Arterial to end-tidal Pco2 difference during exercise in normoxia and severe acute hypoxia: importance of blood temperature correction.
Negative arterial to end-tidal pco2 differences ((a-ET)pco2) have been reported in normoxia. To determine the influence of blood temperature on (a-ET)pco2, 11 volunteers (21 ± 2 years) performed incremental exercise to exhaustion in normoxia (Nx, Pio2: 143 mmHg) and hypoxia (Hyp, Pio2: 73 mmHg), while arterial blood gases and temperature (ABT) were simultaneously measured together with end-tidal pco2 (PE tco2). After accounting for blood temperature, the (a-ET) pco2 was reduced (in absolute values) from -4.2 ± 1.6 to -1.1 ± 1.5 mmHg in normoxia and from -1.7 ± 1.6 to 0.9 ± 0.9 mmHg in hypoxia (both P < 0.05). The temperature corrected (a-ET)pco2 was linearly related with absolute and relative exercise intensity, VO2, VCO2, and respiratory rate (RR) in normoxia and hypoxia (R(2): 0.52-0.59). Exercise CO2 production and PE tco2 values were lower in hypoxia than normoxia, likely explaining the greater (less negative) (a-ET)pco2 difference in hypoxia than normoxia (P < 0.05). At near-maximal exercise intensity the (a-ET)pco2 lies close to 0 mmHg, that is, the mean Paco2 and the mean PE tco2 are similar. The mean exercise (a-ET)pco2 difference is closely related to the mean A-aDO2 difference (r = 0.90, P < 0.001), as would be expected if similar mechanisms perturb the gas exchange of O2 and CO2 during exercise. In summary, most of the negative (a-ET)pco2 values observed in previous studies are due to lack of correction of Paco2 for blood temperature. The absolute magnitude of the (a-ET)pco2 difference is lower during exercise in hypoxia than normoxia.
Department of Physical Education, University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain Research Institute of Biomedical and Health Sciences (IUIBS), Las Palmas de Gran Canaria, Canary Islands, Spain.
José
J
Losa-Reyna
Department of Physical Education, University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain Research Institute of Biomedical and Health Sciences (IUIBS), Las Palmas de Gran Canaria, Canary Islands, Spain.
Rafael
R
Torres-Peralta
Research Institute of Biomedical and Health Sciences (IUIBS), Las Palmas de Gran Canaria, Canary Islands, Spain Department of Mathematics, University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain.
Juan José González
JJ
Henriquez
Department of Physical Education, University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain Research Institute of Biomedical and Health Sciences (IUIBS), Las Palmas de Gran Canaria, Canary Islands, Spain lopezcalbet@gmail.com.
José A L
JA
Calbet
Blood temperature; gas exchange; gradient; hypoxia; pco
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