Quantification of smooth muscle in human airways by polarization-sensitive optical coherence tomography requires correction for perichondrium.

Quantifying airway smooth muscle (ASM) in patients with asthma raises the possibility of improved and personalized disease management. Endobronchial polarization-sensitive optical coherence tomography (PS-OCT) is a promising quantitative imaging approach that is in the early stages of clinical translation. To date, only animal tissues have been used to assess the accuracy of PS-OCT to quantify absolute (rather than relative) ASM in cross sections with directly matched histological cross sections as validation. We report the use of whole fresh human and pig airways to perform a detailed side-by-side qualitative and quantitative validation of PS-OCT against gold-standard histology. We matched and quantified 120 sections from five human and seven pig (small and large) airways and linked PS-OCT signatures of ASM to the tissue structural appearance in histology. Notably, we found that human cartilage perichondrium can share with ASM the properties of birefringence and circumferential alignment of fibers, making it a significant confounder for ASM detection. Measurements not corrected for perichondrium overestimated ASM content several-fold (P < 0.001, paired t test). After careful exclusion of perichondrium, we found a strong positive correlation (r = 0.96, P < 0.00001) of ASM area measured by PS-OCT and histology, supporting the method's application in human subjects. Matching human histology further indicated that PS-OCT allows conclusions on the intralayer composition and in turn potential contractile capacity of ASM bands. Together these results form a reliable basis for future clinical studies.NEW & NOTEWORTHY Polarization-sensitive optical coherence tomography (PS-OCT) may facilitate in vivo measurement of airway smooth muscle (ASM). We present a quantitative validation correlating absolute ASM area from PS-OCT to directly matched histological cross sections using human tissue. A major confounder for ASM quantification was observed and resolved: fibrous perichondrium surrounding hyaline cartilage in human airways presents a PS-OCT signature similar to ASM for birefringence and optic axis orientation. Findings impact the development of automated methods for ASM segmentation.

Postnatal steroids as lung protective and anti-inflammatory in preterm lambs exposed to antenatal inflammation.

BACKGROUND: Lung inflammation and impaired alveolarization precede bronchopulmonary dysplasia (BPD). Glucocorticoids are anti-inflammatory and reduce ventilator requirements in preterm infants. However, high-dose glucocorticoids inhibit alveolarization. The effect of glucocorticoids on lung function and structure in preterm newborns exposed to antenatal inflammation is unknown. We hypothesise that postnatal low-dose dexamethasone reduces ventilator requirements, prevents inflammation and BPD-like lung pathology, following antenatal inflammation. METHODS: Pregnant ewes received intra-amniotic LPS (E.coli, 4 mg/mL) or saline at 126 days gestation; preterm lambs were delivered 48 h later. Lambs were randomised to receive either tapered intravenous dexamethasone (LPS/Dex, n = 9) or saline (LPS/Sal, n = 10; Sal/Sal, n = 9) commencing <3 h after birth. Respiratory support was gradually de-escalated, using a standardised protocol aimed at weaning from ventilation towards unassisted respiration. Tissues were collected at day 7. RESULTS: Lung morphology and mRNA levels for inflammatory mediators were measured. Respiratory support requirements were not different between groups. Histological analyses revealed higher tissue content and unchanged alveolarization in LPS/Sal compared to other groups. LPS/Dex lambs exhibited decreased markers of pulmonary inflammation compared to LPS/Sal. CONCLUSION: Tapered low-dose dexamethasone reduces the impact of antenatal LPS on ventilation requirements throughout the first week of life and reduces inflammation and pathological thickening of the preterm lung IMPACT: We are the first to investigate the combination of antenatal inflammation and postnatal dexamethasone therapy in a pragmatic study design, akin to contemporary neonatal care. We show that antenatal inflammation with postnatal dexamethasone therapy does not reduce ventilator requirements, but has beneficial maturational impacts on the lungs of preterm lambs at 7 days of life. Appropriate tapered postnatal dexamethasone dosing should be explored for extuabtion of oxygen-dependant neonates.

Adipose tissue in the small airways: How much is enough to drive functional changes?

