Morphological Progression of Emphysema on Thin-section CT

Quantitative assessment of pulmonary function in lymphangioleiomyomatosis patients using high-resolution computed tomography and pulmonary function tests

Background

To explore the feasibility of using quantitative high-resolution computed tomography (HRCT) to evaluate pulmonary function in patients with pulmonary lymphangioleiomyomatosis (PLAM).

Methods

Pulmonary function tests (PFTs) were performed in 30 patients with pathologically confirmed PLAM with the use of HRCT. These results were correlated with quantitative HRCT in 21 patients.

Results

There were significant correlations between the HRCT parameters for lung function and PFT parameters. Among these parameters, emphysema volume (EV), pulmonary volume with a pixel index less than the trigger threshold (−950 HU) to account for a proportion of total lung volume [PI-950 (%)] and forced expiratory volume in 1 second/forced vital capacity [FEV1/FVC (%)] had the strongest correlations, reaching values between −0.71 and −0.68. HRCT lung function might therefore also be helpful for predicting changes in lung function before and after treatment.

Conclusions

HRCT is helpful for the assessment of pulmonary function in PLAM patients and can assist in the clinical evaluation of lung function and treatment response in patients with this disease.

Comparison of respiratory system impedance in asthma and COPD: A prospective observational study

BACKGROUND AND OBJECTIVE

A single assessment of within-breath variations of respiratory system reactance (Xrs) at 5 Hz (ΔX5) measured by the forced oscillation technique (FOT) has been reported to be useful for the detection of pathophysiological changes in chronic obstructive pulmonary disease (COPD) and asthma. We examined longitudinal changes in respiratory system resistance (Rrs) and Xrs during tidal breathing between stable asthma and COPD patients in order to clarify the features of changes of respiratory system impedance and airflow limitation for these conditions.

METHODS

Between April 2013 and September 2013, outpatients with a COPD or asthma diagnosis were recruited. We examined forced expiratory volume in 1 s (FEV₁ ) and FOT every 6 months until September 2015. Annual changes were estimated from the linear regression curve slope.

RESULTS

We included 57 and 93 subjects with COPD and asthma, respectively. The median follow-up period was 26 months (range: 24-29 months). Within-breath analysis showed that the difference between mean Rrs at 5 Hz and 20 Hz was significantly lower, and ΔX5 more negative, in COPD than in asthma patients. With regard to annual changes, only ΔX5 was significantly different, more negative, in COPD than in asthma patients. Comparing between COPD subjects of Global Initiative Chronic Obstructive Lung Disease (GOLD) stage I/II and those with asthma, there were no significant differences in respiratory system impedance at enrolment, while annual change in ΔX5 was significantly more negative in mild COPD than in asthma patients.

CONCLUSION

ΔX5 may be useful for long-term assessment of airflow limitation in COPD.

Longitudinal changes in structural abnormalities using MDCT in COPD: do the CT measurements of airway wall thickness and small pulmonary vessels change in parallel with emphysematous progression?

Background

Recent advances in multidetector computed tomography (MDCT) facilitate acquiring important clinical information for managing patients with COPD. MDCT can detect the loss of lung tissue associated with emphysema as a low-attenuation area (LAA) and the thickness of airways as the wall area percentage (WA%). The percentage of small pulmonary vessels <5 mm² (% cross-sectional area [CSA] <5) has been recently recognized as a parameter for expressing pulmonary perfusion. We aimed to analyze the longitudinal changes in structural abnormalities using these CT parameters and analyze the effect of exacerbation and smoking cessation on structural changes in COPD patients.

Methods

We performed pulmonary function tests (PFTs), an MDCT, and a COPD assessment test (CAT) in 58 patients with COPD at the time of their enrollment at the hospital and 2 years later. We analyzed the change in clinical parameters including CT indices and examined the effect of exacerbations and smoking cessation on the structural changes.

