Internal Jugular Vein Flow in the Sitting Position

All volunteers will be fully awake throughout the study and be kept comfortable. A cross will be marked where the left and right IJV cross the level of C6. This is where all the measurements will be taken in 3 different conditions at rest, jugular occlusion and valsalva maneuver. At each conditions, the left and right IJV will be scanned with an ultrasound measuring the cross sectional area and Doppler velocity of the IJV. The least amount of pressure will be used to press on the ultrasound probe and the measurements will be obtained at end inspiration. The IJV flow is then calculated.