Obesity is a contributing factor to asthma severity; while it has long been understood that obesity is related to greater asthma burden, the mechanisms though which this occurs have not been fully elucidated. One common explanation is that obesity mechanically reduces lung volume through accumulation of adipose tissue external to the thoracic cavity. However, it has been recently demonstrated that there is substantial adipose tissue within the airway wall itself, and that the presence of adipose tissue within the airway wall is related to body mass index. This suggests the possibility of an additional mechanism by which obesity may worsen asthma, namely by altering the behaviour of the airways themselves. To this end, we modify Anafi & Wilson's classic model of the bistable terminal airway to incorporate adipose tissue within the airway wall in order to answer the question of how much adipose tissue would be required in order to drive substantive functional changes. This analysis suggests that adipose tissue within the airway wall on the order of 1%-2% of total airway cross-sectional area could be sufficient to drive meaningful changes, and further that these changes may interact with volume effects to magnify the overall burden.

Heterogeneity of Airway Smooth Muscle Remodeling in Asthma.

Rationale: Ventilatory defects in asthma are heterogeneous and may represent the distribution of airway smooth muscle (ASM) remodeling. Objectives: To determine the distribution of ASM remodeling in mild-severe asthma. Methods: The ASM area was measured in nine airway levels in three bronchial pathways in cases of nonfatal (n = 30) and fatal asthma (n = 20) and compared with control cases without asthma (n = 30). Correlations of ASM area within and between bronchial pathways were calculated. Asthma cases with 12 large and 12 small airways available (n = 42) were classified on the basis of the presence or absence of ASM remodeling (more than two SD of mean ASM area of control cases, n = 86) in the large or small airway or both. Measurements and Main Results: ASM remodeling varied widely within and between cases of nonfatal asthma and was more widespread and confluent and more marked in fatal cases. There were weak correlations of ASM between levels within the same or separate bronchial pathways; however, predictable patterns of remodeling were not observed. Using mean data, 44% of all asthma cases were classified as having no ASM remodeling in either the large or small airway despite a three- to 10-fold increase in the number of airways with ASM remodeling and 81% of asthma cases having ASM remodeling in at least one large and small airway. Conclusions: ASM remodeling is related to asthma severity but is heterogeneous within and between individuals and may contribute to the heterogeneous functional defects observed in asthma. These findings support the need for patient-specific targeting of ASM remodeling.

Distribution, composition, and activity of airway-associated adipose tissue in the porcine lung.

Patients with comorbid asthma-obesity experience greater disease severity and are less responsive to therapy. We have previously reported adipose tissue within the airway wall that positively correlated with body mass index. Accumulation of biologically active adipose tissue may result in the local release of adipokines and disrupt large and small airway function depending on its anatomical distribution. This study therefore characterized airway-associated adipose tissue distribution, lipid composition, and adipokine activity in a porcine model. Airway segments were systematically dissected from different locations of the bronchial tree in inflation-fixed lungs. Cryosections were stained with hematoxylin and eosin (H&E) for airway morphology, oil red O to distinguish adipose tissue, and Nile blue A for lipid subtype delineation. Excised airway-associated adipose tissue was cultured for 72 h to quantify adipokine release using immunoassays. Results showed that airway-associated adipose tissue extended throughout the bronchial tree and occupied an area proportionally similar to airway smooth muscle within the wall area. Lipid composition consisted of pure neutral lipids (61.7 ± 3.5%), a mixture of neutral and acidic lipids (36.3 ± 3.4%), or pure acidic lipids (2.0 ± 0.8%). Following tissue culture, there was rapid release of IFN-γ, IL-1ß, and TNF-α at 12 h. Maximum IL-4 and IL-10 release was at 24 and 48 h, and peak leptin release occurred between 48 and 72 h. These data extend previous findings and demonstrate that airway-associated adipose tissue is prevalent and biologically active within the bronchial tree, providing a local source of adipokines that may be a contributing factor in airway disease.

Airway-associated adipose tissue accumulation is increased in a kisspeptin receptor knockout mouse model.

Airway-associated adipose tissue increases with body mass index and is a local source of pro-inflammatory adipokines that may contribute to airway pathology in asthma co-existing with obesity. Genetic susceptibility to airway adiposity was considered in the present study through kisspeptin/kisspeptin receptor signalling, known to modulate systemic adiposity and potentially drive airway remodelling. Therefore, the aim of the study was to determine the effects of kisspeptin/kisspeptin receptor signalling in the lung, focusing on airway-associated adipose tissue deposition and impact on airway structure-function. Wild-type, heterozygous and kisspeptin receptor knockout mice were studied at 6 or 8 weeks of age. Lung mechanics were assessed before and after methacholine challenge and were subsequently fixed for airway morphometry. A separate group of mice underwent glucose tolerance testing and bronchoalveolar lavage. At 6 weeks of age, kisspeptin/kisspeptin receptor signalling did not affect body adiposity, airway inflammation, wall structure or function. Despite no differences in body adiposity, there was a greater accumulation of airway-associated adipose tissue in knockout mice. By 8 weeks of age, female knockout mice displayed a non-diabetic phenotype with increased body adiposity but not males. Airway-associated adipose tissue area was also increased in both knockout females and males at 8 weeks of age, but again no other respiratory abnormality was apparent. In summary, airway-associated adipose tissue is decoupled from body adiposity in prepubescent mice which supports a genetic susceptibility to fatty deposits localised to the airway wall. There was no evidence that airway-associated adipose tissue drives pathology or respiratory impairment in the absence of other environmental exposures.

