Dolphins slow their hearts down to avoid 'the bends'

Nov. 24 (UPI) -- Prior to diving, dolphins slow their hearts down to conserve oxygen and avoid decompression syndrome, sometimes called "the bends."

According to a new study, published Tuesday in the journal Frontiers in Physiology, dolphins can adjust their heart rate depending on how long they spend beneath the surface.

For the study, researchers worked with three male bottlenose dolphins that handlers trained to hold their breath for different lengths of time.

The scientists used a custom-built device to monitor the dolphins' breathing, and the team attached electrocardiogram sensors to track their heart rates.

"We trained the dolphins for a long breath-hold, a short one and one where they could do whatever they want," Andreas Fahlman said in a news release.

"When asked to hold their breath, their heart rates lowered before or immediately as they began the breath-hold. We also observed that the dolphins reduced their heart rates faster and further when preparing for the long breath-hold, compared to the other holds," said Fahlman, a researcher at Fundación Oceanogràfic in Valencia, Spain.

Researchers compared the dolphins' ability to slow their heart rate to humans' ability to slow their breathing.

"This allows them to conserve oxygen during their dives, and may also be key to avoiding diving-related problems such as decompression sickness," Fahlman said.

Studying the ways whales and dolphins prepare for and execute dives, long and short, can help marine biologists and conservationists better understand the impacts of human activities and noise pollution on the behavior and health of marine mammals.

"If this ability to regulate heart rate is important to avoid decompression sickness, and sudden exposure to an unusual sound causes this mechanism to fail, we should avoid sudden loud disturbances and instead slowly increase the noise level over time to cause minimal stress," Fahlman said. "In other words, our research may provide very simple mitigation methods to allow humans and animals to safely share the ocean."

Researchers said the study was only possible thanks to the relationship between the captive dolphins and their trainers.

"The close relationship between the trainers and animals is hugely important when training dolphins to participate in scientific studies," said Andy Jabas, who helped train the dolphins at Siegfried and Roy's Secret Garden and Dolphin Habitat at the Mirage in Las Vegas.

"This bond of trust enabled us to have a safe environment for the dolphins to become familiar with the specialized equipment and to learn to perform the breath-holds in a fun and stimulating training environment. The dolphins all participated willingly in the study and were able to leave at any time," Jabas said.