Results

The CAT score and forced expiratory volume in 1 second (FEV₁) did not significantly change during the follow-up period. The parameters of emphysematous changes significantly increased. On the other hand, the WA% at the distal airways significantly decreased or tended to decrease, and the %CSA <5 slightly but significantly increased over the same period, especially in ex-smokers. The parameters of emphysematous change were greater in patients with exacerbations and continued to progress even after smoking cessation. In contrast, the WA% and %CSA <5 did not change in proportion to emphysema progression.

Conclusion

The WA% at the distal bronchi and the %CSA <5 did not change in parallel with parameters of LAA over the same period. We propose that airway disease and vascular remodeling may be reversible to some extent by smoking cessation and appropriate treatment. Optimal management may have a greater effect on pulmonary vascularity and airway disease than parenchymal deconstruction in the early stage of COPD.

Effect of threshold on the correlation between airflow obstruction and low attenuation volume in smokers assessed by inspiratory and expiratory MDCT

BACKGROUND

The estimation of emphysematous changes is very sensitive to computed tomography (CT) threshold level. In clinical practice, the predetermined threshold is usually set at -950 Hounsfield units (HU) for the detection of low attenuation volume (LAV). However, threshold levels that are tightly connected to pulmonary function abnormalities have not been determined.

PURPOSE

To determine the threshold level for calculating an LAV that closely reflects airflow limitation in patients with chronic obstructive pulmonary disease (COPD).

MATERIAL AND METHODS

Seventy-six consecutive non-COPD smokers and COPD patients underwent paired inspiratory and expiratory multidetector CT (MDCT). LAV% was segmented every 10 HU between -1000 and -750 HU to examine the correlation between LAV% and indexes of obstructive impairment.

RESULTS

LAV% gradually increased as the threshold level increased on both inspiratory and expiratory images. LAV% on inspiratory images was higher than that on expiratory images at all threshold levels between -1000 and -750 HU. The threshold level that correlated with obstructive impairment differed between the two images: -930 HU on inspiratory and -870 or -880 HU on expiratory images.

CONCLUSION

LAV% dramatically changed according to the threshold level on both inspiratory and expiratory images, indicating that LAV% is dependent on the attenuation threshold level in patients with COPD. The threshold linking LAV% to airflow limitation was higher on expiratory than on inspiratory images.

Quantitative CT measurements of small pulmonary vessels in chronic obstructive pulmonary disease: do they change on follow-up scans?

The aims of this study were to perform a longitudinal evaluation of the cross-sectional area (CSA) of small pulmonary vessels and the extent of emphysema measured on computed tomography (CT) scans of patients with chronic obstructive pulmonary disease (COPD), and to correlate the pulmonary vascular measurements with extent of emphysema. The institutional review board approved this retrospective study and waived the need for patients' informed consent. Seventy-four patients with COPD who underwent both initial and follow-up CT scans at an interval of ≥12 months were analysed. The CSA of small pulmonary vessels <5 mm(2) was measured, and the percentage of total CSA of the area of the lung (%CSA<5 ) was calculated. The extent of emphysema was assessed as the percentage of low attenuation area (%LAA, <-950 Hounsfield units). Comparisons between initial and follow-up measurements were performed using the Wilcoxon signed-rank test. The relationship between longitudinal changes in %CSA<5 and %LAA during the follow-up period was assessed using the Spearman rank correlation. The %LAA increased significantly on follow-up CT scans (P<0·0001). The %CSA<5 was slightly decreased on follow-up scans, but the difference was not significant. Although longitudinal change in %LAA was positively correlated with duration of follow-up period (ρ = 0·505, P<0·0001), longitudinal change in %CSA<5 was not. In conclusion, there was a progressive increase in the extent of emphysema over time, but no significant decrease in the CSA of small pulmonary vessels over the same time period.

