what's the difference in arterial bp [systolic] in patient 2498 measured at 2104-08-29 07:00:00 compared to the value measured at 2104-08-29 06:00:00?
select ( 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 = 2498 ) ) and chartevents.itemid in ( select d_items.itemid from d_items where d_items.label = 'arterial bp [systolic]' and d_items.linksto = 'chartevents' ) and chartevents.charttime = '2104-08-29 07:00:00' ) - ( 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 = 2498 ) ) and chartevents.itemid in ( select d_items.itemid from d_items where d_items.label = 'arterial bp [systolic]' and d_items.linksto = 'chartevents' ) and chartevents.charttime = '2104-08-29 06:00:00' )