Yanagi H; Toneyama Medical Center, Toyonaka, Osaka, 560-8552, Japan.
Miki K; Koyama K; Miyamoto S; Mihashi Y; Nagata Y; Hashimoto K;
Hashimoto H; Fukai M; Maekura T; Yonezawa R; Sakaguchi S; Nii T; Matsuki
T; Tsujino K; Kida H

BMC Pulmonary Medicine. 24(1):550, 2024 Oct 31.

BACKGROUND: In patients with chronic obstructive pulmonary disease (COPD),
the clinical use of the minute ventilation-carbon dioxide production
([Formula: see text]E-[Formula: see text]CO2) slope has been reported as a
measure of exercise efficiency, but the oxygen uptake efficiency slope
(OUES), i.e., the slope of oxygen uptake ([Formula: see text]O2) versus
the logarithmically transformed [Formula: see text]E, has rarely been
reported.

METHODS: We hypothesized that the [Formula: see text]E-[Formula: see
text]CO2 slope is more useful than OUES in clinical use for the
pathophysiological evaluation of COPD. Then, we investigated the
cardiopulmonary exercise testing parameters affecting each of these slopes
in 122 patients with all Global Initiative for Chronic Obstructive Lung
Disease (GOLD) COPD grades selected from our database.

RESULTS: Compared with the GOLD I-II group (n = 51), peak [Formula: see
text]O2 (p < 0.0001), OUES (p = 0.0161), [Formula: see text]E at peak
exercise (p < 0.0001), and percutaneous oxygen saturation (SpO2) at peak
exercise (p = 0.0004) were significantly lower in the GOLD III-IV group (n
= 71). The GOLD III-IV group was divided into two groups by the exertional
decrease in SpO2 from rest to peak exercise: 3% or less (the
non-desaturation group: n = 23), or greater than 3% (the desaturation
group: n = 48). OUES correlated only weakly with peak [Formula: see
text]O2, [Formula: see text]E at peak exercise, and the difference between
inspired and expired mean O2 concentrations (DELTAFO2) at peak exercise,
i.e., an indicator of oxygen consumption ability throughout the body, in
the GOLD III-IV group with exertional hypoxemia. In contrast, the
[Formula: see text]E-[Formula: see text]CO2 slope was significantly
correlated with DELTAFO2 at peak exercise, regardless of the COPD grade
and exertional desaturation. Across all COPD stages, there was no
correlation between the [Formula: see text]E-[Formula: see text]CO2 slope
and [Formula: see text]E at peak exercise, and stepwise analysis
identified peak [Formula: see text]O2 (p = 0.0345) and DELTAFO2 (p <
0.0001) as variables with a greater effect on the [Formula: see
text]E-[Formula: see text]CO2 slope.

CONCLUSIONS: The OUES may be less useful in advanced COPD with exertional
hypoxemia. The [Formula: see text]E-[Formula: see text]CO2 slope, which is
independent of [Formula: see text]E, focuses on oxygen consumption ability
and exercise tolerance in COPD, regardless of the exertional hypoxemia
level and COPD grade. Therefore, the [Formula: see text]E-[Formula: see
text]CO2 slope might be useful in establishing or evaluating tailor-made
therapies for individual patient’s pat