Fig. 1

End-tidal carbon dioxide partial pressures (P_ETCO₂, top), heart rate (HR, middle), and mean arterial pressure (MAP, bottom) during both heat stress and LBNP where subjects inhaled either a hypercapnic gas mixture (CO₂ trial) or room air (Air trial). In the CO₂ trial subjects inhaled a 5% CO₂ gas mixture prior to the onset of LBNP. Pre-LBNP indicates the responses prior to the LBNP challenge while heat stressed. Severe LBNP indicates the responses at the highest heart rate achieved during LBNP (i.e., prior to any bradycardia), End of LBNP indicates the responses at the end of LBNP. *, indicates difference from the Air trial (P < 0.05); † and ‡, indicate difference from Pre-LBNP, and Severe LBNP, respectively (P < 0.05). Individual data were plotted with different symbols