Repeated Apneas and Hypercapnic Ventilatory Response Before and After Apnea Training

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: ΔV_E/ΔP_etCO₂). It was hypothesized that HCVR is decreased by repeated breath hold maximal efforts (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 different occasions. In the first visit, subjects performed a HCVR test, whereas in the second visit they completed five 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 five RBHE separated by 2-min intervals. Subsequently, in a third and a fourth condition, subjects repeated the experimental protocol of the second and first visit.

RESULTS: Although breath hold time (BHT) increased after apnea training in the NBH group by ∼46%, CO₂ sensitivity slopes were not different among experimental conditions and groups (2.8 0.3, 2.9 0.4 L min¹ mmHg¹ in the CBH and 2.7 0.5, 2.7 0.3 L min¹ mmHg¹ in the NBH during the second and third visit, respectively).

CONCLUSION: HCVR after five 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.

Bourdas DI, Tsakiris TS, Pavlakis KI, Triantafillou DV, Geladas ND. Repeated apneas and hypercapnic ventilatory response before and after apnea training. Aerosp Med Hum Perform. 2015; 86(1):2733.