title: Methods for identifying respiratory oscillations disclose altitude effects.
abstract: The respiration of 16 supine subjects was monitored at sea level and at an altitude of 3,050 m. Breath shape was defined by inspiratory and expiratory durations [TI, TE] and volumes  [VI, VE], total breath duration [Tt], and ventilation [.VE(=VE/Tt)]. Dynamic breath pattern analysis revealed that the chronological sequences of these variables often display large sustained oscillations. Depending on their relative phase the simultaneous oscillations in VE and Tt are "compensating" or "reinforcing." The first typifies the traditional view that breath-to-breath changes in VE and Tt oscillate in phase, i.e., deeper breaths are longer thereby reducing ventilatory fluctuations. For the reinforcing oscillations breath-to-breath changes in VE and Tt oscillate out-of-phase, i.e., deeper breaths tend to be shorter, thereby enhancing ventilatory fluctuations. The observed amplitudes of the reinforced .VE oscillations are as large as 75% of the mean .VE level. In five subjects strong reinforcing oscillations with characteristic period of 20.6 +/- 3.5 (SD) s accompanied high-altitude exposure (most prominently after acclimatization) and did not appear to be a function of acid-base balance.
mesh_terms: D000531:Altitude; D006801:Humans; D008168:Lung / Q000502:physiology; D008433:Mathematics; D008722:Methods; D011187:Posture; D012119:Respiration; D013990:Tidal Volume; D013997:Time Factors; D014939:Work of Breathing