Intermittent calf compression reverses lower limb pooling and improves cardiovascular control during passive orthostasis.

When upright, venous pooling and capillary filtration reduce the effective circulating volume and are key contributors to susceptibility to syncope (fainting). Recurrent syncope has a devastating impact on quality of life. Static calf compression garments are frequently prescribed for patients with syncope, but have questionable efficacy. Intermittent calf compression, which mimics the skeletal muscle pump to minimize pooling and filtration, is a potential alternative that holds promise for the management of syncope. We aimed to evaluate use of intermittent calf compression compared to commonly prescribed compression stockings, and determine the optimal intermittent calf compression paradigm, for improvement of orthostatic fluid shifts and cardiovascular control. We evaluated heart rate, blood pressure, stroke volume, cardiac output and peripheral resistance (finger plethysmography with Modelflow™) and calf pooling and filtration (calf circumference; strain gauge plethysmography) during a series of 10-min head-upright tilts. We first compared (protocol one) low (ICLF; 4 s on, 11 s off) and high (ICHF; 4 s on, 6 s off) frequency 0-100 mm Hg intermittent calf compression with static elastic and inelastic compression stockings and a placebo condition (n = 19, 5 males, aged 23.5 ± 0.1 years). We then compared (protocol two) ICLF applied at 0-40 mm Hg, 0-60 mm Hg, 0-80 mm Hg and 0-100 mm Hg as well as a placebo condition (n = 15, 5 males, aged 22.7 ± 0.5 years). The intervention order was randomized. In protocol one, all compression conditions significantly reduced calf circumference (p < 0.001) compared to placebo after 10-min upright; however, this reduction was greater in ICLF (-0.88 ± 0.18%) and ICHF (-1.14 ± 0.21%) conditions than both elastic (+0.49 ± 0.17%) and inelastic (-0.01 ± 0.19%) compression (p < 0.001). ICLF and ICHF, but not elastic or inelastic compression, were associated with improved stroke volume (p ≤ 0.001), allowing cardiac output to be maintained at a reduced heart rate (p < 0.001) without increases in vascular resistance responses, increasing hemodynamic reserve. ICHF showed no significant benefit over ICLF, evidenced by the lack of significant difference between ICLF and ICHF in any parameter measured. In protocol two, 0-60 mm Hg ICLF was considered the optimal intermittent compression because it was the lowest pressure that abolished the increase in calf circumference during orthostasis, while improving SV (p = 0.002), and reducing HR (p < 0.001) throughout tilt. Intermittent calf compression from 0 to 60 mm Hg ICLF is the optimal intermittent compression paradigm to ameliorate orthostatic fluid shifts and improve hemodynamic control. Commonly prescribed static calf compression garments do not improve orthostatic cardiovascular responses.