DYNAMIC HYPER-INFLATION AND VENTILATOR DEPENDENCE IN CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

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Abstract
In advanced chronic obstructive pulmonary diseases, functional residual capacity (FRC) can be markedly increased by dynamic mechanisms involving expiratory flow limitation. Respiratory mechanics were studied in a seated ventilator-dependent man with such changes. Relaxed expiration was flow-limited; pressures of 9-27 cm H2O (varying with lung volume) could be applied to the airway opening (Pao) without decreasing expiratory flow rate. The FRC was at least 2 l above relaxation volume. Inspiratory total resistance was 16 cm H2O/l per s. Compliance of the lung was 0.16, chest wall 0.04 and respiratory system 0.032 l/cm H2O. Recoil pressures at end-inspiration and end-expiration, respectively, were 6.5 and 1.5 cm H2O for the lung, 33 and 11 cm H2O for chest wall and 38 and 12 cm H2O for the respiratory system. The chest wall recoiled inward at all times, pleural pressure was always substantially positive (11-33 cm H2O), expiratory flow was maximal and jugular veins were always full and nonpulsating. Inspiratory work was about 0.27 kg .cntdot. m/breath (7 times normal), most of it elastic work done on the chest wall.