First post!
Just some replies to some of the things I've read on here if I may, from someone who works with respiratory disease every day, and with an interest in aviation medicine (which is why i came here in the first place...)
The Powerbreathe will not increase your lung function dramatically, they are useful for those under physiotherapists because their respiratory muscles have wasted due to disease. Put simply, this is because the majority of the lung function values we look at such as PEF (Peak Expiratory Flow) and FEV1 (Forced Expiratory Volume in 1 second) to diagnose airway obstruction are not down to respiratory muscle strength, but a function of the air-carrying capacity of your airways, which stands to reason will be lower if they are narrower, such as in an asthma patient. If your airways are narrowed and your numbers reduced, no matter how hard you are able to blow you will always get the same numbers because there is a maximum rate at which air can travel through a small tube . This can only be increased by increasing the diameter of the airway by reducing long-standing inflammation (brown inhaler) and reducing muscle constriction by way of medication (blue inhaler)
To billabongbill: Even if your lung function values are reduced, you may be what we refer to as a 'normal variant'. Everybody has predicted values based on age and height, but that number will be within a normal range that depends on which guidelines you read. Occasionally we will see patients that are outside the normal range, both high and low; it just means that their lungs are smaller/larger than average, but that those lungs are working properly. Your specialist took a look at your full results and came to that correct conclusion, passing that on to the relevant authorities who should pass you fit. 'Passing' has no technique apart from blow as hard as you possibly can! People (mainly people with a little bit of knowledge of lung function) become too fixated on the patient's 'normal' peak flow readings and forget that there is a large variant in the population that have the same age and height as you!
For those who get wheezy on cold days and when exposed to dust, I find that a lot of my patients who report this have PEF and FEV1 within normal ranges and would pass any medical on these numbers alone. These patients require 'provocation tests' like running around the car park! It's an excellent test, especially on a cold day, although treadmill running indoors will give you a similar effect. Exercise induced-asthma is categorised by a fall in FEV1 of 15% after 6 minutes running. If you have an allergic type asthma we can induce airway constriction with chemicals such as methacoline or histamine - the amount needed to drop FEV1 by 20% will categorise the severity of your illness.
Regarding asthmatics taking inhalers to 'pass the test': if the person doing the test is only looking at PEF and FEV1 then it may work, but if they are experienced and look at other things on the test then they will still see that you have distinct characteristics on your results and flag it up regardless of recent ventolin use - I can spot a controlled asthmatic a mile off. I always ask that patients don't use any inhalers prior to testing, because it then allows me to perform a 'reversibility' assessment, ie how much the inhalers can reverse the airflow limitation, and whether their treatment is optimal.
Sorry for the long post - If anyone has any specific questions please ask away.