by Tom O’Neill
Raouf Amin, MD, Director of the Division of Pulmonary Medicine, believes computational modeling, with an assist from aerospace engineering principles, could be transformative in planning upper-airway surgical strategies.
Pediatric surgery and aerospace engineering might seem to occupy parallel universes — but not anymore for children with sleep apnea.
Researchers at Cincinnati Children’s and the University of Cincinnati’s Department of Aerospace Engineering and Engineering Mechanics are using the mechanical concepts of computational 3D modeling, air flow, turbulence, resistance and fluid dynamics to bring a new level of precision to a decidedly non-mechanical task: the surgical correction of obstructive sleep apnea (OSA).
Fueled by more than $3.8 million in funding from the National Institutes of Health, a research team with a wide variety of talents has designed and begun testing a 3D computer software modeling system that can replicate the unique geometry of an individual child’s upper-airway. Within three to five years, these rotating, interactive, full-color models may become available to help surgeons test surgical scenarios, select ideal approaches, and practice procedures long before patients reach the operating room.
Ten years ago, the idea of applying aerospace principles to surgical planning would have sounded unlikely at best, says Raouf Amin, MD, Director of the Division of Pulmonary Medicine.
“To think that bioengineers would be instrumental to advancing this research in sleep apnea, or to say we were going to import the science of aerospace and apply it to the airway, no, most probably, that would have been considered science-fiction,” Amin says.
MEDICINE MEETS ROCKET SCIENCE
In Cincinnati, bridging the worlds of surgery and aerospace engineering has been as simple — and remarkable — as crossing a street called Albert Sabin Way that passes between the research towers of Cincinnati Children’s and the medical campus of the University of Cincinnati.
When he joined the project in 2010, engineering expert Goutham Mylavarapu, PhD, had no biomedical experience. Yet by 2014, he had co-authored a paper in the Journal of Biomechanics that used computational fluid dynamics to characterize how air ebbs and flows as it moves through the human airway.
“It took me a year just to understand the medical principles,” he says with a slight laugh. “Now, I tell my wife, perhaps I should go back to school and become an MD.”
Indeed, learning each other’s terminology and scientific procedures required plenty of communication. But team members were motivated by the stakes involved.
In the past three years, Cincinnati Children’s has experienced a 20 percent spike in children visiting its sleep study lab to be assessed for sleep disorders. The assessments have grown from 2,184 in fiscal year 2013 to 2,626 in fiscal year 2015.
The prevalence of sleep apnea, the most common form of sleep disorder, is rising for a number of reasons. Childhood obesity plays a role, as do improved diagnostic systems and increased public awareness of the health risks of sleep apnea.
Any child can be affected by a sleep disorder; children with Down syndrome or craniofacial abnormalities are particularly susceptible. Untreated, sleep disorders can lead to compromised cognitive function, excessive daytime sleepiness, academic struggles, behavioral challenges and weight fluctuation. Some studies suggest that sleep apnea symptoms can mimic ADHD, bringing the risk of misdiagnosis.
Many children with sleep apnea can be treated with non-surgical options like weight-loss programs or CPAP breathing devices. But some children, particularly those with Down syndrome, find the CPAP mask and its head straps intolerable. These and other children with significant structural issues affecting their airways require a more invasive, surgical approach.
CREATING AN AIRWAY SURGERY RESEARCH AGENDA
Stacy Ishman, MD, MPH
Aerospace science has the potential to transform surgical techniques, says Stacey Ishman, MD, MPH, Surgical Director of the Upper Airway Center and Director of Otolaryngology Outcomes Research.
“This could fundamentally change our approach in two ways,” she says. “Some patients should never undergo surgery, so by seeing the outcome beforehand, you can avoid the side effects and the pain. The other is in considering several surgical options. Which is best, what are the priorities?”
Amin agrees that the upper airway presents a tricky surgical landscape. Below the larynx, the airway is stiffer, which supports long-lasting surgical outcomes. But above the larynx, the elasticity of softer tissues complicates everything. Treating residual obstruction at multiple levels of the upper-airway can require multiple procedures, and success rates hover at about 60 percent.
“Sometimes the improvement is not sustained,” Amin says. “The most challenging problem is how to estimate the soft tissue.”
The new modeling system can help surgeons better understand the dynamics of how soft tissue will react to resection. With more data to characterize the phenotype, the odds of providing a lasting treatment improve, Amin says.
DYMOSA STUDY PROVIDES DATA
Measuring air flow over a cantilever attached to a cylinder, researchers can see how upper-airway walls (above) respond differently from rigid structures (below).
Since 2010, Amin, Sally Shott, MD, Division of Otolaryngology, and other colleagues have been conducting a study called Dynamic Computational Modeling of Obstructive Sleep Apnea (DYMOSA). The NIH has supported the work with an initial three-year RO1 grant and subsequent extensions.
The project involves experts from Otolaryngology, Pulmonary Medicine, Sleep Medicine, Radiology, Anesthesia and, of course, the space guys at UC. The team is one of very few in the world conducting cine MRI imaging of the airways of children with Down syndrome who also have persistent OSA. Cine is a form of MRI that captures the flow of cerebrospinal fluid.
“There’s not a lot of great data out there,” Ishman says. “And kids with Down syndrome were underrepresented in what studies did exist.”
Researchers knew this much: By age 4, almost 60 percent of children with Down syndrome suffer abnormal sleep, and eight out of 10 exhibit sleep apnea by age 9. Studies show that virtually every child with Down syndrome will develop sleep apnea at some point in childhood.
Anatomy betrays them. They have higher prevalence of midface hypoplasia with smaller airway size in the oral cavity, nose, nasopharynx and at the base of tongue. They have a larger-than-average volume of tongue tissue. Poor muscle tone also contributes to airway collapse.
In addition, a 50 percent incidence of underlying heart abnormalities in children with Down places them at higher risk for developing the more severe consequences associated with sleep apnea.
To date, 55 children with Down syndrome have participated in the DYMOSA study. If virtual surgery modeling proves effective for this group, the approach can be adjusted for other pediatric populations with OSA, the researchers contend.
CASE REPORTS APPEAR PROMISING
Amin, Ishman, Shott and colleagues examine DYMOSA’s encouraging progress in a prospective case report called “New Frontiers in the Treatment of OSA in Children: Computational Modeling of the Airway for Surgical Planning.”
The report focuses on three types of virtual surgeries performed on airway models created for each subject: A 2-millimeter base-of-tongue resection, a 4-millimeter resection, and a virtual palate reconstruction (palatoplasty). At 10 liters/minute of air flow, upper-airway resistance decreased by 46 percent for the 2-mm resection and 48 percent for the 4-mm approach. When the palate also was excised, air resistance decreased an additional 16 percent.
“Computational modeling of the airway and associated virtual surgery allow for pre-operative planning that provides the surgeon with information both on ‘where’ to operate, and on ‘how much’ tissue to remove for potentially improved post-operative success,” the authors wrote.