Swimming and asthma. Benefits and deleterious effects.

Swimming is a common pastime activity and competitive sport for patients with asthma. One reason for such popularity may be the low asthmogenicity of swimming compared with landbased activities. Review of available evidence suggests that swimming induces less severe bronchoconstriction than other sports. The mechanisms for this protective effect of swimming are not clear, but there is some experimental evidence intimating that it results in part from the high humidity of inspired air at water level, which reduces respiratory heat loss (and possibly osmolarity of airways mucus). Beneficial roles of horizontal posture and of water immersion have been tested but not confirmed. Swimming poses two potentially deleterious effects to the patient with asthma. One is the exaggerated parasympathetic tone due to the 'diving reflex', that has been shown to trigger bronchoconstriction. The other is airway irritation because of chlorine and its derivatives. Swimming as a training modality has definite benefits for the patient with asthma. These include an increase in aerobic fitness and a decrease in asthma morbidity. There is no conclusive evidence, however, that swim training causes a decrease in the severity or frequency of exercise-induced bronchoconstriction.