Correct. My asthma is well controlled and my before and after FEV1 results were around 111 and 125% of predicted values respectively from memory. I entirely agree regarding a physiotherapist.
Merely posting my experiences and costs involved, Im sure there are cheaper/more expensive and better/worse people to do it however I found literally no 'accredited specialists' IE respiratory consultants who would/could including my local private hospital who didn't do the tests.