Peripheral airways as a determinant of ventilatory function in the human lung

Association between exposure to a mixture of benzene, toluene, ethylbenzene, xylene, and styrene (BTEXS) and small airways function: A cross-sectional study

BACKGROUND

Lung is one of the primary target organs of benzene, toluene, ethylbenzene, xylene, and styrene (BTEXS). Small airways dysfunction (SAD) might be a sensitive indicator of early chronic respiratory disease. Here, we explored the relationships between exposure to BTEXS and small airways function, and identified the priority control pollutants in BTEXS mixtures.

METHODS

635 petrochemical workers were recruited. Standard spirometry testing was conducted by physicians. The cumulative exposure dose (CED) of BTEXS for each worker was estimated. The peak expiratory flow (PEF), forced expiratory flow between 25 and 75% of forced vital capacity (FEF25∼75%), and the expiratory flow rate found at 25%, 50%, and 75% of the remaining exhaled vital capacity (MEF25%, MEF50%, and MEF75%) were measured. SAD was also evaluated based on measured parameters. The associations between exposure to BTEXS individuals or mixtures and small airways function were evaluated using generalized linear regression models (GLMs) and quantile g-computation models (qgcomp). Meanwhile, the weights of each homolog in the association were estimated.

RESULTS

The median CED of BTEXS are 9.624, 19.306, 24.479, 28.210, and 46.781 mg/m³·years, respectively. A unit increase in ln-transformed styrene CED was associated with a decrease in FEF25∼75% and MEF50% based on GLMs. One quartile increased in BTEXS mixtures (ln-transformed) was significantly associated with a 0.325-standard deviation (SD) [95% confidence interval (CI): -0.464, -0.185] decline in FEF25∼75%, a 0.529-SD (95%CI: -0.691, -0.366) decline in MEF25%, a 0.176-SD (95%CI: -0.335, -0.017) decline in MEF75%, and increase in the risk of abnormal of SAD [risk ratios (95%CI): 1.520 (95%CI: 1.143, 2.020)]. Benzene and styrene were the major chemicals in BTEXS for predicting the overall risk of SAD.

CONCLUSION

Our novel findings demonstrate the significant association between exposure to BTEXS mixture and small airways function decline and the potential roles of key homologs (benzene and styrene) in SAD.

Airway Remodeling in Asthma

Asthma is an inflammatory disease of the airways that may result from exposure to allergens or other environmental irritants, resulting in bronchoconstriction, wheezing, and shortness of breath. The structural changes of the airways associated with asthma, broadly referred to as airway remodeling, is a pathological feature of chronic asthma that contributes to the clinical manifestations of the disease. Airway remodeling in asthma constitutes cellular and extracellular matrix changes in the large and small airways, epithelial cell apoptosis, airway smooth muscle cell proliferation, and fibroblast activation. These pathological changes in the airway are orchestrated by crosstalk of different cell types within the airway wall and submucosa. Environmental exposures to dust, chemicals, and cigarette smoke can initiate the cascade of pro-inflammatory responses that trigger airway remodeling through paracrine signaling and mechanostimulatory cues that drive airway remodeling. In this review, we explore three integrated and dynamic processes in airway remodeling: (1) initiation by epithelial cells; (2) amplification by immune cells; and (3) mesenchymal effector functions. Furthermore, we explore the role of inflammaging in the dysregulated and persistent inflammatory response that perpetuates airway remodeling in elderly asthmatics.

Asthma in the elderly and late-onset adult asthma

Elderly asthmatics are at a higher risk for morbidity and mortality from their asthma than younger patients. There are important age-related physiologic and immunologic changes that complicate the presentation, diagnosis, and management of asthma in the aged population. Evidence suggests that elderly asthmatics are more likely to be underdiagnosed and undertreated. Additionally, elderly patients with asthma have highest rates of morbidity and mortality from their disease than younger patients. The underlying airway inflammation of asthma in this age group likely differs from younger patients and is felt to be non-type 2 mediated. While elderly patients are underrepresented in clinical trials, subgroup analysis of large clinical trials suggests they may be less likely to respond to traditional asthma therapies (ie, corticosteroids). As the armamentarium of pharmacologic asthma therapies expands, it will be critical to include elderly asthmatics in large clinical trials so that therapy may be better tailored to this at-risk and growing population.

