Conflict of interest statement: Peninsula Health Care Pty Ltd provided funding to finance the travel expenses of three technicians and part purchase of equipment.
The effect of partial acclimatization to high altitude on loop gain and central sleep apnoea severity
Article first published online: 25 JUN 2012
© 2012 The Authors. Respirology © 2012 Asian Pacific Society of Respirology
Volume 17, Issue 5, pages 835–840, July 2012
How to Cite
ANDREWS, G., AINSLIE, P. N., SHEPHERD, K., DAWSON, A., SWART, M., LUCAS, S. and BURGESS, K. R. (2012), The effect of partial acclimatization to high altitude on loop gain and central sleep apnoea severity. Respirology, 17: 835–840. doi: 10.1111/j.1440-1843.2012.02170.x
- Issue published online: 25 JUN 2012
- Article first published online: 25 JUN 2012
- Accepted manuscript online: 20 MAR 2012 03:06AM EST
- Received 22 November 2011; invited to revise 12 December 2011, 28 December 2011; revised 19 December 2011, 11 January 2012; accepted 13 January 2012 (Associate Editor: David Hui).
- central sleep apnoea;
- high altitude;
- loop gain;
- partial arterial carbon dioxide concentration;
Background and objective: Loop gain is an engineering term that predicts the stability of a feedback control system, such as the control of breathing. Based on earlier studies at lower altitudes, it was hypothesized that acclimatization to high altitude would lead to a reduction in loop gain and thus central sleep apnoea (CSA) severity.
Methods: This study used exposure to very high altitude to induce CSA in healthy subjects to investigate the effect of partial acclimatization on loop gain and CSA severity. Measurements were made on 12 subjects (age 30 ± 10 years, body mass index 22.8 ± 1.9, eight males, four females) at an altitude of 5050 m over a 2-week period upon initial arrival (days 2–4) and following partial acclimatization (days 12–14). Sleep was studied by full polysomnography, and resting arterial blood gases were measured. Loop gain was measured by the ‘duty cycle’ method (duration of hyperpnoea/cycle length).
Results: Partial acclimatization to high-altitude exposure was associated with both an increase in loop gain (duty cycle fell from 0.60 ± 0.05 to 0.55 ± 0.06 (P = 0.03)) and severity of CSA (apnoea-hypopnoea index increased from 76.8 ± 48.8 to 115.9 ± 20.2 (P = 0.01)), while partial arterial carbon dioxide concentration fell from 29 ± 3 to 26 ± 2 (P = 0.01).
Conclusions: Contrary to the results at lower altitudes, at high-altitude loop gain and severity of CSA increased.