Blood cadmium levels and oxygen desaturation during the 6‐minute walk test in patients with chronic obstructive pulmonary disease

Abstract

Background and Objectives: chronic obstructive pulmonary disease (COPD) is characterized by persistent airflow limitation and a history of exposure to noxious stimuli. Cigarette smoking is the most important causal factor for developing COPD. Cadmium, a minor metallic element, is one of the main inorganic components in tobacco smoke. Inhaled cadmium was associated with a decline in lung function, gas exchange impairment, and the development of obstructive lung disease. Patients with COPD who had oxygen desaturation during the 6‐min walk test (6MWT) had a significantly worse prognosis than non‐desaturation in COPD patients. Nonetheless, few studies have addressed the influence of blood cadmium levels on exercise‐induced oxygen desaturation in COPD patients. Our objective was to assess the potential impact of blood cadmium levels on oxygen de-saturation during the 6MWT among COPD patients. Materials and Methods: we performed a retrospective analysis of patients with COPD who were examined for blood cadmium levels in a tertiary care referral center in Taiwan, between March 2020 and May 2021. The 6‐min walk test was per-formed. Normal control subjects who had no evidence of COPD were also enrolled. Results: a total of 73 COPD patients were analyzed and stratified into the high‐blood cadmium group (13 patients) and low‐blood cadmium group (60 patients). A total of 50 normal control subjects without a diagnosis of COPD were enrolled. The high‐blood cadmium group had a significantly higher extent of desaturation than the low‐blood cadmium group. The frequency of desaturation during 6MWT revealed a stepwise‐increasing trend with an increase in blood cadmium levels. A multivariable logistic regression model revealed that blood cadmium levels were independently associated with desaturation during the 6MWT (odds ratio 12.849 [95% CI 1.168–141.329]; p = 0.037). Conclusions: our findings indicate that blood cadmium levels, within the normal range, were significantly associated with desaturation during 6MWT in patients with COPD.