Hello Marc,
You can allways use global variables to access data from outside the procedure that is running actually, but in my point of view you should avoid to do it, not only for memory purposes, but mainly because then your code will be much harder to understand.
If I understoood your application, you have a loop acquiring data and you want to process it. You can either make a subvi with the processing and place it inside the acquisition loop, or use some kind of data transfer to outside, like queues or even user event structures, there are some examples on how to use these in LabVIEW and on the Web.
Is you see the attached file (an example from LabVIEW), inside the look they are making the acquisition and afterwords writing to the file inside the loop.
Hope it helps,
Paulo