Multiorgan loss of tissue
The researchers found that patients with baseline DLCO < 60% were more likely to be women (46% versus 28%), and to have a lower BMI (25 vs. 27), higher pack-year history (54 vs. 43), the same spirometric values but lower IC/TLC ratio (.37 vs. .40), a lower walk distance (443 vs. 485 meters), higher dyspnea (MRC score 1.1 vs. .7), similar exacerbation rate, higher BODE index (.5 vs. .2) and higher mortality than patients with higher DLCO % predicted values. This group, Dr. de Torres and colleagues suggest, represents a multiorgan loss of tissue, a phenotype associated with worse clinical outcomes and prognosis.
“Low DLCO in these patients,” Dr. de Torres said in an interview, “could mainly be secondary to coexistent emphysema, which is the most common cause of low DLCO in this population. Also possible, but less likely, is coexistent pulmonary hypertension.” He noted further that “This study opens the door to research specifically testing if such is the case, and if it is, for clinicians to use available therapies to prevent adverse outcomes.”
Comorbidity burden
Patients with GOLD I COPD die more often of cardiovascular disease instead of underlying lung disease, according to Richard H. Zou, MD, and Jessica Bon, MD, of the University of Pittsburgh, in an accompanying editorial in the journal CHEST.
Increased mortality rates, they suggest, may be related to higher comorbidity burden, particularly comorbidities associated with cardiovascular-related health. Subclinical cardiovascular disease is a common comorbidity in COPD, and concomitant endothelial dysfunction has been associated with both cardiovascular disease and early emphysema in smokers. They may have disproportionately reduced DLCO levels because of parenchymal destruction.
“This study suggests that DLCO can be used to identify patients with GOLD I COPD at increased death risk and that individuals with mild airflow obstruction with DLCO <60% predicted are a clinical phenotype distinct from those with higher DLCO levels,” Dr. Zhou and Dr. Bon concluded.
The researchers and the editorialists declared that they had no disclosures. One of the three cohorts assessed in the current study (CHAIN cohort in Spain) received funding from AstraZeneca.