Aims: Objectives During acute bronchial obstruction, the work of breathing increases, while a reduction in perfusion of respiratory muscles due to hyperinflation and/or mechanical constraints may impair the contraction. To test this hypothesis, tissue oxygenation of intercostal muscles was assessed by NIRS in healthy subjects breathing freely or against an expiratory load (EL).Methods: 11 active men (23 ± 2 years) were included in the study. Subjects breathed freely for 5 min in unloaded condition (Ctrl) then for 20 min through a positive EL of 20 cmH2O (Threshold PEP, Respironics). Tissue saturation index (TSI) of intercostal muscle and the changes in concentration of oxy, deoxy and total haemoglobin [O2Hb], [HHb] and [tHb] were measured in the 7th intercostal space by NIRS (Oxymon Mk III, Artinis). Ventilation (VE), O2 uptake and CO2 production (VCO2), (Metamax, Cortex), dyspnea (Borg scale) and pulmonary volumes and capacities (Hyp’Air, Medisoft) were also measured.Results: Tidal volume and VE increased during EL (ptextless0.001) while breathing frequency was decreased (ptextless0.05). Ti, Ttot, Ti/Ttot and Vt/Te were greater with EL and dyspnea occurred. [tHb] and [O2Hb] were decreased as compared to Ctrl (-5.16 µmol and -3.54 µmol, ptextless0.05), [HHb] did not change. TSI was 68 ± 8 % during Ctrl and did not change with EL. RER increased as well as VE/VCO2 (+14.6, ptextless0.001); conversely PetCO2 significantly decreased.Conclusions: Tissue saturation index and [O2Hb] were not significantly altered by EL, whereas [tHb] was reduced. Despite this reduction in Hb muscle concentration, the oxygen availability in the intercostal muscles did not seem to be reduced during an acute airway obstruction suggesting an adaptation of blood flow to EL.FootnotesCite this article as: European Respiratory Journal 2018 52: Suppl. 62, PA3359.This is an ERS International Congress abstract. No full-text version is available. Further material to accompany this abstract may be available at www.ers-education.org (ERS member access only).