<qa>  What is the maximum tidal volume of MVV?Study design: healthy subjects with normal lung function will perform MVV at increasing breathing frequencies and maximal tidal volume, from 10 to 100 cycles per minute. Inspiratory capacity IC will be measured at rest and after each 12 seconds of MVV in order to detect DH. From the moment DH appeares at a given frequency, only one additional MVV at a higher breathing frequency will be conducted to confirm DH. 