Читать книгу Respiratory Medicine - Stephen J. Bourke - Страница 80

The forced expiratory volume in 1 second (FEV₁) is the volume of air expelled in the first second of a maximal forced expiration from a position of full inspiration. It is reduced in any condition that reduces VC, but is particularly reduced when there is diffuse airway obstruction. In diffuse airway obstruction therefore, the ratio FEV ₁ :FVC is lower than would be predicted in health. When interpreting results it is important to understand what normal is. During a forced expiratory manoeuvre, the proportion of air expelled in the first second varies with age. For people in their 20s that volume should be at least 85% of the total, while people in their 80s should be able to expel at least 70% in the first second.

When the ratio FEV ₁ :FVC is reduced, this pattern is referred to as an obstructive defect and is most commonly seen in asthma and COPD. When lung volume is restricted (by, for example, reduced lung compliance chest deformity or muscle weakness), the VC and FEV₁ are both reduced, roughly in proportion, so that the FEV₁:FVC ratio is essentially normal. This pattern of ventilatory impairment is referred to as a restrictive defect.