Changes in dying patients first occur in the kidneys and liver, said William M. Lamers Jr., who co-founded the nation's second hospice during the early 1970s.

Eventually, the kidneys become damaged until they no longer can do their job: to remove toxins from the body. As toxins build up in the system, blood pressure drops and other organs such as the heart and lungs also begin to fail.

``It's sort of like a cascade ... one system after another goes,'' Lamers said.

Supplying artificial nutrition won't restore kidneys that have shut down, he said.

Wednesday afternoon marked the start of the 13th day after Schiavo's feeding tube was removed.

Lamers, who lives in California, said he couldn't speculate on her condition or how close she might be to death because there were too many variables.

The length of survival after a feeding tube is removed involves such factors as the patient's amount of fatty tissue and muscle tissue, Lamers said. The body consumes those tissues as fuel in lieu of food and water.

Jay Carpenter, a Clearwater internist who spoke on behalf of Schiavo's parents, said there is no way to tell whether Schiavo's organs are beyond help. He said he knows of no studies that show how a person without food and water for two weeks would react to rehydration.

``I heard this morning that a doctor made a statement that it would be futile or even harmful to rehydrate Terri at this point,'' Carpenter said Wednesday. ``That [statement] is irresponsible.''

Carpenter said he has not examined Schiavo for three years but has spoken to her parents about their observations.

Reporter Thomas W. Krause contributed to this report.