Cerebrovascular CO₂ responsiveness (CCR) in relation to normocapnic cerebral blood flow velocity (V_mean) and hematocrit (Ht). Both in SCD patients (●; n = 23) and healthy controls (Δ; n = 16), CCR was not related to either (A) V_mean (r_s = 0.07, P =.8 and r_s = −0.05, P = .9 respectively) or (B) hematocrit (r_s = −0.18, P = .4 and r_s = 0.07, P = .8 respectively).