Airway mucosal blood flow in humans. Response to adrenergic agonists

Angiogenesis in the lung

Both systemic (tracheal and bronchial) and pulmonary circulations perfuse the lung. However, documentation of angiogenesis of either is complicated by the presence of the other. Well-documented angiogenesis of the systemic circulations have been identified in asthma, cystic fibrosis, chronic thromboembolism and primary carcinomas. Angiogenesis of the vasa vasorum, which are branches of bronchial arteries, is seen in the walls of large pulmonary vessels after a period of chronic hypoxia. Documentation of increased pulmonary capillaries has been shown in models of chronic hypoxia, after pneumonectomy and in some carcinomas. Although endothelial cell proliferation may occur as part of the repair process in several pulmonary diseases, it is separate from the unique establishment of new functional perfusing networks defined as angiogenesis. Identification of the mechanisms driving the expansion of new vascular beds in the adult needs further investigation. Yet the growth factors and molecular mechanisms of lung angiogenesis remain difficult to separate from underlying disease sequelae.

Effect of airway acidosis and alkalosis on airway vascular smooth muscle responsiveness to albuterol

Background

In vitro and animal experiments have shown that the transport and signaling of β₂-adrenergic agonists are pH-sensitive. Inhaled albuterol, a hydrophilic β₂-adrenergic agonist, is widely used for the treatment of obstructive airway diseases. Acute exacerbations of obstructive airway diseases can be associated with changes in ventilation leading to either respiratory acidosis or alkalosis thereby affecting albuterol responsiveness in the airway. The purpose of this study was to determine if airway pH has an effect on albuterol-induced vasodilation in the airway.

Methods

Ten healthy volunteers performed the following respiratory maneuvers: quiet breathing, hypocapnic hyperventilation, hypercapnic hyperventilation, and eucapnic hyperventilation (to dissociate the effect of pH from the effect of ventilation). During these breathing maneuvers, exhaled breath condensate (EBC) pH and airway blood flow response to inhaled albuterol (ΔQ̇_aw) were assessed.

Results

Mean ± SE EBC pH (units) and ΔQ̇_aw (μl.min^-1.mL^-1) were 6.4 ± 0.1 and 16.8 ± 1.9 during quiet breathing, 6.3 ± 0.1 and 14.5 ± 2.4 during eucapnic hyperventilation, 6.6 ± 0.2 and -0.2 ± 1.8 during hypocapnic hyperventilation (p = 0.02 and <0.01 vs. quiet breathing), and 5.9 ± 0.1 and 2.0 ± 1.5 during hypercapnic hyperventilation (p = 0.02 and <0.02 vs quiet breathing).

Conclusions

Albuterol responsiveness in the airway as assessed by ΔQ̇_aw is pH sensitive. The breathing maneuver associated with decreased and increased EBC pH both resulted in a decreased responsiveness independent of the level of ventilation. These findings suggest an attenuated response to hydrophilic β₂-adrenergic agonists during airway disease exacerbations associated with changes in pH.

Trial registration

Registered at clinicaltrials.gov: NCT01216748.

Airway gas exchange and exhaled biomarkers

During inspiration and expiration, gases traverse the conducting airways as they are transported between the environment and the alveolar region of the lungs. The term "conducting" airways is used broadly as the airway tree is thought largely to provide a conduit for the respiratory gases, oxygen and carbon dioxide. However, despite a significantly smaller surface area, and thicker barrier separating the gas phase from the blood when compared to the alveolar region, the airway tree can participate in gas exchange under special conditions such as high water solubility, high chemical reactivity, or production of the gas within the airway wall tissue. While these conditions do not apply to the respiratory gases, other gases demonstrate substantial exchange of the airways and are of particular importance to the inflammatory response of the lungs, the medical-legal field, occupational health, metabolic disorders, or protection of the delicate alveolar membrane. Given the significant structural differences between the airways and the alveolar region, the physical determinants that control airway gas exchange are unique and require different models (both experimental and mathematical) to explore. Our improved physiological understanding of airway gas exchange combined with improved analytical methods to detect trace compounds in the exhaled breath provides future opportunities to develop new exhaled biomarkers that are characteristic of pulmonary and systemic conditions.

New methods for monitoring dynamic airway tissue oxygenation and perfusion in experimental and clinical transplantation

A dual circulation, supplied by bronchial and pulmonary artery-derived vessels, normally perfuses the airways from the trachea to the terminal bronchioles. This vascular system has been highly conserved through mammalian evolution and is disrupted at the time of lung transplantation. In most transplant centers, this circulation is not restored. The Papworth Hospital Autopsy study has revealed that an additional attrition of periairway vessels is associated with the development of chronic rejection, otherwise known as the bronchiolitis obliterans syndrome (BOS). Experimental studies subsequently demonstrated that airway vessels are subject to alloimmune injury and that the loss of a functional microvascular system identifies allografts that cannot be rescued with immunosuppressive therapy. Therefore, surgical and medical strategies, which preserve the functionality of the existent vasculature in lung transplant patients, may conceivably limit the incidence of BOS. Given these unique anatomic and physiological considerations, there is an emerging rationale to better understand the perfusion and oxygenation status of airways in transplanted lungs. This article describes novel methodologies, some newly developed by our group, for assessing airway tissue oxygenation and perfusion in experimental and clinical transplantation.

Smooth muscle in tissue remodeling and hyper-reactivity: airways and arteries

Smooth muscle comprises a key functional component of both the airways and their supporting vasculature. Dysfunction of smooth muscle contributes to and exacerbates a host of breathing-associated pathologies such as asthma, chronic obstructive pulmonary disease and pulmonary hypertension. These diseases may be marked by airway and/or vascular smooth muscle hypertrophy, proliferation and hyper-reactivity, and related conditions such as fibrosis and extracellular matrix remodeling. This review will focus on the contribution of airway or vascular smooth dysfunction to common airway diseases.

