Elastic recoil changes in early emphysema

Premature birth affects the degree of airway dysanapsis and mechanical ventilatory constraints

NEW FINDINGS

What is the central question of this study? Adult survivors of preterm birth without (PRE) and with bronchopulmonary dysplasia (BPD) have airflow obstruction at rest and significant mechanical ventilatory constraints during exercise compared with those born at full term (CON). Do PRE/BPD have smaller airways, indexed via the dysanapsis ratio, than CON? What is the main finding and its importance? The dysanapsis ratio was significantly smaller in BPD and PRE compared with CON, with BPD having the smallest dysanapsis ratio. These data suggest that airflow obstruction in PRE and BPD might be because of smaller airways than CON. Adult survivors of very preterm birth (≤32 weeks gestational age) without (PRE) and with bronchopulmonary dysplasia (BPD) have obstructive lung disease as evidenced by reduced expiratory airflow at rest and have significant mechanical ventilatory constraints during exercise. Airflow obstruction, in any conditions, could be attributable to several factors, including small airways. PRE and/or BPD could have smaller airways than their counterparts born at full term (CON) owing to a greater degree of dysanaptic airway development during the pre- and/or postnatal period. Thus, the purpose of the present study was to compare the dysanapsis ratio (DR), as an index of airway size, between PRE, BPD and CON. To do so, we calculated DR in PRE (n = 21), BPD (n = 14) and CON (n = 34) individuals and examined flow-volume loops at rest and during submaximal exercise. The DR, using multiple estimates of static recoil pressure, was significantly smaller in PRE and BPD (0.16 ± 0.05 and 0.10 ± 0.03 a.u.) compared with CON (0.22 ± 0.04 a.u.; both P < 0.001) and smallest in BPD (P < 0.001). The DR was significantly correlated with peak expiratory airflow at rest (r = 0.42; P < 0.001) and the extent of expiratory flow limitation during exercise (r = 0.60; P < 0.001). Our findings suggest that PRE/BPD might have anatomically smaller airways than CON, which might help to explain their lower expiratory airflow rate at rest and during exercise and further our understanding of the consequences of preterm birth and neonatal O₂ therapy.

Pulmonary kinematics from image data: a review

The effects of certain lung pathologies include alterations in lung physiology negatively affecting pulmonary compliance. Current approaches to diagnosis and treatment assessment of lung disease commonly rely on pulmonary function testing. Such testing is limited to global measures of lung function, neglecting regional measurements, which are critical for early diagnosis and localization of disease. Increased accessibility to medical image acquisition strategies with high spatiotemporal resolution coupled with the development of sophisticated intensity-based and geometric registration techniques has resulted in the recent exploration of modeling pulmonary motion for calculating local measures of deformation. In this review, the authors provide a broad overview of such research efforts for the estimation of pulmonary deformation. This includes discussion of various techniques, current trends in validation approaches, and the public availability of software and data resources.

The history of COPD

The evolution of knowledge concerning COPD and its components--emphysema, chronic bronchitis, and asthmatic bronchitis--covers 200 years. The stethoscope and spirometer became important early tools in diagnosis and assessment. Spirometry remains the most effective means of identification and assessment of the course of COPD and responses to therapy, and is grossly underused for this purpose. Knowledge of the pathogenesis, course and prognosis, and new approaches to therapy have dramatically improved our understanding of this important clinical entity. Smoking cessation improves the early course of disease. Long-term oxygen improves the length and quality of life in selected patients with hypoxemia. Surgery benefits a select few. Today, COPD is a steadily growing global healthcare problem, with increasing morbidity and mortality. Early identification and prevention, and treatment of emerging stages of disease through smoking cessation and a growing number of bronchoactive drugs promises to change the outcome.

Definition, epidemiology, course, and prognosis of COPD

Chronic obstructive pulmonary disease (COPD) is now recognized as our nation's most rapidly growing health problem. It ranks as the 4th most common killer and is the only disease in the top 10 whose rank is rising. In 2000, more women than men (59,936 vs 59,118) died of COPD (1). The National Heart, Lung, and Blood Institute has calculated that in 2001, COPD was a $34.4 billion burden on society (both direct and indirect costs) (2). Two new initiatives, the National Lung Health Education Program (NLHEP) (3,4) and the Global Initiative for Chronic Obstructive Lung Disease (5), promote the early diagnosis and intervention of COPD. Both initiatives offer guidelines for the care of patients with all stages of COPD. The NLHEP recommends spirometry in all current or former smokers age > or = 45 years and anyone with symptoms of chronic cough, excessive dyspnea on exertion, or wheezing (6). "Test your lungs, know your numbers" is the motto of the NLHEP. Most patients with COPD are first seen by their primary care practitioner well before symptoms or signs of moderate-to-advanced stages of the disease are present. Thus, the primary care practitioner, working on the front line, is in the position to make a difference in the treatment and outcome of this devastating disorder.

