Influence of jacket tightness and pressure on raised lung volume forced expiratory maneuvers in infants

While the use of the raised volume rapid thoraco-abdominal compression (RVRTC) technique has been shown to provide new insights into airway and pulmonary pathophysiology in infants, and appears to resemble the spirometric techniques used in older subjects, there is as yet no consensus regarding measurement procedures, which are known to vary considerably between laboratories (Gappa [1999] Pediatr Pulmonol 28:391-393). The aims of this study were to assess the effects of tightness of jacket fit, the efficiency with which pressure is transmitted from the jacket to the intrathoracic airways, and the effect of jacket pressure on parameters derived from the RVRTC technique. Paired forced expiratory maneuvers were performed in 20 infants with the jacket snugly or loosely wrapped around the infant's torso, and in a further 21 infants using "optimal" or a higher jacket pressure (P(j)) (1-2 kPa above "optimal" P(j)). When either a loosened jacket or a higher than "optimal" P(j) was used, forced expired flow at low lung volumes (FEF(75)) was significantly reduced by, on average, 8% and 7%, respectively. There were, however, minimal changes in forced vital capacity (FVC) or forced expired volume in 0.4 sec (FEV(0.4)). The observed changes may have been due to the increased pressure transmitted to the intrathoracic structures under these experimental conditions, and emphasize the need to assess optimal jacket pressure within each infant when using the RVRTC technique. In addition, when using a loosened jacket or a higher than "optimal" P(j), chest wall and upper airway reflexes such as glottic closure, peripheral airway closure, and negative flow dependence were more evident.