Proximate cause is that which, in a natural and continuing sequence, produces the disability.
However, natural progression of a disease while a person is working does not constitute cause or aggravation. For conditions of employment to bring about aggravation of any underlying disease, the employment factors must be capable of aggravating or accelerating the disease. There is a continuing and irreversible change in the underlying condition, thus adversely altering the course of the condition or disease process. A logical explanation for the physician's underlying opinions, fundamental reasons and beliefs concerning causal relationship. That which produces the injury in a natural and continuous sequence, unbroken by an efficient and intervening cause and without which the result would not have occurred.