Declining Lung Function:How to Warn Smokers

Q:How can I best demonstrate to my patients who smoke the accelerated decline in pulmonary function that occurs in smokers over time, in hopes of motivating them to quit smoking?

A: A simple spirometer is a crucial tool for all clinicians who treat patients who smoke or who have dyspnea, asthma, chronic obstructive pulmonary disease (COPD), or restrictive lung disorders. The National Lung Health Education Program recommends spirometric testing to detect airway obstruction from asthma or COPD in all current and former smokers 45 years or older and in any patient who has chronic cough, dyspnea on exertion, mucus hypersecretion, or wheezing.¹ The most comprehensive listing of values for the major spirometric measurements-forced expiratory volume in 1 second (FEV₁) and forced vital capacity (FVC)-can be found in the third National Health and Nutrition Examination Study (NHANES III).² Normal values from a large population sample are reported by sex, height, and age from 8 to 80 years. Thus, it is easy to identify the normal age-related rate of decline in FEV₁. In the average-size man, FEV₁ usually drops 25 to 30 mL/y (Figure 1). In persons who are susceptible to lung damage from tobacco smoke or industrial hazards, the rate of decline is 2 or 3 times greater. After a lower respiratory tract infection, such as influenza, patients sometimes experience step losses (as much as 200 to 300 mL following an acute exacerbation) in FEV₁. The rate of decline in FEV₁ is a powerful prognostic indicator. As demonstrated in the Lung Health Study, smoking cessation often results in slight increases in FEV1, and the decline in respiratory function is much slower than in smokers who do not quit.³ The NHANES III survey also concluded that the forced expiratory volume in 6 seconds (FEV6), is a good surrogate for FVC. This makes spirometric testing easier for both the technician and the patient. Another study has shown that FEV₁/FEV₆ is an acceptable surrogate for FEV₁/FVC in the diagnosis of obstructive and restrictive ventilatory disorders.⁴ The concept of lung age is another means of demonstrating the accelerated rate of decline in respiratory function in smokers.^5,6 Lung age is the chronologic age at which a person’s FEV1 is normal. Thus, a 40-year-old male smoker who is 5 ft 11 in tall and who has an FEV1 of 3.5 L actually has a lung age of 70. This concept can be a powerful motivator in helping patients quit smoking (Figure 2).

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