Impact of moderate altitude on lung diseases and risk of high altitude illnesses.

A large world population resides at moderate altitudes. In the Valley of Mexico (2240 m above sea level) and for patients with respiratory diseases implies more hypoxemia and clinical deterioration, unless supplementary oxygen is prescribed or patients move to sea level. A group of individuals residing at 2500 or more meters above sea level may develop acute or chronic mountain disease but those conditions may develop at moderate altitudes although less frequently and in predisposed individuals. In the valley of México, at 2200 m above sea level, re-entry pulmonary edema has been reported. The frequency of other altituderelated diseases at moderate altitude, described in skiing resorts, remains to be known in visitors to Mexico City and other cities at similar or higher altitudes. Residents of moderate altitudes inhale deeply the city's air with all pollutants and require more often supplementary oxygen.