Breathing variability during wakefulness and NREM sleep in humans

Natarajan Rajagopalan, R. D. Hubmayr, P. M. Simon

Research output: Contribution to journalArticlepeer-review


Introduction: Breath-to-breath variability in humans during wakefulness and NREM sleep has been studied using flow measurements obtained while breathing through a mask connected to a pneumotachograph or using volume measurements obtained by breathing unencumbered with a respiratory inductance plethysmograph (respitrace) in place. Varying results among previous studies may be explained by instrumentation-induced changes in breathing pattern, respitrace measurement inaccuracies due to posture changes during sleep, or short recording periods. Purpose: We examined ventilation changes and breathing pattern variability in normal humans during wakefulness, stage II, and stage III-IV sleep without instrumentation using a specially constructed recumbent body plethysmograph. Our recording period during both wakefulness and NREM sleep (30 minutes each) was also extended beyond that reported in previous studies. Methods: Four subjects (mean age 29 yrs, range 18-35) underwent an overnight sleep study after a previous night of sleep deprivation. Breath-by-breath measurements of tidal volume (VT), total respiratory cycle duration (TTOT), inspiratory (TI) and expiratory (TE) duration, mean inspiratory flow (VT/TI), and minute ventilation (VE) were obtained from our LabVIEW-based computerized acquisition-analysis system. We calculated mean values of VT, TTOT, TI, TE, and VT/TI for wakefulness and sleep stages II and III-IV. We examined breath-to-breath variability by calculating the coefficient of variation. Results: During NREM sleep, time spent in stage II was 40% and in stage III-IV was 60%. The mean VT was 448±75cc during wakefulness, 408±65cc during stage II, and 400±85cc during stage HI-IV; mean coefficient of variation for VT was 29%, 34%, and 16%, respectively. The mean TTOT was 3.99±0.28sec during wakefulness compared with 4.39±0.17sec during stage II and 4.26±0.37sec during stage III-IV. The mean coefficient of variation for TTOT was 21%, 13%, and 7% respectively. During wakefulness, mean VE was 6840±1148cc, which decreased to 5593±635cc during stage II and to 5878±699cc during stage III-IV. No other systematic changes in other variables (TI, TE, TI/TTOT, and VT/TI) were noted. Conclusions: We conclude that VT and VE fall and TTOT increases (i.e., frequency decreases) during NREM sleep compared with wakefulness. There is a greater variability in VT than in TTOT during both wakefulness and sleep. Variability in oreathing during NREM sleep is greater during stage II than stage III-IV. Clinical Implications: We have described a new non-invasive device to more accurately measure breathing during sleep.

Original languageEnglish (US)
Pages (from-to)199S
Issue number4 SUPPL.
StatePublished - Oct 1996

ASJC Scopus subject areas

  • Pulmonary and Respiratory Medicine
  • Critical Care and Intensive Care Medicine
  • Cardiology and Cardiovascular Medicine


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