title: A method to correct for the influence of gas density on maximal expiratory flow rate.
abstract: Maximal expiratory flow rate (Vmax) was measured at 20, 35, 50, 65, and 80% vital capacity in 4 young healthy subjects breathing air, SF6/O2, and He/O2 mixtures. The flows of SF6/O2 and He/O2 were corrected to normal alveolar gasflow by means of only the density of the gases. The values for normal alveolar gasflow and corrected SF6/O2 flow were identical at 35% VC and larger volumes while the values for normal alveolar gasflow and corrected He/O2 flow were not. The results indicate that in young healthy subjects it is possible to correct Vmax at lung volumes above 35% VC for the changes induced by an increase in density of the gas breathed, provided viscosity is not much changed. Without correction, Vmax after O2-breathing will be underestimated by about 6%, compared with Vmax for normal alveolar gas, whereas a change in alveolar CO2 concentrations between 3 and 9% only causes a 1% decrease of Vmax.
mesh_terms: D000293:Adolescent; D000328:Adult; D000403:Airway Resistance; D002245:Carbon Dioxide / Q000378:metabolism; D003720:Densitometry; D005260:Female; D006801:Humans; D008176:Lung Volume Measurements; D008297:Male; D008448:Maximal Expiratory Flow Rate; D011650:Pulmonary Alveoli / Q000378:metabolism; D012119:Respiration; D014797:Vital Capacity
chemical_list: D002245:Carbon Dioxide