|Title||Heart rates of emperor penguins diving at sea: implications for oxygen store management|
|Publication Type||Journal Article|
|Year of Publication||2014|
|Authors||Wright A.K, Ponganis K.V, McDonald B.I, Ponganis P.J|
|Journal||Marine Ecology Progress Series|
|Type of Article||Article|
|Keywords||Aerobic dive limit; antarctica; depletion; Diving physiology; ECG; Electrocardiogram; Emperor; energetics; exercise; Gas exchange; Heart rate; king penguins; metabolic-rate; Oxygen store management; penguin; performance; perfusion; Peripheral; saturation; stroke rates|
Heart rate (f(H)) contributes to control of blood oxygen (O-2) depletion through regulation of the magnitude of pulmonary gas exchange and of peripheral blood flow in diving vertebrates such as penguins. Therefore, we measured H during foraging trip dives of emperor penguins Aptenodytes forsteri equipped with digital electrocardiogram (ECG) recorders and time depth recorders (TDRs). Median dive f(H) (total heartbeats/duration, 64 beats min(-1)) was higher than resting H (56 beats min(-1)) and was negatively related to dive duration. Median dive f(H) in dives greater than the 5.6 min aerobic dive limit (ADL; dive duration associated with the onset of a net accumulation of lactic acid above resting levels) was significantly less than the median dive f(H) of dives less than the ADL (58 vs. 66 beats min(-1)). f(H) profile patterns differed between shallow (<50 m) and deep dives (>250 m), with values usually declining to levels near resting f(H) in shallow, short-duration dives, and to levels as low as 10 beats min(-1) during the deepest segments of deep dives. The total number of heartbeats in a dive was variable in shallow dives and consistently high in deep dives. A true bradycardia (f(H) below resting levels) during segments of 31% of shallow and deep dives of emperor penguins is consistent with reliance on myoglobin-bound O-2 stores for aerobic muscle metabolism that is especially accentuated during the severe bradycardias of deep dives. Although f(H) is low during the deepest segments of deep dives, the total number and distribution of heartbeats in deep, long dives suggest that pulmonary gas exchange and peripheral blood flow primarily occur at shallow depths.