COPD: clinical phenotypes

Different phenotypic presentations in advanced stages of COPD are less common than in years past because of therapies that alter the manifestations of disease. Early stages of COPD are often asymptotic, but may present as asthma, chronic bronchitis, emphysema or combinations. Unusual presentations at young age are not common, but may be dramatic.

COPD in perspective

In the last 200 years or so, the recognition, diagnosis, and understanding of the pathogenesis of COPD have evolved considerably. Over the past few decades, various definitions of COPD and its "components" also have developed. Despite this, however, the treatment options for patients with this relentlessly progressive disorder are relatively limited. In the mid-19th century, the introduction of the spirometer yielded a powerful tool for the diagnosis of COPD. The currently available small, cheap spirometers hold great promise to help patients and their physicians closely monitor lung function. Early recognition of the close associations among emphysema and, more recently, small airways disease, and impaired airflow is discussed. This review also stresses the importance of the identification of COPD in its initial stages and the early onset of appropriate treatment. The therapy for COPD has changed in the last 40 years. Drug therapies in the 1960s included potassium iodide and ephedrine. Corticosteroids were not used, and oxygen therapy and exercise were actually contraindicated. Modern therapy for COPD is now more systematic and includes the use of bronchodilators and corticosteroids to improve airflow, in addition to oxygen therapy, pulmonary rehabilitation and, in selected patients, lung volume reduction surgery. The causal link between the chronic inhalation of tobacco smoke and COPD is beyond doubt, and smoking cessation remains the most important goal for patients. It is hoped that new, more effective therapies will soon be available for the treatment of this disabling disorder to provide improvement in symptoms and patient quality of life and to reduce or stop the rate of disease progression and mortality in patients with COPD.

Influence of lung parenchymal destruction on the different indexes of the methacholine dose-response curve in COPD patients

STUDY OBJECTIVES

The interpretation of nonspecific bronchial provocation dose-response curves in COPD is still a matter of debate. Bronchial hyperresponsiveness (BHR) in patients with COPD could be influenced by the destruction of the parenchyma and the augmented mechanical behavior of the lung. Therefore, we studied the interrelationships between indexes of BHR, on the one hand, and markers of lung parenchymal destruction, on the other.

PATIENTS AND METHODS

COPD patients were selected by clinical symptoms, evidence of chronic, nonreversible airways obstruction, and BHR, which was defined as a provocative dose of a substance (histamine) causing a 20% fall in FEV(1) (PC(20)) of </= 8 mg/mL. BHR was subsequently studied by methacholine dose-response curves to which a sigmoid model was fitted for the estimation of plateau values and reactivity. Model fits of quasi-static lung pressure-volume (PV) curves yielded static lung compliance (Cstat), the exponential factor (KE) and elastic recoil at 90% of total lung capacity (P90TLC). Carbon monoxide (CO) transfer was measured with the standard single-breath method.

RESULTS

Twenty-four patients were included in the study, and reliable PV data could be obtained from 19. The following mean values ( +/- SD) were taken: FEV(1), 65 +/- 12% of predicted; reversibility, 5.6 +/- 3.1% of predicted; the PC(20) for methacholine, 4.3 +/- 5.2 mg/mL; reactivity, 11.0 +/- 5.6% FEV(1)/doubling dose; plateau, 48.8 +/- 17.4% FEV(1); transfer factor, 76.7 +/- 17.9% of predicted; transfer coefficient for carbon monoxide (KCO), 85.9 +/- 22.6% of predicted; Cstat, 4.28 +/- 2.8 kPa; shape factor (KE), 1.9 +/- 1.5 kPa; and P90TLC, 1.1 +/- 0.8 kPa. We confirmed earlier reported relationships between Cstat, on the one hand, and KE (p < 0.0001), P90TLC (p = 0.0012), and KCO percent predicted (p = 0.006), on the other hand. The indexes of the methacholine provocation test were not related to any parameter of lung elasticity and CO transfer.

CONCLUSION

BHR in COPD patients who smoke most probably is determined by airways pathology rather than by the augmented mechanical behavior caused by lung parenchymal destruction.