Acute effects of salmeterol and fluticasone propionate alone and in combination on airway blood flow in patients with asthma

BACKGROUND

The airway contains airway smooth muscle and airway vascular smooth muscle. The acute effects of inhaled long-acting β(2)-adrenergic agonists (LABAs) alone, or in combination with an inhaled glucocorticoid (ICS), on airway smooth muscle tone in asthma are known; however, to the best of our knowledge, their effect on airway vascular smooth muscle tone has not been investigated previously. The objective of this study was to investigate the immediate effects of a LABA and an ICS alone and in combination on airway blood flow (Qaw) as an index of airway vascular smooth muscle tone in patients with stable asthma.

METHODS

Fourteen subjects with moderate asthma inhaled single doses of salmeterol (50 μg), fluticasone propionate (250 μg), salmeterol/fluticasone propionate (50/250 μg), or placebo; Qaw was measured before and serially for 240 min after drug administration.

RESULTS

Mean Qaw increased after salmeterol and salmeterol/fluticasone propionate, with peaks at 60 min of 34% and 40%, respectively, and returned to baseline by 240 min after inhalation. Fluticasone propionate alone caused a transient decrease in mean Qaw. The maximal changes in Qaw, which occurred at different times, were 60% for salmeterol, 67% for salmeterol/fluticasone propionate, and -19% for fluticasone propionate (P < .05 vs placebo for all).

CONCLUSIONS

The LABA salmeterol has an acute vasodilator action on the airway of subjects with stable asthma. The addition of fluticasone propionate, which by itself causes vasoconstriction, does not attenuate the salmeterol-induced vasodilation, suggesting that fluticasone propionate potentiates the vasodilator effect of salmeterol. The vasodilation could be of clinical benefit by promoting the vascular clearance of inflammatory mediators including spasmogens from the airway.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT01231230; URL: www.clinicaltrials.gov.

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.

Airway vascular reactivity and vascularisation in human chronic airway disease

Altered bronchial vascular reactivity and remodelling including angiogenesis are documented features of asthma and other chronic inflammatory airway diseases. Expansion of the bronchial vasculature under these conditions involves both functional (vasodilation, hyperperfusion, increased microvascular permeability, oedema formation, and inflammatory cell recruitment) and structural changes (tissue and vascular remodelling) in the airways. These changes in airway vascular reactivity and vascularisation have significant pathophysiological consequences, which are manifest in the clinical symptoms of airway disease. Airway vascular reactivity is regulated by a wide variety of neurotransmitters and inflammatory mediators. Similarly, multiple growth factors are implicated in airway angiogenesis, with vascular endothelial growth factor amongst the most important. Increasing attention is focused on the complex interplay between angiogenic growth factors, airway smooth muscle and the various collagen-derived fragments that exhibit anti-angiogenic properties. The balance of these dynamic influences in airway neovascularisation processes and their therapeutic implications is just beginning to be elucidated. In this review article, we provide an account of recent developments in the areas of vascular reactivity and airway angiogenesis in chronic airway diseases.

Exercise-related change in airway blood flow in humans: relationship to changes in cardiac output and ventilation

This study examined the relationship between airway blood flow (Q(aw)), ventilation (V(E)) and cardiac output (Q(tot)) during exercise in healthy humans (n=12, mean age 34+/-11 yr). Q(aw) was estimated from the uptake of the soluble gas dimethyl ether while V(E) and Q(tot) were measured using open circuit spirometry. Measurements were made prior to and during exercise at 34+/-5 W (Load 1) and 68+/-10 W (Load 2) and following the cessation of exercise (recovery). Q(aw) increased in a stepwise fashion (P<0.05) from rest (52.8+/-19.5 microl min(-1) ml(-1)) to exercise at Load 1 (67.0+/-20.3 microl min(-1) ml(-1)) and Load 2 (84.0+/-22.9 microl min(-1) ml(-1)) before returning to pre-exercise levels in recovery (51.7+/-13.2 microl min(-1) ml(-1)). Q(aw) was positively correlated with both Q(tot) (r=0.58, P<0.01) and V(E) (r=0.50, P<0.01). These results demonstrate that the increase in Q(aw) is linked to an exercise related increase in both Q(tot) and V(E) and may be necessary to prevent excessive airway cooling and drying.

Rapid corticosteroid effect on beta(2)-adrenergic airway and airway vascular reactivity in patients with mild asthma

BACKGROUND

Long-term glucocorticoid therapy has been suggested to improve airway and airway vascular smooth muscle responsiveness to inhaled beta(2)-agonists in patients with asthma.

OBJECTIVE

We sought to assess whether a single dose of an inhaled glucocorticoid acutely potentiates beta(2)-adrenergic airway and airway vascular smooth muscle reactivity in asthma.

METHODS

In 10 asthmatic and 10 healthy subjects, airway blood flow and FEV(1) were measured before and 30 minutes after fluticasone or placebo inhalation and 15 minutes after the subsequent inhalation of racemic albuterol (0.6 mg or 1.25 mg) or (R)-albuterol (0.3 mg or 0.6 mg).

RESULTS

In healthy subjects all albuterol formulations increased airway blood flow equally after placebo or fluticasone pretreatment. In asthmatic subjects airway blood flow response was blunted after placebo and acutely restored after fluticasone pretreatment. Fluticasone pretreatment did not increase FEV(1) responses to any albuterol formulation, except 0.6 mg racemic albuterol.

CONCLUSION

A single dose of an inhaled glucocorticoid restores beta(2)-adrenergic airway vasodilator responses in patients with mild asthma. The mechanism of this rapid glucocorticoid effect remains to be clarified.

