Pulmonary function vascular index predicts prognosis in idiopathic interstitial pneumonia

Pulmonary hypertension (PH) is associated with increased mortality in fibrotic idiopathic interstitial pneumonia (IIP). We hypothesize that baseline K(CO) (diffusing capacity of carbon monoxide/alveolar volume) and 6-month decline in K(CO) reflect PH, thus predicting mortality in IIP.

All IIP referrals (2004-2007) were identified (n = 269). 192 had pulmonary function at 6 months. Fifty-two (27%) died during follow-up (median 22.5 months). Outcome was evaluated for early (1 year from 6-month pulmonary function) and overall mortality. A vascular index best predicting mortality was identified (using baseline and 6-month decline in K(CO) ) and evaluated against PH at echocardiography.

Baseline and 6-month decline in K(CO) were associated with early and overall mortality. A positive vascular index (baseline K(CO) % ≤ 50% and/or ≥15% decline in K(CO) at 6 months; n = 40) was strongly predictive of early and overall mortality. Neither a diagnosis of idiopathic pulmonary fibrosis nor PH predicted early death when incorporated into this model. In patients without baseline PH, with follow-up echocardiography (n = 60), a positive vascular index was associated with PH at follow-up.

A vascular index comprised of baseline and 6-month decline in K(CO) strongly predicted increased mortality and development of PH on echocardiography. In, K(CO) may be an important marker for pulmonary vascular disease and its associated mortality.