Evaluation of spirometry-gated computed tomography to measure lung volumes in emphysema patients

Abstract

IntroductionIn emphysema patients, being evaluated for bronchoscopic lung volume reduction (BLVR), accurate measurement of lung volumes is important. Total Lung Capacity (TLC) and Residual Volume (RV) are commonly measured by body-plethysmography, but can also be derived from chest computed tomography (CT). Spirometry-gated CT scanning potentially improves the agreement of CT and body-plethysmography.ObjectiveTo compare lung volumes derived from spirometry-gated CT and “breath-hold-coached” CT to the reference standard: body-plethysmography.MethodsIn this single centre retrospective cohort study, emphysema patients, evaluated for BLVR, underwent body-plethysmography, inspiration (TLC) and expiration (RV) CT-scan with spirometer guidance (“gated group”) or with breath-hold-coaching (“non-gated group”). Quantitative analysis was used to calculate lung volumes from the CT.ResultsWe included 200 patients (age 62±8 years, FEV1 29.2±8.7%, TLC 7.50±1.46 L, RV 4.54±1.07 L). The mean CT-derived TLC was 280(±340)ml lower compared to body-plethysmography in the gated group (n=100), and 590(±430)ml lower for the non-gated group (n=100) (both p<0.001). The mean CT-derived RV was 300(±470)ml higher in the gated group and 700(±720)ml higher in the non-gated group (both p<0.001). Pearson correlation factors were 0.947 for TLC gated, 0.917 for TLC non-gated, 0.823 for RV gated, 0.693 for RV non-gated, 0.539 for %RV/TLC gated and 0.204 for %RV/TLC non-gated. The differences between the gated and non-gated CT results for TLC and RV were significant for all measurements (p<0.001).ConclusionIn severe COPD patients with emphysema, CT-derived lung volumes are strongly correlated to body-plethysmography lung volumes, and especially for RV, more accurate when using spirometry-gating.

Comparison of lung volumes measured with computed tomography and whole-body plethysmography – a systematic review

“…Seven articles provided absolute measurements of RV [ 7–13 ] ( Table 3 ). The mean difference between p-RV and CT-RV was −603 mL (maximum: −1060 mL, minimum: −290 mL), and the average percent deviation was −17.8% (maximum: −39.1%, minimum: −6.0%).…”

Size-matching in lung transplantation by computed tomography for end-stage interstitial disease: a retrospective analysis

“…Moreover, the volumes measured by CT volumetry and plethysmography may differ because of the way CT acquisition was made. In our hospital, patients are breath-hold-coached by a standard voice recording during CT acquisition, but it has been shown in a study in severe chronic obstructive pneumopathy disease patients with emphysema that spirometry gating in CT helps to improve agreement with body plethysmography results ( 32 ). Indeed, in the study by Bakker et al , the mean ± SD CT-derived TLC was 280±340 mL lower compared to body plethysmography in the gated group (n=100), and 590±430 mL lower for the non-gated group (n=100) (both P<0.001) ( 32 ).…”

Recent advances in bronchoscopic lung volume reduction for severe COPD patients

“…Advances also have been made on substituting pulmonary function testing with the HRCT. Bakker et al [11] compared, in a retrospective single-centre study, RVs derived from spirometry-gated CT with body plethysmography. They demonstrated a high correlation between these two methods.…”