Strength and Cycle Time of Ventilatory Oscillations in Unacclimatized Humans at High Altitude

Respiration was monitored with magnetometers in 12 healthy supine young adults at sea level, and in an altitude chamber at simulated high altitudes ooof 8,000, 9,000, 11,000 and 14,000 feet. Periodic breathing which was strong enough to include apnea at the time of minimum ventilation was seen in all subjects at high altitude. The cycle time of periodic breathing ranged from 12 to 34 seconds. On average across the population the incidence of periodic breathing increased with altitude. The cycle time of the periodic pattern increased as the strength of the pattern increased. After normalizing to a standard pattern strength, cycle time decreased as altitude increased. The study was repeated 3 weeks later on 7 of the subjects. The standard cycle time at 14,000 feet of each subject in the second series was the same as in the first series to within, on the average, 6%. Each subject studied at 11,000 feet in both series reproduced his cycle time to within, on the average, 9%. The variation of standard cycle time for a given subject is less than the variation across the population, indicating characteristic cycle times for some individuals (one-way ANOVA, P less than 0.025).