Murder or a Legitimate Medical Procedure: the Withdrawal of Artificial Nutrition & Fluids from a Patient in a Persistent Vegetative Condition

What is the historical meaning of “ordinary means” to sustain human life? And what has been the understanding for over 500 years of Catholic moral analysis of the obligation to sustain life?
Is it, as Pope John Paul II insisted in an allocution to a meeting of the Vatican’s Pontifical Academy for Life in March, 2000 that food and water must always be provided for patients in a persistent vegetative condition (PVS). Artificial nutrition and fluids, he writes, are not medical measure, but “natural” and therefor are “ordinary means” that are always morally required.”
PVS is a state of permanent unconsciousness. The record for maintaining a patient in that condition is 37 years, 111 days.