Development of a dimethyl ether (DME) sensor using platinum nanoparticles and thick-film printing

A portable and cost-effective technique to measure the dimethyl ether (DME) concentrations has been developed. It is based on an electrochemical principle measuring the oxidation current of DME at an applied potential of +0.2V versus a Ag/AgCl reference electrode. Thick-film printing technique is used for the fabrication of this DME sensor, and platinum nanoparticles in the crystallite size of 5.5 nm are used for the modification of the working electrode surface. This modification enhances the sensor performance significantly leading to a higher sensitivity of the sensor comparing to bare platinum electrode. Evaluation and characterization of this sensor are carried out over the DME concentration range of 0-7% (v/v), and a linear relationship between sensor outputs and the DME concentrations with an average R(2) of 0.996 exists. The reproducibility of the sensor is also very good. This electrochemically based DME sensor fabricated by thick-film screen printing technique and using the platinum nanoparticles to enhance its performance will be valuable and practical for the estimation of the airway mucosal blood flow.

A simplified noninvasive method to measure airway blood flow in humans

Our laboratory has previously developed and validated a noninvasive soluble gas uptake method to measure airway blood flow (Qaw) in humans (Onorato DJ, Demirozu MC, Breitenbücher A, Atkins ND, Chediak AD, and Wanner A. Am J Respir Crit Care Med 149: 1132-1137, 1994; Scuri M, McCaskill V, Chediak AD, Abraham WM, and Wanner A. J Appl Physiol 79: 1386-1390, 1995). The method has the disadvantage of requiring eight breath-hold maneuvers for a single Qaw measurement, a complicated data analysis, and the inhalation of a potentially explosive gas mixture containing dimethylether (DME) and O2. Because of these shortcomings, the method thus far has not been used in other laboratories. We now simplified the method by having the subjects inhale 500 ml of a 10% DME-90% N2 gas mixture to fill the anatomical dead space, followed by a 5- or 15-s breath hold, and measuring the instantaneous DME and N2 concentrations and volume at the airway opening during the subsequent exhalation. From the difference in DME concentration in phase 1 of the expired N2 wash-in curve multiplied by the phase 1 dead space volume and divided by the mean DME concentration and the solubility coefficient for DME in tissue, Qaw can be calculated by using Fick's equation. We compared the new method to the validated old method in 10 healthy subjects and found mean +/- SE Qaw values of 34.6 +/- 2.3 and 34.6 +/- 2.8 microl.min(-1).ml(-1), respectively (r = 0.93; upper and lower 95% confidence limit +2.48 and -2.47). Using the new method, the mean coefficient of variation for two consecutive measurements was 4.4% (range 0-10.4%); inhalation of 1.2 mg albuterol caused a 53 +/- 14% increase in Qaw (P = 0.02) and inhalation of 2.4 mg methoxamine caused a 32 +/- 7% decrease in Qaw (P = 0.07). We conclude that the new method provides reliable values of and detects the expected changes in Qaw with vasoactive drugs. The simplicity and improved safety of the method should improve its acceptability for the noninvasive assessment of Qaw in clinical research.

Airway blood flow reactivity in healthy smokers and in ex-smokers with or without COPD

STUDY OBJECTIVES

Cigarette smoking has been associated with impaired endothelium-dependent relaxation responses in the brachial and coronary arteries (endothelial dysfunction). The aim of the present study was to determine whether the airway circulation is also affected and whether pharmacologic treatment has an effect on endothelial function in patients with COPD.

METHODS AND PATIENTS

Airway blood flow (Qaw) responses to therapy with inhaled albuterol, which causes endothelium-dependent vasodilation, were measured with a noninvasive soluble-gas-uptake technique in age-matched healthy current smokers (n = 10), healthy ex-smokers (n = 10), ex-smokers with COPD (n = 10), and healthy lifetime nonsmokers. In the ex-smokers with COPD, the albuterol responsiveness measurement was repeated after 4 weeks of treatment with fluticasone/salmeterol and after a drug washout period of 4 or 8 weeks.

RESULTS

The mean (+/- SE) baseline Qaw values ranged between 40.7 +/- 3.9 and 50.9 +/- 2.8 microL/min/mL anatomic dead space in the four groups (differences were not significant). The mean FEV(1) was 53.4 +/- 2.3% predicted in the ex-smokers with COPD. Albuterol inhalation increased mean Qaw significantly in lifetime nonsmokers (50.1 +/- 8.3% predicted; p < 0.05) and healthy ex-smokers (37.2 +/- 3.4% predicted; p < 0.05), but not in healthy current smokers (13.9 +/- 3.2% predicted; difference was not significant) and ex-smokers with COPD (9.7 +/- 4.5% predicted; difference was not significant). While fluticasone/salmeterol did not change Qaw significantly, it restored albuterol responsiveness (67.6 +/- 11.1% predicted; p < 0.05) in the ex-smokers with COPD; this effect was no longer seen after the drug washout period.

CONCLUSIONS

Cigarette smoking is associated with a blunted vasodilator response to inhaled albuterol in the airway as an expression of endothelial dysfunction, with a partial recovery of albuterol responsiveness after smoking cessation in healthy ex-smokers but not in ex-smokers with COPD. In the latter group, combined glucocorticoid/long-acting beta(2)-adrenergic agonist treatment restores albuterol responsiveness. The role of endothelial dysfunction in the physiopathology of COPD remains to be examined.

