Scientists were surprised to find a high rate of heart arrhythmias in bottlenose dolphins and Weddell seals during deep-sea dives.
In the past researchers believed the normal dive response in marine mammals involved a significant reduction in heart rate, but researchers were unsure as to how these animals gathered enough energy to catch prey under these conditions, the University of California, Santa Cruz reported. The phenomenon was perplexing because the normal response to exercise is an increase in heart rate. The new findings suggest the conflict between these two heart rates can lead to cardiac arrhythmias.
"This study changes our understanding of bradycardia in marine mammals," said Terrie Williams, a professor of ecology and evolutionary biology at UC Santa Cruz. "The heart is receiving conflicting signals when the animals exercise intensely at depth, which often happens when they are starting their ascent. We're not seeing lethal arrhythmias, but it is putting the heart in an unsteady state that could make it vulnerable to problems."
The researchers observed the heart rates during these deep dives alternated rapidly between periods of bradycardia and tachycardia causing an arrhythmia rate of as high as 70 percent.
"We tend to think of marine mammals as completely adapted to life in the water. However, in terms of the dive response and heart rate, it's not a perfect system," Williams said. "Even 50 million years of evolution hasn't been able to make that basic mammalian response impervious to problems."
The study's findings could provide insight into stranding events involving deep-diving marine mammals, because these processes are similar to flight responses. The conclusion could also have implication for human deep-sea divers and those who swim in extremely cold waters.
"It may be that the same conflicting signals we saw in dolphins and seals are causing arrhythmias in some triathletes," Williams said.
The findings were published in a recent edition of the journal Nature Communications.
