Increased thickness of the adventitia and a low lung volume lead to smooth muscle contraction being less antagonized by lung elastic recoil transmitted to the alveolar wall via alveolar attachments. Increased lung compliance, such as associated with physiological ageing or with pulmonary emphysema can also result in a smaller elastic load to the airway smooth muscle and greater airway narrowing. A high lung volume and a stiff lung (low compliance) increase the elastic afterload and there is less smooth muscle shortening and less airway narrowing.