Fetal Growth Restriction and Asthma: Is the Damage Done?

Trajectories of airway remodeling and functional impairment in asthma are consistent with the notion that airway pathology precedes or coincides with the onset of asthma symptoms and may be present at birth. An association between intrauterine growth restriction (IUGR) and asthma development has also been established, and there is value in understanding the underlying mechanism. This review considers airway pathophysiology as a consequence of IUGR that increases susceptibility to asthma.

Azithromycin inhibits mucin secretion, mucous metaplasia, airway inflammation, and airways hyperresponsiveness in mice exposed to house dust mite extract.

Excessive production, secretion, and retention of abnormal mucus is a pathological feature of many obstructive airways diseases including asthma. Azithromycin is an antibiotic that also possesses immunomodulatory and mucoregulatory activities, which may contribute to the clinical effectiveness of azithromycin in asthma. The current study investigated these nonantibiotic activities of azithromycin in mice exposed daily to intranasal house dust mite (HDM) extract for 10 days. HDM-exposed mice exhibited airways hyperresponsiveness to aerosolized methacholine, a pronounced mixed eosinophilic and neutrophilic inflammatory response, increased airway smooth muscle (ASM) thickness, and elevated levels of epithelial mucin staining. Azithromycin (50 mg/kg sc, 2 h before each HDM exposure) attenuated HDM-induced airways hyperresponsiveness to methacholine, airways inflammation (bronchoalveolar lavage eosinophil and neutrophils numbers, and IL-4, IL-5, IL-6, IL-10, IL-12, IL-13, and RANTES levels), and epithelial mucin staining (mucous metaplasia) by at least 50% (compared with HDM-exposed mice, P < 0.05). Isolated tracheal segments of HDM-exposed mice secreted Muc5ac and Muc5b (above baseline levels) in response to exogenous ATP. Moreover, ATP-induced secretion of mucins was attenuated in segments obtained from azithromycin-treated, HDM-exposed mice (P < 0.05). In additional ex vivo studies, ATP-induced secretion of Muc5ac (but not muc5b) from HDM-exposed tracheal segments was inhibited by in vitro exposure to azithromycin. In vitro azithromycin also inhibited ATP-induced secretion of Muc5ac and Muc5b in tracheal segments from IL-13-exposed mice. In summary, azithromycin inhibited ATP-induced mucin secretion and airways inflammation in HDM-exposed mice, both of which are likely to contribute to suppression of airways hyperresponsiveness.

Growth of the airway smooth muscle layer from late gestation to childhood is mediated initially by hypertrophy and subsequently hyperplasia.

BACKGROUND AND OBJECTIVE: The airway smooth muscle (ASM) layer thickens during development. Identifying the mechanism(s) for normal structural maturation of the ASM reveals pathways susceptible to disease processes. This study characterized thickening of the ASM layer from foetal life to childhood and elucidated the underlying mechanism in terms of hypertrophy, hyperplasia and extracellular matrix (ECM) deposition. METHODS: Airways from post-mortem cases were examined from seven different age groups: 22-24 weeks gestation, 25-31 weeks gestation, term (37-41 weeks gestation), <0.5 year, 0.5-1 year, 2-5 years and 6-10 years. The ASM layer area (thickness), the number and size of ASM cells and the volume fraction of ECM were assessed by planimetry and stereology. RESULTS: From late gestation to the first year of life, normalized ASM thickness more than doubled as a result of ASM hypertrophy. Thereafter, until childhood, the ASM layer grew in proportion to airway size, which was mediated by ASM hyperplasia. Hypertrophy and hyperplasia of ASM were accompanied by a proportional change in ECM such that the broad composition of the ASM layer was constant across age groups. CONCLUSION: These data suggest that the mechanisms of ASM growth from late gestation to childhood are temporally decoupled, with early hypertrophy and subsequent proliferation. We speculate that the developing airway is highly susceptible to ASM thickening in the first year of life and that the timing of an adverse event will determine structural phenotype.

