Feb. 26, 2004 It will come as no surprise to parents that the most common illness among small children in America today is the middle-ear infection.
Each year, Americans spend $5 billion on ear infections. Doctors often prescribe two different antibiotics for the same infection. For more serious cases, they perform 500,000-plus surgeries annually, by inserting a tube in the ear drum to alleviate pressure caused by infections.
Nonetheless, about 20 percent of children have repeated episodes of ear infections that persist into adolescence and even adulthood. Chronic infections can lead to loss of hearing and balance, as well as to more critical inner-ear infections.
Meanwhile, researchers scramble to develop new antibiotics as bacteria become resistant to existing drugs.
Samir Ghadiali, professor of mechanical engineering and mechanics at Lehigh University in Bethlehem, Pa., thinks there is a better way to tackle the problem.
Ghadiali, a member of Lehigh's Bioengineering and Life Sciences Program, studies the biomechanical and biophysical properties that govern the eustachian tube, which connects the middle ear to the back of the nose and the upper throat and which helps to regulate air pressure inside the ear.
Ghadiali's work is an example of the growing role played by engineers in the quest to find and test new remedies for medical problems.
Although eustachian tube dysfunction is the primary cause of middle-ear disease, he says, antibiotics and ear tubes do not seek to improve the tube's function.
"The goal of our research is to identify the causes of eustachian tube dysfunction," says Ghadiali. "We hope this leads to the development of novel treatment therapies that target the underlying cause of middle-ear disease."
The eustachian tube is a complex system of muscle, cartilage, and fat tissue. In healthy adults, it opens and closes three or four times a day, and more frequently when an excursion into higher altitudes causes a change in air pressure and triggers the ears to pop. An infection causes the ears to pop more frequently, but a more serious affliction may prevent the eustachian tube from opening and closing altogether.
Ghadiali applies engineering principles, such as fluid dynamics and solid mechanics, and engineering tools, including finite element analysis and mathematical modeling, to simulate how the eustachian tube opens.
"If we can open the eustachian tube," he says, "this will help prevent bacteria from accumulating and inflammation from occurring in the middle ear. An infection may clear up regardless of the antibiotic. This will decrease the number of pills that doctors need to prescribe."
Ghadiali collaborates with doctors and medical researchers at Children's Hospital of Pittsburgh (CHP), where he is a former research professor. At CHP, Ghadiali designed a testing apparatus to measure the mechanical properties of the eustachian tube. He also developed mathematical models to interpret and quantify those properties.
Mathematical models, says Ghadiali, allow researchers to study the eustachian system more efficiently and across a much wider range of situations than can be done by merely doing physical experiments in a laboratory. The models also enable researchers to change the parameters of their experiments in a more precise manner.
After researchers run a computer simulation on their model, says Ghadiali, they do a corresponding physical experiment in the lab to see how closely their results match. If a simulation faithfully reproduces the experiments, the model on which it is based can be used in other tests.
One goal of Ghadiali's research is to answer a question that has long baffled doctors - why the eustachian tube opens and closes easily in some people and not in others.
Engineers, he says, can answer that question by modeling the functioning of a healthy eustachian tube and using the model to predict the physical behavior of a diseased tube.
"Up until recently, researchers have visualized the ear's interior and speculated why the eustachian tube does or does not open," Ghadiali says. "We are attempting to push past this limitation by taking the same imaging data [from people who do not have ear infections] and creating mathematical models. By going from the image to the model, we can simulate whether or not the tube will open and we can quantify certain parameters, such as how long the tube will stay open."
Ghadiali also hopes to apply his models to each of the six or seven distinct "patient populations" identified by doctors as having eustachian tubes that, for differing reasons, resist opening. By learning why the tube does not open in a specific group, he says, researchers believe they can fashion a solution for that particular group.
Chronic ear infections are often a developmental phenomenon, Ghadiali says, because anatomy changes as a person ages. Ghadiali and his colleagues are examining children from a few months to 2 years old, those aged 2 to 6, those aged 7 to 12, and teenagers, as well as patients who have undergone cleft-palate surgeries, another group which is prone to chronic infections.
From a mechanical engineering standpoint, says Ghadiali, many physical parameters could cause ear infections. These include the elastic properties of tissues, the size of tissues, and the adhesion properties on the surface of the eustachian tubes.
"We don't know which of these are crucial in the different patient populations," says Ghadiali. "Until we do, we're operating in the dark. We can design therapies, such as tissue engineering to modify elasticity of tissues, but we don't know which therapy to use."
Ghadiali is also investigating, at the molecular level, the mucus buildup that is triggered by the presence of certain proteins and that could play a role in ear infections.
"We are enhancing all of our mathematical models to account for these molecular-adhesion forces. This is a multi-scale fluid dynamics problem."
Ghadiali has a Ph.D. in biomedical engineering from Tulane University.
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