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 sa cs/lungs) as a N-2 and O-2 reservoir in deep-diving penguins, diving respir atory volume (V-DR), heart rate (f(H)), venous P-N2, blood volume (V-b) and hemoglobin (Hb) concentration were measured in king penguins (Aptenodytes patagonicus) during forced submersions and compressions equivalent to depth s up to 136 m, V-DR 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 f(H) averaged 30+/-7 beats min(-1) (N=18), approxim ately 20% of pre- and post-submersion values. Venous P-N2 values during and after submersions as deep as 11.2 ATA (102 m) were all less than 2.8 atmos pheres N-2 (283 kPa) above ambient pressure, a previously measured threshol d for symptomatic bubble formation. Mean V-b was 83+/-8 ml kg(-1) (N=6); [H b] was 17.6+/-0.7 g dl(-1) (N=7), On a mass-specific basis, mean V-DR, and therefore total available N-2, is 41% of that in shallow-diving penguin spe cies. Total body O-2 stores, calculated from measured V-DR, V-b, [Hb], musc le mass and myoglobin concentration, are 45 ml kg(-1), with 23 % in the res piratory system. This small respiratory fraction in comparison with that in shallow-diving penguins suggests a lesser reliance on the respiratory oxyg en store for extended breath-holding and also a reduced uptake of nitrogen at depth.