Observations on the pathogenesis of chronic airflow obstruction in smokers: implications for the detection of "early" lung disease

Association between the CYP1A1 gene polymorphism and susceptibility to emphysema and lung cancer

Aim-To investigate cytochrome P4501A1 (CYP1A1) polymorphism and susceptibility to emphysema and lung cancer.Methods-A novel polymerase chain reaction (PCR) for genotyping the CYP1A1 polymorphism, corresponding to putative low or high enzyme activity, was developed to genotype lung cancer resection samples which had been assessed macroscopically for the presence of centriacinar and panacinar emphysema. Samples were collected and genotyped from a group of patients with chronic obstructive airways disease. A control group of anonymous blood donations was genotyped to determine the basal levels of the polymorphism in the Scottish population.Results-The high activity allele of the CYP1A1 gene is associated with susceptibility to centriacinar emphysema and lung cancer but not panacinar emphysema. CYP1A1 polymorphism is not linked to lung cancer in the absence of emphysema, nor to chronic obstructive airways disease which is the clinical manifestation of emphysema, particularly of the panacinar type.Conclusions-Susceptibility to emphysema and lung cancer is associated with polymorphism of the P4501A1 gene. A trend towards damage of centriacinar pattern has been detected, which supports the theory that centriacinar emphysema results from local, direct damage to the respiratory bronchioles from exposure to cigarette smoke.

Which spirometric indices best predict subsequent death from chronic obstructive pulmonary disease?

BACKGROUND

Previous epidemiological studies have related mortality from chronic obstructive pulmonary disease (COPD) to forced expiratory volumes (FEV(1) or FEV(0.75)) and it is unknown whether other spirometric indices might have greater predictive power.

METHODS

A case-control study of fatal COPD was conducted within a cohort of London civil servants who performed forced expiratory spirograms in 1967-9 and were followed up for mortality over 20 years. The spirograms of 143 men who died of COPD (ICD8 491, 492 or 519.8) were compared with those of 143 controls individually matched for age, height, and smoking habit who survived longer than their matched case. Flow rates in different parts of the spirogram were compared within case-control pairs and analysed as predictors of fatal COPD by conditional logistic regression.

RESULTS

Within pair case:control ratios of FEV(1), mid expiratory flow rates (e.g. FEF(50-75)) and FEF(75-85) were highly intercorrelated (r>0.7) but correlations with FEF(85-95) were weaker (r<0.5). All indices except the FEV(1)/FVC ratio were stronger predictors of death from COPD within the first 10 years than of later deaths (15-19 years). After adjustment for FEV(1), mid expiratory flow rates independently predicted fatal COPD but end expiratory flow rates did not. The FEV(1) adjusted mortality ratios associated with a 10% decrement in each index were 2.24 (95% CI 1.54 to 3.76) for FEF(50-75), 1.20 (95% CI 1.00 to 1.42) for FEF(75-85), and 1.10 (95% CI 0.96 to 1.26) for FEF(85-95).

CONCLUSION

This study confirms FEV(1) and mid expiratory flow rates as powerful predictors of mortality from COPD, and suggests that measurement of end expiratory flow rates would add little extra predictive information.

Cross-sectional follow-up of a flu-like respiratory illness among fiberglass manufacturing employees: endotoxin exposure associated with two distinct sequelae

Over a period of 10 years, employees in a manufacturing plant experienced sporadic flu-like episodes after work in a basement containing a recirculated washwater mist. We report a cross-sectional study to define the flu-like illness and bioaerosol exposures. High concentrations of gram-negative bacteria (GNB) (> 10(7) cfu/ml) and endotoxin (range 34-46 micrograms/ml) were found in the water. Mist contained > 10(3) cfu/m3 of GNB, and endotoxin up to 13,900 to 27,800 ng/m3. Few fungi and thermotolerant Bacillus species and no Actinomycetes, Legionella species, or amoeba were found in washwater. Airborne levels of fungi were of the same species and magnitudes as outdoor samples. Subjects volunteered (n = 28) because of a history of flu-like symptoms or were randomly selected (n = 102) from workers with and without current exposure to the basement. No acute cases were examined. Cases did not fulfill criteria for hypersensitivity pneumonitis (HP) and high levels of IgG antibodies to water-borne antigens were not observed. However, among 20 subjects indicating a history of severe flu-like episodes (severe basement flu, SBF), diffusion capacity (DLCO) was significantly lower (p = 0.015) than among other workers. The prevalence of SBF was independent of smoking. Cases occurred in clusters, and SBF was more common among workers with intermittent exposure to the basement (19 cases) than with daily exposure (1 case). These findings suggest that SBF and associated chronically depressed DLCO resulted from toxic injury following high-level endotoxin exposure. Asthma was prevalent in the study population, particularly among employees with daily, rather than intermittent, exposure to endotoxin-containing mist (odds ratio 6.7, p = 0.02). Thus, endotoxin exposure in this study was associated with two distinct sequelae depending on the temporal pattern of exposure.

