Pathogenesis of EIB
There are two proposed theories – osmotic and thermal –
explaining the occurrence of EIB. The osmotic theory assumes that
hyperventilation during physical effort leads to loss of water from the
surface of the respiratory epithelium, causing disorders in cell ion
homeostasis and an increase in mucus osmolarity. Respiratory tract wall
contains mast cells and eosinophils, that when stimulated release
inflammatory mediators, leading to a form of bronchospasm. A higher
concentration of inflammatory cells in the sputum of patients suffering
from EIB supports this theory.
The thermal theory , assumes that heat loss of the airways with
their subsequent reheating by incoming air after exercise, may lead to
an increase in mucus secretion, swelling and inflammation of tissues,
which ultimately causes narrowing of the airways. Additionally, cold air
stimulates parasympathetic nerve stimulation, which through vagal tone
leads to bronchoconstriction with simultaneous constriction of the
venous vessels in an attempt to limit heat loss. At the end of physical
effort, reflex dilatation of vessels occurs. All these factors
ultimately lead to narrowing of the airways, increasing in their
air-resistance14.
Among competitive athletes practicing winter sports, it is suspected
that EIB is caused by chronic exposure to cold air during vigorous
breathing, which results in damage to the respiratory epithelium and its
repair. In summer sports it is suggested that chronic exposure to
environmental allergens may be related to elevated circulating levels of
IgE15.
EIB is often diagnosed among swimmers and is linked to substances added
to pool water. During swimming, athletes inhale chlorine-rich water
molecules above the surface of the swimming pool, which irritate the
respiratory tract. Repeated exposure to these substances can lead to the
inflammation, epithelial damage and development of EIB and asthma.
Other causes of respiratory tract irritation in athletes may be due toenvironmental factors , such as airborne allergens (e.g. pollen).
It has been observed that people training in cold air, e.g. hockey,
figure skaters and speed skaters, may be more exposed to higher
concentrations of nitrogen dioxide (NO2) and particles
left over by ice leveling machines. Athletes training on the streets,
e.g. runners or cyclists, are more likely to inhale polluted street air.
Furthermore, among children who regularly play team games in the open
air, there is a greater risk of developing symptoms of asthma,
especially in an ozone-rich environment. McConnell et al. observed a
greater risk of developing asthma in athletes training more actively and
spending more time outside. Hyperventilation and breathing by mouth are
conducive to ozone, which progressively reaches more distant parts of
the respiratory tract. According to one study, the development of asthma
may be associated with neglecting EIB symptoms, which over time may lead
to airway remodeling and development of asthma16.