Gary Horndeski was early into his plastic surgery practice in the 1990s when he noticed that his tummy tuck patients continued to lose excess fat and maintain their new weights without trying. He says he might have shrugged it off as a coincidence if it weren't for his engineering background. Instead, he speculated that a person's satiety could be controlled by additional intra-abdominal pressure.
Horndeski—an aspiring electrical engineer before detouring into medicine in 1972 to avoid the Vietnam War draft—had studied mechanics at Case Western Reserve University, in Cleveland, which was one of the first universities in the country with a biomedical engineering department. "I'm the product of that marriage," he says.
As a medical student, he would often build Heathkits for fun, once prophetically putting together a digital scale. Two decades later, he found himself looking at the human stomach with the eye of an engineer. It wasn't the first time Horndeski had adapted engineering techniques to plastic surgery—he had already applied some civil engineering concepts to breast reduction procedures.
Horndeski's epiphany about weight loss came about because he had already reengineered the standard tummy tuck. The established procedure involves suturing the left and right sides of abdominal fascia—an elastic tissue that overlies the muscles and weakens with pregnancy and age—to each other. Instead, Horndeski reinforces the fascia with synthetic mesh. It's a technique he'd picked up from doing abdominal reconstruction surgery during a fellowship at M.D. Anderson Cancer Center, in Houston, from 1988 to 1989. His patients with the plastic mesh seemed to have no trouble keeping their weight down; also, the mesh increased external pressure on the stomach. Was there a connection? Horndeski hypothesized that receptors within the stomach wall respond to that pressure just as those in a normal eater tell the brain to stop eating when the stomach is full.
"The brain has a reference level of what's considered full and compares it to the information sent by the stomach receptors," says Horndeski. Recipients of a standard tummy tuck put weight back on because the abdominal wall is not reinforced. Patients with the mesh reinforcement feel too full to eat for several days after surgery. "Once they lose intra-abdominal fat, the pressure on the stomach eases and then they can eat again," he says. "A girdle won't work, because it doesn't provide nearly the same pressure as mesh."
In preparation for a 2010 paper on the subject, Horndeski discovered supporting animal and human studies from the 1940s to 2007. He worked out a block diagram that models the human weight feedback system as an operational amplifier (an integrated circuit that amplifies output) and then quantified "how food amplifies your weight and how that information is fed back into the brain."
Horndeski has a patent pending on the concept and is waiting for the hospital where he operates, Angleton Danbury Medical Center, in Texas, to approve this surgery for weight loss. "I was able to connect the dots between stomach pressure and weight loss in large part because of my backgrounds in math and system theory, which is unusual for a plastic surgeon," he says.