The most important function of the respiratory system is the exchange of gases, the introduction of oxygen from the ambient air into the blood through the lungs, specifically the alveoli (during inspiration) and the elimination of CO2 from the venous blood produced by cellular metabolism at outside air (during exhalation).
The study of pulmonary function is an essential part of the evaluation of diseases of the respiratory system and is essential for the diagnosis and management of diseases as prevalent as chronic obstructive pulmonary disease (COPD) and bronchial asthma, among others.
The techniques used for the examination are non-invasive, except arterial blood gas analysis, which consists of extracting blood from the radial artery to know exactly the amount of oxygen and CO2 in arterial blood.
There are several tests to assess lung function:
It consists of the analysis of the magnitude of the lung volumes and the speed with which they can be mobilized (aerial flows). The respiratory maneuver to be performed is simple, but it is essential the patient's cooperation, and the preparation of the technician who performs it, otherwise, its results will not be valuable and may even lead to confusion.
The indications for spirometry are as follows:
• Evaluation of respiratory symptoms or signs
• Measurement of the effect of disease on lung function.
• Follow-up of individuals at risk of lung disease, such as smokers over 35 years of age, persistent respiratory symptoms or occupational or occupational exposure to toxic substances that can cause respiratory affection.
• Preoperative assessment of surgical risk, especially of thoracic surgery or high abdominal surgery.
• Assessment of the therapeutic response to different drugs.
• Estimation of severity and prognosis in respiratory diseases or other organs that affect respiratory function.
• Assessment of the state of health prior to programs of intense physical activity.
• Assessment of the degree of incapacity for work.
• Epidemiological studies.
• Clinical research.
Spirometry has some contraindications that must be taken into account when considering the need for such an examination:
• Recent acute hemoptysis
• Retinal detachment
• Recent myocardial infarction (<7 days)
• Recent pneumothorax
Although the basic test in the functional exploration of RA is spirometry, sometimes we need to extend the examination with procedures that allow us to measure the volumes of air that the lungs can not mobilize.
Carbon monoxide diffusion test
In order to know the situation of pulmonary gas exchange, the carbon monoxide diffusion test is performed, which consists of measuring the amount in ml of carbon monoxide that diffuses through the alveolocapillary membrane (from the alveolar gas to the blood ) per unit of time.
Arterial blood gas
Arterial blood gas analysis is also a basic technique for assessing lung gas exchange. It involves puncturing the radial artery, using local subcutaneous anesthesia, drawing blood from it and determining the pH, partial pressure of oxygen and carbon dioxide.
By this technique we will know if the patient has or not respiratory insufficiency. It is also possible to know the amount of oxygen in the blood (SaO2, arterial oxygen saturation) in an approximate but reliable way using the non-invasive pulse oximeter.
All these tests evaluate the respiratory function at rest, but if we want to know the behavior of the cardiorespiratory apparatus during the effort we must resort to the tests or tests of effort .