Hypoxemia as a potential risk factor of endothelial dysfunction and arterial stiffness in patients with chronic obstructive pulmonary disease

Summary. This study was aimed at evaluation of role of hypoxemia in development of endothelial dysfunction (ED) and arterial stiffness (AS) in patients with COPD. AS of large vessels and ED were measured by photoplethysmography. Stiffness index (SI) and reflection index (RI) were calculated: The SI indicates the pulse wave velocity in large arteries. The RI is primarily related to small vessel tonus. ED was assessed using the RI dynamics following inhalation of salbutamol (Δ RISLB). Hypoxemia was evaluated using blood gas analysis, night-time pulse oximetry, basal oxygen saturation (SpO2), duration of periods with SpO2 < 88 %, minimal SpO2, and 6-minute walking test (6MWT). All patients were males with II to IV GOLD stage COPD, the mean age 64.5 ± 7.6 years, FEV1 37.7 ± 14.1 %pred., SaO2 90.5 ± 5.5 %, РаО2 63.2 ± 11.2 mm Hg, РаСО2 40.6 ± 5.4 mm Hg, breathing frequency 22.4 ± 2.6 per 1 min, heart beat rate 80.7 ± 13.4 per 1 min, BMI 25.12 ± 5.86 kg / m2, and smoking history 40 (35–50) packyears. Relationships were found between Δ RISLB and basal SpO2 (R = 0.38; p = 0.04), duration of periods with SpO2 < 88 % (R = –0.48; p = 0.01), minimal SpO2 (R = 0.44; p = 0.02); duration of periods with SpO2 < 88 % during night sleep (R = –0.42; p = 0.04) and resting daytime blood oxygen tension PаО2 (R = 0.42; p = 0.04). ED was significantly more severe in 16 patients with hypoxemia (РаО2 ≤ 60 mm Hg) compared to 25 patients with РаО2 > 60 mm Hg (0 [–1.7–1.3] % vs 2.00 [0.35–12.35] %; р ≤ 0.04). Therefore, increased hypoxemia in COPD patients was accompanied by a significant decrease in lung function. AS was related to hypoxemia in 6MWT. The lower minimal SpO2 and the longer periods with SpO2 < 88 % in 6MWT were, the higher photoplethysmographic SI was. The results support the crucial role of hypoxemia in arterial wall mechanical disorders and ED in patients with COPD.