155* Noninvasive evaluation of pulmonary disease using volumetric capnography in adult patients with cystic fibrosis

Abstract

Volumetric capnography is a technique that analyses the pattern of CO2 elimination as a function of expired volume. Expired gas receives CO2 from three sequential compartments forming three recognizible phases on the capnogram. Phase 1 contains gas from proximal conducting airways. Phase 2 represents the transitional region characterized by an increasing CO2 concentration, and phase 3 represents alveolar gas (alveolar plateau). Here we present the results of volumetric capnography in 114 normal controls (Group 1) and 11 adult patients with cystic fibrosis (Group 2) with two abnormal sweat chloride concentrations. Age was 33.6±11.4 (1) and 34.3±11.7 (2). All patients had severe pulmonary involvement: FVC= 57.9±25.9; FEV1= 41.9±23.4; FEV1%=58.4±10.6. All of them had diffuse bronchiolitis and bronchiectasis on HRCT. Capnography revealed in Groups 1 and 2, respectively: respiratory rate (RR) = 12.9±3.5 and 20.6±8.4, p = 0.001; expiratory volume (Ve): 693.2±245.9 and 537.1±151.5, p = 0.03. Peak expiratory flow (PEF): 26.5±8.9 and 30.1±7.8, p = 0.11. Phase3 slope (P3Slp): 7.80±2.36 and 43.56±31.95, p< 0.001. P3Slp/Ve = 0.014±0.007 and 0.124±0.144, p< 0.001. Expiratory time (Te): 3.1±1.1 and 2.1±1.5, p< 0.001. Patients had obstructive defects with concomitant low vital capacities. Values of capnography in patients suggest a restrictive respiratory pattern. A large phase 3 slope was found in patients. Gas transport by diffusion is the dominant mechanism in acinar spaces. Steepened phase 3 slopes may represent increased diffusional resistance in peripheral lung. Small tidal volumes also produce steeper slopes. Phase 3 slope/Ve was still significantly greater in patients. These alterations can be expected in lungs with diffuse bronchiectasis. Supported by: UNICAMP.