FVC deterioration, airway obstruction determination, and life span in Ataxia telangiectasia

Rationale: Forced vital capacity (FVC) values decrease with progress of the disease in Ataxia telangiectasia (AT). Objective: To study the effect of this process on airway obstruction determination and life span in AT. Methods: Clinical data and yearly best spirometry maneuvers were collected retrospectively from 37 AT patients (196 spirometry tests) during 5.4 +/- 1.8yrs (initial age 4-21 y). Twelve patients were walking (7 of them had recurrent respiratory system infections); 25 subjects were confined to wheelchair, of them 8 patients were towards end-stage lung disease. Spirometry indices included Forced Vital Capacity (FVC), mid-expiratory-flow (FEF25-75), and tidal volume (VT). We calculated FEF25-75/FVC and VT/FVC ratios. Results: FVC declined from 67 +/- 8 while walking to 19 +/- 6 % predicted values. FEF25-75 values that were elevated (116 +/- 23 % predicted) while walking, decreased to 69 +/- 27 % predicted at end-stage where 7 patients responded to bronchodilators. VT/FVC ratio was 0.25 +/- 0.06 while walking, increased to 0.35 once on wheelchairs, and further increased to 0.57 +/- 0.19 at end-stage disease. FEF25-75/FVC ratio was 2.54 +/- 0.70 above normal (similar to 1.0) increasing to 4.16 +/- 0.75 at end stage. A sharp elevation was seen in FEF25-75/FVC ratio when FEV1 was still similar to 45 % predicted and 2-years prior to death. Conclusions: Having a low baseline-FVC (60% predicted) artificially raises FEF25-75 values, so FEF25-75 of "mild obstruction" values may indicate severe airway obstruction in AT subjects. VT/FVC and FEF25-75/FVC ratios may therefore assist in revealing higher than normal breathing effort. The results further suggest adding VT/FVC and FEF25-75/FVC ratios to pulmonary function assessments in patients with AT. (C) 2015 Elsevier Ltd. All rights reserved.