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.

Emphysema type in relation to silica dust exposure in South African gold miners

The relationship between silica dust exposure in gold mines and the type of emphysema was studied in a group of 1,553 white gold miners who had undergone autopsy examination between 1974 and 1987. Of particular interest was the contrast between centriacinar and panacinar emphysema as they relate to silica exposure and the presence of silicosis. Subjects with significant emphysema, that is, with an emphysema score of 30% or more, were classified as having predominantly panacinar or predominantly centriacinar emphysema, and compared to those without emphysema (emphysema score less than or equal to 10%). Of those who had significant emphysema (greater than or equal to 30%), 24% had predominantly panacinar, 43% predominantly centriacinar, and 33% were classified as mixed. The odds ratios (OR) for the association between each emphysema type and dust exposure (one unit of the cumulative dust index) were found to be statistically significant and of equal magnitude [1.019, with a 95% confidence interval (CI) of 1.005 to 1.033 for panacinar and 1.019 with a 95% CI of 1.007 to 1.031 for centriacinar emphysema]. In 163 nonsmokers insignificant panacinar emphysema was more common than centriacinar emphysema. The results indicate that a miner with 20 yr in high-dust occupations has a 3.5 (1.7;6.6) times higher odds of having a significant degree of emphysema at autopsy than a miner not in a dusty occupation. This is likely to be true of smoking miners only because there were only four nonsmokers with an emphysema score between 30 and 40%.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicity of intratracheally instilled cotton dust, cellulose, and endotoxin

Cotton dust includes respirable particles containing endotoxin and elastase, agents associated with emphysema. To examine whether a respirable fraction of cotton dust could produce emphysema in an animal model, we intratracheally instilled hamsters with respirable cotton dust particles (0.75 mg/100-g animal), mass median aerodynamic diameter less than or equal to 4.8 microns, twice weekly for 6 wk. We also examined whether instilled endotoxin (255 micrograms/100-g animal) could produce emphysema in hamsters and whether cellulose (0.75 mg/100-g animal) is an appropriate inert comparison dust. A saline-instilled group was the control. Hamsters were killed 8 wk after the last instillation. Static pressure-volume deflation curves of air-filled excised lungs were analyzed to measure lung distensibility. Lungs were fixed in inflation using glutaraldehyde and were examined morphometrically to obtain surface area and numbers of granulomata. Endotoxin-treated animals had increased distensibility, reduced surface-to-volume (S/V) ratio, and morphologically apparent mild centrilobular emphysema. Cellulose-treated animals had decreased distensibility, normal S/V ratio, and significant numbers of granulomata with patchy areas of thickened interalveolar septa. Cotton-dust-instilled animals had normal distensibility, reduced S/V ratio, significant numbers of granulomata, and mild centrilobular emphysema. These data suggest that cotton dust produces a significant parenchymal lesion with elements similar to both the emphysematous response to endotoxin and the fibrotic nodular response to cellulose.

The role of allergy and nonspecific airway hyperresponsiveness in the pathogenesis of chronic obstructive pulmonary disease

Although the information that has been reviewed leaves many questions unanswered, some conclusions can be drawn from available data. (1) Smoking appears to increase the risk of sensitization to certain inhaled antigens encountered in the workplace; however, there is no definite evidence that smoking increases the frequency or intensity of allergy to common aeroallergens in the general population. On average, smokers have higher serum total IgE concentrations and blood eosinophil counts than do nonsmokers, but the mechanisms underlying these alterations are not clear. Analysis of these relationships is complicated by observations suggesting that atopic persons are less likely to become and to remain regular cigarette smokers. (2) Long-term cigarette smoking may be associated with increased nonspecific airway responsiveness, although the magnitude of this effect is relatively small when one adjusts for prechallenge level of pulmonary function. This effect of smoking may be more pronounced in atopic persons. (3) Atopy, as assessed by skin testing and serum IgE concentrations, is associated with asthma, nonspecific airway hyperresponsiveness, and reduced pulmonary function level in population data. However, there is no clear evidence that atopy is a risk factor for irreversible airflow obstruction in persons without asthma. Population data do not indicate how much of the reduction in pulmonary function associated with atopy and asthma is potentially reversible. (4) Blood eosinophil count appears inversely related to the level of pulmonary function and directly related to the rate of decline of pulmonary function among nonsmokers. Reports vary concerning whether the relationship of eosinophil count to level of pulmonary function remains after excluding subjects with diagnosed asthma. This relationship may be determined largely by a clinically distinguishable subset of nonsmokers with "asthmatic bronchitis." Presumably, these observations reflect an adverse impact of eosinophilic inflammation in the airways or lung parenchyma. It is not clear whether this represents an allergic response because skin-test reactivity to common aeroallergens and serum total IgE concentration do not show similar relationships to reduced level and rapid decline of pulmonary function. (5) Among smokers, nonspecific airway hyperresponsiveness appears to be associated with an accelerated longitudinal decline of pulmonary function, although most studies indicating this association are limited by either a retrospective design or lack of adjustment for prechallenge level of pulmonary function.(ABSTRACT TRUNCATED AT 400 WORDS)

