3D Model of the Nasal Airway of the dog

For years the work of drug or explosive detection has relied on our wonderful canine companions with advanced nasal recognition of these chemical compounds. Some experts believe the canine nose exceeds the human sense of smell by a factor of at least 10,000 and possibly as much as 100,000. Even in today’s high tech world, trained dogs are still the best bomb detectors.

A few years ago with funding from the Office of Naval Research, Eric Paterson, a senior research associated at Penn State University reconstructed the canine nasal airway by using high resolution MRI images and created a 3D model to study the fluid mechanics and odorant transport of the canine ofaction with the object of coming up with a better mechanical equivalent.

When a dog sniffs, Patersone explains, odorant-laden air passes through the nasal vestibule and then through a labyrinth of exquisite complexity. This is nature’s solution to packing a large srface area in a small volume – crucial for delivering odors to millions of olfactory receptors, specialized proteins embedded in the olfactory epithelium. “Smelling” occurs when odorant molecules bind to these eecptors and produce signals that are interpreted by the brain.

To get a closer look at the proces, Brent Craven, then a graduate student in mechanical and nuclear engineering, and now an ARL research associate, created a computational fluid dynamics model based on the equations of fluid motion and high resolution MRI of an actual dog’s airway.

So Craven and his colleagues created a computer model of a canine nose. First, they scanned the nasal airway of a mixed-breed cadaver with high-resolution magnetic resonance imaging. “We then had to make our model simulate how dogs sniff,” says Craven. But because that skill had also never been studied (although it has been in humans and rats), the researchers outfitted seven dogs, including a Pomeranian and a Labrador retriever, with a special muzzle. The device measured their rate of sniffing as they smelled things such as spoonfuls of peanut butter and tuna. Despite the wide range of sizes and weights, “all the dogs sniffed at about the same frequency, five times per second,” says Craven. That’s the same rate at which they pant. But “we knew they were sniffing and not simply breathing,” says Craven, because high-speed videos showed “their nostrils flaring, which happens when they’re sniffing, not when they’re breathing.” The team also mapped the flow of air into the dogs’ noses as they sniffed, enabling them to calculate the nostrils’ aerodynamic reach.

When the computer nose started sniffing, it picked up some surprising results. “First, the simulation showed that when a dog sniffs, each nostril pulls in a separate odor sample,” says Craven. Via its olfactory sensors, “the dog can tell which nostril is pulling in the scent,” so it knows which direction to go when tracking. Further, the researchers report today in the Journal of the Royal Society Interface, a dog’s nose has a unique nasal airflow pattern, which helps transport odor molecules quickly via a single airway to the olfactory recess. Here, the smell is retained in the maze of scent receptors even after the dog exhales; the odor is not expelled as it is with humans. It’s “very similar” to a rat’s airway, says Craven, who expects that this pattern will be found in any mammal with a keen sense of smell.

“One of the questions we are trying to answer is why dogs sniff so fast,” says Craven. Using the EnSight software, they are able to analyze simulation results of their model of a Labrador retriever sniffing at 5 Hz (5 sniffs per second), the nominal sniff frequency of a dog that size. The eventual goal is to create a complete virtual dog’s nose, complete with virtual scent receptors that are located in the back of the nose.

“It’s a significant study that provides compelling evidence” for why dog noses “make sense of scents in an extremely fine-tuned way,” says Marc Bekoff, an ethologist specializing on canids at the University of Colorado, Boulder. That’s a necessary step for scientists interested in “artificial nose machines,” such as narcotic or explosive detectors, says John Kauer, a neurophysiologist at Tufts University in Boston.

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