Complexity and emergent phenomena

Complex biological systems operate under non-equilibrium conditions and exhibit emergent properties associated with correlated spatial and temporal structures. These properties may be individually unpredictable, but tend to be governed by power-law probability distributions and/or correlation. This article reviews the concepts that are invoked in the treatment of complex systems through a wide range of respiratory-related examples. Following a brief historical overview, some of the tools to characterize structural variabilities and temporal fluctuations associated with complex systems are introduced. By invoking the concept of percolation, the notion of multiscale behavior and related modeling issues are discussed. Spatial complexity is then examined in the airway and parenchymal structures with implications for gas exchange followed by a short glimpse of complexity at the cellular and subcellular network levels. Variability and complexity in the time domain are then reviewed in relation to temporal fluctuations in airway function. Next, an attempt is given to link spatial and temporal complexities through examples of airway opening and lung tissue viscoelasticity. Specific examples of possible and more direct clinical implications are also offered through examples of optimal future treatment of fibrosis, exacerbation risk prediction in asthma, and a novel method in mechanical ventilation. Finally, the potential role of the science of complexity in the future of physiology, biology, and medicine is discussed.

Changes in volume-corrected whole-lung density in smokers and former smokers during the ITALUNG screening trial

PURPOSE

To evaluate with a volume-corrected whole-lung approach changes in lung density over 2 years consistent with progression of pulmonary emphysema in smokers and former smokers enrolled in the ITALUNG trial of lung cancer screening using low-dose computed tomography (LDCT).

MATERIALS AND METHODS

A total of 103 subjects (mean age 63±4 y with a pack-year history of at least 20) underwent 2 whole-lung LDCT examinations 2 years apart. Visual assessment was made independently by 2 experienced observers on the initial LDCT examination with a 0 to 4 grading system for each of 6 regions (right and left upper, mid, and lower lung). The whole-lung 15th percentile of attenuation coefficient and relative area (RA) at -910 HU, both corrected to the individual lung volume (Perc15v and RA910v), were measured on the 2 LDCT examinations. The intrasubject variability of Perc15v and RA910v was previously determined in 32 other subjects of the trial examined using the same scanner and technique twice over a 3-month interval for suspicious nodules.

RESULTS

The 2 operators agreed on the presence of mild to severe emphysema (visual score ≥1 in at least 1 region) at initial LDCT examination in 24 (23%) of the 103 subjects. Fifteen subjects (15%) showed a Perc15v change between the 2 examinations exceeding the lower 95% limit of agreement, indicating progression of emphysema with a mean difference in lung density of -14.7%±2.6%. Ten of the 15 were identified as showing emphysema progression by RA910v as well. No association was observed between progression of emphysema and visual evidence of emphysema at initial LDCT examination, smoking status, or pack-years at baseline, or intervening changes in smoking habits.

CONCLUSION

Once variations in inspiratory lung volumes are taken into account, changes in lung density over 2 years consistent with progression of pulmonary emphysema in elderly smokers and former smokers are uncommon.

Longitudinal study of spatially heterogeneous emphysema progression in current smokers with chronic obstructive pulmonary disease

BACKGROUND

Cigarette smoke is the main risk factor for emphysema, which is a key pathology in chronic obstructive pulmonary disease (COPD). Low attenuation areas (LAA) in computed tomography (CT) images reflect emphysema, and the cumulative size distribution of LAA clusters follows a power law characterized by the exponent D. This property of LAA clusters can be explained by model simulation, where mechanical force breaks alveolar walls causing local heterogeneous lung tissue destruction. However, a longitudinal CT study has not investigated whether continuous smoking causes the spatially heterogeneous progression of emphysema.

METHODS

We measured annual changes in ratios of LAA (LAA%), D and numbers of LAA clusters (LAN) in CT images acquired at intervals of ≥ 3 years from 22 current and 31 former smokers with COPD to assess emphysema progression. We constructed model simulations using CT images to morphologically interpret changes in current smokers.

