instruction: when did patient 6170's arterial bp mean first measure today?
response: SELECT chartevents.charttime FROM chartevents WHERE chartevents.icustay_id IN (SELECT icustays.icustay_id FROM icustays WHERE icustays.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 6170)) AND chartevents.itemid IN (SELECT d_items.itemid FROM d_items WHERE d_items.label = 'arterial bp mean' AND d_items.linksto = 'chartevents') AND DATETIME(chartevents.charttime, 'start of day') = DATETIME(CURRENT_TIME(), 'start of day', '-0 day') ORDER BY chartevents.charttime LIMIT 1