Expiratory loading modulates the quadriceps muscle pump-induced venous return during rhythmic isometric exercise.

Area of Science:

• Physiology
• Exercise Physiology
• Cardiovascular Physiology

Background:

• Venous return is crucial for exercise performance, aided by the skeletal muscle pump.
• Expiratory loading can increase intra-abdominal pressure, potentially hindering venous return from lower limbs.
• The specific impact of expiratory loading on the quadriceps muscle pump's contribution to venous return is not well understood.

Purpose of the Study:

• To investigate the effect of expiratory loading on venous return facilitated by the quadriceps muscle pump.
• To determine if increased expiratory pressure influences the blood flow augmentation during quadriceps contractions.

Main Methods:

• Healthy participants performed isometric quadriceps contractions with controlled breathing.
• Expiratory loading (20 cmH2O mouth pressure) was applied during the expiratory phase, synchronized with muscle contraction.
• Femoral vein blood flow (Qfv) was measured using Doppler ultrasound with and without expiratory load.

Main Results:

• Quadriceps muscle contraction significantly increased femoral vein blood flow (Qfv).
• The contraction-induced increase in Qfv was significantly smaller under expiratory loading conditions compared to no loading (497.6 vs. 694.8 mL/min).
• No significant differences in force or electromyography were observed between loading conditions.

Conclusions:

• Increased expiratory loading may partially impair the quadriceps muscle pump's ability to enhance venous return during light-intensity exercise.
• These findings suggest a potential mechanism by which expiratory resistance could affect cardiovascular responses during physical activity.