RESULTS

D was decreased in current and former smokers, whereas LAA% and LAN were increased only in current smokers. The annual changes in LAA%, D, and LAN were greater in current, than in former smokers (1.03 vs. 0.37%, p=0.008; -0.045 vs. -0.01, p=0.004; 13.9 vs. 1.1, p=0.007, respectively). When LAA% increased in model simulations, the coalescence of neighboring LAA clusters decreased D, but the combination of changes in D and LAN in current smokers could not be explained by the homogeneous emphysema progression model despite cluster coalescence. Conversely, a model in which LAAs heterogeneously increased and LAA clusters merged somewhat in relatively advanced emphysematous regions could reflect actual changes.

CONCLUSIONS

Susceptibility to parenchymal destruction induced by continuous smoking is not uniform over the lung, but might be higher in local regions of relatively advanced emphysema. These could result in the spatially heterogeneous progression of emphysema in current smokers.

BODE-index, modified BODE-index and ADO-score in chronic obstructive pulmonary disease: relationship with COPD phenotypes and CT lung density changes

COPD is a heterogeneous disorder whose assessment is going to be increasingly multidimensional. Grading systems such as BODE (Body-Mass Index, Obstruction, Dyspnea, Exercise), mBODE (BODE modified in grading of walked distance), ADO (Age, Dyspnea, Obstruction) are proposed to assess COPD severity and outcome. Computed tomography (CT) is deemed to reflect COPD lung pathologic changes. We studied the relationship of multidimensional grading systems (MGS) with clinically determined COPD phenotypes and CT lung density. Seventy-two patients underwent clinical and chest x-ray evaluation, pulmonary function tests (PFT), 6-minute walking test (6MWT) to derive: predominant COPD clinical phenotype, BODE, mBODE, ADO. Inspiratory and expiratory CT was performed to calculate mean lung attenuation (MLA), relative area with density below-950 HU at inspiration (RAI(-950)), and below -910 HU at expiration (RAE(-910)). MGS, PFT, and CT data were compared between bronchial versus emphysematous COPD phenotype. MGS were correlated with CT data. The prediction of CT density by means of MGS was investigated by direct and stepwise multivariate regression. MGS did not differ in clinically determined COPD phenotypes. BODE was more closely related and better predicted CT findings than mBODE and ADO; the better predictive model was obtained for CT expiratory data; stepwise regression models of CT data did not include 6MWT distance; the dyspnea score MRC was included only to predict RA-950 and RA-910 which quantify emphysema extent. BODE reflect COPD severity better than other MGS, but not its clinical heterogeneity. 6MWT does not significantly increase BODE predictivity of CT lung density changes.

Low agreement of visual rating for detailed quantification of pulmonary emphysema in whole-lung CT

BACKGROUND

Multidetector spiral computed tomography (CT) has opened the possibility of quantitative evaluation of emphysema extent in the whole lung. Visual assessment can be used for such a purpose, but its reproducibility has not been established.

PURPOSE

To assess agreement of detailed assessment of pulmonary emphysema on whole-lung CT using a visual scale.

MATERIAL AND METHODS

Thirty patients with chronic obstructive pulmonary disease underwent whole-lung inspiratory CT. Four chest radiologists rated the same 22 ± 2 thin sections using a visual scale which defines a range of emphysema extent between 0 and 100. Two of them repeated the rating two months later. Inter- and intra-operator agreement was evaluated with the Bland and Altman method. In addition, the percentage of emphysema at -950 Hounsfield units in the whole lung was determined using fully automated commercially available software for 3D densitometry.