Inhaled corticosteroids reduce asthma-associated airway hyperperfusion through genomic and nongenomic mechanisms

Inhaled corticosteroids have both genomic and nongenomic actions on the tracheobronchial (airway) vasculature in patients with bronchial asthma. Genomic actions involve the activation or repression of target genes associated with inflammation, and reduce inflammatory hyperperfusion in the airway. In contrast, nongenomic actions are mediated by rapid cellular mechanisms, and induce transient vasoconstriction. This article reviews recent progress on the mechanisms by which inhaled corticosteroids reverse inflammatory blood flow changes in the airway in asthma.

Airway blood flow reactivity in smokers

Cigarette smoking has been associated with impaired endothelium-dependent relaxation responses in the brachial and coronary arteries (endothelial dysfunction). The aim of the present study was to determine if the airway circulation is also affected and if airway treatment has an effect on endothelial function. Airway blood flow (Q(aw)) responses to inhaled albuterol as an index of endothelial function were measured in age-matched healthy current smokers, healthy ex-smokers, ex-smokers with COPD and healthy lifetime non-smokers; in the ex-smokers with COPD, the albuterol responsiveness was repeated after a 4-week treatment with an inhaled glucocorticoid/beta(2)-adrenergic agonist combination drug. Mean baseline Q(aw) was similar in the four groups. Albuterol inhalation increased mean Q(aw) in lifetime non-smokers (50.1+/-8.3%; p<0.05) and in healthy ex-smokers (37.2+/-3.4%; p<0.05) but not in healthy current smokers (13.9+/-3.2%; p=NS) and ex-smokers with COPD (9.7+/-4.5%; p=NS). While drug treatment per se did not change Q(aw) significantly, it restored albuterol responsiveness (+67.6+/-11.1%; p<0.05) in the ex-smokers with COPD. Thus, cigarette smoking is associated with endothelial dysfunction in the airway, with a partial recovery of endothelial function after smoking cessation in healthy ex-smokers but not in ex-smokers with COPD. In the latter, combined glucocorticoid/beta(2)-adrenergic agonist treatment restores albuterol responsiveness.

Bronchoprotective Effects of Single Doses of Salmeterol Combined With Montelukast in Thermally Induced Bronchospasm

STUDY OBJECTIVES

Salmeterol (S) and montelukast (M) individually inhibit the obstructive consequences of thermal stimuli such as exercise and hyperventilation (HV), but there is no information on whether these drugs can interact positively.

DESIGN

Randomized trial.

SETTING

University teaching hospital.

PARTICIPANTS

Atopic asthmatic patients with sensitivity to thermal provocations.

INTERVENTIONS

Eleven asthmatic patients generated stimulus-response curves to isocapnic HV while breathing frigid air without any interventions and then after pretreatment with 42 mug of S, 10 mg of M, and the combination. The order of testing was randomly determined.

MEASUREMENTS AND RESULTS

Minute ventilation (Ve) was increased in 20-L increments until FEV(1) fell >or= 15%. Measurements were obtained before and 1 h after drug administration, and then again 5 min after each bout of HV. In the nonintervention trial, the provocation commenced after the patients presented to the laboratory. In the control challenge, the mean (+/- SEM) FEV(1) decreased 24.6 +/- 1.7% from baseline. S and M both increased the mean prechallenge FEV(1) significantly (S, 10.4 +/- 1.7% [p < 0.01]; M, 4.1 +/- 1.3% [p = 0.02]; S + M, p = 0.01). The combination of S + M produced greater bronchodilatation (mean improvement, 12.4 +/- 2.3%) than M alone (p = 0.004), but not greater than S alone (p = 0.80). Both drugs blunted the obstructive response similarly (protection: M, 34.6 +/- 15.1%; S, 60 +/- 8.7%; p = 0.13). The benefits added arithmetically with the combined regimen (protection with S + M, 84.9 +/- 5.5%; p = 0.01 vs S alone; p = 0.003 vs M alone).

CONCLUSION

These data indicate that the concurrent administration of single standard doses of S and M appears to provide greater protection against thermal stimuli than does either drug alone. Further experimentation will be required to ascertain whether the combination will provide additional clinical benefits to patients over those of the single agents.

Correlation of exhaled breath temperature with bronchial blood flow in asthma

In asthma elevated rates of exhaled breath temperature changes (Δe°T) and bronchial blood flow (Q_aw) may be due to increased vascularity of the airway mucosa as a result of inflammation.

We investigated the relationship of Δe°T with Q_aw and airway inflammation as assessed by exhaled nitric oxide (NO). We also studied the anti-inflammatory and vasoactive effects of inhaled corticosteroid and β₂-agonist.

Δe°T was confirmed to be elevated (7.27 ± 0.6 Δ°C/s) in 19 asthmatic subjects (mean age ± SEM, 40 ± 6 yr; 6 male, FEV₁ 74 ± 6 % predicted) compared to 16 normal volunteers (4.23 ± 0.41 Δ°C/s, p < 0.01) (30 ± 2 yr) and was significantly increased after salbutamol inhalation in normal subjects (7.8 ± 0.6 Δ°C/ s, p < 0.05) but not in asthmatic patients. Q_aw, measured using an acetylene dilution method was also elevated in patients with asthma compared to normal subjects (49.47 ± 2.06 and 31.56 ± 1.6 μl/ml/min p < 0.01) and correlated with exhaled NO (r = 0.57, p < 0.05) and Δe°T (r = 0.525, p < 0.05). In asthma patients, Q_aw was reduced 30 minutes after the inhalation of budesonide 400 μg (21.0 ± 2.3 μl/ml/min, p < 0.05) but was not affected by salbutamol.

Δe°T correlates with Q_aw and exhaled NO in asthmatic patients and therefore may reflect airway inflammation, as confirmed by the rapid response to steroids.

