Strained breathing is a natural respiratory pattern,
with cardiovascular implications. It is associated with
social factors, attention, expectation, and anxiety and
with defense behavior in animals. An inhibition of active
behavior is characteristic. Strained breathing is based
on the functional heterogeneity of the medullary postinspiratory
neurons. In stressful circumstances, muscle tension and
laryngeal reflexes induce a strong reduction of airflow
in the glottis, resulting in a prolonged Stage I of expiration
and an elevated intrathoracic pressure. The resulting elevations
of blood pressure and CO2 level further stimulate
the strained breathing pattern. The straining factor intrathoracic
pressure is an important psychophysiological parameter.
Functional aspects of strained breathing may be an elevated
brain perfusion and the prevention of hyperventilation.
It induces blood pressure oscillations and respiratory
sinus arrhythmia. Frequent strained breathing may contribute
to cardiovascular pathology and sleep apnea, creating a
link between functional behavior and disease.