Abnormal renal resistive index in patients with mild-to-moderate chronic obstructive pulmonary disease

Arterial rigidity and endothelial dysfunction are systemic manifestations of chronic obstructive pulmonary disease (COPD). The decrease in renal vascular resistance in order to adapt the increase in glomerular filtration rate after oral protein loading is known as normal renal functional reserve. We tested the hypothesis that COPD patients, even in those with mild-to-moderate airflow obstruction, are affected by systemic inflammation associated with abnormal renal functional reserve.

The study enrolled 24 current smokers with a cigarette smoking history ≥ 25 pack-years and 8 nonsmokers with normal spirometry as control. Doppler sonography detected the renal resistive index (RRI) before and after oral protein loading to determine the renal functional reserve. Pulmonary function and serum tumor necrosis factor α (TNF-α) levels were analyzed to compare with the renal functional reserve.

The smokers were stratified into 3 groups (Group 1: smokers with normal spirometry, Group 2: mild COPD, Group 3: moderate COPD); nonsmokers as Group 4. The baseline RRI levels were similar in Group 1 and Group 4. After protein loading, the RRI elevated in all smoking groups; moreover, Group 3 had the highest RRI and with longer duration than other groups. The smokers with higher serum TNF-α levels had a longer RRI elevation. Multiple linear regression revealed forced expiratory volume in one second (FEV1), serum TNF-α levels and aging were independently predictive factors of impaired renal functional reserve.

A greater impairment in renal functional reserve of COPD patients was correlated with more severe airway obstruction and inflammation.