Lung density and lung mass in emphysema

Mean lung density (dm) and radiologic (VLx) lung volume can be calculated using CT scan data. As many emphysematous patients are overdistended, the analysis of dm alone could be meaningless. However, lung mass (m) can be calculated as the product of dm and VLx. Twenty-four patients suspected of mild or severe emphysema as judged by roentgenographic and physiologic examinations as well as 16 healthy subjects were included in the protocol. They all underwent both a CT scan of the whole lung and functional tests from which the following were derived: airway resistance, forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), total lung capacity (TLC), CO transfer capacity, quasi-static compliance at functional residual capacity (FRC), and blood gases. All CT scans were performed at the FRC of each patient. The dm was lower in emphysema patients than in healthy subjects, as m was greater in patients than in healthy subjects; 1,303 +/- 398 g and 997 +/- 133 g, respectively. Although dm values were significantly correlated to FEV1, FEV1/FVC, and TLC, m values were not correlated to any of these functional indices. Unexpectedly, these results show that most patients (22/24) with emphysema have a normal or increased lung mass. Normal or above normal m values might be due to oversecretion in some patients. Nevertheless, the synthesis of new tissue due to chronic inflammation is the most likely explanation that could account for this finding.

The senile lung. Comparison with normal and emphysematous lungs. 2. Functional aspects

Senile lungs are characterized by a homogeneous enlargement of the alveolar airspaces, without fibrosis or destruction of their walls. Study of the functional characteristics of excisea senile lungs showed an increase in minimal air and a shift to the left of the elastic recoil pressure-volume curves, less pronounced than in emphysematous lungs. Maximal expiratory volumes and flows were normal. Total lung capacity was not significantly increased, but this may be a consequence of preagonal edema. Comparison of normal, senile, and emphysematous lungs showed a close relationship between recoil pressures and mean linear intercept, Lm, and between forced expiratory volume in 1 s and diameter and density of the membranous bronchioles. It is concluded that airspace enlargement may precede emphysema and may be responsible for changes in lung elasticity. In this respect, senile lungs are an example of the functional changes caused by an isolated airspace enlargement.

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.

Total lung capacity. An insensitive measure of impairment in patients with asbestosis and chronic obstructive pulmonary disease?

The total lung capacity (TLC) is frequently used as a measure of respiratory impairment in patients with asbestosis. Because asbestosis and chronic obstructive pulmonary disease (COPD) exert opposite effects on the TLC, it may be an insensitive measure of impairment in patients with both abnormalities. To assess this, we compared asbestos-exposed patients with functional evidence of COPD and radiographic evidence of interstitial fibrosis (group 1) to those with interstitial fibrosis alone (group 2). Despite the two groups being comparable in degree of radiographic "fibrosis," no case of restrictive impairment (reduced TLC) was identified among those with both interstitial fibrosis and COPD (group 1), compared to 33 percent of those with interstitial fibrosis alone (group 2). In addition, those patients with both interstitial fibrosis and COPD, compared to those with interstitial fibrosis alone, were found to have greater impairment as measured by alveolar-arterial oxygen difference and diffusing capacity. We conclude that the TLC is an insensitive measure of impairment due to asbestosis in patients with the common setting of coexistent asbestosis and COPD.

Comparison of five methods of analyzing respiratory pressure-volume curves

Five methods of analyzing the deflation limb of respiratory pressure-volume (PV) curves obtained from seven groups of rats that had undergone various treatments were compared. The five methods utilized measurements of: y intercept and slope with simple exponential curve fitting; area under the curve; volumes at fixed pressures; shape constant, k, of the sigmoid curve described by Paiva et al. (Respir. Physiol. 23:317, 1975); and quasi-static compliance. The seven groups of rats were treated as follows: control (n = 10); high tar/nicotine cigarette smoke exposure (n = 10); low tar/nicotine cigarette smoke exposure (n = 9); intratracheal elastase (n = 10); intratracheal elastase plus sham smoke exposure (n = 10); intratracheal elastase plus high tar/nicotine cigarette smoke exposure (n = 9); and intratracheal elastase plus low tar/nicotine cigarette smoke exposure (n = 10). Elastase treatment caused a leftward and upward shift of the PV curve and this shift was augmented by exposure to either high tar/nicotine or low tar/nicotine cigarette smoke. Using Duncan's multiple range test, we found that the y-intercept measurement of method 1, the area under the curve, volumes at fixed pressures, and quasi-static compliance methods were better able to differentiate PV curves between groups than were the slope measurement of method 1 and the shape constant measurement of method 4.

Subclinical effects of smoking. Physiologic comparison of healthy middle-aged smokers and nonsmokers and interrelationships of lung function measurements

Measurements of ventilatory function, distribution of ventilation, diffusing capacity, and lung mechanics were made on healthy middle-aged smokers and nonsmokers drawn from a randomly selected population in order to assess the effects of cigarette smoking and the interrelationships of the several indices of lung function. Although very few subjects had abnormal function, there were significant differences in most indices of function between smokers and nonsmokers. For the total group studied, there were significant correlations between various indices of function. A significant proportion of the variance in diffusing capacity and in diffusing capacity per liter of lung volume can be accounted for by an index of lung recoil which may, in turn, be related to size of terminal air spaces.