<qa>  What is the measurement of lung density?The investigators will perform pulmonary function testing at baseline and compare degree of obstruction according to HIV status while adjusting for other clinical variables that influence lung function. Assessment of degree of emphysema and its distribution can be accomplished using quantitative CT morphometry density analysis. This technique measures lung density by pixel analysis expressed in Hounsfield units HU or its inverse ml of gasgram of tissue which increases proportionately with the magnitude of emphysema. These measurements have been histologically-verified and give quantitative, reproducible measurements of percentage and distribution of lung considered normal, mildly emphysematous, and severely emphysematous. The investigators will compare emphysema in the HIV and HIV- subjects and compare progression over time. 