THU0424 Near-infrared spectroscopy during exercise and recovery in children with juvenile dermatomyositis
Authors: G.E.A. Habers, R. de Knikker, M. van Brussel, E. Hulzebos, D.F. Stegeman, A. van Royen, T. Takken
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> Children with Juvenile Dermatomyositis (JDM) suffer from diminished exercise tolerance<sup>1-5</sup>, a clinical condition that may be linked to microvascular disturbances in the muscle tissue<sup>6</sup>. Near-infrared spectroscopy (NIRS) may represent a useful tool to assess this hypothesis since it allows the in vivo examination of oxygenation and hemodynamics in muscle tissue at the microvascular level during physical exercise. <h3>Objectives</h3> NIRS was used to compare children with JDM with children in 2 control groups (clinical and healthy) in their muscle oxygenation and hemodynamics during incremental cycling exercise and recovery. <h3>Methods</h3> Eleven children with JDM, 10 children with Juvenile Idiopathic Arthritis (JIA; clinical controls), and 13 healthy children performed a maximal incremental test on a cycle ergometer. NIRS was used to measure concentration changes compared to rest of oxygenated hemoglobin (Δ[O<sub>2</sub>Hb]) and total hemoglobin (Δ[tHb]) of the vastus medialis (VM) and vastus lateralis (VL) muscle during exercise and recovery. Both signals were normalized to allow comparisons between children of the same group, as well as between groups. Of each signal, the rest value was assigned a value of 0 arbitrary units and the maximal value reached during recovery was assigned a value of 1 arbitrary unit. All values between these two time points were normalized to this scale. Normalized Δ[O<sub>2</sub>Hb] and Δ[tHb] values at unloaded cycling and at 25%, 50%, 75%, and 100% of maximal work rate (W<sub>peak</sub>) were determined as well as the half recovery times (T<sub>half</sub>) of both signals. All variables were compared between the 3 groups. <h3>Results</h3> Δ[tHb] values in the VM muscle were effected by group at work rates of 25% (p&lt;0.05; χ<sup>2</sup>(2)=6.55; η<sup>2</sup>=0.20), 50% (p=0.01; χ<sup>2</sup>(2)=9.19; η<sup>2</sup>=0.28), 75% (p&lt;0.01; χ<sup>2</sup>(2)=9.91; η<sup>2</sup>=0.30), and 100% (p&lt;0.05; χ<sup>2</sup>(2)=6.15; η<sup>2</sup>=0.19) of W<sub>peak</sub>. The concerning Δ[tHb] values were lower in children with JDM compared with healthy children at all these relative work rates (p&lt;0.01). More specifically, in healthy children, the median Δ[tHb] value was similar to baseline at a work rate of 25% of W<sub>peak</sub>, and this value increased with work rates at higher percentages of W<sub>peak</sub>, indicating an increase in blood volume with increasing exercise intensity. Conversely, in children with JDM, the median Δ[tHb] value was below baseline at a work rate of 25% of W<sub>peak</sub>, and this value remained below baseline throughout exercise. No group effects were found for Δ[tHb] in the VL muscle at all time points, Δ[O<sub>2</sub>Hb] in both muscle groups at all time points, and T<sub>half</sub> of Δ[O<sub>2</sub>Hb] and Δ[tHb] in both the VM and VL muscle. <h3>Conclusions</h3> In the current study, a difference was found between children with JDM and healthy children with respect to the change in total blood volume of the VM muscle from rest to incremental exercise. This result may suggest that children with JDM may experience difficulties in increasing muscle blood volume with more strenuous exercise. <h3>References</h3> Hicks et al. (2002). Drinkard et al. (2003). Takken et al. (2003). Takken et al. (2008). Groen et al. (2010). Grundtman et al. (2009). <h3>Disclosure of Interest</h3> None Declared