Is (V) over dotO2 supressed during nonapnoeic facial submersion?

The mammalian dive response (DR) is described as oxygen-conserving based on measures of bradycardia, peripheral vasoconstriction, and decreased ventilation ((V) over dot(E)). Using a model of simulated diving, this study examined the effect of nonapnoeic facial submersions (NAFS) on oxygen consumption ((V) over dot O-2). 19 participants performed four 2-min NAFS with 8 min of rest between each. Two submersions were performed in 5 degrees C water, 2 in 25 degrees C water. Heart rate (HR) was collected using chest strap monitors. A tube connected to the inspired port of a non-rebreathing valve allowed participants to breathe during facial submersion. Expired air was directed to a metabolic cart to determine (V) over dot O-2 and (V) over dot(E). Baseline (BL) HR, (V) over dot O-2, and (V) over dot(E) values were determined by the average during the 2 min prior to facial submersion; cold shock response (CSR) values were the maximum during the first 30 s of facial submersion; and NAFS values were the minimum during the last 90 s of facial submersion. A 2-way repeated-measures ANOVA indicated that both HR and (V) over dot(E) were greater during the CSR (92.5 +/- 3.6 beats/min, 16.3 +/- 0.8 L/min) compared with BL (78.9 +/- 3.2 beats/min, 8.7 +/- 0.4 L/min), while both were decreased from BL during the NAFS (60.0 +/- 4.0 beats/min, 6.0 +/- 0.4 L/min) (all, p < 0.05). HRCSR was higher and HRNAFS lower in 5 degrees C versus 25 degrees C water (p < 0.05), while (V) over dot(E) was greater in 5 degrees C conditions (p < 0.05). (V) over dot O-2 exceeded BL during the CSR and decreased below BL during the NAFS (BL: 5.3 +/- 0.1, CSR: 9.8 +/- 0.4, NAFS: 3.1 +/- 0.2 mL.kg(-1).min(-1), p < 0.05). The data illustrate that NAFS alone contributes to the oxygen conservation associated with the human DR.