Formal systematic reviews on selected topics covered in the guideline were performed by the Center for Clinical Health Policy Research at Duke University Medical Center. These reviews covered the efficacy of selected treatments for cough associated with the common cold and acute bronchitis. Treatments included inhaled bronchodilators, antitussive (cough suppressant) therapies, and protussive therapies. Antitussive therapies (ie, cough suppressants) included drugs that affect mucociliary factors, the afferent limb of the cough reflex, the cough center, the efferent limb of cough reflex, and the skeletal muscles. Protussive therapies were subdivided into pharmacologic treatments and mechanical devices. The review of mechanical devices contained evidence on expiratory muscle training, huffing, positive expiratory pressure, chest physiotherapy and postural drainage, autogenic drainage, high-frequency air flow oscillation devices such as the Flutter (Scandipharm; Birmingham, AL) and Acapella (DHD Healthcare; Wampsville, NY), devices that provide high-frequency chest compressions (ThAIRapy bronchial Drainage System or ABI Vest; Hill-Rom; St. Paul, MN), percussive devices (Percussionaire device; Medical Specialities; New Orleans, LA), mechanical insufflation/exsufflation devices such as the In-Exsufflator, Coffaltor, Cough-Alator (J.H. Emerson; Cambridge, MA), electrical stimulation of respiratory muscles, and assisted cough with manual compressions of the lower thorax and abdomen.