Endobronchial Treatment of Emphysema with One-Way Valves

Heterogeneity of specific gas volume changes: a new tool to plan lung volume reduction in COPD

OBJECTIVE

The aim of this work was to investigate if regional differences of specific gas volume (SVg) in the different 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, ΔSVg (ΔSVg = SVg,TLC - SVg,RV, where SVg,TLC and SVg,RV are specific gas volume at TLC and RV, respectively) vs ΔV (ΔV = V,TLC-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 defined to quantify the range of variability of ΔSVg/ΔV in all bronchopulmonary regions.

RESULTS

In patients with COPD, SVg,TLC and SVg,RV were significantly higher and ΔSVg variations lower than in healthy subjects (P < .001). In COPD, ΔSVg/ΔV slopes were lower in upper lobes than in lower lobes. In healthy subjects, the entire lung, lobes, and bronchopulmonary segments all showed similar ΔSVg/ΔV slopes, whereas in COPD a high variance was found. As a consequence, HI was significantly higher in subjects with COPD than in healthy subjects (0.80 ± 0.34 vs 0.15 ± 0.10, respectively; P < .001).

CONCLUSIONS

SVg variations within the lung are highly homogeneous in healthy subjects. Regions with low ΔSVg/ΔV (ie, more pronounced gas trapping) should be considered as target areas for LVR. Regions with negative values of ΔSVg/ΔV identify where collateral ventilation is present. HI is helpful to assess the patient in the different stages of disease and the effect of different LVR treatments.

The role of the emphysema multidisciplinary team in a successful lung volume reduction surgery programme†

OBJECTIVES

Lung volume reduction surgery (LVRS) for advanced emphysema is well established, with strong evidence from the National Emphysema Treatment Trial. However, there is still reluctance to offer the procedure, and many have looked for alternative, unproven treatments. The multidisciplinary approach has been well established in treatment of lung cancer and, more recently, in coronary artery surgery. We reviewed our practice to validate the role of our multidisciplinary team approach in our LVRS programme.

METHODS

Our multidisciplinary approach employs respiratory physicians, radiologists and surgeons involved in case selection, who meet on a regular basis. Cases are selected on the basis of clinical presentation, imaging (radionuclide lung perfusion and computerized tomography) and respiratory physiology. Retrospective analysis of prospectively collected data on 633 patients referred for lung volume reduction surgery between July 1995 and July 2013.

RESULTS

Six hundred and thirty-three patients (422 male) were referred for LVRS, of whom 253 [178 male; median age 61 years (range 37-79 years)] underwent 292 LVRS procedures.There were 268 video-assisted thoracoscopic surgical procedures, of which 13 were one-stage bilateral procedures and 37 required a staged second side. Overall median hospital stay was 13 (4-197) days, during which 11 patients died. Prolonged hospital stay was associated with increasing age and with duration of air leak, which in turn was associated with diffusion capacity and forced expiratory volume in 1 s.

CONCLUSIONS

The outcomes of a successful LVRS programme are not only dependent on good surgical technique and post-operative care. Case selection and work-up by a dedicated multidisciplinary approach for emphysema patients plays an invaluable and integral part in an LVRS programme.

Influence of CT reconstruction settings on extremely low attenuation values for specific gas volume calculation in severe emphysema

RATIONALE AND OBJECTIVES

Emphysema is characterized by lung tissue destruction and trapped gas. On computed tomographic (CT) images, this may be expressed by widespread areas with high specific gas volume (SV(g)). SV(g) is highly sensitive to very low attenuation values, which frequently occur in the CT images of patients with severe emphysema. The purpose of the present work was to study if and how different reconstruction settings and different scanners significantly influence SV(g) distribution, particularly in the very low attenuation range.

MATERIALS AND METHODS

Two sets of CT images taken from two different CT scanners at two different lung volumes in 10 healthy volunteers and 18 subjects with severe emphysema were analyzed. Images were reconstructed using two different settings of reconstruction parameters: (1) thin slice thickness and sharp filter and (2) thick slice thickness and smooth filter. For each set of images, average values of SV(g) and their variation (ΔSV(g)) from total lung capacity to residual volume were calculated in the whole lung.

RESULTS

Very low attenuation values are always present in CT images when reconstructed with thin slice thickness and a sharp filter and in very large numbers in patients with severe emphysema. SV(g) values were in general significantly higher in patients with emphysema than in healthy subjects, at both total lung capacity and residual volume (P < .001), and were significantly influenced by the reconstruction filter (P < .001) and CT scanner (P < .001). ΔSV(g) was lower in patients with emphysema than in healthy subjects (P < .001) and was significantly affected by the reconstruction setting but not by the CT scanner.

CONCLUSIONS

The disproportionate effect of low-attenuation pixels on SV(g) likely causes overestimation of the severity of emphysema and trapped gas. This can be significantly reduced, however, by using thick slices and a smooth filter for image reconstruction. ΔSV(g) is generally robust for quantifying the functional impairment of the lung in severe emphysema.