Cardiovascular Effects From Venous Blood Pooling in the Lower Limbs During Prolonged Sitting.

Purpose: To investigate whether venous blood pooling in the lower limbs from prolonged sitting induces harmful cardiovascular effects by reducing stroke volume (SV) and cardiac output (CO).

Methods: A randomized crossover trial involving 16 participants (mean age = 24.8 years ± 6.0 years, 44% women, 1 dropout) was conducted. The trial consisted of 2 conditions: cuff and noncuff, both involving 2 hours of prolonged sitting with tourniquets placed proximal to each knee. In the cuff condition, the tourniquets were inflated to subdiastolic pressure, allowing arterial inflow but preventing venous outflow. Venous blood pooling was assessed by measuring calf circumference. Cardiac Doppler sonography was used to measure CO, SV, and heart rate (HR) before and after the sitting period.

Results: Although the interaction effect between venous blood pooling and CO was not statistically significant (P = .190), there was a significant main effect for time (effect size [ES] = 0.36, β = -0.238, 5.42% decrease). A medium-sized time-by-condition interaction effect for SV was observed (ES = 0.37, β = 6.165), with a 5.87% decrease in the cuff condition and a 2.81% increase in the noncuff condition. Furthermore, there was a large interaction effect for venous blood pooling as measured by calf circumference (ES = 1.98, β = -0.987), with a 3.69% increase in the cuff condition and a 0.03% increase in the noncuff condition.

Discussion: Understanding the physiological adaptations that occur during prolonged sitting can provide insight into how and how often to interrupt sitting to prevent deleterious cardiovascular effects. SV decreased during the sitting period of 120 minutes in the cuff condition and increased slightly during in the noncuff condition. However, the changes in CO and HR were more variable and were not perfectly in line with the authors' hypotheses.

Conclusion: The findings indicate that as venous blood pooling increases during prolonged sitting, SV decreases, suggesting venous blood pooling influences certain hemodynamic changes associated with prolonged sitting.