The Amazing Physiology of Pearl Divers

There are about 2,000 “Ama” left in Japan—female pearl divers who plunge unaided to the bottom of the ocean 100 to 150 times a day, holding their breath for up to two minutes at a time while swimming vigorously to collect pearls and food. The profession is an ancient one, mentioned in texts almost 2,000 years ago, and even 60 years ago there were more than 15,000 Ama.

The physiology of pearl diving is amazing, thanks to the body’s intricate response to the sensation of diving. When your body detects a lack of breathing and cold water on the face, a series of automatic responses kick in, constricting your blood vessels, increasing your blood pressure, and causing your heart rate to drop. While diving, pearl divers often see their heart rate drop to half its resting value—even though they’re swimming hard.

How does the body handle these unique demands? Based on comparative studies of diving mammals like seals and whales, you’d expect the divers to have much more compliant (i.e., elastic) arteries in order to maintain circulation while underwater.

A neat new study led by Hirofumi Tanaka of the University of Texas, US, along with collaborators in Japan, published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, takes a look at this question. They assembled a remarkable group of 115 lifelong Japanese pearl divers, with an average age of 66, and compared them with matched groups of physically active and inactive controls from the same fishing villages.

The results are actually less clear-cut than I might have guessed. Arterial stiffness, which was assessed using a couple of different techniques including ultrasound measurements, was indeed lower in the divers than in their sedentary peers.

But it wasn’t significantly different between the divers and the physically active non-diver group, who exercised regularly as part of city-operated fitness programs. As a result, it’s not clear whether the arterial benefits have anything to do with diving itself, or whether it’s simply a result of being active.
The most surprising results are the measurements of lung function. Contrary to what you might expect, the divers didn’t have super-lungs. In fact, their performance on some measures was even worse than the sedentary control group. For example, the peak expiratory flow in the physically active group was 4.9 liters per second, compared to 4.2 in the sedentary group and 3.9 in the divers.

Why would this be? The researchers note that pearl divers use a particular breathing method when they dive: “After surfacing from the ocean, they open their mouths slightly letting out a loud and low whistle slowly on expiration. This maneuver is thought to protect their lungs and prevent excessive hyperventilation that could lead to unconsciousness.”

It’s possible that lifelong use of this breathing pattern changes their lung function in some way. In fact, the researchers note, “many of the pearl divers could not perform forced expiration required for the spirometer testing in spite of a number of attempts.”
That seems a little odd to me—but then again, the idea of diving under the ocean for up to two minutes at a time, a hundred times a day, year after year, also seems amazing and unusual. I don’t have deep insights to draw from this study, other than that it’s a cool glimpse into a remarkable (and disappearing) subculture.

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