To better understand wheezing, it helps to understand the anatomy of the lungs.
Inside the chest, the windpipe, or trachea, divides into two smaller tubes: the right bronchus and the left bronchus. The right bronchus enters the right lung and the left bronchus enters the left lung. The right bronchus and left bronchus branch into smaller and smaller tubes.
The smallest tubes, called bronchioles, end in tiny air sacs, called alveoli. Blood flows very close to the walls of the alveoli. Oxygen and carbon dioxide pass between the air and the bloodstream through the wall of the alveoli.
- Castro-Rodriguez JA, Rodrigo GJ. beta-agonists through metered-dose inhaler with valved holding chamber versus nebulizer for acute exacerbation of wheezing or asthma in children under 5 years of age: a systematic review with meta-analysis. J Pediatr. 2004 Aug;145(2):172-7. 
- Hypersensitivity pneumonitis. Allergy Asthma Proc. 2004 Jul-Aug;25(4 Suppl 1):S40-1. 
- Keeley D, McKean M. Asthma and other wheezing disorders of childhood. Clin Evid. 2003 Jun;(9):287-317. 
- Miranowski AC, Grammer LC. Occupational immunologic lung disease. Allergy Asthma Proc. 2004 Jul-Aug;25(4 Suppl 1):S36-7. 
- Roback MG, Dreitlein DA. Chest radiograph in the evaluation of first time wheezing episodes: review of current clinical practice and efficacy. Pediatr Emerg Care. 1998 Jun;14(3):181-4.