The effect of expiratory resistance on femoral venous blood flow during light-intensity dynamic exercise

Background: The muscle pump, which refers to the intermittent compression of the leg veins by muscle contractions (i.e., the muscle pump), plays an important role in enhancing venous return. Previous studies have reported that respiratory muscle pressure modulates femoral vein blood flow velocity both at rest and during leg exercise. Furthermore, increased expiratory resistance, as observed in patients with chronic obstructive pulmonary disease, has been shown to affect femoral vein blood flow during calf exercise. However, the skeletal muscles involved in ankle movements are smaller compared to the quadriceps, which are more commonly recruited during dynamic exercises in humans. Purpose: The purpose of this study was to clarify the effect of expiratory resistive breathing on changes in femoral vein blood flow (Qfv) during dynamic, light-intensity leg exercise. Methods: Twelve healthy young participants (age 20±1 yrs, mean±SE) completed both resting and exercise trials. During each trial, participants controlled their breathing for 1-2 minutes with a tidal volume approximately 1.5 times greater than spontaneous breathing and a breathing frequency of 20 breaths/min (duty cycle 1:1, i.e., 1.5 seconds inspiration, 1.5 seconds expiration), with or without an expiratory load of +20 cmH 2 O. In the exercise trial, participants performed dynamic knee extension and flexion exercise at a light intensity (12-20 watts), with the expiratory phase synchronized to right quadriceps contraction (i.e., knee extension). Femoral venous blood velocity and diameter were continuously measured using Doppler ultrasound. Results: In the resting trial, Qfv during expiratory phase was lower (p<0.001) with voluntary hyperventilation and expiratory resistance (43±14 ml/min) compared to without resistance (114±33 ml/min). In the exercise trial, quadriceps muscle contractions increased Qfv. However, the increase in Qfv during exercise with expiratory resistance (544±61 ml/min) was not different (P=0.137) from that without expiratory resistance (555±39 ml/min). Conclusion: These results suggest that expiratory resistance does not significantly modulate venous return during light-intensity dynamic lower limb exercise involving the quadriceps. This study was supported by JSPS KAKENHI #23K10633, #23K24736. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.