what does the isovolumetric pressure - flow curves represent?
it plots expiratory airflow against against pleural pressure which is measured at different lung volumes
what is vital capacity?
maximal inspiration to maximal expiration down to residual volume
why does EPP occurs at lower airflow at 25% VC than at 50% VC
because at lower lung volumes, alveolar elastic recoil pressure is reduced, lowing the driving force for airflow
how does restrictive diseases alter lung volumes?
because the lungs cannot fully expand all volumes decrease
how does obstructive diseases alter lung volumes
increased residual and functional residual capacity due to trapped air in between breaths and decreased vital capacity because air is trapped at the end of expiration
what causes air trapping?
- dynamic airway compression
- mucus plugging
- narrowing airways
- loss of elastic recoil
what is relaxation volume?
the volume where no muscles are active and the lungs-chest wall system are fully relaxed
why does effort independence happen?
because as lung volume decreases, elastic recoil pressure falls and intrapleural pressure rises due to muscle effort. this leads to dynamic compression and beyond a certain point increasing efferots just compresses the airways further instead of increasing airflow
