Acknowledgements
The authors are grateful to Respironics® for providing the devices for respiratory training.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
The first author has a grant from the “Funda o para a Ci ncia e a Tecnologia”, SFRH/BD/30714/2006. This work was supported by “Funda o para a Ci ncia e Tecnologia” -PIC/IC/82765/2007.