[Chronic obstructive bronchopneumopathies. What should be measured? When and how?].

Tobacco smoking, which is the main cause of chronic obstructive lung disease, produces two different disorders, each following an independent course: hypersecretion of mucus and impairment of ventilation. The most significant as regards prognosis is the latter. Its early detection requires fine respiratory function tests, notably flow-volume loops. At the chronic lung obstruction stage, conventional spirometry provides information on the degree of obstruction, and other additional tests can be used to investigate for possible emphysema. The potential repercussions of the disease on gas exchanges must be assessed by measuring arterial blood gases. Such measurements are usually performed on subjects awake and at rest, but they can be supplemented by exercise tests or examinations during sleep. A critical analysis of the values obtained is useful to decide whether oxygen therapy is needed and to follow up this treatment in patients with chronic respiratory failure.