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 inhaled racemic and (R)-albuterol on airway vascular smooth muscle tone in healthy and asthmatic subjects

Although the relative effect of racemic and (R)-albuterol on airway smooth muscle tone have been investigated in patients with airflow obstruction, the comparative effectiveness of these drugs in relaxing airway vascular smooth muscle is unknown. Therefore, we determined the actions of inhaled racemic and (R)-albuterol on airway mucosal blood flow (Qaw) normalized for anatomic dead space as an index of airway vascular smooth muscle tone in 11 healthy subjects and 10 subjects with mild asthma. We also monitored the forced expiratory volume in 1 second (FEV1) as an index of airway smooth muscle tone. Mean +/- SE baseline Qaw was 43.1 +/- 1.5 microl x min(-1) x ml(-1) in healthy subjects and 53.4 +/- 2.1 microl x min(-1) x ml(-1) in asthmatic subjects (p < 0.01). The corresponding values for FEV1 were 95.6 +/- 1.4 and 86.8 +/- 2.5% respectively, of predicted (p = 0.01). Racemic and (R)-albuterol caused a transient, dose-dependent increase of Qaw in healthy, but not in asthmatic subjects; the responses were not different between the two drugs. The FEV1 tended to increase more in asthmatics than in healthy subjects, again without a difference between the two drugs. These results show that racemic and (R)-albuterol have comparable effects on airway vascular smooth muscle and suggest that the blunted airway vascular smooth muscle response to albuterol in asthmatics is not related to (S)-albuterol.

Effects of cold dry air nasal stimulation on airway mucosal blood flow in humans

Several studies have demonstrated that nasal challenges can induce reflex responses in the respiratory system. Some authors have described bronchoconstriction and modification of the pattern of breathing following nasal challenges by irritants and cold air. We propose to determine the effect of nasal stimulation with cold dry air on airway mucosal blood flow (Qaw) in the proximal tracheal bronchial tree of healthy humans. Nine healthy subjects participated in the study. Baseline measurement Qaw, nasal airway resistance (NAR) and airway caliber by specific airways conductance (SGaw) were followed by nasal challenge with cold dry air. Qaw, NAR and Sgaw were determined after the challenge. In those subjects in which a significant decline in Qaw was recorded the protocol was repeated after pretreatment with nasal anesthesia using topical lidocaine. Cold dry air challenge produced a significant decrease in mean Qaw for the nine subjects and this response was abolished by pretreatment with nasal anesthesia using topical lidocaine. There was no significant change in Sgaw and NAR after the challenge and topical lidocaine anesthesia. Our data indicates that nasal stimulation with cold dry air leads to a reduction in Qaw and that this effect may be mediated by a nasal reflex.

Analysis of expired air for oxidation products

Chronic inflammation is a critical feature of chronic obstructive pulmonary disease, cystic fibrosis, and asthma. This inflammation is associated with the increased production of reactive oxygen species or oxidative stress in the lungs. Oxidative stress may have several adverse effects and may amplify the inflammatory process; however, monitoring oxidative stress is difficult and may not be reflected by changes in blood markers. We have therefore developed several noninvasive markers in the exhaled breath that may indicate oxidative stress in the lungs, and we studied these in relationship to the severity of chronic inflammatory lung diseases. We analyzed the exhaled breath for the content of nitric oxide as a marker of inflammation, carbon monoxide as a marker of oxidative stress, and ethane, which is one of the end products of lipid peroxidation. In addition, we measured the concentration of markers of oxidative stress such as isoprostanes in exhaled breath condensate. Our results confirm that there are increased inflammation, oxidative stress, and lipid peroxidation in lung disease, as shown by elevated levels of nitric oxide, carbon monoxide, and ethane, respectively. The finding of lower levels of these gases in patients on steroid treatment and of higher levels in those with more severe lung disease, as assessed by lung function tests and clinical symptoms, reinforces the hypothesis that the noninvasive measurement of exhaled gases maybe useful in monitoring the underlying pathologic pathways of lung disease. Longitudinal studies are required to assess the clinical usefulness of these measurements in the monitoring of chronic inflammatory lung disease.

Pulmonary and bronchial circulations: contributions to heat and water exchange in isolated lungs

The relative contribution of the pulmonary and bronchial circulatory systems to heat and water exchange in normal lungs was evaluated in 20 isolated, in situ perfused dog lungs and in four patients undergoing elective cardiopulmonary bypass. In isolated dog lungs, if the pulmonary artery was perfused at a nominal flow rate (0.5 l/min), bronchial artery perfusion (up to 70 ml/min) did not significantly affect the expired gas temperature. When the lungs were not perfused through either system, 8 min of ventilation with cool, dry gas decreased the temperature of the expired gas by 6.2 +/- 1.4 degrees C. Selective perfusion of bronchial arteries at 68 +/- 10 mmHg resulted in a mean flow rate of 28 +/- 16 ml/min and increased the average temperature of the expired gas by 0.6 degrees C. An increase in the rate of bronchial arterial perfusion to 55 +/- 14 ml/min increased the average temperature of the expired gas by 1.3 degrees C. The time constant for equilibration of tritiated water between the perfusate and the lung parenchyma was 130 +/- 33 min for pulmonary arterial perfusion and 35 +/- 13 min for combined bronchial and pulmonary perfusion, which indicated that filtration of water from high-pressure bronchial vessels facilitated water exchange in the lung interstitium. The rate of tracer equilibration was similar between the perfusate and gas in both variants of perfusion, but the ratios of tracer gas to perfusate were different (0.42 +/- 0.06 for pulmonary, 0.98 +/- 0.07 for combined), which indicates that bronchial vessels contribute mainly to the hydration of the bronchial mucosa. In humans, the bronchial blood flow was capable of maintaining heat supply after the initiation of cardiopulmonary bypass. Before bypass, when both pulmonary and bronchial blood flow were present, the mean time constant of the temperature decay after a switch to ventilation with cool, dry gas was 35 +/- 12 s. The average temperature difference between the blood and expired gas was 2.4 +/- 0.50 degrees C. After 5 min of dry gas ventilation, the temperature difference between the expired gas and initial blood temperature decreased an average of 3.8 +/- 0.06 degrees C (P < 0.05). The time constant of temperature decay increased to 56 +/- 14 s (P < 0.05). We conclude that bronchial perfusion has a less important role in the temperature balance of the respiratory tract compared with pulmonary arterial perfusion because heat flux is "flow limited" but is important in providing water for hydration of the mucosal surface and interstitial compartments of peribronchial tissues.

