Читать книгу Respiratory Medicine - Stephen J. Bourke - Страница 23

It can easily be seen in the model that, as lung volume decreases, lung elastic recoil (tension within the springs) diminishes, providing less and less support for the floppy airway. It is clear, therefore, that the maximum flow rate achievable is dependent on lung volume and is reduced as lung volume is reduced. For any given lung volume, there will be a maximum expiratory flow that cannot be exceeded, no matter what the effort. You can confirm this by inspecting the shape of a flow loop, which is effectively a graph of the maximal flow rate achievable at each lung volume (see Chapter 3). A true PEFR can only be achieved by beginning forced expiration from a position of full inspiration. I would suggest you’ve been aware of this fact for longer than you realise. Immediately prior to blowing out the candles on your second birthday cake, you probably took a big breath in. At the age of 2, you had an intuitive understanding of the volume dependence of maximal expiratory flow rate.