Parenchymal, bronchiolar, and bronchial measurements in centrilobular emphysema. Relation to weight of right ventricle

Chronic obstructive pulmonary disease

COPD is characterized by airflow limitation that is not fully reversible. The morphological basis for airflow obstruction results from a varying combination of obstructive changes in peripheral conducting airways and destructive changes in respiratory bronchioles, alveolar ducts, and alveoli. A reduction of vascularity within the alveolar septa has been reported in emphysema. Typical physiological changes reflect these structural abnormalities. Spirometry documents airflow obstruction when the FEV1/FVC ratio is reduced below the lower limit of normality, although in early disease stages FEV1 and airway conductance are not affected. Current guidelines recommend testing for bronchoreversibility at least once and the postbronchodilator FEV1/FVC be used for COPD diagnosis; the nature of bronchodilator response remains controversial, however. One major functional consequence of altered lung mechanics is lung hyperinflation. FRC may increase as a result of static or dynamic mechanisms, or both. The link between dynamic lung hyperinflation and expiratory flow limitation during tidal breathing has been demonstrated. Hyperinflation may increase the load on inspiratory muscles, with resulting length adaptation of diaphragm. Reduction of exercise tolerance is frequently noted, with compelling evidence that breathlessness and altered lung mechanics play a major role. Lung function measurements have been traditionally used as prognostic indices and to monitor disease progression; FEV1 has been most widely used. An increase in FVC is also considered as proof of bronchodilatation. Decades of work has provided insight into the histological, functional, and biological features of COPD. This has provided a clearer understanding of important pathobiological processes and has provided additional therapeutic options.

The association between small airway obstruction and emphysema phenotypes in COPD

BACKGROUND

Airflow limitation in COPD is due to a variable combination of small airway obstruction and centrilobular emphysema (CLE) and/or panlobular emphysema (PLE), but the relationship between these three different phenotypes is poorly understood. This study compares the severity of small airway obstruction in both forms of emphysema and determines its relationship with FEV(1).

METHODS

We compared the lung histology of nonsmoking control subjects without emphysema (n = 10) to that of patients with CLE (n = 30) and PLE with (n = 8) and without alpha(1)-antitrypsin (AAT) deficiency (n = 11). The degree of airspace enlargement was measured using the mean interalveolar wall distance (IAWD) [mean linear intercept, Lm], and the evenness of airspace destruction was assessed by the coefficient of variation (CV) of the IAWD. The severity of small airway obstruction was determined by dividing total wall area by the length of the basement membrane to obtain wall thickness.

RESULTS

Lm was greater in all three subgroups of emphysema than in control subjects, and in AAT deficiency than in PLE or CLE. The CV of IAWD was greater in AAT deficiency and CLE than in control subjects and in CLE than in AAT deficiency or PLE. Although small airway wall thickness was greater in CLE and PLE with AAT deficiency than in control subjects, the association between wall thickness and both Lm and FEV(1) was observed only in CLE.

CONCLUSIONS

Small airway wall thickening occurs in CLE and PLE with AAT deficiency but is more closely associated with degree of emphysema and airflow limitation in CLE.

Synergistic neutrophil elastase-cytokine interaction degrades collagen in three-dimensional culture

Proteolytic degradation of extracellular matrix is thought to play an important role in many lung disorders. In the current study, human lung fibroblasts were cast into type I collagen gels and floated in medium containing elastase, cytomix (combination of tumor necrosis factor-alpha, interleukin-1beta, and interferon-gamma), or both. After 5 days, gel collagen content was determined by measuring hydroxyproline. Elastase alone did not result in collagen degradation, but in the presence of fibroblasts, elastase reduced hydroxyproline content to 75.2% (P < 0.01), whereas cytomix alone resulted in reduction of hydroxyproline content to 93% (P < 0.05). The combination of elastase and cytomix reduced hydroxyproline content to 5.2% (P < 0.01). alpha(1)-Proteinase inhibitor blocked this synergy. Gelatin zymography and Western blot revealed that matrix metalloproteinase (MMP)-1, -3, and -9 were induced by cytomix and activated in the presence of elastase. Tissue inhibitor of metalloproteinase (TIMP)-1 and -2 were also induced by cytomix but were cleaved by elastase. We conclude that a synergistic interaction between cytomix and elastase, mediated through cytokine induction of MMP production and elastase-induced activation of latent MMPs and degradation of TIMPs, can result in a dramatic augmentation of collagen degradation. These findings support the notion that interaction among inflammatory mediators secreted by mononuclear cells and neutrophils can induce tissue cells to degrade extracellular matrix. Such a mechanism may contribute to the protease-anti-protease imbalance in emphysema.

