Air and Breathing
An asthma attack is any shortness of breath that requires either medication or some other form of intervention for the asthmatic to breathe normally again. Wheezing is often associated with the attack - whistling or rattling sounds occur when air flows through obstructed airways. Wheezing starts with exhalation, or breathing out, but as the attack progresses, wheezing may then be heard both while inhaling and exhaling. If the attack progresses further, the asthmatic may stop wheezing as small airways become completely blocked.
Air reaches the lung by passing through the windpipe (trachea), which divides into two large tubes (bronchi), one for each lung. Each bronchus further divides into many little tubes (bronchioles), which eventually lead to tiny air sacs (alveoli), in which oxygen from the air is transferred to the bloodstream, and carbon dioxide from the bloodstream is transferred to the air.
Asthma involves only the airways (bronchi and bronchioles), and not the air sacs. The airways trap airborne particles in a thin layer of mucus that covers their surface. The mucus is either coughed-up or swept up into the trachea by cilia, tiny hairs on the lining of the airways. Once the mucus reaches the throat, it can be coughed up or swallowed. The asthmatic's airway is hyper-reactive. In response to stimuli, the airway may become obstructed by:
1. constriction of the muscles in bronchi and bronchioles, narrowing the airway
2. inflammation and swelling of the airway with obstruction of air flow
3. increased mucus production that can obstruct the airway.
With bronchoconstriction, air has a harder time leaving the lungs than entering. The result is prolonged noisy expiration. Breathing becomes labored. If you listen with a stethoscope, you will hear scattered whistles from the narrowed bronchi on breathing out. Later, the small tubes in the lung swell and plug with increased mucus secretion, making the obstruction to airflow worse. This inflammatory, obstructive phase is the most important mechanism of chronic asthmatic bronchitis.
Exhaling through obstructed airways is difficult and stale air remains in the lungs after each breath. This decreases the amount of fresh air that can be taken in with each new breath, and less oxygen is available. This decreased supply of oxygen makes an uncontrolled asthma attack a potentially life-threatening affair.