Our doctors diagnosed my son with amyotrophic lateral sclerosis and recommended a ventilator. I was wondering if we may need to go for a ventilator like the Trilogy 100 or if a BiPAP with S/T might do. Is there a major difference? How is a BiPAP different from a ventilator? AFAIK, a Trilogy machine costs much more than a BiPAP. Why is it so?