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Venous reflux/bidirectional flow:
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Valsalva maneuver induced jugular venous reflux:
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• Valsalva maneuver-like activities which increase intrathoracic pressure may lead to IJV incompetence, known as jugular vein reflux and measured on DS or IVUS.
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*Spontaneous venous reflux:
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• Present on DS examination in the IJV and vertebral veins and for more than 0.88 seconds with the head at 90° and 0°; delayed emptying time on CV.
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*Venous reflux in the intracerebral veins:
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• Reflux/bidirectional flow on DS in the deep cerebral veins is defined as reverse flow for a duration of 0.5 s in one of the intra-cranial veins.
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Abnormal venous flow distribution in extracranial veins:
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• Measurement of blood flow, blood volume and blood velocity by using DS, MR phase contrast imaging, CV or IVUS.
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No flow in extracranial veins:
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• No flow on DS or IVUS or contrast noted in the vein on CV and MRV, despite deep breaths.
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Abnormal posture control of IJV flow:
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• A negative ∆CSA on DS represents the loss of the normal postural control; altered estimation of changes in venous capacitance and venous resistance by posture change on plethysmography.
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