Pulmonary Artery Wedge Pressure Respiratory Variation Increases With Sodium Nitroprusside Vasodilator Challenge

Background: The physiologic factors leading to pulmonary arterial wedge pressure respiratory variation (PAWP_var) are underexplored. We hypothesized that PAWP_var is associated with baseline PAWP and would predict response to sodium nitroprusside (SNP). Methods and Results: We performed a retrospective study of right heart catheterization studies in 51 subjects with SNP challenge at our institution from 2012 to 2019. PAWP_var was defined as expiratory minus inspiratory PAWP. Baseline %PAWP_var was inversely correlated with baseline PAWP (R = –0.5). SNP administration led to increased %PAWP_var (+27%, P <.01). Subjects with low baseline PAWP_var (less than the median) had an increase in PAWP_var with SNP (3 ± 4 mm Hg), whereas those with a high baseline PAWP_var (greater than the median) did not (–0.6 ± 4 mm Hg, P =.003). Those who had a greater than the median PAWP_var increase with SNP had greater cardiac output augmentation compared with those who had less than a median increase in PAWP_var (1.7 ± 1.5 L/min vs 0.9 ± 0.7 L/min, P =.02). An increasing PAWP_var after SNP was associated with significant discrepancy in the number of subjects achieving transplant-acceptable pulmonary vascular resistance (<2.5 Wood units) when calculated by expiratory versus mean PAWP (37 vs 27 subjects, 20% discrepancy rate). Subjects with a higher PAWP_var after SNP were more likely to demonstrate discrepant transplant-acceptable pulmonary vascular resistance calculations comparing expiratory versus mean PAWP than those with lower PAWP_var post-SNP (47% vs 13%, odds ratio 5.5, P =.03). Conclusions: Our findings indicate that PAWP_var is a meaningful physiologic parameter that is influenced by the compliance of the left heart/pulmonary vascular system and its relative preload and afterload states.