Researchers from the Harvard School of Public Health published a new study last month that suggests that young children are more susceptible than adults to particle deposition in their lungs through inhalation.

“Before this paper, everybody thought that baby lungs were a miniature version of adult lungs. They didn’t consider anything about structural change,” said Akira Tsuda, a research scientist at the School ofPublic Health and the leader of the project.

The study, entitled “Nanoparticle Delivery in Infant Lungs,” was conducted in Munich, Germany with the help of scientists from the Helmholtz Zentrum München German Research Center for Environmental Health.

Scientists tested the deposition of particles in rat lungs using radioactively labeled particles. Rats and humans have very similar lung structures, making them the ideal animal model for the study, according to Tsuda.

“By knowing the radioactivity in each organ and tissue of the rat, we could calculate the amount of particles deposited,” said Tsuda.

The results revealed that 21 day-old rats, an age which is equivalent to approximately two human years, were much more susceptible to particle deposition through inhalation.

“This is a startling and surprising finding,” said James P. Butler, senior lecturer on physiology at the School of Public Health. “Until we did this experiment, there were all kinds of speculations that particle deposition would be continuously increasing or decreasing, but the peak [in deposition] in humans is two years.”

Tsuda attributed these results to the phenomenon of chaotic mixing, a theory he pioneered in 1990.

“When we breathe out, we think we breathe out everything. However, some residual air remains in the lung,” he said.

Particles inhaled combine with this residual air in pockets of the lung’s alveoli, leaving behind problematic particle deposits.

The recent study proved that the effects of this chaotic mixing are most profound in children around the age of two.

Dosages for inhaled medicines have been greatly affected by these findings, according to Butler and Tsuda.

“It has been the assumption that we can treat the exposure of children as just small versions of adult humans. That is just not true,” said Butler.

The study found that therapeutic inhalation treatments must be scaled towards the patient.

“In clinical cases, they would estimate doses by body weight,” said Tsuda, adding that this method can lead to the dangerous over- and under-medication of children.

Children around two years of age are also at a higher risk of air pollution, the study reported. Current levels of pollution monitoring are geared toward pollutant deposition levels in adults, and do nottake these differences into account.

Both Tsuda and Butler said they believe there is more research to be done. Tsuda said that using this study’s findings as a foundation, he hopes to further investigate “whether the particles are going from lung surface to the blood stream.”