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J Appl Physiol 83: 591-598, 1997;
8750-7587/97 $5.00
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Journal of Applied Physiology
Vol. 83, No. 2, pp. 591-598, August 1997
GAS EXCHANGE, MECHANICS, AND AIRWAYS

Effects of chest wall counterpressures on lung mechanics under high levels of CPAP in humans

Maurice Beaumont1, Damien Lejeune1, Henri Marotte1, Alain Harf2, and Frédéric Lofaso2

1 Laboratoire de Médecine Aérospatiale, Centre d'Essais en Vol, F-91228 Brétigny-sur-Orge Cédex, and 2 Service de Physiologie-Explorations fonctionnelles and Institut National de la Santé et de la Recherche Médicale U296, Hôpital H. Mondor, F-94010 Créteil, France

Received 26 December 1996; accepted in final form 8 April 1997.

Beaumont, Maurice, Damien Lejeune, Henri Marotte, Alain Harf, and Frédéric Lofaso. Effects of chest wall counterpressures on lung mechanics under high levels of CPAP in humans. J. Appl. Physiol. 83(2): 591-598, 1997.---We assessed the respective effects of thoracic (TCP) and abdominal/lower limb (ACP) counterpressures on end-expiratory volume (EEV) and respiratory muscle activity in humans breathing at 40 cmH2O of continuous positive airway pressure (CPAP). Expiratory activity was evaluated on the basis of the inspiratory drop in gastric pressure (Delta Pga) from its maximal end-expiratory level, whereas inspiratory activity was evaluated on the basis of the transdiaphragmatic pressure-time product (PTPdi). CPAP induced hyperventilation (+320%) and only a 28% increase in EEV because of a high level of expiratory activity (Delta Pga = 24 ± 5 cmH2O), contrasting with a reduction in PTPdi from 17 ± 2 to 9 ± 7 cmH2O · s-1 · cycle-1 during 0 and 40 cmH2O of CPAP, respectively. When ACP, TCP, or both were added, hyperventilation decreased and PTPdi increased (19 ± 5, 21 ± 5, and 35 ± 7 cmH2O · s-1 · cycle-1, respectively), whereas Delta Pga decreased (19 ± 6, 9 ± 4, and 2 ± 2 cmH2O, respectively). We concluded that during high-level CPAP, TCP and ACP limit lung hyperinflation and expiratory muscle activity and restore diaphragmatic activity.

continuous positive airway pressure; +Gz tolerance; positive pressure breathing; lung volumes; pattern of breathing; respiratory muscle activity

0161-7567/97 $5.00 Copyright © 1997 the American Physiological Society




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