Alterations of forced vital capacity (FVC) and one-second forced expiratory volume (FEV1) forms part of the alterations present in chronic asthma. In an area that is aggressive for the health of the asthmatic patients as the city of Mexico for its height, air pollution, overpopulation and migratory flows, the evolution of this disease to be different to other people living in other places with characteristics less damaging their environment. We used spirometry system to study 50 patients staying more than 5 years in the Valley of Mexico
with diagnosis of moderate persistent asthma. Measurmenet made to that end of the values of FVC and FEVi in early morning without using bronchodilators and steroids systemic or topical. Statistic : Missing System. Results: 35 females and 15 males, aged between 18 and 81 years old Standard dev, in female 12.91, mean 39, Standard dev. In male: 13.44, mean 35.5. He won the following most common pattern: Bronchial Hyperreactivity+ normal spirometry 39% in females. Male sex in the peripheral moderate obstruction+ bronchial hyrresponsiveness in 33%. Conclusion: In both sexes the prevalence is the obstruction from mild, moderate and severe. Most patients had bronchial hyperreactivity.