Physiological responses of king penguins during simulated diving to 136 m depth

To evaluate blood N(2) uptake and the role of the respiratory volume (air sacs/lungs) as a N(2) and O(2) reservoir in deep-diving penguins, diving respiratory volume (Vdr), heart rate (fh), venous P(N)(sum), blood volume (V(b)) and hemoglobin (Hb) concentration were measured in king penguins (Aptenodytes patagonicus) during forced submersions and compressions equivalent to depths up to 136 m. Vdr was 69+/-18 ml kg(-)(1) (mean +/- s.d.) in 62 submersions ranging from 4.4 atmospheres absolute (ATA; 1 ATA=101 kPa) (34 m) to 14.6 ATA (136 m). Submersion fh averaged 30+/-7 beats min(-)(1) (N=18), approximately 20 % of pre- and post-submersion values. Venous P(N)(sum) values during and after submersions as deep as 11.2 ATA (102 m) were all less than 2.8 atmospheres N(2) (283 kPa) above ambient pressure, a previously measured threshold for symptomatic bubble formation. Mean V(b) was 83+/-8 ml kg(-)(1) (N=6); [Hb] was 17.6+/-0.7 g dl(-)(1) (N=7). On a mass-specific basis, mean Vdr, and therefore total available N(2), is 41 % of that in shallow-diving penguin species. Total body O(2) stores, calculated from measured Vdr, V(b), [Hb], muscle mass and myoglobin concentration, are 45 ml kg(-)(1), with 23 % in the respiratory system. This small respiratory fraction in comparison with that in shallow-diving penguins suggests a lesser reliance on the respiratory oxygen store for extended breath-holding and also a reduced uptake of nitrogen at depth.