LUNG AND CHEST-WALL MECHANICS IN PATIENTS WITH ACQUIRED-IMMUNODEFICIENCY-SYNDROME AND SEVERE PNEUMOCYSTIS-CARINII PNEUMONIA

The aim of this study was to assess the mechanical characteristics of the respiratory system in patients with acquired immune deficiency syn drome (AIDS) and acute respiratory distress syndrome (ARDS) caused by Pneumocystis carinii pneumonia (PCP). In 12 mechanically ventilated pa tients, total respiratory system mechanics was assessed using the tech nique of rapid airway occlusion during constant flow inflation, and wa s partitioned into lung and chest wall components using the oesophagea l balloon technique, We measured interrupter resistance (Rint), which mainly reflects airway resistance, additional resistance (Delta R) due to viscoelastic behaviour and time constant inequalities, and static elastance (Est). In addition, the static inflation volume-pressure (V- P) curve was assessed, In eight patients, computed tomography scans we re performed within 2 days of the assessment of respiratory mechanics. Compared to values reported in the literature for normal subjects, Es t and Delta R were markedly increased in AIDS patients with PCP, whils t Rint exhibited a relatively smaller increase, These changes, which i nvolved only the lung and airways, were mainly due to the reduction of ventilated lung units, but additional factors mere involved to cause independent modifications of lung stiffness, airway calibre, and visco elastic properties, The changes in Rint, Delta R, and Est were similar to those observed in other studies on patients with ARDS of different aetiologies. At variance with common observations in the latter patie nts, none of the AIDS patients with PCP exhibited an inflection point on the static inflation V-P curve, suggesting little or no alveolar re cruitment during lung inflation. This finding could be related to the distinctive histopathology of Pneumocystis carinii pneumonia, Indeed, computed tomography revealed homogeneous diffuse interstitial and alve olar infiltration rather than the dense, dependent opacities observed in other studies on acute respiratory distress syndrome of different a etiologies.