| Popis: |
The physical nature of the dynamic mechanisms of impedance to gas flow in the lungs has been investigated experimentally and modeled mathematically for many years. This has been particularly true of the mechanisms believed responsible for the fixed upper limits to gas volume flow rates during the effort-independent portion of a maximal exhalation. In 1958, Hyatt, Schilder, and Fry described the relationship between maximum expiratory flow and degree of lung inflation (1) and developed the concept of the maximal expiratory flow-volume curve. Their experimental results showed that over the lower half of the vital capacity, during a maximal exhalation, the flow was effort-independent. Since that time, the effort-independent portion of the maximum expiratory flow-volume curve has been reported to reach as high as 90% of the vital capacity for some subjects (2). |
