Figure 2. Kaplan-Meier plot showing the development of pneumonia over time in the patient groups with mild, moderate, and severe emphysema extent, as determined by computed tomography (CT). The patients were classified into three groups on the basis of emphysema extent, as indicated by the CT measurement of inspiratory volume fraction (%) of the lung below –950 Hounsfield unit (V₉₅₀). The patients in the 33th percentile or less, the 34th to 66th percentile, and the 67th percentile or greater were categorized as having mild, moderate, and severe emphysema, respectively. Logrank (Mantel-Cox) test, p<0.001.