By that standard, what class of disability do they call those people on a slab in the morgue, life-challenged? soul-deprived? Exceptionally dead?
Like the Terri starvers?
This is very important to you, isn't it?
Look at the definition of legal death, brain death, cardiac death, etc. It varies by state.
In Texas, brain death can be used for those on life support - a ventilator and/or a pacemaker. In that case, there is no function in the brain stem. The gold standard, in disputed cases, is a blood flow study of the brain stem, which should show no blood flow at all. I wouldn't be surprised if a PET scan becomes the standard in the future. In obvious cases, as in severe trauma to the head or after a stroke and when there is no drug being used that could depress the Central Nervous System, EEG's that show no brain wave activity in the brain stem could be acceptable.
In cases where a person is found pulseless and without respiration by paramedics, they are usually required to find other signs, such as a documented time since collapse, pooling of blood, severe chest trauma, etc., although that may vary by local criteria.
If you honestly can't tell the difference between dead people and living, disabled people, that's your problem, not mine.