Microscopic and macroscopic measurements of emphysema: relation to carbon monoxide gas transfer

BACKGROUND

Studies of the relation between the severity of structural change in emphysema and physiological abnormality have been based on macroscopic assessments, which have not been truly quantitative or sensitive enough to detect early changes. With a highly reproducible method for measuring emphysema using histological sections and a semiautomatic image analysis system, this quantitative assessment of emphysema was compared with a semiquantitative macroscopic assessment of emphysema and measurements of carbon monoxide gas transfer.

METHODS

Microscopic and macroscopic measurements of emphysema on 44 thoracotomy specimens were compared; only two were from non-smokers. Airspace wall surface area per unit volume was measured microscopically with an automatic image analyser and expressed as both the mean airspace wall surface area per unit volume and the mean value of the five fields with the lowest values. Macroscopic emphysema was measured directly on a tracing of the midsagittal slice using a digitising tablet attached to a microcomputer and expressed as a percentage of the total area of lung. In cases with centriacinar emphysema the number of discrete lesions was counted.

RESULTS

The area of macroscopic emphysema ranged from 0 to 78% of the total area of lung examined, but most patients had less than 1% involvement so that the distribution was highly skewed. Both mean airspace wall surface area per unit volume and the mean of five fields with the lowest airspace wall surface area per unit volume were normally distributed, with mean airspace areas ranging from 8.8 to 25.4 mm2/mm3 (mean 18.1 mm2/mm3). In lobes with centriacinar emphysema the number of discrete lesions correlated with airspace wall surface area per unit volume and with preoperative carbon monoxide transfer factor (TLCO) per unit lung volume. However, other measurements of macroscopic emphysema did not correlate with loss of alveolar wall surface area, and there was considerable overlap between subjects with no or minimal macroscopic emphysema and those with more severe disease. TLCO correlated with both mean airspace wall surface area per unit volume and the mean of five fields with the lowest airspace wall surface area per unit volume but not with the severity of macroscopic emphysema.

CONCLUSION

If emphysema is to be quantified it must be measured microscopically; macroscopic measurements do not, in general, reflect the microscopic loss of airspace wall.

The senile lung. Comparison with normal and emphysematous lungs. 1. Structural aspects

As part of a study of the structural-functional correlations of excised human lungs obtained at autopsy, the parenchyma and peripheral airways were examined by means of morphometric techniques. Among the 30 lungs characterized by the absence of fibrosis, ten differed from the normal and emphysematous lungs by a homogeneous dilatation of the airspaces, in excess of the dimensions predicted on the basis of age. Study of the standard deviations of the mean linear intercepts showed that the airspace dilatation was more regular than in emphysematous lungs; in addition, there was no clear-cut destruction, as estimated from the number of alveolar attachments. These lungs were characterized in addition by an increased thickening of alveolar septa, without inflammation or fibrosis, normal size of the diameter, and reduced density of the membranous bronchioles. Since these lungs were from people older than 60 years, it is assumed that they represent cases of exaggerated airspace enlargement of the aging lung, differing from emphysema by the absence of destruction of alveolar walls. The term "senile lung" is proposed or this condition.

