Background : Constant-load exercise (CLE) tests have been used to evaluate the effectiveness of treatment with long-acting bronchodilators or pulmonary rehabilitation in patients with chronic obstructive pulmonary disease (COPD). However, exercise limitation in the CLE test is due not only to pulmonary dysfunction but also to leg muscular strength and metabolic efficiency of the muscle, which are affected by daily physical activity and exercise habits. The present study was performed to examine the factors involved in exercise limitation in the CLE test other than pulmonary dysfunction in healthy adult volunteers to establish baselines before applying the study in COPD patients.
Methods : Twenty-seven healthy volunteers performed the CLE test using a treadmill at 80％ of maximum load determined by incremental-load exercise (ILE) test up to a maximum of 20 minutes. Subjects were divided into those who were and were not able to complete 20 minutes of the CLE test. The relative exercise load was calculated as : peak oxygen uptake (V_O2) in the CLE test/V_O2 at anaerobic threshold in the ILE test. The metabolic variables and relative exercise load were compared between the two groups.
Results : In the CLE test, the non-completion group showed significantly higher respiratory exchange ratio (RER, ＞1) as a variable of the anaerobic threshold. The relative exercise load of the CLE test and the actual exercise load in the non-completion group were higher compared to the completion group.
Conclusion : This study showed that the high relative exercise load in the CLE test causes the subject to exceed anaerobic threshold and limits maintenance of exercise in the CLE test.

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Purpose : Obstructive sleep apnea (OSA) is a disease characterized by sleep-disordered breathing (SDB) due to upper airway obstruction. Age, body mass index (BMI) and abnormal facial morphology which is evaluated by cephalometry have been reported as risk factors for severe OSA. In addition, the supine sleeping position worsens SDB because it narrows the upper airway. We thought that the percentage of supine position during sleep might be a risk factor for worsening apnea-hypopnea index (AHI) levels but it has not been verified. Therefore, we analyzed that and its gender difference.
Methods : Between May 2008 and May 2020, 228 patients with OSA who underwent full-night polysomnography (PSG) and cephalometry at our hospital were registered retrospectively. We conducted logistic regression analysis using their clinical background, findings on cephalometry and the percentage of supine position during sleep recorded on full-night PSG to identify risk factors for severe AHI levels (≥30 events/h). Subsequently, subanalyses which classified them by gender were performed.
Results : The logistic regression analysis indicated that the percentage of supine position during sleep was a significant risk factor in addition to BMI and the distance from the mandibular plane to the hyoid (MP-H) on cephalometry. A sub-analysis for male patients produced the same results. However, in a sub-analysis for female patients, the risk factors were age and BMI, but not the percentage of supine position during sleep.
Conclusions : The percentage of supine position during sleep is one of the risk factors for severe OSA, but only applies to male patients.

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