Complex sentence: Since the condemned was hanging upside-down, the brain received a continuous blood supply in spite of the severe bleeding, and thus the person being executed remained completely conscious until the saw severed the major blood vessels of the abdomen, and sometimes even longer.
Split into simpler sentences: Since the condemned was hanging upside-down, the brain received a continuous blood supply in spite of the severe bleeding. The condemned would remain completely conscious until the saw severed the major blood vessels of the abdomen, and sometimes even longer.