Exploration fonctionnelle respiratoire

The goal of investigating lung function is to evaluate the severity of a pathological functional impairment of the respiratory system, to elucidate its underlying mechanism, to help for the differential diagnosis and to check therapeutic effects. All these points may be solved by measuring lung volumes, airways permeability and diffusion of gases between air and blood. These tests can show too small (restriction) or too large (distension) lung volumes, bridled air flow through the airways (obstruction) or impaired transfer of gases to the blood (emphysema, fibrosis). They also measure the reversibility of airway obstruction using a bronchodilator, and conversely they may assess bronchi hyper-reactivity to an inhaled irritant substance. The severity of the functional impairment, as well as the recovery of normal function after therapy can be evaluated using tabulated predicted normal values. More sophisticated tests are used to assess decreased strength of the respiratory muscles, ventilatory response to hypercapnia or respiratory behaviour during exercise, especially when basic tests failed to explain the symptoms or the functional impairment. In case of severe respiratory insufficiency, blood gases (O2, CO2) measurements and acid-base equilibrium (pH) are often the only practicable tests.