Eucapnic Hyperventilation

Updated: Dec 16, 2015
Author: Rakesh Vadde, MBBS; Chief Editor: Zab Mosenifar, MD, FACP, FCCP 



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.[1, 2]

Eucapnic hyperventilation has been recommended and used successfully in a wide range of summer and winter athletes for the diagnosis of exercise-induced asthma.[3] 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.[4] 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.[5]

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.[6] 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.[7]

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.[8, 9] Eucapnic hyperventilation is more sensitive than sport-specific field exercise.[8]

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.[10]


Indications of eucapnic hyperventilation include the following:

  • High clinical suspicion of exercise-induced bronchospasm with normal spirometry values (FEV1>80%)
  • If a high clinical suspicion of exercise-induced bronchospasm persists despite negative simple challenge tests like hypertonic saline or methacholine challenge

  • In the setting where asthma needs to be excluded, for example amongst commercial divers or where asthma persists and patients wish to continue taking asthma medication, for example in elite athletes during competition (International Olympic Committee Medical Commission IOC-MC)[4]


Absolute contraindications include the following:

  • Patients with known significant airway obstructions (FEV1< 50% or FEV1< 1.5 L in adults, < 1 L in children)

  • Recent severe acute asthma

  • Recent myocardial infarct or stroke within 3 months

  • Uncontrolled hypertension

  • Known aortic aneurysm

Relative contraindications include the following:

  • Patients with mild-moderate obstruction

  • Spirometry-induced bronchoconstriction

  • Pregnancy

  • Patients using cholinesterase inhibitors

  • Epilepsy


Periprocedural Care


The images below depict eucapnic hyperventilation equipment.

Equipment for Eucapnic Hyperventilation Test Equipment for Eucapnic Hyperventilation Test
Patient undergoing Eucapnic Hyperventilation proce Patient undergoing Eucapnic Hyperventilation procedure


Smoking can interfere with spirometry and eucapnic hyperventilation results by producing false-positive results. If the patient smokes cigarettes or other tobacco products, they must abstain from it for at least 6 hours prior to examination.

Eating and drinking

Patients can eat a normal breakfast or lunch before the procedure; however, they should avoid heavy meal or any alcoholic drinks. Patients should avoid spicy foods and caffeine containing drinks (which may cause heartburn, indigestion, or reflux) on the day of the procedure.

Exercise, cold air

Patient should avoid any strenuous exercise or excess exposure to cold/hot air within 4 hours prior to the test.


Certain medications can interfere with the test results. See the table below.

Table. Medications That Must Be Stopped Prior to Eucapnic Hyperventilation. (Open Table in a new window)

Drug Category


Time prior to test

Inhaled bronchodilators


8 hours


24 hours


48 hours

Oral bronchodilators

Long-acting theophylline

48 hours

Inhaled glucocorticoid


2-3 weeks

Oral glucocorticoid


2-3 weeks

Mast cell stabilizers

Cromolyn sodium

8 hours



72 hours


72 hours


72 hours


72 hours

Leukotriene modifiers


24 hours


24 hours

Patients are not routinely recommended to withhold inhaled and oral steroid for the test, however its anti-inflammatory effect can affect the bronchial response to the trigger.[11]

Elements of Informed Consent

Patients should be educated about the various steps of the procedure. Patient should be aware of the possible complications of test includes asthmalike symptoms, which include chest tightness, cough, and shortness of breath. These complications can be reversed with an inhaled short-acting bronchodilator.




The test is conventionally done with the patient sitting. The mouthpiece of the spirometry is placed in the patient’s mouth and sealed by the lips.


Generally anesthesia is not needed for this procedure


The patient should be clinically stable, and the technician should be trained to manage unwanted response such as bronchospasm. The test is done in a standard pulmonary function laboratory and is generally safe procedure.

Initially, baseline spirometry is performed twice to obtain two values for FEV1 that are reproducible. The better of the two values is taken as baseline FEV1, which has to be greater than 75% of predicted normal for sex, age, and height. For subjects with lower lung function or those known to have moderate to severe asthma, the progressive protocol for eucapnic hyperventilation is recommended.[12]

The patient wears nose clips and orally inhales a mixture of dry hypercapnic air (5% CO2 and 21% O2 balanced with N2). The eucapnic hyperventilation test allows significant hyperventilation at a rate of approximately 30 times per minute. The rate to be achieved can be calculated assessing 30 x FEV1 or 0.85 x maximum voluntary ventilation (MVV),[13] whichever is greater.[8] Further studies regarding the optimal minimum threshold minute ventilation for eucapnic hyperventilation testing in nonathletes need to be established.[14]

Using a large, nondiffusing gas bag and a 2-way nonrebreathing valve, the patient is instructed to actively hyperventilate through the mouthpiece inhaling the balanced gas mixture. The patient is encouraged to maintain this hyperventilation for 6 minutes. The FEV1 is measured immediately after the end of test and then at 5, 10, 15, and 20 minutes.

Although this particular protocol for eucapnic hyperventilation is recommended, the inspired air temperature, ventilation rate, and duration of the test can be changed to simulate the conditions under which the athlete is provoked.

The test result is positive if the FEV1 values measured within 20 minutes after the test falls more than 10% from the baseline.[8]

The percentage fall in FEV1 is calculated as follows:

100 × FEV1 (baseline) - lowest value for FEV1 (posttest)/FEV1 (baseline)

Bronchial responsiveness to a provoking stimulus is often referred to and interpreted as mild, moderate, or severe.

The response is mild if the fall in FEV1 is between 10-19.9% when the ventilation is 60% MVV or more and moderate when the fall is between 20-29.9%. The response is severe when the fall in FEV1 is 30% or more at any level of ventilation or if a fall greater than 10% occurs at a ventilation rate less than 30% MVV.

A short acting beta-agonist is given to the patients who develop bronchospasm and spirometry is repeated after 15 minutes. Patient should be observed until clinically stable. This test still remains subjective, and FEV1 most of the time is effort related.



Medication Summary

No medication is required for the procedure; however, to reverse the bronchospasm induced with hyperventilation, beta-agonist inhalers are used.


Laboratory Medicine

Laboratory Medicine Summary

See the list below:

  • Baseline spirometry

  • Baseline ABG at room air

  • Baseline hemoglobin level