RESULTS

In three of six operator pairs and in one of two intra-operator pairs the Kendall τ test showed a significant correlation between the difference and the average magnitude of visual scores. Among different operators the half-width of 95% limits of agreement (95% LoA) was wide ranging between a score of 14.2-27.7 for an average visual score of 20 and between 18.5-36.8 for an average visual score of 80. Within the same operator the half-width of 95% LoA ranged between a score of 10.9-21.0 for an average visual score of 20 and between 25.1-30.1 for an average visual score of 80. The visual scores of the four radiologists were correlated with the results of densitometry (P < 0.001; r = 0.65-0.81).

CONCLUSION

The inter- and intra-operator agreement of detailed assessment of emphysema in the whole lung using a visual scale is low and decreases with increasing emphysema extent.

Quantitative bronchial luminal volumetric assessment of pulmonary function loss by thin-section MDCT in pulmonary emphysema patients

OBJECTIVES

To determine the capability of quantitative bronchial luminal volume to assess pulmonary function loss and disease severity in pulmonary emphysema patients.

METHODS

Thirty-seven smokers (mean age, 68.1 years) underwent CT examinations and pulmonary function tests. For the quantitative assessment, luminal voxels of trachea and bronchi were computationally counted and the ratio of the following luminal voxels to all luminal voxels was obtained: (1) the lobe bronchi and the peripheral bronchi (Ratio(lobe)), and (2) the main bronchi and the peripheral bronchi (Ratio(main)). To determine the capability of these assessments to predict pulmonary function loss, these ratios were correlated with pulmonary function tests. To determine the capability for predicting disease severity, these ratios were compared between clinical groups.

RESULTS

These ratios were no significant correlated with vital capacity and forced vital capacity (FVC) (p > 0.05), however significantly correlated with forced expiratory volume in 1s (FEV1) (Ratio(lobe): r = 0.61, p < 0.0001, Ratio(main): r = 0.58, p < 0.0005) and FEV1/FVC (Ratio(lobe): r = 0.36, p < 0.05, Ratio(main): r = 0.33, p < 0.05). The Ratio(lobe) of smokers without COPD was significantly different from those of moderate COPD and severe or very severe COPD (p < 0.05), while that of mild COPD was significantly different from that of severe or very severe COPD (p < 0.01). The Ratio(main) of severe or very severe COPD patients was significantly different from those of other groups (p < 0.05).

CONCLUSIONS

Quantitative bronchial luminal volumes were reflected the airflow limitation parameters and was corresponded to clinical groups in emphysema patients.

Quantitative imaging of COPD

Computed tomography has facilitated recognition that chronic obstructive pulmonary disease is not a single disease but encompasses several overlapping entities, including emphysema, bronchitis, and small airways disease. Quantitative computed tomography can effectively characterize and quantify the extent of emphysema, airway wall thickening, and air trapping related to small airways disease.

Hyperpolarized gas MR Imaging of the lung: current status as a research tool

Hyperpolarized gas magnetic resonance imaging has been explored extensively as a promising tool for the quantitative evaluation of regional pulmonary pathophysiology. This noninvasive technique is capable of providing both structural information down to the level of the alveolar microstructure and functional information, such as dynamic ventilation, intrapulmonary partial pressure of oxygen, and alveolar surface area. This study reviews the role of hyperpolarized 3-helium and 129-xenon magnetic resonance imaging in this research.

Quantitative and qualitative assessments of lung destruction and pulmonary functional loss from reduced-dose thin-section CT in pulmonary emphysema patients

RATIONALE AND OBJECTIVES

Academic and clinical interest in reducing radiation from computed tomography (CT) examinations has increased, and the purpose of this study was to determine the capabilities of reduced-dose multidetector-row CT (MDCT) in assessing lung destruction and pulmonary functional loss in pulmonary emphysema patients.

