Background
Eucapnic hyperventilation (eucapnic voluntary hyperpnoea) is a provocative indirect stimulus test used to diagnose exercise-induced asthma or exercise-induced bronchospasm. Exercise-induced asthma (EIA) is defined in a patient with preexisting asthma who has an exacerbation of the asthma with exercise. On the other hand, exercise-induced bronchospasm (EIB) is considered if the patient has no evidence of asthma except during or after exercise.
Eucapnic hyperventilation has been recommended and used successfully in a wide range of summer and winter athletes for the diagnosis of exercise-induced asthma.
At present, the United States Olympic Committee (USOC) requires exercise-induced asthma or exercise-induced bronchospasm to be diagnosed via eucapnic hyperventilation in order for preventive and treatment-related medications to be used in competition.
Provocation with dry powder mannitol has recently been proposed as an alternative to eucapnic hyperventilation. The need to provide objective testing has resulted in a reduction in the number of athletes seeking approval to use an inhaled beta2-agonist.
The mechanisms proposed to explain why the airways narrow in response to intense exercise or eucapnic hyperpnoea of dry air are also likely to account for other symptoms in athletes performing exercise, particularly in the cold.
The response to breathing dry air is thought to cause the airways to narrow by osmotic and thermal consequences of evaporative water loss from the airway surface in response to humidifying the inspired air.
Respiratory symptoms cannot be relied on to make the diagnosis of exercise-induced asthma or exercise-induced bronchospasm. For this reason, the diagnosis should be confirmed with bronchial provocation tests. The two types of Provocative tests are direct and indirect.
Indirect provocation tests such as eucapnic hyperventilation, mannitol, or hypertonic saline are more specific for asthma than hyper-responsiveness to a direct stimulus such as methacholine.
Eucapnic hyperventilation is more sensitive than sport-specific field exercise.
During episodes of hyperventilation, the airways mucosa can dry out, creating a hypertonic environment. In exercise challenge testing, this is often limited by the inability to reach an appropriate level of hyperventilation because exercise is usually cardiac limited; however, the respiratory stimulus is sought. Normal hyperventilation is limited by the development of hypocapnia which can cause significant dizziness, neurological symptoms, and syncope.
Bronchial provocation testing using eucapnic voluntary hyperventilation came into favor when exercise was determined unnecessary to achieve high respiratory rates. The possible side effects of hyperventilation were counteracted with the addition of 4.9% carbon dioxide.