Low diffusing capacity of the lung for carbon monoxide (DLCO) is a key indicator of mortality in group 3 pulmonary hypertension (PH), according to a study. The finding suggests a potential tool to asses patient risk based on DLCO outcomes.
The study, “Survival in pulmonary hypertension due to chronic lung disease: Influence of low diffusion capacity of the lungs for carbon monoxide” was published in the Journal of Heart and Lung Transplantation.
Group 3 PH constitutes a large and diverse group of patients with PH associated with lung diseases, such as chronic obstructive pulmonary disease (COPD) or interstitial lung disease (ILD). Despite being the second most common cause of PH, no treatments are available, and little is known about the prognosis of group 3 PH.
Researchers at the University of Minnesota performed a study to find predictors of survival and disease severity in group 3 PH patients. The study also evaluated how different PH-associated lung diseases affect clinical outcome and survival.
The study enrolled 143 group 3 PH patients (mean age 65 years) with either mild (30%) or severe (70%) PH, based on guidelines set by the World Health Organization (WHO). Apart from COPD (37%) and ILD (43%), patients with obstructive sleep apnea (10%), and combined pulmonary fibrosis and emphysema (10%) were included in the study.
Participants were followed for a median of 1.4 years. There were 69 deaths during the follow-up period, corresponding to 48% of the initial cohort.
DLCO analysis — a common method that predicts the capacity of the lungs to transfer oxygen to blood cells — showed that a low value (lower than 32% predicted) was associated with poorer 1- and 5-year survival (68% and 13%, respectively), compared with a higher DLCO (84% and 60%, respectively).
Importantly, the low-DLCO patient group had a 2 1/2 times higher risk of mortality, compared with high-DLCO patients.
These results were comparable with previous studies, reporting DLCO as a predictor of mortality in group 1 and group 2 PH patients. In addition, researchers found a greater mortality risk in group 3 PH patients with low DLCO compared with group 1 PH patients (those with pulmonary arterial hypertension, PAH) with low DLCO.
Researchers also found that reduced DLCO was strongly associated with lower cardiac output and higher pulmonary vascular resistance (PVR), two factors contributing to pulmonary vascular disease. These two variables were also associated with poor survival.
When looking at the relationship between patient survival and lung disease associated with PH in group 3, the team found a tendency for poorer survival among ILD-PH patients compared with COPD-PH.
Based on the results, the team concluded: “In group 3 patients, DLCO is a major indicator of mortality and in the future could be useful for identifying the highest-risk group 3 patients.”
Researchers also emphasized that “severe Group 3 patients have more cardiac impairment, but long-term survival between mild and severe Group 3 PH patients is equivalent.”