MATERIALS AND METHODS

Twenty-five consecutive smokers (15 men and 10 women; mean age 67.9 years; age range 49-86 years) underwent MDCT examinations using two different effective tube currents (standard-dose protocol [150 mAs] and reduced-dose protocol [50 mAs]). For quantitative and qualitative assessments of lung destruction in each subject, percentage of low attenuation emphysematous destruction areas (%LAAs) were computationally calculated, and visual emphysema scores (ESs) were determined for both protocols. To determine the capabilities for quantitative and qualitative assessments of lung destruction by using reduced-dose protocol, %LAAs and ESs of both protocols were compared statistically. To compare the capabilities for quantitative and qualitative assessments of pulmonary functional loss, %LAAs and ESs of both protocols were correlated with forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC).

RESULTS

%LAAs and ESs had significant correlations between both protocols (%LAAs: r = 0.95, P < .001; ESs: r = 0.97, P < .001). The limits of agreement of %LAAs were -1.8 + or - 9.2%. The agreement of ESs between both protocols was substantial (kappa = 0.70). %LAAs and ESs of both protocols had significant correlations with FEV1/FVC (%LAAs of 150 mAs: r = -0.49, P < .05; %LAAs of 50 mAs: r = -0.44, P < .05; ESs of 150 mAs: r = -0.67, P < .001; ESs of 50 mAs: r = -0.66, P < .001).

CONCLUSION

Reduced-dose MDCT had a potential of substitution for standard-dose MDCT on the both assessments in pulmonary emphysema patients.

Avaliação computacional de enfisema pulmonar em TC: comparação entre um sistema desenvolvido localmente e um sistema de uso livre

OBJETIVO: Apresentar um sistema de visão computacional em imagens de TCAR, desenvolvido localmente e denominado SIStema para a Detecção e a quantificação de Enfisema Pulmonar (SISDEP). Comparar esse sistema a um sistema computacional de acesso livre. MÉTODOS: Foram utilizadas 33 imagens de TCAR de 11 pacientes com DPOC com cortes tomográficos em ápice, hilo e base. O SISDEP foi comparado a Osiris Medical Imaging Software Program quanto à segmentação do parênquima pulmonar; precisão das medidas da área de secção transversal dos pulmões em mm², densidade pulmonar média (DPM), porcentagem da relative area (RA, área relativa) dos voxels com densidade < -950 unidades hounsfield (ra -950), valores de 15º percentil de baixa atenuação (perc15) e visualização das áreas hiperaeradas por máscara colorida. RESULTADOS: Os dois sistemas realizaram uma segmentação pulmonar eficiente; porém o SISDEP o fez de modo automático e mais rápido. Na comparação das medidas de área de secção dos pulmões, DPM, Perc15 e RA -950, houve alta correlação (r² = 0,99; 0,99; 0,99; e 1,00, respectivamente) entre os dois sistemas. A ferramenta de máscara colorida do SISDEP permitiu excelente visualização das áreas hiperaeradas, discriminado-as das áreas normais. CONCLUSÕES: O SISDEP se mostrou eficiente na segmentação dos pulmões e na extração de dados quantitativos da aeração pulmonar com excelente correlação com o sistema Osiris. O SISDEP constitui uma promissora ferramenta computacional para a avaliação diagnóstica e o acompanhamento da evolução do enfisema em imagens de TCAR de pacientes com DPOC.

Assessment of regional progression of pulmonary emphysema with CT densitometry

BACKGROUND

Lung densitometry is an effective method to assess overall progression of emphysema, but generally the location of the progression is not estimated. We hypothesized that progression of emphysema is the result of extension from affected areas toward less affected areas in the lung. To test this hypothesis, a method was developed to assess emphysema severity at different levels in the lungs in order to estimate regional changes.

METHODS

Fifty subjects with emphysema due to alpha(1)-antitrypsin deficiency (AATD) [AATD deficiency of phenotype PiZZ (PiZ) group] and 16 subjects with general emphysema (general emphysema without phenotype PiZZ [non-PiZ] group) were scanned with CT at baseline and after 30 months. Densitometry was performed in 12 axial partitions of equal volumes. To indicate predominant location, craniocaudal locality was defined as the slope in the plot of densities against partitions. Regional progression of emphysema was calculated after volume correction, and its slope identifies the area of predominant progression. The hypothesis was tested by investigating the correlation between predominant location and predominant progression.

