[Pulmonary arterial hypertension in disorders of oxygen diffusion]

Twenty three cases with impairment of greater than 40% of DLCO were studied in a search of frequency, severity and pathophysiological mechanisms of PAH. Hemodinamic studies, pulmonary angiography (PA), lung scan (LS), lung biopsies (LB) were performed. The venous admixture was estimated and expressed as percentage ratio of the cardiac output (Qva/Qt x 100). Anatomical pulmonary artery to vein shunt (Qs/Qt) was estimated breathing pure O2. Ninety one percent of cases had PAH; mild to moderate in 76% of cases. Cardiac index (CI) was less than 2.8 in 26% and greater than 4.2 in 39%. The right ventricular work index (RVWI) was greater than 1.25 in 86%. The alveolar arterial oxygen tension gradient (A-aDO2) was abnormal in all cases (greater than 18 mmHg) with a Qva/Qt of greater than 30% in 78% of these cases. The Qs/Qt was found 6% in 39% of cases.

PAH was mild to moderate in DL impairment. The RVWI was usually increased with a normal or high CI. Increase in Qva/Qt that result from V/Q abnormalities and extreme impairment of DL is to be considered as the major factor functional features in the genesis of PAH. Reduction of the cross sectional area of the pulmonary vascular bed and lung function abnormalities are equally important relevants features in the genesis of PAH.