Repeated apneas and hypercapnic ventilatory response before and after apnea training

摘要

BACKGROUND: Habitual exposure to carbon dioxide (CO2) is expected, but it is not proven, to dull ventilatory sensitivity to CO2 by reducing hypercapnic ventilatory response (HCVR) as it is expressed by the slope of the derived response curve (CO2 sensitivity: δ VE/δ Pet CO2). It was hypothesized that HCVR is decreased by repeated breath hold maximal eff orts (RBHE) before and after apnea training in comparison with no training and the control condition. METHODS: Two groups of breath holders, a control (CBH) group and novices to breath hold activities (NBH), visited the laboratory on four diff erent occasions. In the fi rst visit, subjects performed a HCVR test, whereas in the second visit they completed fi ve successive RBHE separated by 2-min intervals. Another HCVR test was performed 2 min after cessation of the last apnea. For the next 14 d, only the NBH group trained by performing daily fi ve RBHE separated by 2-min intervals. Subsequently, in a third and a fourth condition, subjects repeated the experimental protocol of the second and fi rst visit. RESULTS: Although breath hold time (BHT) increased after apnea training in the NBH group by ~46%, CO2 sensitivity slopes were not diff erent among experimental conditions and groups (2.8 ± 0.3, 2.9 ± 0.4 L. min-1. mmHg-1 in the CBH and 2.7 ± 0.5, 2.7 ± 0.3. L min-1. mmHg-1in the NBH during the second and third visit, respectively). CONCLUSION: HCVR after fi ve RBHE or 14 d of apnea training was not decreased despite the achieved BHT enhancement. Hypercapnic dullness of ventilation is a complex biological process which takes more than 14 d of training to develop.