Could be perhaps that it's just a general fitness issue? I do a lot of swimming and find it works wonders for bolstering one's lung function. Being one of those filthy smokers (quiet at the back please) I was very aware of the massive improvement when I got fit and active again.
That test down at Gatwick is a bugger though. I didn't understand what it was I was actually doing when I took it, felt like I'd belted out too much in the initial blast and had nothing left to keep going with. As it turned out I could have got away with blowing substantially less on the initial blast. Started to make a little more sense when I skimmed back through the ATPL HPL book; seems to be a combined test of peak-flow, tidal and residual lung capacity, or err, something like that.