Abstract
BACKGROUND: The impact of fibrosing interstitial lung disease (F-ILD) on the oxygenation of peripheral and respiratory muscles during exercise remains poorly understood. Specifically, it's unclear whether regional blood flow influences exercise capacity in these patients, and if so, to what degree. OBJECTIVES: This study aimed to investigate changes in oxygenation and blood flow volume of the intercostal (IC) and quadriceps femoris (QF) muscles during exercise in patients with F-ILD. METHODS: Muscle oxygenation (SmO2) and total haemoglobin (tHb) changes of IC and QF were measured in 36 F-ILD patients using near-infrared spectroscopy (NIRS) during six-minute walking test (6MWT). Resting, minute-by-minute change, and average data were analyzed. RESULTS: At rest, SmO2 was significantly higher in IC compared to QF (p<0.001). When adjusted for SmO2 at rest, SmO2 at the different time points during 6MWT, average SmO2 during 6MWT, and lowest SmO2 during 6MWT did not differ between QF and IC muscles. Also, SmO2 did not vary significantly during 6MWT in either QF (F=2.193) or IC muscle (F=1.262). THb increased more in QF than in IC. THb of IC inversely correlated to respiratory functions and 6MWT distance. CONCLUSION: Peripheral and respiratory muscle oxygenation in F-ILD seems to be normal. However, blood flow volume in exercising muscle, not muscle oxygenation, may be a contributing factor to exercise intolerance. Patients with poorer respiratory function may require excessive blood flow in their respiratory muscles which in turn may limit the blood flow available for exercising peripheral muscles.