A new study has identified the way in which human airways are affected by very dry atmospheres, which are set to increase due to climate change.
The study found that breathing dry air triggers the body’s inflammatory and immune responses, with implications for respiratory conditions like asthma, chronic bronchitis and chronic cough.
The research team predict that most of the population of the continental United States will be at higher risk of airway inflammation by the latter half of this century, due to higher temperatures and drier air.
Researchers at Imperial College London teamed up with colleagues at Johns Hopkins University and the University of Carolina to find out how breathing dry air affects the mucous surfaces of human airways, including the mouth, nose, larynx, trachea and lungs.
They wanted to focus on a thermodynamic element of the atmosphere known as the ‘vapour pressure deficit’ (VPD) - a measure of how ‘thirsty’ air can be. Rising temperatures due to climate change mean that VPD in the atmosphere is predicted to increase at a rapid rate.
In a series of experiments and calculations, they found that breathing in a drier atmosphere, with a high VPD, dehydrates the upper airways through evaporation. This thins the mucous on the surfaces and creates pressure on the cells lining the airways. That pressure triggers the body’s inflammatory and immune responses.
Inflammation of the airways can cause or exacerbate conditions like asthma, chronic bronchitis, allergic rhinitis and chronic cough, and will potentially exacerbate lung diseases. The researchers say that human mucosa dehydration presents a critical threat to human health.
Professor Fan Chung of Imperial’s National Heart and Lung Institute said: “We have identified that VPD is a major element that causes these problems and will be much more important as the temperature goes up in drier conditions. We believe this will be one mechanism by which climate change will provoke the onset of various respiratory conditions and diseases.”
The research project encompassed different elements. Firstly the researchers carried out mathematical modelling and calculations to explore how the vapour pressure deficit in the air is affected by high temperature.
Next, they exposed cultures of human cells that line the upper airway, known as human bronchial epithelium, to dry air. Cells that experienced periods of dry air (with a high VPD) showed thinner mucus and released high concentrations of cytokines - proteins that are potent in causing inflammation of the airways and activating immune cells.
These findings were confirmed by a study in which genetically-modified mice that could not hydrate their airways were exposed intermittently to dry air for a week. The airways, already inflamed to start with, showed further inflammation with tissue damage and changes in immune cell activity.
Finally a continental US climate model simulation was carried out to assess the increased risk of breathing-induced inflammation of human airways as a consequence of rising VPD accompanying rising global temperatures.
In the full report, published in Communications Earth & Environment, the researchers say that this dehydration and inflammation can be worsened by mouth breathing (which is on the increase due to conditions such as obesity and allergic rhinitis) as well as increasing exposure to air-conditioned and heated indoor air.
Professor Chung has carried out previous research into the mechanism of chronic cough which found that rehydration of the upper airways using a salt spray can reduce coughing frequency. This indicates that dehydration of the airways may cause cough hypersensitivity. He said: “More research is needed to determine why some individuals are more prone to the effects of arway dehydration. And we urgently need to find successful ways to rehydrate individual airways, whether that is by behaviour change, sprays or other therapies.”
Other research partners included Boston University, Illinois Institute of Technology, and Sensory Cloud Inc.
Global warming risks dehydrating and inflaming human airways is published in Communications Earth and Environment.
This report was based on press materials provided by Johns Hopkins University.
Article text (excluding photos or graphics) © Imperial College London.
Photos and graphics subject to third party copyright used with permission or © Imperial College London.
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Samantha Rey
Communications Division
