Use a producer/consumer loop pattern. Put the logic for acquiring the data (which you didn't show here) in the producer loop, and analysis and data saving in the consumer loop.
The downside though is that your queue will grow without bounds. How long does this test need to run for? (hint: "forever" is not an option...)
Mike...
PS: Also get rid of the save measurement express VI. That routine in a loop is inherently inefficient because each time it executes it opens the file, writes to it and then closes it back up. Open the file once outside the consumer loop, write to it as needed in the loop, and then close it when the program stops. This change might allow the consumer loop to keep up with the producer.