RESULTS

As expected, the PiZ patients showed more basal emphysema than the non-PiZ group (craniocaudal locality, - 40.0 g/L vs - 6.2 g/L). Overall progression rate in PiZ patients was lower than in non-PiZ subjects. A significant correlation was found between craniocaudal locality and progression slope in PiZ subjects (R = 0.566, p < 0.001). In the non-PiZ group, no correlation was found.

CONCLUSIONS

In the PiZ group, the more emphysema is distributed basally, the more progression was found in the basal area. This finding suggests that emphysema due to AATD spreads out from affected areas.

Oxygen-enhanced magnetic resonance imaging versus computed tomography: multicenter study for clinical stage classification of smoking-related chronic obstructive pulmonary disease

RATIONALE

Oxygen-enhanced magnetic resonance imaging (MRI) has been proposed as a useful tool for assessing regional morphological and functional changes in chronic obstructive pulmonary disease (COPD).

OBJECTIVES

To prospectively and directly compare the efficacy of O(2)-enhanced MRI and quantitative computed tomography (CT) for smoking-related pulmonary functional loss assessment and clinical stage classification of smoking-related COPD.

METHODS

One hundred sixty smokers were classified into four age- and gender-matched groups by using the GOLD criteria for smokers: Smokers without COPD (n = 40), Mild COPD (n = 40), Moderate COPD (n = 40), and Severe or Very Severe COPD (n = 40). All smokers underwent O(2)-enhanced MRI, multidetector-row CT, and pulmonary function test. Mean relative enhancement ratio on O(2)-enhanced MRI and CT-based functional lung volume (FLV) on quantitative CT were calculated. To compare the efficacy of O(2)-enhanced MRI and quantitative CT for pulmonary functional loss assessment, both indexes were correlated with pulmonary functional parameters. To determine the efficacy of two methods for clinical stage classification, the four clinical groups' mean relative enhancement ratio and CT-based FLV were statistically compared.

MEASUREMENTS AND MAIN RESULTS

Correlations of both indexes with pulmonary functional parameters were significant (P < 0.0001). Pulmonary functional parameters and mean relative enhancement ratio for the four clinical groups showed significant differences (P < 0.05). CT-based FLVs of smokers without COPD and mild COPD were significantly different from those for moderate COPD and severe or very severe COPD (P < 0.05).

CONCLUSIONS

O(2)-enhanced MRI is effective for pulmonary functional loss assessment and clinical stage classification of smoking-related COPD and quantitative CT.

Phenotypes of chronic obstructive pulmonary disease

The current clinical classification of smoking-related lung disease fails to take into account the heterogeneity of chronic obstructive pulmonary disease (COPD). With an increased understanding of pathophysiologic variation, COPD now clearly represents a spectrum of overlapping diseases with important extrapulmonary consequences. A "phenotype" describes the outward physical manifestations of a particular disease, and compromises anything that is part of the observable structure, function or behavior of an individual. Such phenotypic distinctions in COPD include: frequent exacerbator, pulmonary cachectic, rapid decliner, airways hyperresponsiveness, impaired exercise tolerance, and emphysema versus airways disease. These variable manifestations, each with unique prognostic, clinical and physiologic ramifications, represent distinct phenotypes within COPD. While all of these phenotypes have smoking as a common risk factor, the other risk factors that determine these phenotypes remain poorly understood. An individual smoker has variable expression of each phenotype and there is mounting evidence that COPD phenotypes have different clinical outcomes. These phenotypes can be broadly classified into one of three groups: clinical, physiologic and radiographic. This review presents the evidence for the spectrum of COPD phenotypes with a focused discussion on the pathophysiologic, epidemiologic and clinical significance of each subtype.