Early emphysema. Ten years' evolution

In this study, functional evolution over ten years was evaluated in 13 patients with early emphysema. The diagnosis was made on the basis of a decrease in single-breath DCO (55 +/- 14 percent predicted, mean +/- 1 SD), a loss of elastic recoil (CL,st = 0.76 +/- 0.25 L/cm H2O), and only minor airway obstruction (FEV1 = 87 +/- 13 percent predicted, Sgaw = 0.09 +/- 0.04 cm H2O-1.s-1), and compatible chest radiographs. During the ten years, there was a decrease in FEV1 of 0.89 +/- 0.40 L p less than 0.001), with a range of 0.20 to 1.55 L (which could not clearly be related to smoking habits or to initial lung function), a decrease in elastic recoil (p less than 0.05, with a decrease of Ptp, TLC by 6 +/- 7 cm H2O; p approximately equal to 0.05), an increase in TLC of 0.46 +/- 0.80 1 (p approximately equal to 0.05), and in RV/TLC of 9 +/- 3 percent (p less than 0.001). The resistance of the upstream segment (ratio Ptp/Vmax) increased slightly but generally remained within normal limits. In conclusion, patients with early emphysema resemble those with classic COPD, with a mean yearly decline in FEV1 similar to that in COPD.

Rate of increase in pulmonary distensibility in a longitudinal study of smokers

To examine the hypothesis that an abnormally rapid increase in pulmonary distensibility occurs in cigarette smokers, 39 adult smokers (24 men), mean age 47 (SD 8) years, who were not disabled were studied on two occasions over a mean interval of 3.5 (SD 0.5) years. Exponential analysis of static pressure-volume data obtained during deflation of the lungs gave the exponent K, an index of distensibility. Total lung capacity (TLC) was measured in a body plethysmograph. At entry into the longitudinal study means values for K and static recoil pressure in the 39 smokers available for follow up were similar to those obtained in the original group of 101 smokers (73 men), mean age 42 (SD 11) years, in the cross sectional study. Over the interval of the study, ln K and TLC increased and FEV1 decreased at rates greater than those found in a previous longitudinal study of 34 non-smokers (24 men), mean age 42 (SD 15) years. In the longitudinal study of smokers the observed changes in K and in recoil pressure over the interval of study were greater than the values obtained from the regression slopes found in the cross sectional study of smokers. On the basis of the regression model used previously in the longitudinal study of non-smokers, the age coefficient for ln K was greater than that found in the non-smokers (p less than 0.01). The regression model also showed that the slope of ln K on age increased in older subjects. Because K is related to peripheral airspace size, a rapid rate of increase in K identifies smokers in whom airspace size is increasing abnormally rapidly. In this study the rate of increase in K and the variation between subjects was sufficient to explain the magnitude of the increased pulmonary distensibility found in cigarette smokers who present with emphysema.

CT measurements of lung density in life can quantitate distal airspace enlargement--an essential defining feature of human emphysema

We used a computerized microscopic image analysis system to directly measure the surface area of distal air spaces in methacrylate-embedded blocks randomly selected from inflation-fixed lobes that were resected from 45 patients as treatment of their peripheral lung tumors. In 28 of these patients, a preoperative computer tomography (CT) scan, at 6 and 10 cm below the sternal notch, was used to generate frequency histograms of CT numbers (measured as EMI units), a measure of lung density, in pixels from the lung or lobe that was subsequently resected. A similar CT number histogram was also derived from the lateral two fifths of the area of lobe/lung that was to be resected. The EMI unit that defined the lowest fifth percentile of this latter histogram correlated (n = 28, r = -0.77, p less than 0.001) with the mean value of the surface area of the walls of distal airspaces per unit lung volume (AWUV) in the five 1 mm x 1 mm microscopic fields with the lowest AWUV values, out of the 20 to 35 such fields examined in each patient. In the 34 of the 45 patients in whom we also measured volume-corrected diffusing capacity (DLCO/VA), this also correlated (n = 34, r = 0.84, p less than 0.001) with this value of AWUV, which measures the surface area of airspaces distal to the terminal bronchioles--reflecting an increase in airspace size, a defining characteristic of emphysema. However, a low DLCO/VA is nonspecific, whereas an abnormally low regional lung density is more likely to be specific for emphysema. In addition, highlighting those pixels of the CT display with low CT numbers (i.e., EMI units -500 [air] to -450, where zero = water) can locate areas of macroscopic emphysema, as shown by subsequent pathologic examination. Thus the quantitative CT scan can diagnose, quantitate, and locate mild to moderate emphysema, in humans, in life, noninvasively.