Respiratory function tests

"These tests are simple and the most important thing is the collaboration of the patient".


Respiratory function tests allow us to analyze how the lung and airways work and thus diagnose the type and degree of severity of respiratory diseases.

The respiratory system is responsible for introducing and transmitting to the blood the oxygen needed for energy metabolism.

It is also responsible for eliminating much of the toxic waste derived from the combustion of heat that allows us to perform our daily activities.

Imagen del icono de la consulta de Segunda Opinión. Clínica Universidad de Navarra

Do you need our help?
Contact with us

When are respiratory function tests indicated?

These are simple tests, where the important thing is the collaboration of the patient to follow the instructions that are indicated.

They do not require fasting. It is very important not to take inhaled medication (sprays or nebulizations) from the night before the test (generally 12 hours before). Unless otherwise specified by your physician, there is generally no problem with oral medications.

For bronchoprovocation or exercise tests, you should avoid drinking coffee or exercising in the previous six hours.

Do you have any of these diseases?

You may need to have respiratory function tests

Types of respiratory function tests

Simple spirometry is a simple and easy to perform test. It is indispensable for the diagnosis of some diseases such as asthma or chronic obstructive pulmonary disease and to follow their evolution and response to treatment. This test examines the volumes of air that are capable of mobilizing the lung. This is done using a flow meter (pneumotachograph) that quantifies the milliliters of air per second that pass through it.

The test is usually performed while seated. It consists of taking air and pouring it through a nozzle connected to a tube containing the pneumotachograph, following the instructions of the technician, who strongly encourages its performance.

In order to know if the levels measured are adequate, there are some formulas for the values known as normal in a similar population, for a certain age, weight and height.

In the so-called forced spirometry, in which all the air must be taken in and expelled in the shortest time possible, the maximum air flows that can be generated are also known, and with this, the calibre of the airways (trachea and bronchi) can be determined.

Spirometry with bronchodilation
Once spirometry is performed, it is sometimes repeated after an inhaled drug is administered to see if the caliber of the airway is increased with medication.

They try to examine whether the bronchial tubes react to various substances or situations by decreasing their caliber.

Thus, the ducts can be provoked in different ways:

  • Through exercise (with bicycle, treadmill, free run, etc.).
  • By inhaling cold or dry air.
  • With various substances (such as carbacol, histamine, methacholine, etc.).
  • Subsequently, a series of spirometries are performed.

These tests must always be carried out in a hospital environment. They are useful for the diagnosis of asthma, exercise asthma or the detection of "excessively hyperreactive or especially sensitive" airways, which may be due to various causes.

With spirometry we know the volume of air that the lung can mobilize and how fast it can do so. However, the lung is not completely emptied and somewhat more complex techniques are needed to assess lung size or total lung capacity.

There are diseases that pathologically increase total lung capacity, while others decrease it, either by decreasing lung size or by decreasing the size of the chest cavity that contains the lungs.

The measurement of lung volumes can be done in several ways:

  • Plethysmography: This involves breathing air inside a closed cabin of known volume and finding the lung capacity by means of physical formulas that relate pressures and volumes. It also allows to know the resistance of the airways to the passage of air.
  • Helium Dilution Method: It is based on breathing a quantity of helium.
  • Method of washing N2: based on breathing oxygen at 100% concentration that diffuses throughout the lung and then collected for analysis. The inhalation of these gases in no case poses a danger to the body.

The aim is to evaluate the capacity of the pulmonary alveoli to diffuse a gas into the blood. The surface of the alveoli is enormous, approximately the size of a soccer field.

In some diseases this surface is altered or thickened, making it difficult for oxygen to pass through. The test is performed by inhaling an amount of carbon monoxide in minimal concentrations and holding your breath for 10 seconds to allow the gas to diffuse into the blood.

Subsequently, the gas exhaled from the lungs is analyzed and, using various formulas, the so-called carbon monoxide diffusion capacity (COD) is obtained. For its correct interpretation, it is necessary to know the levels of hemoglobin in the blood.

Its values are decreased in diseases, such as emphysema, pulmonary fibrosis, pulmonary hypertension, etc.

Where do we do it?


The Department of Pneumology
of the Clínica Universidad de Navarra

Specializing in smoking and tobacco-related diseases, the Department has over 15 years of experience in smoking cessation and lung cancer early detection programs.

The department's specialists have received training at leading centers around the world, including centers in the United States, and have extensive experience in the diagnosis and treatment of all respiratory diseases, both common and rare.

Imagen de la fachada de consultas de la sede en Pamplona de la Clínica Universidad de Navarra

Why at the Clínica?

  • Leading clinical assistance with great work in research and teaching.
  • Specialized nursing team.
  • We work together with the Sleep Unit and the Lung Cancer Area.