Prognostic value of pulmonary diffusing capacity for carbon monoxide and ventilation-perfusion SPECT findings in pulmonary arterial hypertension.

Reduced pulmonary diffusing capacity for carbon monoxide (D LCO ) can be observed in pulmonary arterial hypertension (PAH) and associates with increased mortality. However, the prognostic value of D LCO when corrected for haemoglobin (D LCOc ), an independent modifier of D LCO , remains understudied. Additionally, the prognostic role of ventilation (V)-perfusion (Q) emission computed tomography (V/Q SPECT) findings in patients with PAH, which may concurrently be performed to rule out chronic thromboembolic pulmonary hypertension, is uncertain. A retrospective cohort study was conducted on 152 patients with PAH referred to a tertiary hospital for evaluation from January 2011 to January 2020. Lung function tests, clinical data and V/Q SPECT were ascertained. Cox regression analysis was performed to evaluate the association between D LCOc , D LCO and V/Q SPECT defects at referral with all-cause mortality. In equally adjusted Cox regression analysis, each percentage increase in D LCOc % predicted (%pred) (hazard ratio (HR) 0.97; 95% CI: 0.94-0.99) and D LCO %pred (HR 0.97; 95% CI: 0.94-0.99) was similarly associated with all-cause mortality. There was no detectable difference in area under the curve for prediction of all-cause mortality by D LCOc %pred and D LCO %pred (C-index 0.71 and 0.72, respectively, P = 0.85 for difference). None of the defects noted on V/Q SPECT were significantly associated with mortality, but mismatched defects were associated with lower values of D LCOc %pred and D LCO %pred. D LCOc %pred and D LCO %pred perform equally as prognostic markers in PAH, supporting the use of either metric when available for prognostic stratification.