Spirometric gated quantitative computed tomography of the lung in healthy smokers and nonsmokers

RATIONALE AND OBJECTIVES

The authors investigated the influence of cigarette smoking on healthy, asymptomatic smokers and nonsmokers with the help of spirometric triggered quantitative computed tomography. In our prospective study, the authors compared conventional lung function parameters with the computed tomography values (lung attenuation, lung area).

METHODS

The study group comprised 40 healthy volunteers consisting of 20 smokers and nonsmokers (20 females and 20 males). The corresponding groups have been matched concerning their age, height, body mass, (cigarette) pack years. Computer tomography scans were triggered at 35%, 50%, 70% and 95% of vital capacity at a defined apical and a basal level.

RESULTS

Functional residual capacity (FRC), total lung capacity and airway resistance showed close correlations to lung parenchymal attenuation values especially at full inspiration and expiration. For example, the authors found a correlation coefficient of r = -0.845 (P < or = 0.001) concerning the FRC and lung attenuation values in the apical lung at 35% of vital capacity in male smokers. Male smokers proved to have a significantly higher pulmonary lung density at all inspiratory states than the other groups (P < or = 0.05; Student's t test). Although male smokers had a higher vital capacity they showed a smaller cross-sectional area increase of the lung during inspiration than nonsmokers. This phenomenon is a result of the decreasing compliance of the smoker's lung, due to small airways disease and hypoxic vasoconstriction.

CONCLUSIONS

Spirometric-triggered quantitative computed tomography has proved to be a sensitive diagnostic device for the investigation of early pathomorphologic changes in healthy, asymptomatic cigarette smokers.

Respiratory bronchiolitis-associated interstitial lung disease and its relationship to desquamative interstitial pneumonia

Respiratory bronchiolitis is a mild inflammatory reaction commonly noted in asymptomatic cigarette smokers. We reviewed 18 cases of respiratory bronchiolitis-associated interstitial lung disease (RB/ILD), which had been diagnosed on the basis of clinical evaluation and open-lung biopsy. All patients were cigarette smokers. The sex distribution of the patients was approximately equal, and their mean age was 36 years. Chest roentgenograms showed reticular or reticulonodular infiltrates in 72% of the patients. Histologically, inflammation of the respiratory bronchioles, filling of the bronchiolar lumens and surrounding alveoli with finely pigmented macrophages, associated interstitial inflammation, and mild fibrosis were noted. In most patients, respiratory improvement ensued when they stopped smoking. Because of histologic similarities to desquamative interstitial pneumonia (DIP), the 18 cases of RB/ILD were compared with 36 cases of DIP. DIP tended to occur in older persons, caused more severe symptoms, displayed ground glass infiltrates on chest roentgenograms, was characterized by more severe interstitial disease on pulmonary function tests, and was often associated with progressive respiratory disease.

Relationship between collateral flow resistance and alveolar pores in the aging beagle dog

Controversy exists over the effect of aging on the alveolar pores of Kohn and the functional relevance of observed changes in alveolar pore structure. We investigated the relationship between collateral resistance (Rcoll), as a measurement of the resistance to collateral flow through collateral channels, and the change in number and size of alveolar pores in the aging beagle dog. Healthy beagle dogs from a closed colony were divided into five groups having mean ages of 3, 6, 9, 12, and 14 yr. Rcoll was measured in anesthetized dogs using a wedged-catheter technique. Following euthanasia, the dogs were necropsied, and the same lung lobe was microdissected along a major intrapulmonary airway, allowing sampling of terminal and respiratory bronchioles from the same airway generation in each dog. Scanning electron microscopy was performed on alveoli adjacent to these bronchioles. There was a significant rise in Rcoll with age. Alveolar pore size and number increased significantly with age, which would be anticipated to reduce Rcoll if the alveolar pores provided a major pathway for collateral ventilation in the dog lung. These findings suggest that the alveolar pores are functionally inoperative for collateral ventilation in the lung at functional residual capacity, possibly because they remain closed at a low lung volume and/or are covered by surfactant.

