Smoking and Pulmonary Fibrosis

Pulmonary fibrosis (PF), a chronic illness affecting the respiratory system, is characterized by the thickening and stiffening of lung tissue, which causes scar tissue to form. Although the exact cause of PF is not known, there are many factors linked to the development of the disease. These factors also affect survival and can be used by physicians as prognostic predictors.

Smoking and pulmonary fibrosis

Smoking is a main risk factor for PF. Far more smokers and ex-smokers develop PF than do people who never smoked. Recent research has shown that both mild smokers and ex-smokers share similar prognoses as it relates to PF.

According to the Mayo Clinic, complications of PF might include:

  • Pulmonary hypertension (high blood pressure in the lungs) – unlike systemic high blood pressure, this condition only affects the arteries in the lungs. It begins when the smallest arteries and capillaries are compressed by scar tissue, causing increased resistance to blood flow.
  • Right-sided heart failure – a serious condition that occurs when the heart’s lower right chamber has to pump harder than usual to move blood through partially blocked pulmonary arteries.
  • Respiratory failure – occurring when blood oxygen levels fall dangerously low.
  • Lung cancer – long-standing PF also increases the risk of developing lung cancer.
  • Other complications – including blood clots or collapsed lungs also can occur.

Smoking and survival in pulmonary fibrosis

Even though smoking is considered to be an independent risk factor for the development of PF, the exact relationship between smoking and survival in PF is not clear.

For example, some studies reported better survival for current smokers with idiopathic pulmonary fibrosis (IPF). In addition, although survival and severity-adjusted survival were found to be higher in non-smokers than in former smokers, smokers scored better outcomes compared to former smokers. This may be explained by what is known as the “healthy smoker effect” (see category below).

A different study also reported that survival could be extended in PF patients who are cigarette smokers at the time of their initial evaluation, when compared to former smokers or non-smokers. The study found that, compared to non-smokers, current smokers had less crackles on chest examination and more frequent digital clubbing, and more evidence of pulmonary hypertension on chest radiograph, among other findings.

Cigarette smoking also alters the appearance of lung tissue in PF patients. This may partially explain the longer survival in current smokers. The study found that PF patients who are smokers showed lower overall cellularity, but higher and more severe alveolar space cellularity. This likely reflects increased inflammation due to ongoing accumulation of macrophages (cells of the immune system) as a result of smoking.

The ‘Healthy Smoker’ Effect

But studies like those mentioned above seem to present puzzling results. There seems to be sufficient evidence to support the concept of the “healthy smoker.”  as an individual who takes up the habit because his/her lungs are relatively resistant to the effects of smoking. If correct, this means that the studies showing these results might have underestimated the consequences of smoking on lung function.

Some have compared the “healthy smoker” phenomenon to that observed in the “healthy worker effect,” a concept coined to describe the mortality experience of occupational groups that tend to have a higher resistance to exposure than the general population.

A search for the potential mechanisms by which cigarette smoking affects patients with PF may provide insights on the development of new therapeutic-targeted agents against smoking-induced progression of PF.

There is no doubt that smoking is detrimental to lung function. Evidence comes from multiple studies confirming that smoking is associated with an increased rate of lung-function loss over time. Smoking always damages your lungs and your airways. Learn about the American Lung Association’s programs to help you or a loved one quit smoking, or call the Lung HelpLine at (800) LUNG-USA (800) 586-4872).

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