instruction: how much does patient 25668's patient's heart rate change measured at 2100-07-31 16:00:00 compared to the value measured at 2100-07-31 15:00:00?
response: 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 = 25668)) AND chartevents.itemid IN (SELECT d_items.itemid FROM d_items WHERE d_items.label = 'heart rate' AND d_items.linksto = 'chartevents') AND chartevents.charttime = '2100-07-31 16:00:00') - (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 = 25668)) AND chartevents.itemid IN (SELECT d_items.itemid FROM d_items WHERE d_items.label = 'heart rate' AND d_items.linksto = 'chartevents') AND chartevents.charttime = '2100-07-31 15:00:00')