Overview of upper respiratory tract vapor uptake studies

This review is aimed at highlighting toxicologically relevant physiological and biochemical factors that influence the delivery of inhaled vapors to nasal tissues. Numerous experiments in rodents have shown that vapor uptake efficiencies are dependent on vapor solubility (as measured by blood:air partition coefficient) and inspiratory flow rate. Nasal tissues are rich in xenobiotic metabolizing enzymes, and it has been shown experimentally through the use of metabolic inhibitors that inspired vapors are metabolized in nasal tissue and that this process serves to enhance inspired vapor uptake efficiency in that site. Metabolism-based species differences in vapor uptake have been observed among rodent species. Concentration-dependent changes in vapor uptake have also been observed and related to saturation of local metabolic pathways at high exposure concentrations. Therefore, appropriate consideration of local metabolism is necessary for comprehensive high- to low-dose or species extrapolations of nasal toxicity data. Recent studies have provided evidence of sensory nerve-mediated reflex responses that alter nasal vascular function and may alter nasal inspired vapor dosimetric relationships. In toto, these studies also indicate the need to define uptake behavior for a vapor of interest over a wide range of exposure concentrations due to the possibility of nonlinear metabolism kinetics or the induction of nasal reflex and/or toxic responses. Such data are required for the formulation of a robust nasal dosimetry model.

Adrenergic airway vascular smooth muscle responsiveness in healthy and asthmatic subjects

The purpose of the present study was to determine the responsiveness of airway vascular smooth muscle (AVSM) as assessed by airway mucosal blood flow (Qaw) to inhaled methoxamine (alpha(1)-agonist; 0.6-2.3 mg) and albuterol (beta(2)-agonist; 0.2-1.2 mg) in healthy [n = 11; forced expiratory volume in 1 s, 92 +/- 4 (SE) % of predicted] and asthmatic (n = 11, mean forced expiratory volume in 1 s, 81 +/- 5%) adults. Mean baseline values for Qaw were 43.8 +/- 0.7 and 54.3 +/- 0.8 microl. min(-1). ml(-1) of anatomic dead space in healthy and asthmatic subjects, respectively (P < 0.05). After methoxamine inhalation, the maximal mean change in Qaw was -13.5 +/- 1.0 microl. min(-1). ml(-1) in asthmatic and -7.1 +/- 2.1 microl. min(-1). ml(-1) in healthy subjects (P < 0.05). After albuterol, the mean maximal change in Qaw was 3.0 +/- 0.8 microl. min(-1). ml(-1) in asthmatic and 14.0 +/- 1.1 microl. min(-1). ml(-1) in healthy subjects (P < 0.05). These results demonstrate that the contractile response of AVSM to alpha(1)-adrenoceptor activation is enhanced and the dilator response of AVSM to beta(2)-adrenoceptor activation is blunted in asthmatic subjects.

A lung model describing uptake of organic solvents and roles of mucosal blood flow and metabolism in the bronchioles

A simple lung model (mucosal blood flow and metabolism model, MBM model) was developed to describe the uptake of organic solvents and investigate the role of mucosal blood flow and metabolism. The model separates the lung into four compartments, the peripheral bronchial tract (gas phase), the mucus layer lining the wall surface of the tract, the alveolar space (gas phase), and the alveolar blood. Solvent molecules are absorbed in the mucus layer during inhalation and released during exhalation. The deposited solvent diffuses radially into the mucosal tissue of the respiratory tract and transfers to the mucosal blood flow. To describe this behavior, a hypothetical mucosal blood flow throughout the mucus layer was used. The solvent in the mucosal tissue may be also metabolized, and a hypothetical metabolism in the mucus layer was used. The rate of the hypothetical mucosal blood flow was determined to be 5.2 ml/min based on the best fitting of previously obtained data for seven polar organic solvents. The MBM model predicts that as the blood-air partition coefficient (lambda(B)) increases from 0.1 to 20, the relative end-exhalation (E(end)) will decrease from 0.89 to 0.07, and as lambda(B) increases to 500, E(end) will increase to 0.33. After lambda(B) = 500, E(end) is predicted to decrease again, and at lambda(B) = 10000, E(end) is 0.09. The model also predicts that as lambda(B) increases from 0.1 to 10, the relative uptake (U) increases from 0.08 to 0.61, and as lambda(B) increases to 150, U decreases to 0.50. After lambda(B) = 150, U increases again, and at lambda(B) = 10,000, U is 0.8. The predictions show good agreement with values observed in human experimental studies. The MBM model predicts that uptake by the mucosal blood (U(Al)) would be equal to uptake by the alveolar blood (U(Mu)) at lambda(B) of 1000 and U(Al) is more than 90% of total uptake at lambda(B) > 10,000. The model also shows that U is significantly increased by the mucosal metabolism at lambda(B) between 50 and 5000. Especially, U in the case of CL(Mu) = 100 ml/min is higher by 0.3 than that in the nonmucosal metabolism.

