Heterogeneity of Specific Gas Volume Changes

Abstract

OBJECTIVE: Th e aim of this work was to investigate if regional diff erences of specifi c gas volume (SVg ) in the diff erent regions (lobes and bronchopulmonary segments) in healthy volunteers and patients with severe emphysema can be used as a tool for planning lung volume reduction (LVR) in emphysema.METHODS: CT scans of 10 healthy subjects and 10 subjects with severe COPD were obtained at end-inspiration (total lung capacity [TLC]) and end-expiration (residual volume [RV]). For each subject, D SVg ( D SVg 5 SVg,TLC 2 SVg,RV, where SVg,TLC and SVg,RV are specifi c gas volume at TLC and RV, respectively) vs D V ( D V 5 V,TLC 2 V,RV, where V,TLC and V,RV are lung volume at TLC and RV, respectively) was plotted for the entire lung, each lobe, and all bronchopulmonary segments. For each subject, a heterogeneity index (HI) was defi ned to quantify the range of variability of D SVg/ D V in all bronchopulmonary regions . RESULTS:In patients with COPD, SVg,TLC and SVg,RV were signifi cantly higher and D SVg variations lower than in healthy subjects ( P , .001). In COPD, D SVg/ D V slopes were lower in upper lobes than in lower lobes. In healthy subjects, the entire lung, lobes, and bronchopulmonary segments all showed similar D SVg/ D V slopes, whereas in COPD a high variance was found. As a consequence, HI was signifi cantly higher in subjects with COPD than in healthy subjects (0.80 Ϯ 0.34 vs 0.15 Ϯ 0.10, respectively; P , .001).CONCLUSIONS: SVg variations within the lung are highly homogeneous in healthy subjects. Regions with low D SVg/ D V (ie, more pronounced gas trapping) should be considered as target areas for LVR. Regions with negative values of D SVg/ D V identify where collateral ventilation is present. HI is helpful to assess the patient in the diff erent stages of disease and the eff ect of diff erent LVR treatments. LAA 5 low attenuation area; LAA-856 5 lung pixels with an attenuation of Յ 2 856 HU on expiratory CT scan; LAA-950 5 lung pixels with an attenuation of Յ 2 950 HU on inspiratory CT scan; LLL 5 left lower lobe; LUL 5 left upper lobe; LVRS 5 lung volume reduction surgery; ROI 5 region of interest; RLL 5 right lower lobe; RUL 5 right upper lobe; RV 5 residual volume; SVg 5 specific gas volume; SVg,r 5 regional specifi c gas volume; TLC 5 total lung capacity AFFILIATIONS: From the TBMLab

Continuous quantitative measurement of the proximal airway dimensions and lung density on four-dimensional dynamic-ventilation CT in smokers

“… 22 – 24 On combined inspiratory–expiratory CT scans, Salito et al found that the heterogeneity of the gas volume change among bronchopulmonary regions was significantly higher in patients with COPD than in healthy subjects. 30 Based on these observations and other previous publications describing the heterogeneity of the air distribution on MR in patients with COPD, 32 – 35 it is logical that respiratory lung movement would be heterogeneous in patients with more severe airflow limitation, which would appear as an uneven time curve of the MLD in this study. In fact, when compared to a smoker without COPD ( Figure 3 ), some severe patients with COPD demonstrated uneven MLD curves during ventilation in this study ( Figure 4 ).…”

“…This has been suggested by previous studies that evaluated the respiratory movement of the diaphragm on MR 22 – 26 and the regional lung densities on combined inspiratory–expiratory CT scans. 30 , 31 Iwasawa et al reported that paradoxical movements of the diaphragm, which are observed as a mixed upward and downward diaphragmatic motion during lung ventilation on cine-MR, are frequently observed in patients with emphysema or COPD. 22 – 24 On combined inspiratory–expiratory CT scans, Salito et al found that the heterogeneity of the gas volume change among bronchopulmonary regions was significantly higher in patients with COPD than in healthy subjects.…”

Asynchrony in respiratory movements between the pulmonary lobes in patients with COPD: continuous measurement of lung density by 4-dimensional dynamic-ventilation CT

“…The latest study analyzing xenon-CT in COPD patients has shown that decreased air distribution is observed even in the non-emphysematous, apparently normal lung areas, suggesting the presence of other coexisting conditions such as proximal or small airway disease in COPD 25. Considering that inhomogeneous air distribution by ventilation has also been demonstrated by paired inspiratory and expiratory CT6–9 and hyperpolarized xenon or helium MR,12,13 our observation of asynchronized, heterogeneous lung movement by ventilation in COPD is consistent with these previous publications and further expands the 4-dimensional imaging approach.…”

Regional Lung Sound Asynchrony in Chronic Obstructive Pulmonary Disease Patients

“…Parenchymal destruction in emphysematous lesions reduces elastic recoil, causing small airway narrowing and closure [24]. Furthermore, emphysematous lesions are heterogeneous in terms of regional lung emptying [25]. It is thought that in emphysematous lesions, air flow distribution is considerably complex and heterogeneous, and heterogeneous distribution of emphysematous lesions might further exacerbate airflow asynchrony in the lung.…”