Cor pulmonale: correlation with central airway lesions, peripheral airway lesions, emphysema, and control of breathing

We have analyzed the heart and lung findings in 31 patients in the National Institutes of Health (NIH) Nocturnal Oxygen Therapy Trial (NOTT) with particular emphasis on cor pulmonale. Increased right ventricular weight was related to decreased bronchiolar diameter, decreased ratio of bronchiolar diameter to external arterial diameter, and an increased proportion of airways less than 400 microns in diameter. No relationship was found between the severity of emphysema, mucous gland enlargement, peripheral airway mucous plugging, or other measurement of central and peripheral airways. Patients with right ventricles weighing more than 100 g had higher pulmonary artery pressures at rest and higher arterial CO2 levels than those weighing 100 g or less. When the patients were divided into Types A, B, and X according to Burrows' criteria, those with Type X had a higher volume proportion of mucous glands; type B were intermediate; and Type A had the smallest. The amount of bronchial muscle was less in Type B patients than in Type A, and right ventricles weighted less in Type A patients than in Type B. Hypoxic ventilatory drive was lower in Type B patients than in Type A. Absolute right ventricular weight appeared to be a better measurement of right ventricular enlargement than relative right ventricular weight in the NIH NOTT patients. We conclude that right ventricular weight in patients with hypoxic chronic airflow obstruction (CAO) is related to airway narrowing, and that the Type B syndrome is associated with decreased ventilatory drive.

Effects of bronchoconstrictors and bronchodilators on a novel human small airway preparation

Human lung bronchiolar segments (about 2 mm long and with a diameter of 0.6-1.5 mm) were dissected and circular muscle tension recorded. Airways were identified by histology and in some preparations by relaxant responses to noradrenaline (0.1-10 microM). Adenosine (1-100 microM) produced only very weak contractions, whereas carbachol (EC50 = 0.40 microM), histamine (EC50 = 0.63 microM), prostaglandin D2 (EC50 = 0.50 microM), substance P (EC50 = 4.6 microM) and ATP (1-100 microM) produced much greater ones. The contractions generally developed rapidly and were stable. The mean maximum increase in tension achieved with the most efficient constrictor, carbachol, was 0.5 g. ATP was the least efficient producing only about 40% of carbachol's maximum. Terbutaline, theophylline and enprofylline relaxed carbachol (2.0 microM = EC70)-contracted preparations. Terbutaline (3-3000 nM) relaxed 4 out of 11 bronchioles. Theophylline (10-4000 microM) and enprofylline (1-400 microM) consistently relaxed the bronchiolar preparations including those exhibiting little responsiveness to the beta 2-adrenoceptor agonist. Since enprofylline (which does not block adenosine receptors) was a five times more potent relaxant than theophylline and since adenosine produced only weak contractions, antagonism of adenosine receptors is probably not involved in relaxation of the small airways. It is suggested that the present data, which apparently differ from those obtained with lung parenchymal strips, are of relevance for human small airways responsiveness.

Weights of the body and cardiac ventricles in pulmonary emphysema

We analysed statistically the association of emphysema, determined on inflation fixed specimens, with the weights of the body and heart, and of the cardiac ventricles, weighed separately, in 170 male and 86 female adult autopsies. The cases were grouped according to the cause of death into cardiovascular, cancer and other deaths. In men the body weight was inversely proportional to the severity of emphysema, but no association existed between the body weight and the cause of death. In male cardiovascular deaths the total heart weight, total ventricular weight and the weight of the left ventricle with the septum were also inversely proportional to the severity of emphysema while this was not true in the other deaths. In male cardiovascular deaths a decrease, and in the other deaths an increase, of the weight of the free wall of the right ventricle was associated with an increasing severity of emphysema. In all male deaths, however, the left to right ratio decreased with an increasing severity of emphysema. Thus, pulmonary emphysema is associated both with a general atrophy, including the myocardium, and a mainly relative right ventricular hypertrophy. An absolute right ventricular hypertrophy, however, seems to accompany emphysema only in the absence of other major cardiovascular diseases.

