(AP) -- The 9-year-old patient sits still, munching on popcorn and sipping grape juice while he gets an ultrasound of his heart.
Every so often, he wiggles free long enough to swing from the ceiling or stick out his tongue before resuming a statue-like pose. Orangutans aren't known for their patience, but this one, named Satu, has been trained to let researchers at Zoo Atlanta perform echocardiograms on him while he's awake.
It's part of a groundbreaking national project - the Great Ape Heart Project housed in Atlanta - that researches heart disease in the rust-colored apes. Heart problems are the No. 1 killer of orangutans, gorillas and other apes living in captivity, and the disease threatens the work researchers have done to help increase the population of the endangered species.
"We don't really know what is causing it. Once we can understand that, hopefully we can treat it," said Hayley Murphy, director of veterinary services at Zoo Atlanta. "Our ultimate goal would be to prevent it in these amazing animals, these endangered species. We're really trying hard to get a handle on this."
Researchers have been collecting data on gorilla heart disease for a decade, but zoos are just now starting to gather that information on orangutans. In February, Zoo Atlanta was the first facility to perform an awake echocardiogram on an orangutan.
Now the zoo, through the Great Ape Heart Project, is encouraging other organizations to do awake procedures, too, and send in the data.
Healthy apes can be put under anesthesia but the drugs are dangerous for those already suffering from heart problems. Awake procedures expand the amount of data researchers can collect, Murphy said.
"It's really cool to be able to follow an animal from infancy to adulthood. Nobody's ever done that," she said. "So it's going to give us a lot of clues as to when does heart disease start? What does it look like when it starts? Does it change over time?"
What's more, researchers hope to determine how similar apes and humans are when it comes to cardiac disease. The hearts look the same on an ultrasound, but that doesn't necessarily mean that disease affects them the same way. Already, the oldest orangutan at Zoo Atlanta, 40-year-old Alan, is taking human prescription drugs to help arrest the spread of his heart disease. However, researchers aren't sure how effective the drugs are because there is so little data on what a healthy orangutan heart looks like.
Satu and other orangutans at the zoo were trained for awake ultrasounds and blood draws through positive reinforcement using treats and praises. It took months of training to work up to a heart ultrasound that produced a usable image.
Much of the work depends on donations and volunteers, including ultrasound technicians from local hospitals who perform the tests on their own time. The project's website lists supplies like syringes, microscopes, ultrasound machines and medical scrubs on its donation page.
On a recent day, Satu sat for more than half an hour while technicians performed a cardiac ultrasound on him. A laptop sitting nearby showed black and white images of his pumping heart and broadcast the thump, thump, thump of the valves opening and closing.
Afterward, zoo workers drew blood from another orangutan, Madu, while she sat quietly waiting for treats. The 28-year-old ape rested her arm in a large plastic tube built specially for blood withdrawals, which once had to be done with the animal under anesthesia, a lengthy procedure.
The blood will be used to establish biomarkers that can help chart the progression of heart disease and possible treatments.
Training the apes to sit still long enough for any medical procedure can take up to a few months, depending on the animal. Patti Frazier, primate keeper at Zoo Atlanta, said she typically starts by teaching the orangutan to present his chest, then slowly introduces each element of the test.
For the ultrasound, those elements included the wand they push against the ape's chest, the gel used on the instrument and the laptop that records the images. Trainers also must get the apes accustomed to a hospital volunteer who records each image.
Frazier said one ape didn't like the wand and when told to show his chest, covered it with hay before turning toward his trainer. Another animal, an older orangutan, has a large throat sack that must be moved to the side so the keeper can place the wand directly on his chest.
At best, an animal will hold still for 30 seconds, but most are calm for just a few seconds, long enough to get a usable image, before they wiggle free, Frazier said.
As zoos across the country begin to do awake ultrasounds, the information will be sent to Atlanta to be included in the Great Ape Heart Project's database, a single place researchers can go to find out more about ape cardiac health.
"The idea that everybody is pulling together resources and data and efforts to answer some of the questions on a much larger scale is really exciting," said Kristen Lukas, curator of conservation and science at Cleveland Park Metro Zoo in Ohio. "It's a significant issue."
There are more than 200 orangutans at 55 zoos across the United States. The animals hale from Sumatra and Borneo in Indonesia, where deforestation and population growth has caused the Sumatran orangutan numbers to plummet to just 4,500.
Researchers hope the heart project can help those populations grow, too.
"When you get to this level of endangerment, you have to bring every tool to bear," said Lori Perkins, vice president of collections at Zoo Atlanta and head of the species survival plan for orangutans in the U.S. "Every tool that could be critical to their survival, you've got to throw it in."
Associated Press writer Kate Brumback contributed to this report.
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