Nicotine as a result mucus cannot be moved easily out

nicotine. As a result, mucus cannot be moved easily out of
the passageways. Also, stimulation of excess mucus
secretion occurs, which further exacerbates the condition.
Inhibition of the alveolar macrophages also occurs, so they
become less effective in combating infection.
2. The infection, excess mucus, and inflammatory edema of
the bronchiolar epithelium together cause chronic
obstruction of many of the smaller airways.
3. The obstruction of the airways makes it especially difficult
to expire, thus causing entrapment of air in the alveoli and
overstretching them. This effect, combined with the lung
infection, causes marked destruction of as much as 50 to
80 percent of the alveolar walls. Therefore, the final picture
of the emphysematous lung is that shown in Figures 43-4
(top) and 43-5.

4. The physiological effects of chronic emphysema are variable,
depending on the severity of the disease and the relative degrees of
bronchiolar obstruction versus lung parenchymal destruction. Among
the different abnormalities are the following:
1. The bronchiolar obstruction increases airway resistance
and results in greatly increased work of breathing. It is
especially difficult for the person to move air through the
bronchioles during expiration because the compressive
force on the outside of the lung not only compresses the
alveoli but also compresses the bronchioles, which further
increases their resistance during expiration.
2. The marked loss of alveolar walls greatly decreases the
diffusing capacity of the lung, which reduces the ability of
the lungs to oxygenate the blood and remove CO2 from
the blood.
3. The obstructive process is frequently much worse in some
parts of the lungs than in other parts, so some portions of
the lungs are well ventilated, whereas other portions are
poorly ventilated. This situation often causes extremely
abnormal ventilation-perfusion ratios, with a very low V A
/Q in some parts (physiological shunt), resulting in poor
aeration of the blood, and very high V A /Q in other parts
(physiological dead space), resulting in wasted ventilation,
with both effects occurring in the same lungs.
4. Loss of large portions of the alveolar walls also decreases
the number of pulmonary capillaries through which blood
can pass. As a result, the pulmonary vascular resistance

often increases markedly, causing pulmonary
hypertension, which in turn overloads the right side of the
heart and frequently causes right-sided heart failure.
Chronic emphysema usually progresses slowly over many years. Both
hypoxia and hypercapnia develop because of hypoventilation of many alveoli
plus loss of alveolar walls. The net result of all these effects is severe,
prolonged, devastating air hunger that can last for years until the hypoxia
and hypercapnia cause death—a high penalty to pay for smoking.