Real-time microcirculatory monitoring during intradialytic exercise using an earlobe laser Doppler flowmeter: an exploratory preliminary study

Abstract Background Intradialytic exercise is recommended to improve exercise capacity, physical function, and quality of life in patients undergoing maintenance hemodialysis (HD). However, objective and practical physiological indicators for monitoring circulatory responses during intradialytic exercise remain limited in routine clinical settings. Laser Doppler flowmeter (LDF) enables noninvasive assessment of microcirculatory blood flow and may provide a useful method for monitoring peripheral circulation during exercise. This study aimed to (1) evaluate changes in earlobe microcirculatory blood flow during intradialytic exercise, (2) examine its association with perceived exercise intensity, and (3) explore its potential as a real-time circulatory monitoring parameter. Methods Seventeen patients undergoing maintenance HD participated in this observational study. A 20-min intradialytic exercise program consisting of lower-limb resistance and stretching exercises was performed during dialysis sessions. Bilateral earlobe blood flow and pulse rate were continuously measured using LDF. Relative changes from baseline were calculated at 5-min intervals (5, 10, 15, and 20 min). The stability index (SI), defined as the coefficient of variation of the blood flow signal, was calculated to evaluate microcirculatory stability. Perceived exertion was assessed using the modified Borg scale. Statistical analyses included paired t-tests, Wilcoxon signed-rank tests, and Pearson correlation analysis. Results Earlobe blood flow increased significantly during intradialytic exercise compared with baseline, reaching a maximum increase of approximately 1.9-fold of the resting level. A strong positive correlation was observed between earlobe blood flow and perceived exertion assessed by the Borg scale ( r = 0.938, p < 0.001). Despite the increase in blood flow, the stability index did not change significantly during exercise, indicating that microcirculatory fluctuations remained stable throughout the exercise period. Conclusions Earlobe blood flow increased during intradialytic exercise and correlated with perceived exertion, while microcirculatory variability remained stable. These findings indicate that earlobe blood flow may reflect acute peripheral circulatory responses to exercise. However, given the exploratory nature of this preliminary study, including the small sample size and lack of control conditions, further studies are needed to validate its clinical applicability.