My dad has emphysema and uses 6 lpm on constant flow. He is a mouth breather and does better on constant flow. He has an Inogen G3 (pulse flow) but it's quite heavy for him to cart around. He would like to be more mobile and is looking for ANY portable, constant flow portable oxygen solutions that may be lighter than the Inogen G3 (would need 6 lpm). Can anyone recommend any makes/models/solutions for a lighter portable? What about a liquid oxygen solution - is that better / lighter so he can be more mobile / do more errands? Does anyone have any specific recommendations on manufacturer or model? Thank you all!