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Figure 2. Sample of Respitrace (respiratory induction plethysmography) curves illustrating difference between quiet breathing (QB) and coughing. Displacement of curve represents thoracic excursion of subject. Displacement is less during QB (a1–b1) than during coughing (a2–b2). Chest wall movement, and therefore depth of respiration, was greater during coughing than QB. Similarly, slope of Respitrace curve indicates rate of change of thoracic movement. Hence, steepest part of curve (estimated at c1 and c2) indicates period of most rapid chest wall movement. Due to powerful forced expiration involved in coughing maneuver, maximum slope of curve is far greater during coughing (c2) than during QB (c1). Nitz JC, Perrier J, Cook P. In-vivo trial results of a novel ultrasonic cough stimulator. J Rehabil Res Dev. 2012; 49(9):1421–30.http://dx.doi.org/10.1682/JRRD.2011.07.0121