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Systemic oxygen extraction during exercise at high altitude

2014; Elsevier BV; Volume: 114; Issue: 4 Linguagem: Inglês

10.1093/bja/aeu404

1471-6771

Daniel Martín, Alexandra Cobb, Paula Meale, Kay Mitchell, Mark Edsell, Michael G. Mythen, Michael P. W. Grocott, Tom Adams, Lindsay Biseker, Adam Booth, Oliver Burdall, Alexandra Cobb, Andrew F. Cumpstey, Steve Dauncey, Mark Edsell, James Farrant, Martin Feelisch, Bernadette Fernandez, Oliver Firth, Edward M. Gilbert, Daniel Grant, Michael P. W. Grocott, Phil Hennis, Laura Jackson, Will Jenner, Jildou van der Kaaij, Maryam Khosravi, Edith Kortekaas, Denny Levett, Zeyn Mahomed, Daniel Martín, Paula Meale, Jim Milledge, Kay Mitchell, Damian J. Mole, Oliver Moses, Michael G. Mythen, Fabio Rigat, Alasdair F. O’Doherty, Alex P. Salam, M. E. Sanborn, Adam Sheperdigian, Fiona Shrubb, Jo Simpson, Nick P. Talbot, Liesel Wandrag, Savini Wijesingha, Wilby Williamson, Tom Woolley, Heng Yow,

Cardiovascular and exercise physiology

Classic teaching suggests that diminished availability of oxygen leads to increased tissue oxygen extraction yet evidence to support this notion in the context of hypoxaemia, as opposed to anaemia or cardiac failure, is limited.At 75 m above sea level, and after 7-8 days of acclimatization to 4559 m, systemic oxygen extraction [C(a-v)O2] was calculated in five participants at rest and at peak exercise. Absolute [C(a-v)O2] was calculated by subtracting central venous oxygen content (CcvO2) from arterial oxygen content [Formula: see text] in blood sampled from central venous and peripheral arterial catheters, respectively. Oxygen uptake [Formula: see text] was determined from expired gas analysis during exercise.Ascent to altitude resulted in significant hypoxaemia; median (range) [Formula: see text] 87.1 (82.5-90.7)% and [Formula: see text] 6.6 (5.7-6.8) kPa. While absolute C(a-v)O2 was reduced at maximum exercise at 4559 m [83.9 (67.5-120.9) ml litre(-1) vs 99.6 (88.0-151.3) ml litre(-1) at 75 m, P=0.043], there was no change in oxygen extraction ratio (OER) [C(a-v)O2/CaO2] between the two altitudes [0.52 (0.48-0.71) at 4559 m and 0.53 (0.49-0.73) at 75 m, P=0.500]. Comparison of C(a-v)O2 at peak [Formula: see text] at 4559 m and the equivalent [Formula: see text] at sea level for each participant also revealed no significant difference [83.9 (67.5-120.9) ml litre(1) vs 81.2 (73.0-120.7) ml litre(-1), respectively, P=0.225].In acclimatized individuals at 4559 m, there was a decline in maximum absolute C(a-v)O2 during exercise but no alteration in OER calculated using central venous oxygen measurements. This suggests that oxygen extraction may have become limited after exposure to 7-8 days of hypoxaemia.