TY - JOUR
T1 - Hypocapnia during hypoxic exercise and its impact on cerebral oxygenation, ventilation and maximal whole body O2 uptake
AU - Siebenmann, Christoph
AU - Sørensen, Henrik
AU - Jacobs, Robert A.
AU - Haider, Thomas
AU - Rasmussen, Peter
AU - Lundby, Carsten
PY - 2013/1/5
Y1 - 2013/1/5
N2 - With hypoxic exposure ventilation is elevated through the hypoxic ventilatory response. We tested the hypothesis that the resulting hypocapnia reduces maximal exercise capacity by decreasing (i) cerebral blood flow and oxygenation and (ii) the ventilatory drive.Eight subjects performed two incremental exercise tests at 3454m altitude in a blinded manner. In one trial end-tidal PCO2 (PETCO2) was clamped to 40mmHg by CO2-supplementation. Mean blood flow velocity in the middle cerebral artery (MCAvmean) was determined by trans-cranial Doppler sonography and cerebral oxygenation by near infra-red spectroscopy.Without CO2-supplementation, PETCO2 decreased to 30±3mmHg (P<0.0001 vs isocapnic trial). Although CO2-supplementation increased MCAvmean by 17±14% (P<0.0001) and attenuated the decrease in cerebral oxygenation (-4.7±0.9% vs -5.4±0.9%; P=0.002) this did not affect maximal O2-uptake. Clamping PETCO2 increased ventilation during submaximal but not during maximal exercise (P=0.99).We conclude that although hypocapnia promotes a decrease in MCAvmean and cerebral oxygenation, this does not limit maximal O2-uptake. Furthermore, hypocapnia does not restrict ventilation during maximal hypoxic exercise.
AB - With hypoxic exposure ventilation is elevated through the hypoxic ventilatory response. We tested the hypothesis that the resulting hypocapnia reduces maximal exercise capacity by decreasing (i) cerebral blood flow and oxygenation and (ii) the ventilatory drive.Eight subjects performed two incremental exercise tests at 3454m altitude in a blinded manner. In one trial end-tidal PCO2 (PETCO2) was clamped to 40mmHg by CO2-supplementation. Mean blood flow velocity in the middle cerebral artery (MCAvmean) was determined by trans-cranial Doppler sonography and cerebral oxygenation by near infra-red spectroscopy.Without CO2-supplementation, PETCO2 decreased to 30±3mmHg (P<0.0001 vs isocapnic trial). Although CO2-supplementation increased MCAvmean by 17±14% (P<0.0001) and attenuated the decrease in cerebral oxygenation (-4.7±0.9% vs -5.4±0.9%; P=0.002) this did not affect maximal O2-uptake. Clamping PETCO2 increased ventilation during submaximal but not during maximal exercise (P=0.99).We conclude that although hypocapnia promotes a decrease in MCAvmean and cerebral oxygenation, this does not limit maximal O2-uptake. Furthermore, hypocapnia does not restrict ventilation during maximal hypoxic exercise.
KW - Altitude
KW - Central fatigue
KW - Hypoxic ventilatory response
KW - NIRS
KW - Respiratory muscle fatigue
KW - Ventilatory limitation
UR - http://www.scopus.com/inward/record.url?scp=84871925662&partnerID=8YFLogxK
U2 - 10.1016/j.resp.2012.08.012
DO - 10.1016/j.resp.2012.08.012
M3 - Journal article
C2 - 22922610
AN - SCOPUS:84871925662
SN - 1569-9048
VL - 185
SP - 461
EP - 467
JO - Respiratory Physiology and Neurobiology
JF - Respiratory Physiology and Neurobiology
IS - 2
ER -