Bronchial thermoplasty reduces ventilation heterogeneity measured by multiple breath nitrogen washout.

BACKGROUND: Despite demonstrated symptomatic benefit from bronchial thermoplasty (BT), the underlying pathophysiological benefits have been uncertain. The purpose of the present study was to relate clinical benefit after BT to changes in lung physiology, focusing on ventilation homogeneity assessed using multiple breath nitrogen washout (MBNW), and how this may be affected by changes in airway volume and resistance. METHODS: Consecutive patients (n = 21) with severe asthma scheduled for BT, were evaluated at baseline, 6 weeks and 6 months after completion of treatment. Assessments included the Asthma Control Questionnaire (ACQ), medication usage, exacerbation frequency, spirometry, plethysmography and MBNW. Eighteen of these patients underwent detailed CT evaluation for the estimation of airway volume at baseline and then after the left lung had received BT treatment but prior to right lung treatment. Data are mean ± STDEV. RESULTS: Patients responded to BT with an improvement in ACQ from 3.4 ± 0.8 at baseline to 2.0 ± 1.1 at 6 months (p < 0.001). Steroid requiring exacerbations fell from 3.1 ± 2.9 in the 6 months prior to BT to 1.4 ± 1.7 following BT (p < 0.001). Significant reductions in maintenance oral steroid dosing and short acting beta agonist use were observed. Airway volume measured by CT scanning significantly increased after treatment. The FEV1 improved from 1.34 ± 0.65 l to 1.52 ± 0.76 l (p = 0.024). The Residual Volume fell from 2.87 ± 0.89 l to 2.71 ± 0.93 l (p = 0.008) and Total Airway Resistance (Raw) from 10.58 ± 6.56 to 7.64 ± 3.74 cmH2O.s.l-1 (p = 0.020). The Lung Clearance Index (LCI) was 187 ± 63% predicted at baseline and improved after treatment from 12.7 ± 3.3 to 11.8 ± 2.4 (p = 0.049). The improvement in LCI correlated with the improvement in Raw (r = 0.463, p = 0.035). CONCLUSION: Clinical benefit after BT is accompanied by improvements in lung physiology, including normalisation of lung homogeneity that seems to be driven by airway dilation and reduced resistance.

Phenotype- and patient-specific modelling in asthma: Bronchial thermoplasty and uncertainty quantification.

Theoretical models can help to overcome experimental limitations to better our understanding of lung physiology and disease. While such efforts often begin in broad terms by determining the effect of a disease process on a relevant biological output, more narrowly defined simulations may inform clinical practice. Two such examples are phenotype-specific and patient-specific models, the former being specific to a group of patients with common characteristics, and the latter to an individual patient, in view of likely differences (heterogeneity) between patients. However, in order for such models to be useful, they must be sufficiently accurate, given the available data about the specific characteristics of the patient. We show that, for asthma in particular, this approach is promising: phenotype-specific targeting may be an effective way of selecting patients for treatment based on their airway remodelling phenotype, and patient-specific targeting may be viable with the use of a clinically-plausible dataset. Specifically we consider asthma and its treatment by bronchial thermoplasty, in which the airway smooth muscle layer is directly targeted by thermal energy. Patient-specific and phenotype-specific models in this context are considered using a combination of biobank data from ex vivo tissue samples, CT imaging, and optical coherence tomography which allows more detailed resolution of the airway wall structures.

Fatty airways: implications for obstructive disease.

Epidemiological studies report that overweight or obese asthmatic subjects have more severe disease than those of a healthy weight. We postulated that accumulation of adipose tissue within the airway wall may occur in overweight patients and contribute to airway pathology. Our aim was to determine the relationship between adipose tissue within the airway wall and body mass index (BMI) in individuals with and without asthma.Transverse airway sections were sampled in a stratified manner from post mortem lungs of control subjects (n=15) and cases of nonfatal (n=21) and fatal (n=16) asthma. The relationship between airway adipose tissue, remodelling and inflammation was assessed. The areas of the airway wall and adipose tissue were estimated by point count and expressed as area per mm of basement membrane perimeter (Pbm). The number of eosinophils and neutrophils were expressed as area densities.BMI ranged from 15 to 45 kg·m-2 and was greater in nonfatal asthma cases (p<0.05). Adipose tissue was identified in the outer wall of large airways (Pbm >6 mm), but was rarely seen in small airways (Pbm <6 mm). Adipose tissue area correlated positively with eosinophils and neutrophils in fatal asthma (Pbm >12 mm, p<0.01), and with neutrophils in control subjects (Pbm >6 mm, p=0.04).These data show that adipose tissue is present within the airway wall and is related to BMI, wall thickness and the number of inflammatory cells. Therefore, the accumulation of airway adipose tissue in overweight individuals may contribute to airway pathophysiology.

