RT Journal Article SR Electronic T1 Late-breaking abstract: Time-dependent effect of acute hypoxia on brain excitability in healthy humans JF European Respiratory Journal JO Eur Respir J FD European Respiratory Society SP p4729 VO 38 IS Suppl 55 A1 Samuel Verges A1 Thomas Rupp A1 Marc Jubeau A1 Bernard Wuyam A1 Stéphane Perrey A1 Patrick Levy A1 Guillaume Millet YR 2011 UL http://erj.ersjournals.com/content/38/Suppl_55/p4729.abstract AB Some studies have shown altered cortex excitability in hypoxemic patients suffering from COPD or OSAS. Recently, contradictory results regarding the effect of hypoxia (H) on cortex excitability have been reported in healthy subjects, possibly depending on H exposure duration. We evaluated the effects of 1 and 3 hours H on motor cortex excitability, intracortical inhibition and supraspinal voluntary activation (VA) using transcranial magnetic stimulation (TMS). TMS to the quadriceps cortex area and femoral nerve electrical stimulations were performed in normoxia and H (FiO2 = 12%) in 10 healthy subjects. Motor-evoked potentials (MEPs at 50-100% maximal voluntary contraction - MVC), recruitment curves (MEPs at 30-100% maximal stimulator power output at 50% MVC), cortical silent periods (CSP) and VA were measured. One hour H did not modify any parameters of brain excitability but reduced VA probably due to the repetition of contractions 1-h apart (98±2% vs. 95±4%; p=0.01). Conversely, 3 h H significantly increased i) MEPs of the rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM) at all force levels (e.g. at 50% MVC, RF: +26±35%, VL: +15±24%, VM: +17±15%) and stimulator power outputs (e.g. at 70% maximal power, RF: +17±23%, VL: +18±37%, VM: +8±15%), and ii) CSP at all force levels (e.g. at 50% MVC, RF: +23±39%, VL: +27±31%, VM: +24±37%) (all p<0.05), but did not modify VA (98±1% vs. 97±2%; p=0.21). These data demonstrate a time-dependent H-induced increase in cortex excitability and intra-cortical inhibition, without changes in VA. The impact of these cortical changes on physical or cognitive performances needs to be elucidated to better understand the effects of hypoxemia in patients.