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Positive effort dependence of maximal expiratory flow
Journal of Applied Physiology (Bethesda, Md. : 1985)
|February 1, 1987
Summary
Maximal expiratory flow can be effort dependent over a larger vital capacity range than previously thought. This effort dependence is linked to chest wall shape changes, not intrinsic lung mechanisms.
Area of Science:
- Pulmonary Physiology
- Respiratory Mechanics
Background:
- Maximal expiratory-flow volume (MEFV) curves are generally considered effort-independent over most of the vital capacity (VC).
- Previous understanding suggests limited effort dependence in normal subjects.
Purpose of the Study:
- To investigate the effort dependence of maximal expiratory flow over the vital capacity.
- To differentiate between chest wall mechanics and intrinsic lung factors contributing to effort dependence.
Main Methods:
- Studied seven normal males using isovolume pressure-flow (IVPF) curves.
- Manipulated transpulmonary pressure while maintaining constant effort (pleural pressure).
- Utilized respiratory inductive plethysmography to assess chest wall emptying patterns.
Main Results:
- Five of seven subjects exhibited positive effort dependence between 50-80% VC.
- Varying transpulmonary pressure at constant effort did not increase flow.
- Altering chest wall emptying patterns altered maximal expiratory flows.
Conclusions:
- Maximal expiratory flow can be effort dependent over a greater portion of VC than commonly recognized.
- Effort dependence may stem from central airway changes related to chest wall shape during forced expiration.