instruction: when was the first time the respiration for patient 016-18575 was less than 35.0 today?
response: SELECT vitalperiodic.observationtime FROM vitalperiodic WHERE vitalperiodic.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '016-18575')) AND vitalperiodic.respiration < 35.0 AND NOT vitalperiodic.respiration IS NULL AND DATETIME(vitalperiodic.observationtime, 'start of day') = DATETIME(CURRENT_TIME(), 'start of day', '-0 day') ORDER BY vitalperiodic.observationtime LIMIT 1