KEITH BURGESS, 1. 2. SAMUEL J E LUCAS, 3. KELLY SHEPHARD, 1. ANDREW DAWSON, 1. MARIANNE SWART, 1. KATE N THOMAS, 3. REBEKAH A I LUCAS, 3. JOSEPH DONNELLY, 3. KAREN C PEEBLES, 3. RISHI BASNYAT, 4, 5. and PHILIP N AINSLIE, 6.
1. Peninsula Sleep Laboratory, Sydney, New South Wales, Australia; 2. Department of Medicine, University of Sydney, Sydney, New South Wales, Australia; 3. University of Otago, Dunedin, New Zealand; 4. Nepal International Clinic, Kathmandu, Nepal; 5. Banner Good Samaritan Hospital Medical Centre, Phoenix Arizona; and 6. Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagen Campus, Canada.

Abstract

Background and Methods:
Although periodic breathing during sleep at high altitude occurs almost universally,the likely mechanisms and independent effects of altitude and acclimatization have not been clearly reported. Data from 2005 demonstrated a significant relationship between decline in cerebral blood flow (CBF) at sleep onset and subsequent severity of central sleep apnoea that night. We suspected that CBF would decline during partial acclimatization. We hypothesized therefore that reductions in CBF and its reactivity would worsen periodic breathing during sleep following partial acclimatization.

Methods:
Repeated measures of awake ventilatory and CBF responsiveness, arterial blood gases during wakefulness.and overnight polysomnography at sea level, upon arrival(days 2–4), and following partial acclimatization (days 12–15) to5,050 m were made on 12 subjects.

Results:
The apnea-hypopnea index (AHI) increased from to 77  49 on days 2–4 to 116  21 on days 12–15(P  0.01). The AHI upon initial arrival was associated with marked elevations in CBF (28%, 68  11 to 87  17 cm/s; P  0.05) and its reactivity to changes in PaCO2 [90%, 2.0  0.6 to 3.8  1.5cm·s1·mm Hg1 hypercapnia and 1.9  0.4 to 4.1  0.9cm·s1·mm Hg1 for hypocapnia (P  0.05)]. Over 10 days, the increases resolved and AHI worsened. During sleep at high altitude large oscillations in mean CBF velocity (CBFv) occurred, which were 35% higher initially (peak CBFv  96 cm/s vs. peak CBFv  71cm/s) than at days 12–15.

Conclusions:
Our novel findings suggest that elevations in CBF and its reactivity to CO2 upon initial ascent to high altitude may provide a protective effect on the development of periodic breathing during sleep (likely via moderating changes in central PCO2).

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Published On: April 15th, 2013 /