Secondhand smoke is associated with a number of diseases and conditions, including cancer, heart disease, and emphysema. It is an irritant to lung tissue and blood vessels.

Researchers at the University of Colorado-Denver are currently studying how secondhand smoke affects the lungs of rats, and so far it appears that secondhand smoke triggers a complex inflammatory response.

• Enlargement in the alveolar air space of the rats’ lung. That is, the space in the lung’s alveoli, the tiny sacs where oxygen-carbon dioxide exchange takes place during respiration, increased. This suggest that the alveolar structure had begun to break down, much as it does in early emphysema.
• The researchers also noted increased numbers of white blood cells called macrophages in the alveolar space of the rats exposed to secondhand smoke, indicating that the rats’ bodies had mounted an immune response.
• There were also increased levels of interleukin-18, a cytokine produced by macrophages and associated with strong inflammatory reactions and tissue destruction.
• Inhibit the growth and proliferation of endothelial cells in the small blood vessels of the rats’ lungs. Decreased endothelial cells render the blood vessel wall less elastic and more permeable, which can lead to chronic inflammation as seen in chronic obstructive pulmonary diseases like emphysema and chronic bronchitis.

Source : www.sciencedaily.com/releases/2010/08/100826141230.html