Susceptibility to hypoxia and breathing control changes after short-term cold exposures

BACKGROUND Hypoxia is the reduction of oxygen availability due to external or internal causes. There is large individual variability of response to hypoxia. OBJECTIVE The aim of this study was to define individual and typological features in susceptibility to hypoxia, its interrelation with hypoxic and hypercapnic ventilatory responses (HVR and HCVR, respectively) and their changes after cold acclimation. DESIGN Twenty-four healthy men were tested. HVR and HCVR were measured by the rebreathing method during hypoxic and hypercapnic tests, respectively. These tests were carried out in thermoneutral conditions before and after cold exposures (nude, at 13°C, 2 h daily, for 10 days). Susceptibility to hypoxia (sSaO2) was determined as haemoglobin saturation slope during hypoxic test. RESULTS It was found that HVR and HCVR significantly increased and susceptibility to hypoxia (sSaO2) tended to decrease after cold acclimation. According to sSaO2 results before cold exposures, the group was divided into 3: Group 1--with high susceptibility to hypoxia, Group 2--medium and Group 3--low susceptibility. Analysis of variances (MANOVA) shows the key role of susceptibility to hypoxia and cold exposures and their interrelation. Posterior analysis (Fisher LSD) showed significant difference in susceptibility to hypoxia between the groups prior to cold acclimation, while HVR and HCVR did not differ between the groups. After cold acclimation, susceptibility to hypoxia was not significantly different between the groups, while HCVR significantly increased in Groups 1 and 3, HVR significantly increased in Group 3 and HCVR, HVR did not change in Group 2. CONCLUSIONS Short-term cold exposures caused an increase in functional reserves and improved oxygen supply of tissues in Group 1. Cold exposure hypoxia has caused energy loss in Group 3. Group 2 showed the most appropriate energy conservation reaction mode to cold exposures. No relation was found between the thermoregulation and the susceptibility to hypoxia.