Scientists have uncovered the secret behind one of nature’s most remarkable designs: the human lung. For years, the asymmetric design of our lungs has puzzled experts. And now, researchers from IIT Madras have found the reason to this asymmetry.

Prof Mahesh Panchagnula, Department of Applied Mechanics and Biomedical Engineering and Debjit Kundu, PhD Research Scholar, IIT Madras delved deep into the architecture of our lung — which unlike a perfectly symmetrical tree, branches out unevenly — to find out why they are designed the way they are.

Through sophisticated mathematical models, the scientists have demonstrated that this seemingly imperfect design is actually a master-stroke in evolutionary engineering, optimised not just for breathing but for protecting us from airborne threats.

Protective design

Says Debjit Kundu: “Take the structure of the lungs. The right lung is larger than the left lung. This is of course to accommodate the heart. However, this asymmetry is seen throughout the structure of the lungs, even down to the airway bifurcation units. This has been suggested to have a functional importance, which we have explored in our research.”

The study modelled how different degrees of asymmetry in lung branching affects its functions. A slight deviation from perfect symmetry enhances the lung’s filtration capability significantly, offering better protection against inhaled pollutants and pathogens at a relatively minor cost to other lung functions.

In essence, nature has designed our lungs to prioritise protection against environmental hazards, reflecting the lung’s role as a critical barrier against airborne diseases.

By constructing geometric models of the lung’s bronchial trees, the researchers were able to meticulously replicate its asymmetrical branching patterns. The models were grounded in morphometric parameters that helped to capture the essence of lung’s complex structure. Employing deterministic equations, the research team precisely defined the branching angles, diameters and lengths of bronchial segments, providing a realistic and accurate representation of the lungs’ anatomical features.

The investigation into the degree of asymmetry in the bronchial tree sheds light on its significant impact on the airway network’s branching pattern and structure. A crucial aspect of the study involved analysing the cut-off diameter within the bronchial tree, which influences the airflow and particle deposition across the tracheobronchial tree. This parameter is key to understanding how the lung’s structure affects its function, particularly in filtering inhaled particles.

Through computational simulations grounded in these geometric models, the researchers explored how varying levels of asymmetry affect functional parameters of the bronchial tree — such as the number of terminal branches, fluidic resistance to breathing, total lung volume and efficiency in particle deposition. These simulations, validated against experimental data, provide insights into the intricate relationship between lung structure and its crucial functions, including airflow, gas exchange and the filtration of inhaled particles, offering a new perspective on the lung’s evolutionary design optimised for both breathing and defence against airborne threats.

Beyond the Lab

The study, published in Scientific Reports, opens up promising avenues across multiple disciplines, from clinical practices to public health initiatives. In the realm of respiratory disease research, insights into how lung asymmetry influences particle filtration can deepen our understanding of conditions like asthma, COPD and respiratory infections, paving the way for novel diagnostic and treatment strategies.

Prof Mahesh Panchagnula, said, “A potential application of this work is to understand the acinar ramifications of diseased lung conditions as well as inter-subject variability. The modelling efforts of this study could be a key factor in developing efficient and personalised drug delivery systems in the future”.

The mathematical models and parameters developed through this study also offer tools for biomedical engineering, facilitating the design of advanced respiratory devices. It sheds light on the relationship between air quality and respiratory health, providing critical data for environmental health studies and policy-making aimed at mitigating pollution-related health risks.