tokens: Maximal Expiratory Flow Rates such as Peak Expiratory Flow Rate ( PEFR ) , rates at 25 % , 50 % and 75 % of forced vital capacity ( V max 25 % , V max 50 % and V max 75 % ) and forced expiratory flow during the middle half of forced vital capacity ( FEF 25 - 75 % ) were measured in 273 healthy non - smoking adults ( 144 males , 129 females ) aged 15 - 63 years living in Madras .