GSTM1 and chronic obstructive pulmonary disease: The overshoot in Δ oxy [Hb-Mb] and Δ SmO2 responses was more pronounced in people with COPD compared with healthy controls (p < 0.001), while the Δ deoxy [Hb-Mb] and Δ total [Hb-Mb] responses were not different between groups (p = 0.991 and p = 0.251, respectively) (Fig. 2).