EFFECTS OF 48 HOURS OF LEG SUSPENSION ON FEMORAL ARTERY VASCULAR PROPERTIES

Abstract

Physical inactivity is associated with an increased risk of cardiovascular mortality. Vascular changes contributing to this increased risk are largely unknown. In order to study the effect of inactivity on vascular properties, without profound systemic effects like in bed rest and space flight, the leg suspension model was used. This model has been used successfully to study effects of inactivity on strength. However, effects on vascular properties have not been reported. PURPOSE To determine short term vascular adaptations to 48 hours of inactivity using the leg suspension model. METHODS In 6 subjects one leg was suspended for 48 hours, while subjects used crutches for walking. Before and after leg suspension foot volume (measured by water displacement) and maximal voluntary contraction (MVC) of the quadriceps muscle were determined to test effectiveness of the inactivation. Resting blood flow in the common femoral artery (CFA) and superficial femoral artery (SFA), and the hyperemic response in the SFA after 13 minutes of arterial occlusion were measured by echo doppler ultrasound. RESULTS In the suspended leg quadriceps MVC decreased from 736 ± 123 N to 698 ± 105 N, p < 0.05 and foot volume increased from 1145 ± 114 ml to 1173 ± 117 ml, p < 0.05. CFA blood flow was unaltered (before: 238 ± 74 ml/min, after 307 ± 129 ml/min). While resting SFA blood flow was unchanged (before: 129 ± 67 ml/min, after 102 ± 53 ml/min), the hyperemic response in the SFA was markedly decreased (before: 864 ± 259 ml/min, after 584 ± 150 ml/min, p < 0.05), suggesting functional vascular adaptation to inactivity. CONCLUSION Leg suspension for a short period of 48 hours is effective in changing quadriceps muscle strength and foot volume, changes that have previously been described after 28 days of suspension. While resting CFA and SFA blood flow are not affected by 48 hours of leg suspension, the hyperemic response in the SFA is significantly diminished, suggesting fast adaptation of vascular properties to inactivity.