diseases of the blood vessels in the lung, either inflammatory (pulmonary vasculitis) or hypertrophic (pulmonary hypertension). lung conditions that increase d l c o . alveolar hemorrhage goodpasture's syndrome, polycythemia, left to right intracardiac shunts, due increase in volume of blood exposed to inspired gas. asthma due to better perfusion of apices of lung. this is caused by increase in pulmonary arterial pressure and/or due to more negative pleural pressure generated during inspiration due to bronchial narrowing. history in one sense, it is remarkable that dlco has retained such clinical utility. the technique was invented to settle one of the great controversies of pulmonary physiology a century ago, namely the question of whether oxygen and the other gases were actively transported into and out of the blood by the lung, or whether gas molecules diffused passively. remarkable too is the fact that both sides used the technique to gain evidence for their respective hypotheses. to begin with, christian bohr invented the technique, using a protocol analogous to the steady state diffusion capacity for carbon monoxide, and concluded that oxygen was actively transported into the lung. his student, august krogh developed the single breath diffusion capacity technique along with his wife marie, and convincingly demonstrated that gasses diffuse passively, a finding that led to the demonstration that capillaries in the blood were recruited into use as needed – a nobel prize–winning idea.