|Title||Extreme bradycardia and tachycardia in the world's largest animal|
|Publication Type||Journal Article|
|Year of Publication||2019|
|Authors||Goldbogen J.A, Cade D.E, Calambokidis J, Czapanskiy M.F, Fahlbusch J., Friedlaender A.S, Gough W.T, Kahane-Rapport S.R, Savoca M.S, Ponganis K.V, Ponganis P.J|
|Type of Article||Article|
|Keywords||blue whale; body-size; cardiac function; Dive response; Diving; Heart rate; heart-rate; mass; mechanics; scaling; Science & Technology - Other Topics; whale|
The biology of the blue whale has long fascinated physiologists because of the animal's extreme size. Despite high energetic demands from a large body, low mass-specific metabolic rates are likely powered by low heart rates. Diving bradycardia should slow blood oxygen depletion and enhance dive time available for foraging at depth. However, blue whales exhibit a high-cost feeding mechanism, lunge feeding, whereby large volumes of prey-laden water are intermittently engulfed and filtered during dives. This paradox of such a large, slowly beating heart and the high cost of lunge feeding represents a unique test of our understanding of cardiac function, hemodynamics, and physiological limits to body size. Here, we used an electrocardiogram (ECG)-depth recorder tag to measure blue whale heart rates during foraging dives as deep as 184 mand as long as 16.5 min. Heart rates during dives were typically 4 to 8 beats min(-1) (bpm) and as low as 2 bpm, while after-dive surface heart rates were 25 to 37 bpm, near the estimated maximum heart rate possible. Despite extreme bradycardia, we recorded a 2.5-fold increase above diving heart rate minima during the powered ascent phase of feeding lunges followed by a gradual decrease of heart rate during the prolonged glide as engulfed water is filtered. These heart rate dynamics explain the unique hemodynamic design in rorqual whales consisting of a large-diameter, highly compliant, elastic aortic arch that allows the aorta to accommodate blood ejected by the heart and maintain blood flow during the long and variable pauses between heartbeats.