 increased the Qbr (s-p) and Qbr (P less than 0.05), while Qep was unchanged. During all experimental conditions the simultaneous measurements of Qbr and Qbr (s-p) were not different from each other (P less than 0.001). The upstream pressure for Qbr (s-p) increased from 30 to 50 cm H2O (P less than 0.05). Intralobar bronchial blood flow is drained almost entirely through the pulmonary circulation, and PG-I2 in the LLL pulmonary circulation increases systemic blood flow to the LLL, probably acting at the level of a systemic arteriole.

Endobronchial changes in chronic pulmonary venous hypertension

The bronchial venous system closely communicates with the pulmonary circulation. To assess the changes in the bronchial circulation in chronic pulmonary venous hypertension, fiberoptic bronchoscopy and right heart catheterization were performed in 31 patients with mitral stenosis. Nonpulsatile submucosal vessel dilatation, consistently seen in all patients and called the vessel dilatation score, was assessed visually by three independent bronchoscopists. The vessel dilatation score was correlated more closely with pulmonary artery wedge pressure (r = 0.687) (p less than 0.001) than to mean pulmonary artery pressure (r = 0.531) (p less than 0.01) and right atrial pressure (r = 0.178) (NS). The vessel dilatation score decreased after reduction of the left atrial load by surgery. These results suggest that the dilated vessels observed in patients with mitral stenosis are bronchial veins that are engorged secondary to increased blood flow via bronchopulmonary anastomoses.

Calcitonin gene-related peptide and the lung: neuronal coexistence with substance P, release by capsaicin and vasodilatory effect

The occurrence and distribution of calcitonin gene-related peptide (CGRP) in the lower airways was studied by means of immunohistochemistry and radioimmunoassay (RIA) in combination with high performance liquid chromatography (HPLC). CGRP-like immunoreactivity (-LI) was observed in nerves from the epiglottis down to peripheral bronchi in rat, cat and guinea pig and also in human bronchi. Double staining revealed colocalization of CGRP-LI and substance P (SP)-LI in cell bodies of nodose and jugular ganglia as well as in axons and nerve terminals of the airways. Systemic capsaicin pretreatment induced a marked loss of the CGRP- and SP-immunoreactive (-IR) nerves in the lower airways. CGRP-IR was also present in epithelial endocrine cells and neuroepithelial bodies. The content of CGRP-LI as measured with RIA in guinea pig bronchi was significantly lower after capsaicin pretreatment. Analysis of human bronchial extracts revealed that CGRP-LI coeluted with synthetic human CGRP on HPLC. In the isolated perfused guinea pig lung capsaicin exposure caused overflow of CGRP-LI suggesting release from peripheral branches of sensory nerves. Both in vivo experiments in the guinea pig measuring insufflation pressure as well as in vitro studies on isolated guinea pig and human bronchi showed that whereas tachykinins contracted bronchial smooth muscle no contractile or relaxing effect was elicited by human or rat CGRP. However, CGRP caused relaxation of serotonin precontracted guinea pig and human pulmonary arteries. In conclusion, the presence and release of CGRP-LI from capsaicin sensitive nerves in the lower airways adds another possible mediator, in addition to tachykinins, of vascular reactions upon sensory nerve irritation.

Exercise-induced pulmonary haemorrhage in the horse: results of a detailed clinical, post mortem and imaging study. IV. Changes in the bronchial circulation demonstrated by C.T. scanning and microradiography

The purpose of this study was to use radiographic contrast techniques and special imaging methods to identify and high-light bronchial arterial involvement in lung lesions associated with exercise-induced pulmonary haemorrhage (EIPH) in horses. The lungs from four horses with histories of EIPH were prepared for computerised tomographic scanning and microradiography by perfusing the broncho-oesophageal artery with a mixture of red latex and either barium or iodine contrast materials while the pulmonary supply received only blue latex. Computerised tomographic scan slices of the prepared inflated lungs were obtained from the caudal tip of the lung to the hilus. Microradiography of selected lung slices was also performed on a Faxitron. Diffuse areas of increased density, with preferential bronchial arterial supply noted on the computerised tomographic scans were confirmed by microradiography. Dense focal and diffuse plexuses of markedly hypertrophied and highly branched bronchial arterial networks were identified, centred around certain small airways. The vascular supply to these plexuses was recruited predominantly from neighbouring bronchial vessels, and in some cases, from the enlarged vasa vasorum of pulmonary arteries sending anastomoses to the affected areas. The authors conclude that bronchial vascular lesions in EIPH cases are the likely origin of haemorrhage; that small airway disease is the probable initiating stimulus for bronchial vascular proliferation in these lesions; and that the morphology and nature of the neovascular tissue in these lesions provides the conditions leading to haemorrhage in the lungs of horses with EIPH.

Exercise-induced pulmonary haemorrhage in the horse: results of a detailed clinical, post mortem and imaging study. III. Subgross findings in lungs subjected to latex perfusions of the bronchial and pulmonary arteries

Latex was injected under pressure into bronchial and pulmonary arteries of the inflated lungs of Thoroughbreds and transverse sections taken to calculate the area of lesions resulting from exercise-induced pulmonary haemorrhage. Extensive areas of dense brown haemosiderin varying from 0 to 45 per cent of total lung volume were identified, predominantly in the dorsocaudal lungfields. Bronchial arterial proliferation appeared to have replaced the pulmonary supply in affected areas of the lung. Closely associated with the staining and bronchial arterialisation, there was widespread small airway disease. The most severely affected bronchioles contained thick gelatinous or mucous exudate or mucoid plugs and had grossly thickened walls. These lesions suggest that the source of haemorrhage in exercise-induced pulmonary haemorrhage is from alveolar capillaries anomalously supplied by the bronchial arterial circulation through the development of pathological shunts. Small airway disease is suggested as being of major importance in the pathogenesis of the disease and may have led to the initial proliferation of the bronchial circulation.