Unraveling a Clinical Paradox: Why Does Bronchial Thermoplasty Work in Asthma?

Bronchial thermoplasty is a relatively new but seemingly effective treatment in subjects with asthma who do not respond to conventional therapy. Although the favored mechanism is ablation of the airway smooth muscle layer, because bronchial thermoplasty treats only a small number of central airways, there is ongoing debate regarding its precise method of action. Our aim in the present study was to elucidate the underlying method of action behind bronchial thermoplasty. We employed a combination of extensive human lung specimens and novel computational methods. Whole left lungs were acquired from the Prairie Provinces Fatal Asthma Study. Subjects were classified as control (n = 31), nonfatal asthma (n = 32), or fatal asthma (n = 25). Simulated lungs for each group were constructed stochastically, and flow distributions and functional indicators (e.g., resistance) were quantified both before and after a 75% reduction in airway smooth muscle in the "thermoplasty-treated" airways. Bronchial thermoplasty triggered global redistribution of clustered flow patterns wherein structural changes to the treated central airways led to a reopening cascade in the small airways and significant improvement in lung function via reduced spatial heterogeneity of flow patterns. This mechanism accounted for progressively greater efficacy of thermoplasty with both severity of asthma and degree of muscle activation, broadly consistent with existing clinical findings. We report a probable mechanism of action for bronchial thermoplasty: alteration of lung-wide flow patterns in response to structural alteration of the treated central airways. This insight could lead to improved therapy via patient-specific, tailored versions of the treatment-as well as to implications for more conventional asthma therapies.

Gestational age at time of in utero lipopolysaccharide exposure influences the severity of inflammation-induced diaphragm weakness in lambs.

The preterm diaphragm is functionally immature compared with its term counterpart. In utero inflammation further exacerbates preterm diaphragm dysfunction. We hypothesized that preterm lambs are more vulnerable to in utero inflammation-induced diaphragm dysfunction compared with term lambs. Pregnant ewes received intra-amniotic (IA) injections of saline or 10 mg lipopolysaccharide (LPS) 2 or 7 days before delivery at 121 days (preterm) or ∼145 days (term) of gestation. Diaphragm contractile function was assessed in vitro. Plasma cytokines, diaphragm myosin heavy chain (MHC) isoforms, and oxidative stress were evaluated. Maximum diaphragm force in preterm control lambs was significantly lower (22%) than in term control lambs ( P < 0.001). Despite similar inflammatory cytokine responses to in utero LPS exposure, diaphragm function in preterm and term lambs was affected differentially. In term lambs, maximum force after a 2-day LPS exposure was significantly lower than in controls (by ~20%, P < 0.05). In preterm lambs, maximum forces after 2-day and 7-day LPS exposures were significantly lower than in controls (by ~30%, P < 0.05). Peak twitch force after LPS exposure was significantly lower in preterm than in controls, but not in term lambs. In term lambs, LPS exposure increased the proportion of MHC-I fibers, increased twitch contraction times, and increased fatigue resistance relative to controls. In preterm diaphragm, the cross-sectional area of embryonic MHC fibers was significantly lower after 7-day versus 2-day LPS exposures. We conclude that preterm lambs are more vulnerable to IA LPS-induced diaphragm dysfunction than term lambs. In utero inflammation exacerbates diaphragm dysfunction and may increase susceptibility to postnatal respiratory failure.

Foetal growth restriction in mice modifies postnatal airway responsiveness in an age and sex-dependent manner.

