Splanchnic pooling in syncope
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We proposed that postural fainting is related to excessive thoracic hypovolemia and splanchnic hypervolemia during orthostasis compared to healthy subjects. We studied 34 patients aged 12-22 years referred for multiple episodes of postural faint and 11 healthy subjects. Subjects were studied supine and during upright tilt to 70o for 30 minutes and subgrouped into S+, historical fainters who fainted during testing (N=24), S-, historical fainters who did not faint during testing (N=10), and controls. Supine venous occlusion plethysmography showed no differences between blood flows of the forearm and calf in S+, S- or control. Cardiac index, total peripheral resistance and blood volume were not different. Using impedance plethysmography, we assessed blood redistribution during upright tilt. This demonstrated decreased thoracic blood volume and increased splanchnic, pelvic and leg blood volumes for all subjects. However, thoracic blood volume was decreased in S+ compared to control correlating well with the maximum upright heart rate. Splanchnic volume was decreased in the S+ and S- groups correlating with the change in thoracic blood volume. Pelvic and leg volume changes were similar for all groups and uncorrelated to thoracic blood volume. Enhanced postural thoracic hypovolemia and splanchnic hypervolemia are associated with postural simple faint.


The  figure shows changes in thoracic, splanchnic, pelvic and leg blood volumes during upright tilt. S+ are patients with a history of fainting who fainted during the test. S-  are patients with a history of fainting who did not faint during the test. There is decreased thoracic blood volume in S+ paired with increased splanchnic blood volume compared to control (p<.01). Splanchnic blood volume was also increased (p<.05) in S- patients. Pelvic and leg blood volume changes were not different from control.


Text Box: % volume

The figure depicts correlations between thoracic impedance and splanchnic (left panel), pelvic (middle panel), and lower limb (right panel) impedances  . Control subjects are shown in black, S+ in blue and S- in red. Splanchnic and thoracic impedance are significantly correlated and vary similarly over all subjects.  Changes in pelvic and leg impedances are unrelated to changes in thoracic impedance.




Splanchnic pooling in syncope
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Decreased Cerebral Autoregulation during Syncope in the Young