Relaxation of human peripheral airway smooth muscle in vitro does not correlate with severity of chronic airflow limitation in vivo

We tested the hypothesis that a defect in relaxation of peripheral airway smooth muscle contributes to chronic airflow limitation in chronic obstructive pulmonary disease (COPD). Twenty subjects underwent lung function measurements prior to thoracotomy. Lung tissue was obtained during surgery and bronchiolar segments were dissected. Smooth muscle function was measured isotonically in organ baths, using L-isoprenaline and the adenylate cyclase activator forskolin. Segments were precontracted with methacholine. Of the 20 subjects, 10 fulfilled the ATS criteria for COPD and had airflow limitation. There was no significant relationship between the degree of airflow limitation in vivo and the sensitivity or maximal response of peripheral airway muscle to methacholine, L-isoprenaline or forskolin in vitro. Furthermore, we found no differences between the mean contractile- and relaxation responses of airways from subjects with versus those without COPD and airflow limitation. Lung tissue from patients who regularly used beta-adrenergic drugs (n = 3) and/or steroids (n = 3) exhibited responses in vitro similar to those from subjects without medication. These results suggest that airflow limitation in COPD is not associated with an impaired relaxability of peripheral airway smooth muscle.

What's new in bronchial obstruction? Experimental pathology and clinico-pathologic correlation

The aim of general pathology, which following Virchow also should be pathophysiology (and pathobiochemistry), is to elucidate general principles and main mechanisms of diseases. Conceptions like reticulo-endothelial system or coronary insufficiency, inflammations and its mediators, modes of metastasis and many comparable topics are examples of this type of scientific approach, and its tools are careful morphological analysis as well as experimental work of different kinds. In pulmonary pathology the obstruction of airways is one of the most important pathogenetical pathways. Among a broad spectrum of pulmonary diseases it is the main symptom of a developing chronic obstructive pulmonary disease (COPD) and the outstanding cause of cardio-respiratory failure. In German literature the last comprehensive survey on general respiratory pathology was written some twenty years ago and a review of the main techniques of investigation was given at about the same time. Since then - parallel to the invention of new measuring techniques and to the progress in clinical pathophysiology - a rapid further development in the understanding of the pathology of respiratory disorders has taken place, particularly in connection with research in chronic bronchitis and emphysema. Some examples of this development and of the present state of discussion will be reviewed briefly.

Effect of cigarette smoking on the tidal carbon dioxide profile

Four indices have been tested for quantitative description of the form of the expiratory partial pressure carbon dioxide curves within a group of 80 male smokers with normal routine spirometry. The control group consisted of 60 healthy nonsmokers whose age and residence matched those of the smokers. The tests demonstrated statistically significant differences between smokers and the control group. Gamma angle index and planimetric index displayed high sensitivity to the quantitative description of the capnographic curves, whereas the concomitant cough and sputum production or the smoking index did not. The data produced show that capnographic indices provide valuable data on ventilation-perfusion ratio dysfunction and also, indirectly, on small airways on smokers with normal conventional spirometry.

Small airways disease

Over the last 10 years the non-specific term "small airways disease" has been applied to a number of histologic lesions seen in the peripheral airways of smokers. It is becoming recognized that airway inflammation is the most important of these lesions. This pathology may be the precursor to the subsequent development of emphysema and is an important cause of the functional abnormality in smokers. A current hypothesis is that small airways disease may be detected early in the smoking careers of subjects who later develop chronic respiratory disability. In these individuals particularly, complete cessation of smoking should be the primary therapeutic goal. With the recent development of special tests to assess small airways function, the presence of small airways disease can be detected in asymptomatic smokers who may have normal routine lung function tests. However, most of the tests to assess airway function are also influenced by other physiological factors such as loss of elastic recoil. We await the results of long term epidemiological studies to confirm the above hypothesis that early small airways disease leads to chronic disability. Without such confirmatory evidence, the routine use of these special tests cannot at present be advocated.

The morphology and morphometry of small airways disease (relevance to chronic obstructive pulmonary disease)

The morphologic and morphometric characteristics of the small airways of the lung and their relationship to airflow as measured by forced expiratory volume in one second (FEV1) were determined in 37 excised human lungs. After fixation the lungs were graded as to the degree of emphysema and the degree of small airway pathology. The internal diameters of the small airways were measured and corrected for shrinkage during processing. The mean bronchiolar diameter was positively correlated with the % predicted FEV1 (p less than 0.001) and negatively correlated with the small airway fibrosis (p less than 0.01). We conclude that fibrosis of the small airways of the lung is associated with a decrease in airway dimension which is in turn correlated with decreased FEV1 in excised human lungs.