Venous pressure changes

In 1-G, as the head moves from standing to supine:

• Vertebral system loses 21mmHg hydrostatic gradient

• Vertebral flow becomes stagnant

• Internal jugular vein falls out of Zone I compression

• Greatly increased internal jugular diameter and flow

In microgravity:

• Vertebral system loses 21mmHg hydrostatic gradient

• Vertebral flow becomes stagnant

• Internal jugular vein remains in Zone I compression

• No increased flow in internal jugular

Vertebral system is in minimal flow

Internal jugular system is in maximal obstruction

Notes:

KEY POINT

Remember the flow changes in Valdueza’s chart.

In microgravity, the vertebral venous system acts the same as in a supine position in 1-G.

The IJ, however, remains in Zone I compression as in a standing position in 1-G, but it also loses the hydrostatic gravitational gradient.

Maximum obstruction, minimal flow in microgravity- the worst of each flow characteristic found in 1-G along with the loss of the gravitational gradient.