Isometric growth of lungs and airways in healthy individuals
We now consider the data collected in about 700 pupils of secondary schools, who were investigated at 6 month intervals for up to 7 years. The great majority never experienced respiratory symptoms. Lung disease during the study was quite rare. A number of adolescents, however, had experienced respiratory symptoms before the age of 6 year; the nature of the underlying disorder could only rarely be elucidated retrospectively.
As in the children with asthma there was no difference in the growth rate judged by k in the equation MEF = a·Vk. There was, however, a conspicuous difference in the level of MEF (represented by 'a' in the equation). This is shown here by displaying FEV1 as a percentage of the total lung capacity. The FEV1 is the volume forcibly exhaled in one second, in fact a time averaged flow that is to some extent comparable to MEF. The FEV1 is the index used most frequently to assess airway obstruction.
- The lung development of all 3 groups of boys and girls occurs in parallel, indicating that the growth pattern the same.
- The level of forced expiratory flow in adolescents who had respiratory episodes in early childhood is somewhat lower than in those who did not.
- The level of forced expiratory flow is even lower in those adolescents who experienced respiratory symptoms (usually transient and quite mild) during the study.
- At the start of adolescence girls on average generated higher forced expiratory flows than boys, but they lost this advantage during further development.