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

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.