Popular Mechanics (USA)

Science How researcher­s solved da Vinci’s 500-year-old heart mystery.

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RESEARCHER­S FINALLY UNDERSTAND THE FUNCtion of a heart feature first described by Leonardo da Vinci 500 years ago. To find the answer, scientists used fractal theory, MRIs, and a lot of computatio­nal elbow grease to shed light on muscular structures called trabeculae. Their study, published in Nature, found this branching, lacy muscle layer plays a part in identifyin­g a patient’s risk of heart disease.

The trabeculae cover the inner surfaces of the heart and were thought to be a remnant of embryonic developmen­t. Leonardo da Vinci drew detailed pictures of the fine, snowflake-like trabeculae after dissecting and examining a heart. “He was quite intrigued by them and he thought they warmed the blood,” says Declan O’Regan, PhD, a clinical scientist and radiologis­t at Imperial College London in the U.K., who worked on the study.

The broad internatio­nal research team tapped a special resource: the UK Biobank, a database of more than 500,000 adult volunteers (O’Regan and his team analyzed a subset of 18,000 people) who have had genetic testing, MRI scans, and other

procedures in order to make their data available to researcher­s around the world.

The study of trabeculae might date back centuries, and scientists have looked at the recurring, weblike, and unusual pattern of muscle fibers for almost 450 years. But that hasn’t been enough to understand why the muscle is there, what it’s doing, or how it develops.

“You can see these structures on all scans of the heart and take for granted what they’re for,” O’Regan says. “We needed machine learning to take the data and analyze it, coupled with access to really large population­s that have imaging as well as genetic informatio­n.” Through this recent research, the team was able to identify common features across different patient imagery, cross-check that with patient records, and begin to draw conclusion­s about the biological purpose behind structural trabeculae.

Before this study, the trabeculae were primarily considered in an embryonic context. “We knew they were important in developing hearts, but their role in adults hadn’t been recognized at all,” O’Regan says. “Our research suggests that they have an important effect on the performanc­e of the heart by improving how much blood can be pumped during each heartbeat.”

O’Regan and his team discovered that people whose hearts had a smoother inner surface— meaning they had fewer trabecular fibers—were at greater risk of heart failure. That could mean the heart pumps blood less efficientl­y in these people, he says. They also found that having too many muscle fibers could actually slow blood flow in the heart and increase the likelihood that a person will develop blood clots. In future research, the team plans to develop computer simulation­s to explore how fluids like blood may interact with deformable surfaces like trabeculae.

The team used mathematic­s and computing power to study how trabeculae develop their characteri­stic lace-like structure. “We used this principle called fractal analysis [on] this pattern of muscles in the heart and began to understand how that muscle develops at a molecular scale,” O’Regan says. “Leonardo was really interested in fractals as well—he was interested in branching patterns of trees and came up with the rule that determined how they branch, bringing those two domains together.”

Fractal analysis appears in everything from mapmaking to telecoms. Every time you zoom in on Google Maps, a major “trunk” branches into smaller and smaller areas. And covering Earth with high-speed internet involves branching from telecommun­ication lines—thick “trunks” that cross the continent—to regional and local networks that reach into your home. In the case of the heart, the trabeculae likewise branch into smaller and smaller threads.

By studying the human genome as well as the trabeculae of their subjects, O’Regan began to pinpoint genes that affect how trabeculae form and function. These discoverie­s could have implicatio­ns for how other body cells form and behave, including nerves and the brain. “There might be a really important mechanism in nature that determines how structures in the body branch and form that treelike pattern,” O’Regan explains.

Humans aren’t the only animals to have trabeculae. The structures are found in all vertebrate­s, so O’Regan’s team speculated “there was a strong likelihood they were doing something important.” Da Vinci, centuries ahead of our time, did, too (see sidebar). O’Regan and his colleagues have built upon the 15th century polymath’s work to develop the tools that can finally unravel the mystery behind these tangled structures.

 ??  ?? In embryos, the trabeculae are thought to diffuse oxygen and nutrients throughout heart tissue.
In embryos, the trabeculae are thought to diffuse oxygen and nutrients throughout heart tissue.

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