I can't speak to Dr. Gilmartin himself, but being a doctor doesn't make you an engineer capable of evaluating a complex medical device. My pulmonogolist is a good doctor and understands how to best configure my own CPAP for my health. He really has little idea how the thing actually works.
Gilmartin doesn't need to know the engineering principles involved, just that it provides the claimed the medicinal benefits. As a doctor that's exactly what he's qualified to assess. Besides, he's a doctor at Havard, there'll be some very qualified engineers around to assess that side of things.