How does mucus behaviour in lungs affect asthma and pollution risks?

The study was conducted by Swarnaditya Hazra, a doctoral research scholar in the Department of Chemical Engineering at IIT Bombay, and Professor Jason R Picardo, Assistant Professor in the same department. It was published in the peer reviewed Journal of Fluid Mechanics.

What happens when mucus increases?

Under normal conditions, mucus forms a thin film along the airway walls. But researchers found that when its volume increases, it does not spread evenly. Instead, it pulls together into ring-shaped humps along the airways, leaving large patches of the wall uncovered.
The team had predicted this outcome before running computer simulations. Professor Picardo said, “It was gratifying to find our expectations borne out.”

Why exposed airways matter

According to the researchers, when parts of the airway wall are left bare, very tiny soot particles in polluted air can settle directly on the exposed tissue.

Professor Picardo explained, “A significant fraction of soot particles has submicron sizes; such tiny particles would deposit on the airway wall by diffusion if the wall were left exposed. Our work shows that the mucus coating becomes patchier as its volume increases.”

Hazra noted that excess mucus can also block airways. “Beyond the lack of coverage, excessive mucus can also lead to the physical plugging of the airways, obstructing the very air we need to survive.”

The link to asthma

For asthma patients, exposure to allergens causes the body to produce more mucus and tighten the airways. Professor Picardo said, “Allergen deposition triggers mucus oversecretion and airway constriction. This in turn results in more of the wall becoming exposed to allergens, whose subsequent deposition amplifies the allergic response. This cycle explains why certain asthma attacks escalate rapidly.”

This creates a fast moving cycle that can worsen symptoms within a short time.

How different particles behave

The study also examined how particles of different sizes move through the lungs. Larger particles tend to crash into the mucus humps and get trapped. Very small particles drift into the exposed areas and settle on the tissue. Medium-sized particles can sometimes slip past both the humps and the exposed patches, avoiding the lung’s defences.

Researchers also studied tiny hair-like structures in the lungs that move mucus upward to clear it. While these are important for cleaning the lungs over time, they are too slow to affect where a particle lands during a single breath.

Targeted inhaled drugs

Researchers believe that understanding how mucus behaves could eventually help in developing targeted inhaled drugs that land exactly where they are needed.

Professor Picardo said, “Our work contributes to this by providing insight into aerosol deposition in the mucus bearing middle airways, which had not been studied before. The grand objective is to build a comprehensive model of the entire lung network.”

The study shows that the physics of mucus, something rarely discussed outside laboratories, may play a crucial role in both pollution related illness and asthma treatment.