Submitted on February 21, 2008
Revised on May 27, 2008
Accepted on July 10, 2008
Leg intravenous pressure during head-up tilt
Jan T. Groothuis, Fleur Poelkens1, Constantijn W Wouters1, Miriam Kooijman, and Maria T.E. Hopman1*
1 Radboud University Nijmegen Medical Centre
* To whom correspondence should be addressed. E-mail: m.hopman{at}fysiol.umcn.nl.
Leg vascular resistance is calculated as the arterial - venous pressure gradient divided by blood flow. During orthostatic challenges it is assumed that the hydrostatic pressure contributes equally to leg arterial as well as to leg venous pressure. Because of venous valves, one may question whether, during orthostatic challenges, a continuous hydrostatic column is formed and if leg venous pressure is equal to the hydrostatic pressure. The purpose of this study was, therefore, to measure intravenous pressure in the great saphenous vein of 12 healthy individuals during 30° and 70° head-up tilt and compare this with the calculated hydrostatic pressure. The height difference between the heart and the right medial malleolus level represented the hydrostatic column. The results demonstrate that there were no differences between the measured intravenous pressure and the calculated hydrostatic pressure during 30° (47.2 ± 1.0 and 46.9 ± 1.5 mmHg, respectively) and 70° head-up tilt (83.9 ± 0.9 and 85.1 ± 1.2 mmHg, respectively). Steady state levels of intravenous pressure were reached after 95 ± 12 s during 30° and 161 ± 15 s during 70° head-up tilt. In conclusion, the measured leg venous pressure is similar to the calculated hydrostatic pressure during orthostatic challenges. Therefore, the assumption that hydrostatic pressure contributes equally to leg arterial as well as to leg venous pressure during orthostatic challenges can be made.
