mean transit time ( mtt ) , coefficient of variation ( cov ) , and index of skewness ( ios ) of transit times were measured , with the more conventional derivatives of the forced expiratory spirogram , in 178 healthy people aged 6-71 yr breathing air , and in 18 healthy adults breathing 20 % oxygen in helium ( o2he ) in addition .
C0231800
expiratory
C0035203
breathing