Figure 3.

Correlation between change in forced expiratory volume in 1 second (FEV₁)% predicted (FEV₁pp) and either sweat chloride (SwCl) or cell-based CFTR (cystic fibrosis transmembrane conductance regulator) activation. (A–D) We compared the strength of the correlation between improved lung function (FEV₁pp) and either a change in SwCl (A and B) or a relative increase in chloride conductance in epithelial cells as measured above (C and D). (A and B) Change in SwCl correlated with change in FEV₁pp over the first week or first year of ivacaftor use (A: 1 wk r = 0.84, R² = 0.71, and P < 0.02; B: 1 yr r = 0.78, R² = 0.60, and P < 0.05). (C and D) In vitro CFTR activation, defined as vx-770/(forskolin + vx-770), correlated with short-term improvement in FEV₁pp (C: 1 wk r = 0.71, R² = 0.51, and P < 0.05; D: 1 yr r = 0.58, R² = 0.34, and P = 0.13). In both assays, participants with G551D (solid circles) versus R117H (open squares) mutations appeared to segregate by response to ivacaftor, but there was overlap in FEV₁pp change.