"Some people in a coma shift to a persistent vegetative state, in which breathing, maintaining normal blood pressure, digesting and eliminating foods continues without the patient's awareness. The vegetative state can last for years or decades." — The Tole Acupuncture & Herbal Medical Centre Sdn Bhd.
Individuals in Persistent Vegetative State (PVS) are seldom on any life-sustaining equipment because the brainstem, the center of physiological functions such as heartbeat, respiration, and gastrointestinal activity, is relatively intact.
Vegetative State vs. Coma: What's the Difference? (Uploaded by 2009PSYC352 on 28 April 2009)
Apallic syndrome, also known as Persistent Vegetative State (PVS), is a condition of patients with severe brain damage who were in a coma but progressed to a wakeful unconscious state, rather than true awareness. The person can still respond to stimulation in varying degrees, as compared to a person in a coma who cannot. After 4 weeks in a Vegetative State (VS), the patient is classified as in a "Persistent Vegetative State". This diagnosis is classified as a "Permanent Vegetative State" (PVS) after approx. one year of being in a Persistent Vegetative State.
2.Causes of apallic syndrome: There are 3 different causes of Permanent Vegetative State (PVS): 
brain injuries, which may be either acute and traumatic, or non-traumatic;
degenerative and metabolic brain disorders; and
severe congenital abnormalities of the central nervous system.
3.Symptoms of apallic syndrome:
Permanent Vegetative State (PVS) patients often open their eyes in response to feeding, which has to be done by others. They are capable of swallowing, whereas patients in a coma subsist with their eyes closed.
PVS patients' eyes may be in a relatively fixed position, or may track moving objects, or move in a completely unsynchronized manner. They may experience sleep-wake cycles, or be in a state of chronic wakefulness.
PVS patients may also exhibit some behaviors that can be construed as arising from partial consciousness, such as grinding their teeth, swallowing, smiling, shedding tears, grunting, moaning, or screaming without any apparent external stimulus.
4.Treatment of apallic syndrome: Individuals in Persistent Vegetative State (PVS) are seldom on any life-sustaining equipment, other than a feeding tube, because the brainstem, the center of physiological functions such as heartbeat, respiration, and gastrointestinal activity, is relatively intact. As opposed to brain death, PVS is not recognized by statute as death in any legal system. In the United States and the United Kingdom, courts have required petitions before termination of life support that demonstrate that any recovery of cognitive functions above a vegetative state is assessed as impossible by authoritative medical opinion.
5.Michael Schumacher, the Formula One legend, who had an accident, while skiing in the French Alps on 29 December 2013, could remain in a "persistent vegetative state" for the rest of his life, even if he wakes up from his coma. He was placed into an artificially-induced coma at the University Hospital in Grenoble, a city in southeastern France, shortly after the crash, to help his brain heal. Such measures, however, normally last only a maximum of 2 weeks. This means that if doctors do bring him out of his artificially-induced coma, he would be unable to speak, move, or feed himself, meaning that his condition would hardly be different from his medically-induced coma. The chance of recovery from Apallic syndrome are far below 50%.