Epidemiological studies demonstrate an association between intrauterine growth restriction (IUGR) and asthma; however the underlying mechanism is unknown. We investigated the impact of maternal hypoxia-induced IUGR on airway responsiveness in male and female mice during juvenility and adulthood. Pregnant BALB/c mice were housed under hypoxic conditions for gestational days 11-17.5 and then returned to normoxic conditions for the remainder of pregnancy. A control group was housed under normoxic conditions throughout pregnancy. Offspring were studied at 2 weeks (juveniles) and 8 weeks (adults), where lung volume was assessed by plethysmography, airway responsiveness to methacholine determined by the forced oscillation technique and lungs fixed for morphometry. IUGR offspring were lighter at birth, exhibited "catch-up growth" by 2 weeks, but were again lighter in adulthood. IUGR males were "hyper-responsive" at 2 weeks and "hypo-responsive" as adults, in contrast with IUGR females who were hyper-responsive in adulthood. IUGR males had increased inner and total wall thickness at 2 weeks which resolved by adulthood, while airways in IUGR females were structurally normal throughout life. There were no differences in lung volume between Control and IUGR offspring at any age. Our data demonstrate changes in airway responsiveness as a result of IUGR that could influence susceptibility to asthma development and contribute to sexual dimorphism in asthma prevalence which switches from a male dominated disease in early life to a female dominated disease in adulthood.

Independent and combined effects of airway remodelling and allergy on airway responsiveness.

Airway remodelling and allergic inflammation are key features of airway hyperresponsiveness (AHR) in asthma; however, their interrelationships are unclear. The present study investigated the separate and combined effects of increased airway smooth muscle (ASM) layer thickness and allergy on AHR. We integrated a protocol of ovalbumin (OVA)-induced allergy into a non-inflammatory mouse model of ASM remodelling induced by conditional and airway-specific expression of transforming growth factor-α (TGF-α) in early growth response-1 (Egr-1)-deficient transgenic mice, which produced thickening of the ASM layer following ingestion of doxycycline. Mice were sensitised to OVA and assigned to one of four treatment groups: Allergy - normal chow diet and OVA challenge; Remodelling - doxycycline in chow and saline challenge; Allergy and Remodelling - doxycycline in chow and OVA challenge; and Control - normal chow diet and saline challenge. Airway responsiveness to methacholine (MCh) and histology were assessed. Compared with the Control group, airway responsiveness to MCh was increased in the Allergy group, independent of changes in wall structure, whereas airway responsiveness in the Remodelling group was increased independent of exposure to aeroallergen. The combined effects of allergy and remodelling on airway responsiveness were greater than either of them alone. There was a positive relationship between the thickness of the ASM layer with airway responsiveness, which was shifted upward in the presence of allergy. These findings support allergy and airway remodelling as independent causes of variable and excessive airway narrowing.

Hyperinflation of bronchi in vitro impairs bronchodilation to simulated breathing and increases sensitivity to contractile activation.

BACKGROUND AND OBJECTIVE: Lung hyperinflation and reduced bronchodilation to deep inspiration (DI) are features of chronic obstructive pulmonary disease (COPD). Hyperinflation might impair the ability of a DI to stretch airway smooth muscle (ASM), as the bronchi operate at a stiff region of the pressure-volume curve. METHODS: Bronchial segments from pig lungs were mounted in an organ bath and equilibrated at either 5 cm H2 O (control) or 20 cm H2 O (hyperinflated) transmural pressure (Ptm ). Cumulative dose-response curves to acetylcholine (ACh) were performed to determine maximal response (Emax ) and sensitivity under static conditions (fixed Ptm ) or during simulated breathing (Δ10 cm H2 O Ptm at 0.25 Hz). The effect of hyperinflation on ASM contraction was further examined in bronchial rings contracted at a short ASM length (reference length, Lref ) or stretched by an additional 30% (length 1.3 times the Lref , 1.3Lref ). RESULTS: Oscillatory loads halved Emax from 61.0 ± 3.8 to 29.7 ± 4.4 cm H2 O (P < 0.0001) in control bronchial segments, but only from 40.0 ± 2.5 to 31.2 ± 2.4 cm H2 O (P < 0.05) in hyperinflated segments. The percentage reduction in active pressure with oscillation was less in hyperinflated compared with control segments (P < 0.01). Sensitivity was not altered by oscillation in either hyperinflated or control segments; however, hyperinflated segments were more sensitive (P < 0.05). The effect of inflation on sensitivity was confirmed using bronchial rings where stretched rings were more sensitive than unstretched rings (P < 0.01). CONCLUSION: Hyperinflated bronchi exhibit reduced bronchodilation to breathing and increased sensitivity to bronchoconstrictor stimuli. Findings suggest that hyperinflation may directly alter airway function by reducing the protective effects of DI and initiating contraction at low doses of contractile stimuli.