EVALUATION OF THE 24-HOUR TROUGH FEV1 FOLLOWING 7 DAYS OF DOSING WITH CHF4226 2µg ONCE DAILY. A MULTICENTER, DOUBLE-BLIND, DOUBLE-DUMMY, RANDOMISED, PARALLEL GROUP, PLACEBO AND ACTIVE (FORMOTEROL 12µg B.I.D.) CONTROLLED STUDY FOLLOWED BY A 3-WEEK OPEN LABEL EXTENSION (TO EITHER CHF4226 2µg Q.D. OR FORMOTEROL 12µg B.I.D. IN A 2:1 RATIO) FOR THE EVALUATION OF SAFETY AND TOLERABILITY