Transient effect of inhaled fluticasone on airway mucosal blood flow in subjects with and without asthma

Topically applied glucocorticosteroids (GS) have been shown to cause local vasoconstriction in normal skin and this phenomenon is commonly used to assess the potency of topical GS (McKenzie skin blanching test). The purpose of the present study was to determine if an inhaled GS, fluticasone propionate (FP), similarly leads to vasoconstriction in the airway mucosa and if subjects with and without asthma have differential vascular responsiveness to GS. In 10 nonsmokers with stable asthma and 10 nonasthmatic nonsmokers, airway mucosal blood flow (Qaw) expressed per milliliter of anatomical dead space and the forced expiratory volume in 1 s (FEV (1)) were determined before and serially after inhalation of FP (88 to 1,760 microg) or placebo. Baseline mean (+/- SE) Qaw was 55.1 +/- 1.0 and 44.2 +/- 1.1 microl x min(-1) x ml(-1) in subjects with and without asthma, respectively (p < 0.001). The corresponding mean FEV(1) values were 2.34 +/- 0.13 and 3.22 +/- 0.12 L (p < 0.001). FP at 880 microg but not placebo produced a transient decrease in mean Qaw with a nadir at 30 min and return toward baseline at 90 min post-inhalation; the maximum mean decrease was 37% in subjects with asthma and 21% in unaffected subjects (p < 0.01); 880 microg of FP was the lowest effective dose. FEV(1) did not change after FP administration in either group. These results demonstrate a transient vasoconstrictive action of inhaled FP in the airway mucosa, with a greater vascular responsiveness in subjects with asthma than in unaffected subjects. The measurement of Qaw may provide a more relevant means of assessing the potency of inhaled GS than the McKenzie skin blanching test. In addition, our observation suggests that inhaled GS have potentially beneficial effects in asthma that is not related to their antiinflammatory action.

Effect of an inhaled glucocorticosteroid on airway mucosal blood flow in mild asthma

We determined airway mucosal blood flow (Qaw) and FEV (1) before and after inhaled albuterol in 19 glucocorticosteroid (GS)-naive patients with mild intermittent asthma, and assessed the effects of a 2-wk course of fluticasone propionate (FP; 440 microg daily) on these parameters. Twelve healthy nonsmokers served as controls. Baseline Qaw was 55.5 +/- 0.7 microl/min/ml (mean +/- SE) in the asthmatic subjects and 44.2 +/- 0.7 microl/min/ml in the controls; the respective FEV(1) values were 2.8 +/- 0.2 L and 3.4 +/- 0.2 L (p < 0.01 for both parameters). Albuterol increased Qaw by 27 +/- 3% in the control subjects (p < 0.01) but had no effect on Qaw in the asthmatic subjects; it increased FEV (1) by 7 +/- 1% and 6 +/- 1% in the two groups, respectively. Qaw decreased to 49.2 +/- 0.8 microl/min/ml (p < 0.05 versus baseline), and the Qaw responsiveness to albuterol was restored ( +21 +/- 2%; p < 0.05) in the asthmatic subjects after FP. Eleven asthmatic subjects stopped using FP at this time; 2 wk later, their Qaw returned to baseline (55.2 +/- 0.9 microl/min/ml) and they lost the Qaw responsiveness to albuterol. Mean ( +/- SE) FEV(1) and FEV(1) responsiveness to albuterol were not affected by FP. The GS-sensitive increase in Qaw and its hyporesponsiveness to albuterol in asthmatic subjects may be consequences of airway inflammation.

Altered contractile sensitivity of isolated bronchial artery to phenylephrine in ovalbumin-sensitized rabbits

We tested the hypothesis that atopy and/or allergic lung inflammation enhances alpha1-adrenoceptor-mediated contractions of the bronchial artery. Bronchial arterial resistance vessels were isolated from rabbits that had undergone either systemic ovalbumin (OVA) sensitization followed by saline aerosol challenge (OVA/saline rabbits), or OVA sensitization followed by OVA aerosol challenge (OVA/OVA rabbits), or no sensitization followed by saline aerosol challenge (control rabbits). In OVA/OVA rabbits, bronchoalveolar lavage and lung histology revealed lymphocytic and eosinophilic inflammation. Arterial rings were contracted with phenylephrine (PE). In endothelium-intact arteries isolated from OVA/saline and OVA/OVA rabbits, PE responsiveness was enhanced compared with that of arteries isolated from controls. The nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester increased the contractile response to PE in all three experimental groups to a similar degree, suggesting that depressed NOS activity was not involved in the enhanced PE responsiveness in OVA/saline and OVA/OVA rabbits. After endothelium removal, arteries from OVA/saline and control rabbits showed similar PE responsiveness, indicating that the enhancement of PE responsiveness was endothelium dependent, possibly due to an endothelial constricting factor. In OVA/OVA rabbits, endothelium-denuded arteries showed decreased PE responsiveness compared with the other two groups; this difference was abolished by NG-nitro-L-arginine methyl ester. We conclude that systemic sensitization with OVA per se enhances PE-induced contractions of isolated bronchial arteries in rabbits by an endothelium-dependent mechanism and that allergic lung inflammation attenuates this effect by increased nonendothelial NOS activity.

Airway mucosal blood flow in bronchial asthma

As an inflammatory airway disease, asthma is expected to be associated with an increase in airway blood flow. We therefore compared airway mucosal blood flow (Qaw) among normal subjects (n = 11) and patients with stable asthma receiving (n = 13) or not receiving (n = 10) long-term inhaled glucocorticosteroid (GS) therapy. Qaw was calculated from the uptake of dimethyl ether in the anatomic dead space minus the most proximal 50 ml (DS), and expressed as blood flow per ml DS. Mean (+/- SE) Qaw was 38.5 +/- 5. 3 microl . min-1 . ml-1 in normals, 68.2 +/- 7.9 microl . min-1 . ml-1 in GS-naive asthmatics (p < 0.01), and 55.4 +/- 5.3 microl . min-1 . ml-1 in GS-treated asthmatics (p < 0.05). Ten minutes after administration of 180 microg albuterol by metered dose inhaler, mean Qaw increased by 83 +/- 26% in normal subjects (p < 0.01), but did not change significantly in GS-naive (+5 +/- 8%) or GS-treated (+32 +/- 15%) asthmatics. These results demonstrate that Qaw is increased in stable asthmatics and resistant to further increase by a standard inhaled dose of a beta-adrenergic agonist.

