Below is part of what I recently sent in a letter:

Biology shows that during life there is metabolism manifesting the interdependence of cells, tissues, organs and systems to maintain the unity of the soul and body. Life is the substantial fact of the unity of the soul and body. No one organ is in charge of the rest of the body. The initiation of the beating of the heart is intrinsic to the heart, When the heart stops
beating, the rest of the body begins to deteriorate.

Pope John Paul II stated: "Death can mean decomposition, disintegration, a separation.  (cf. Salvifici Doloris, n.15; Gaudium et Spes, n. 18).  It occurs when the spiritual principle which ensures the unity of the individual can no longer exercise its functions in and upon the organism, whose elements left to themselves, disintegrate."

Cooling of an organ or the body while alive slows metabolism of the organ or the entire body. Such cooling can be used to protect and preserve an injured organ or the life of a person. Cooling after death can slow disintegration. Thus, contrast the cooling in the living that preserves and protects to the cooling after death that slows disintegration.  Cooling the body of a brain injured living person could save a life, but cooling the body of a dead corpse would have a totally different effect. 

Likewise, the ventilator in the living supports respiration and protects and preserves life. After death the ventilator could move air into a corpse, but there cannot be exchange of oxygen or carbon dioxide because the separation of the soul from the body has already occurred. The ventilator can support life, but when there is no life, the ventilator can do nothing.  These differences are related to someone being alive and someone being dead.

Paul Byrne