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Forced Vital Capacity to Slow inspiratory Vital Capacity ratio: a potential marker for small airways obstruction

¹ Department of Pulmonology ² Pulmonary Function and ³ Lung transplantation, University Medical Center Groningen, University of Groningen, the Netherlands

j.cohen{at}int.umcg.nl

Abstract

BackgroundThe ratio of forced vital capacity to slow inspiratory vital capacity (FVC/SVC) has been reported to reflect small airways obstruction, but its validity as such is still unclear. The aim of this study was to assess the applicability of FVC/SVC as a marker of small airways function in Bronchiolitis Obliterans Syndrome (BOS) after lung transplantation, an example of a disorder with predominantly small airways obstruction causing progressive airflow limitation.

MethodsFVC/SVC was analyzed both cross-sectionally and longitudinally in 39 patients (26 males) with BOS after bilateral lung transplantation (median age 47 years (interquartile range 35-54)), and 36 bilateral lung transplant recipients without BOS (14 males; age 46 (41-53)).

ResultsFVC/SVC decreased significantly during follow-up in BOS stages 1 and 2, by 2.2% and 4.4 % from baseline respectively (p<0.001). This decrease was not significantly associated with the decrease in FEV₁. FVC/SVC increased, though not significantly, by 1.1% in the group not developing BOS, a significant difference from the average fall of 4.4 % in the group developing BOS.

ConclusionsSignificant, yet small decreases in FVC/SVC occur in patients who develop BOS, independent from changes in FEV₁. At a group level FVC/SVC is able to detect small airways changes. These results merit prospective studies to determine the sensitivity of FVC/SVC to quantify small airways dysfunction at an individual level and in other airway diseases.

Key Words: Small airways obstruction • Spirometry • Forced Vital Capacity • Inspiratory Vital Capacity