McCool F D, Leith D E
Clin Chest Med. 1987 Jun;8(2):189-95.
Mucous secretions are normally removed by ciliary beating. When this defense mechanism is impaired or overwhelmed by increased secretions, cough then becomes an important means of secretion removal. For cough to be effective, the linear velocity of gas traveling through the airways should be high. Since the linear velocity of gas is related to flow and the cross-sectional area of the airways, cough is most effective when expiratory flows are great (effort independent) and dynamic compression (effort dependent) leads to a reduction of the cross-sectional area of the larger downstream airways. Cough failures may be related to either inadequate generation of expiratory flow rates (that is, in obstructive lung disease or inspiratory muscle weakness), failure to dynamically compress the airways (that is, in expiratory muscle weakness or increased collapsibility), alterations in airway geometry (that is, in bronchiectasis), or abnormal quantity or quality of mucous production (that is, in chronic bronchitis).
黏液分泌物通常通过纤毛摆动清除。当这种防御机制受损或因分泌物增加而不堪重负时，咳嗽就成为清除分泌物的重要手段。为使咳嗽有效，通过气道的气体线性速度应较高。由于气体线性速度与流量和气道横截面积有关，当呼气流量较大（与用力无关）且动态压缩（与用力有关）导致下游较大气道横截面积减小时，咳嗽最为有效。咳嗽失败可能与呼气流量产生不足（如在阻塞性肺病或吸气肌无力时）、无法动态压缩气道（如在呼气肌无力或可塌陷性增加时）、气道几何形状改变（如在支气管扩张时）或黏液产生的数量或质量异常（如在慢性支气管炎时）有关。
