what was the first arterial bp [systolic] value patient 594 had since 271 days ago?
select chartevents.valuenum 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 = 594 ) ) and chartevents.itemid in ( select d_items.itemid from d_items where d_items.label = 'arterial bp [systolic]' and d_items.linksto = 'chartevents' ) and datetime(chartevents.charttime) >= datetime(current_time,'-271 day') order by chartevents.charttime asc limit 1