Accessible patio doors and overall Accessible Design are very important not only for those who are handicapped but for everyone who appreciates ease of access. Whether it is a low door threshold, a cabinet with sliding shelves or even a light switch with a paddle verses a toggle switch, simple changes in design make access easier, safer and more comfortable for all. AARP has done a great job of identifying many of these areas via a special section of their website covering Housing & Mobility.
As to your specific situation, yes, there are low-threshold, accessible patio door designs for just this purpose. Instead of the traditional sliding patio door, they are available in the more accessible hinged patio door format. For example, door manufacturer Therma-Tru makes something called a public access sill option for a hinged patio door. Instead of the standard 1-9/16-inch-high sill, the public access sill has a height of only half an inch. Moreover, the sill is sloped, making it easier to roll over with a wheelchair or baby carriage. You can check out a profile of the sill in Therma-Tru's product guide; see pages 14 and 15 for more details on this feature for accessible patio doors.