<prompt> The ratio of the forced expiratory volume in the first second of exhalation FEV1 to the total forced vital capacity FVC is reduced in an asthmatic patient. What is the normal ratio of FEV1FVC in an adult male?95806550  <response>: The volume of air expired in the first second of expiration the FEV1, or forced expiratory volume in 1 second, especially when expressed as a ratio with the total amount of air expired during the FVC, is a good index of expiratory airways resistance. In normal young subjects, the FEV1FVC is greater than 0.80; that is, at least 80 of the FVC is expired in the first second. An FEV1FVC of 75 would be more likely in an older person. Patient with airway obstruction caused by asthma will have an FEV1FVC far below 0.80. Ref: Levitzky M.G. 2013. Chapter 2. Mechanics of Breathing. In M.G. Levitzky Ed, Pulmonary Physiology, 8e. 