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Normal breathing during sleep at an altitude of 2240 meters
Rafael J Hernández-Zenteno1, Rogelio Pérez-Padilla, Juan Carlos Vázquez
1Departamento de Fisiología Pulmonar y Laboratorio de Sueño, Instituto Nacional de Enfermedades Respiratorios (INER), Secretaría de Salud (SSA), Mexico City, Mexico.
Background:
Mexico City is located at an altitude of 2240 meters (m) above sea level with a mean barometric pressure of 585 mmHg. Normal PaO2 and PaCO2 values in young subjects are 67 and 31 mmHg, respectively. Sleep desaturation, present in normal subjects at sea level, may be more frequent and severe at moderate altitudes. Our objective was to describe breathing during sleep in normal residents at an altitude of 2240 m above sea level.
Methods:
Non-obese, long-term residents of Mexico City with normal pulmonary function and without sleep-related symptoms completed a nocturnal polysomnogram.
Results:
A total of 23 subjects (12 males and 11 females) were studied. Mean age was 45 years (range 20-76 years). Seven subjects (four >60 years of age) presented sleep-disordered breathing (SDB) with apnea-hypopnea index >or=5 h(-1). Mean SaO2 during sleep was 93 +/- 2% and in all subjects was >or=90%. Five subjects without SDB monitored for PO2 tc maintained values of PO2 tc <60 mmHg during one half of the night. During sleep, mean PCO2et was 35 +/- 3 mmHg, breathing frequency 16 +/- 3, and heart rate 65 +/- 9. These values were maintained throughout sleep stages.
Conclusions:
Normal long-term residents of Mexico City had slightly lower mean oxygen saturation than that at sea level but >or=90% saturation and experienced transient desaturations. Breathing frequency and heart rate were similar to residents at sea level.