thanks very much for the reply!!

in answer to your question, i found the information from Pryor and Prasad, 2008, Physiotherapy For Respiratory and Cardiac Problems.

However Pryor references 'Macklem PT 1974. Physiology of Cough. Transactions of the American Broncho-Esophalogical Association 150-157'
Which i cannot get my hands on.

Hope that helps
thanks again for your reply, as now it does actually make sense to me!!
Need to wait a while before practice on real patients though