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Internal jugular valves are the only venous valves between the heart and the brain. Conditions such as coughing and other precipitating activities may result in retrograde cerebral venous flow because of the absence or presence of internal jugular valve incompetence, allowing brief transmission of high venous pressure and resulting in brain disturbance. Knowledge of these valves and their noninvasive evaluation might be useful in clinical practice. Methods. We applied air contrast ultrasonographic venography to a large sample of healthy subjects

However, color-coded duplex ultrasonography is unreliable and difficult to interpret, because venous flow might be disturbed as a result of pulsation of nearby arteries