Relationship between bronchial and arterial diameters in normal human lungs

In order to find an objective method for measuring narrowing of small airways, eight lungs from four people without lung disease were inflated and fixed at 25 cm of water pressure. Eight to nine blocks were taken at random from each of six parasaggital slices from each lung, sectioned, and stained. The size of the bronchioles (airways without cartilage) in relation to their accompanying arteries was determined. The internal bronchiolar diameter was compared with three different arterial diameters (the internal, external medial, and external adventitial). The ratio of the internal bronchiolar diameter to the external adventitial arterial diameter was constant between lungs (0.62 +/- 0.02) and independent of the method of inflation or the position within the lungs. This ratio may provide a useful index of bronchiolar narrowing in disease.

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

We have investigated the morphological differences responsible for the variability in two tests of pulmonary function, maximal expiratory flow rates (MEF) and the frequency dependence of dynamic compliance (CDYN ratio). Functional measurements were obtained from 53 normal and minimally diseased postmortem human lungs. Morphological measurements performed on these same lungs included airway diameter at three levels in the bronchial tree, the amount of bronchial gland mass, and the alveolar surface to volume ratio. Multiple regression analysis suggests that the diameter of the peripheral conduction airways (membranous bronchioles) is the major morphological determinant for both MEF and the CDYN ratio in lungs at any particular age. Age-dependent changes in both functional tests were associated primarily with differences in the alveolar surface to volume ratio. Minimal emphysema and a lesion associated with cigarette smoking, respiratory bronchiolitis, have no demonstrable effect on either MEF or the CDYN ratio. These studies provide further evidence that the peripheral conducting airways are a major determinant of ventilatory function in the normal human lung.

Quantitation of thick-walled peripheral lung vessels in chronic airways obstruction

The number of thick-walled peripheral lung vessels (defined as vessels of less than 100 mu diameter with two distinct elastic laminae) was calculated in 50 postmortem lungs. The size of the right ventricle, the amount and type of emphysema, and the proportion of small airways lumen in the lung were also quantitated. Eighteen patients had died as a result of chronic airways obstruction, 17 had symptoms of chronic chest disease but died from some unrelated cause, and 15 had no symptoms related to the respiratory system. The mean number of thick-walled peripheral lung vessels (TWPV) was found to be significantly greater in the fatal disease group than in both of the other groups. No significant difference was found between the mean values of the symptomatic and asymptomatic groups. The mean number of TWPV was significantly greater in cases with a right ventricular weight of more than 80 g than in those with a weight of less than 65 g. Positive correlations were found between the number of TWPV and right ventricular weight, total amount of emphysema in the lung, and the amounts of centrilobular and panlobular emphysema. Significant negative correlations were found between the number of TWPV and both the ratio of the weight of the left ventricle to the right ventricle and the proportion of small airways lumen in the lung.

A PATHOLOGICAL study of the lungs and heart in fatal and non-fatal chronic airways obstruction

The lungs and hearts from 50 patients were examined using morphometric techniques to determine the size of the right ventricle, the amount, type, and distribution of emphysema, the size of the bronchial mucous glands, and the proportion of the lung occupied by small airways of less than 2 mm diameter. The patients were divided into three groups according to the clinical history: 18 died as a result of chronic airways obstruction, 17 had symptoms of chronic chest disease but died from some unrelated cause, and 15 had no symptoms related to the respiratory system. The total amount of emphysema was found to be greater in the fatal than the symptomatic group who in turn had more emphysema than the asymptomatic group. A positive correlation was found between the amount of emphysema and the right ventricular weight. The amount of panlobular emphysema in the lung was found to be greater in the fatal group than in the others but this did not apply to the amount of centrilobular emphysema. The amount of panlobular, but not centrilobular, emphysema showed a positive correlation with right ventricular weight. As the total amount of emphysema increased it was found that there was an increase in each of three zones in the lung-apical, middle, and lower. There was no relationship between the bronchial mucous gland size and either the clinical state of the patients with symptoms or the right ventricular weight. The proportion of lung occupied by the lumen of small airways was significantly reduced in the fatal group as compared to the other two groups and also showed a negative (inverse) correlation with right ventricular weight. The total amount of emphysema, the amount of panlobular emphysema, and reduction in small airways lumen in the lung are the three factors in chronic airways obstruction which are quantitatively related to death in chronic airways obstruction and to right ventricular weight.