Effect of body position changes on pulmonary gas exchange in Eisenmenger'ssyndrome

Preliminary studies on sleep of patients with congenital heart disease and Eisenmenger's syndrome (ES) at our institution demonstrated nocturnal worse ning arterial unsaturation, which appeared to be a body position-related ph enomenon. To investigate the potential effect of body position on gas excha nge in ES, we carried out a prospective study of 28 patients (mean age, 34. 8 +/- 11.7 yr) with established ES due to congenital heart disease. in ever y patient, arterial blood gases were performed during both sitting and supi ne positions under three different conditions: room air, while breathing 10 0% oxygen, and after breathing oxygen at a flow rate of 3 L/min through nas al prongs. Alveolar oxygen pressure (Pa-o2) for the calculation of alveolar -arterial oxygen tension differences (AaPo(2)) was derived from the alveola r gas equation using Pace, and assuming R = 1. We used paired t test, repea ted-measures two-way ANOVA with Bonferroni's test, and regression analysis. From sitting to supine position on room air, there was a significant decre ase in Pa-o2 (from 52.5 +/- 7.5 to 47.5 +/- 5.5 mm Hg; p < 0.001) and Sa(o2 ) (from 86.7 +/- 4.6 To 83.3 +/-: 4.9%; p < 0.001), both of which were corr ected by nasal O-2 (to 68.2 +/- 21 mm Hg and to 92 +/- 4%, respectively, p < 0.005). Pa-co2 and pH remained unchanged. The magnitude of the change In Pa-o2 correlated with the change in AaPo(2) on room air (r = 0.77; p < 0.01 ) but not with the change in AaPo(2) on 100% oxygen. It is concluded that i n adult patients with ES there is a significant decrease in Pao(2) and Sao( 2) when they change from the sitting to the supine position. A ventilation- perfusion ((V) over dot/(Q) over dot) distribution abnormality and/or a dif fusion limitation phenomenon rather than an increase: in true shunt may be the mechanisms responsible for this finding. The response to nasal O-2 We o bserved warrants a trial with long-term nocturnal oxygen therapy in these p atients.