Heterogeneity of reduced FEV1 in early adulthood: A looking forward, looking backwards analysis.

Background: Some individuals never achieve normal peak FEV₁ in early adulthood. It is unknown if this is due to airflow limitation and/or lung restriction.

Methods: To investigate this, we: (1) looked forward in 19,791 participants in the Dutch Lifelines general population cohort aged 25-35 years with 5-year follow-up; and (2) looked backwards in 2032 participants in the Swedish BAMSE birth cohort with spirometry at 24 years of age but also at 16 and/or 8 years.

Results: (1) In Lifelines 8.5% of participants had reduced FEV₁ at 25-35 years, 68% due to Preserved Ratio Impaired Spirometry ('PRISm') and 32% to airflow limitation ('low-limited'); besides, 3.8% participants with normal FEV₁ showed airflow-limitation ('normal-limited'). Low-limited and normal-limited, but not PRISm, reported higher smoking exposures and asthma diagnosis than normal (p < 0.05). At 5-year follow-up, 91.2% of participants remained in the same group, and FEV₁ decline was similar in normal and normal-limited participants, but statistically smaller (p < 0.05) in PRISm and low-limited; (2) these observations were largely reproduced in BAMSE at 24 years of age; and, (3) in BAMSE, low-limited or PRISm individuals were already identifiable at 8-16 years of age.

Conclusion: Low peak FEV₁ in early adulthood is most often due to PRISm and results in a significant burden of respiratory symptoms. Only low-limited and normal-limited, but not PRISm, associate with a doctor diagnosis of asthma, and FEV₁ decline was statistically different in PRISm indicating a need for differentiated clinical approaches. These spirometric abnormalities can be already identified in childhood and adolescence.