Smoking and Lung Function Data from the Coronary Artery Risk Development in Young Adults (CARDIA) study was used to assess the effects of smoking on lung function. In 1985--86, the study enrolled about 5,000 people aged 18 to 30 years old in a long term study. Over the next 20 years, study subjects were periodically asked about their habits and their health, including their lung function, was assessed. FIGURE 38.19 is a model based on data from this study, of how lifetime tobacco and marijuana use affects forced expiration.

FIGURE 38.19 Associations between marijuana or tobacco smoking and the change in forced expiration volume (FEV). One joint-year means an average of one joint smoked daily for one year. One pack-year is an average of one pack smoked per day for one year. Dots at the top of the graph show the distribution of observations. Lines below show the modeled association. Blue is marijuana and black is tobacco. The change in FEV₁ is given as milliliters of air.

How did the effects of low-level tobacco smoking on forced expiration volume differ from those of low level marijuana smoking?

To determine: How the effects of low-level tobacco smoking on forced expiration volume differ from those of low-level marijuana smoking.

Concept introduction: Smoking has a wide range of negative health effects. It increases the risk of lung infection and many types of cancer. Tobacco contains more than 40 carcinogens. Tobacco smokers have a higher risk of cardiovascular disease. Another smoking material is marijuana which contains carbon monoxide and an assortment of carcinogens, including arsenic and ammonia, but few studies have not found an increased risk of lung cancer who only smokes marijuana. The people who smoke both marijuana and tobacco seem to have more respiratory problems than those who smoke only tobacco.

Forced expiration volume is the volume of air that an individual can exhale after a deep inhalation. Smoking alters lung function that results in breathing problem that can change the forced expiration volume.

The data represented is based on the study done for effects of smoking to assess lung function by the Coronary Artery Risk Development in Young Adults (CARDIA). The study involves about 5,000 people aged between 18 to 30 years old in a long-term study. The study was followed for 20 years and periodical assessment of habit, health, and lung function was conducted to know how the lifetime use of tobacco and marijuana affects the forced expiration.

Refer to Fig. 38.19 “Association between marijuana or tobacco smoking and the change in forced expiration volume (FEV)” in the textbook, the low-level of tobacco use causes a direct decrease of FEV, but the low level of marijuana use causes an increase in FEV first, and then a decrease in FEV. In comparison to tobacco use, the decrease in FEV is low in the marijuana user.

Tobacco causes decrease in FEV right away, but marijuana causes an increase in FEV first, and then a decrease in FEV.