In patients with recurrent unexplained syncope, exaggerated peripheral venous pooling and impaired circulatory adjustment is thought to contribute to the outcome of a head-up tilt (HUT) test. The present study investigated the role of leg volume changes during venous congestion in the haemodynamic response of patients with recurrent unexplained syncope and the ability to predict the outcome of a HUT test. Changes in calf volume (strain gauge plethysmography), heart rate and arterial blood pressure were recorded in 60 patients with history of unexplained syncope (without postural tachycardia symptom) during venous congestion provoked by pneumatic thigh cuffs while supine at rest and during the initial 10 min of a 45 min 70° HUT test. Twenty-seven patients [age (mean±S.D.), 39±16 years] exhibited symptoms [HUT(+)] and 33 patients (45±14 years) were asymptomatic [HUT(-)]. During venous congestion, mean±S.E.M. calf volume increased in both groups [HUT(-), 4.5±0.2; HUT(+), 4.8±0.4 ml·100 ml-1, not significant), but significantly less during head-upright tilt [HUT(-), 3.3±0.2, P<0.01; HUT(+), 2.6±0.3 ml·100 ml-1, P<0.001] without differences between the groups. During venous congestion, arterial pressure increased significantly in asymptomatic HUT(-) patients, but not in the HUT(+) patients. Calf volume changes did not correlate with a symptomatic outcome to a 70° HUT. The lack of exaggerated venous pooling during venous congestion and the inability of calf volume changes to predict a positive HUT suggest that excessive venous pooling does not contribute to the outcome of HUT. Attenuated changes in arterial pressure during venous congestion while supine suggest impaired adjustment of peripheral resistance to leg venous occlusion.

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