Norepinephrine-induced contraction of isolated rabbit bronchial artery: role of alpha 1- and alpha 2-adrenoceptor activation

The contractile effect of norepinephrine (NE) on isolated rabbit bronchial artery rings (150-300 microns in diameter) and the role of alpha 1- and alpha 2-adrenoceptors (AR) on smooth muscle and endothelium were studied. In intact arteries, NE increased tension in a dose-dependent manner, and the sensitivity for NE was further increased in the absence of endothelium. In intact but not in endothelium-denuded arteries, the response to NE was increased in the presence of both indomethacin (Indo; cyclooxygenase inhibitor) and NG-nitro-L-arginine methyl ester [L-NAME; nitric oxide (NO) synthase inhibitor], indicating that two endothelium-derived factors, NO and a prostanoid, modulate the NE-induced contraction. The alpha 1-AR antagonist prazosin shifted the NE dose-response curve to the right, and phenylephrine (alpha 1-AR agonist) induced a dose-dependent contraction that was potentiated by L-NAME or removal of the endothelium. The sensitivity to NE was increased slightly by the alpha 2-AR antagonists yohimbine and idazoxan, and this effect was abolished by Indo or removal of the endothelium. Similarly, contractions induced by UK-14304 (alpha 2-AR agonist) were potentiated by Indo or removal of the endothelium. These results suggest that NE-induced contraction is mediated through activation of alpha 1- and alpha 2-ARs on both smooth muscle and endothelium. Activation of the alpha 1- and alpha 2-ARs on the smooth muscle causes contraction, whereas activation of the endothelial alpha 1- and alpha 2-ARs induces relaxation through release of NO (alpha 1-ARs) and a prostanoid (alpha 2-ARs).

Clinical perspectives: role of the airway circulation in drug therapy

Theoretically, the airway circulation can regulate the absorption of inhaled drugs, redistribute inhaled drugs within the respiratory tract, and influence the distribution of systemic drugs to the airway. Some of these functions of the airway circulation have been verified experimentally, but not in human subjects. Since pharmacological manipulation of airway blood flow could have therapeutic implications in airway disease, the development of new methods to measure airway blood flow noninvasively in human subjects is needed.

Airway blood flow responses to temperature and humidity of inhaled air

We determined the effect of breathing cold dry air (-39 degrees C, 0.1% relative humidity, RH) and warm humid air (43 degrees C, 100% RH) on airway mucosal blood flow (Qaw) in normal human subjects (n = 8, age 25-53 years) at rest. Qaw was measured with a dimethylether uptake technique which reflects blood flow in the mucosa of large airways corresponding to a 50 ml anatomical dead-space segment extending distally from the trachea. Mean Qaw was 10.1 +/- 1.9 ml min-1 (mean +/- S.D.) during room air breathing (25 degrees C, 70% RH) and decreased to 4.7 +/- 2.1 ml min-1 during cold dry air breathing (p < 0.05). Within 20 min of resuming room air breathing, mean Qaw had returned to baseline. Breathing warm humid air had no significant effect on mean Qaw (8.2 +/- 1.4 ml min-1). These results indicate that quiet breathing of frigid air causes vasoconstriction in central airways.

Effect of lung volume and intrathoracic pressure on airway mucosal blood flow in man

We have recently described an inert soluble gas uptake technique (using dimethyl-ether, DME) for the non-invasive measurement of airway mucosal blood flow (Qaw) in humans. In the present study, we assessed the effects of lung volume and intrathoracic pressure on Qaw, in healthy non-smokers (age range 19-52 years). Qaw was calculated from the steady-state uptake of DME from a 50 ml segment of the anatomic dead space. The mean (+/- SD) Qaw of three consecutive measurements at a lung volume of FRC + 300 ml was 8.3 +/- 2.3, 8.6 +/- 2.6 and 8.3 +/- 2.7 ml.min-1 (n = 13; coefficient of variation 14 +/- 7%). At zero airway pressure, there was an inverse relationship between apparent Qaw on the one hand and lung volume and anatomic dead space (DS) on the other: mean Qaw was 12.2 +/- 5.3, 8.2 +/- 2.5 and 5.3 +/- 2.2 ml.min-1 at RV + 300 ml (DS = 131 +/- 11 ml), FRC + 300 ml (DS = 153 +/- 12 ml) and TLC (DS = 206 +/- 22 ml) positions, respectively (n = 11; P < 0.05 among all three). At a lung volume of FRC + 300 ml, an increase in intrathoracic pressure to +25 cmH2O (modified Valsalva maneuver) decreased mean Qaw to 3.3 +/- 2.8 ml.min-1 while a decrease in intrathoracic pressure to -35 cmH2O (modified Müller maneuver) increased mean Qaw to 17.1 +/- 7.4 ml.min-1 from a control value of 7.2 +/- 2.2 ml.min-1 (n = 7; P < 0.05 among all three). These results indicate that lung volume has an effect on apparent Qaw, presumably by influencing the depth to which the analyzed anatomical dead space segment extends into the bronchial tree. The results also show that changes in intrathoracic pressure alter Qaw, possibly reflecting concomitant changes in left ventricular output and its distribution to intrathoracic and extrathoracic vascular beds.