Validation of the measurement of venous compliance during orthostatic stress

Venous compliance (VC) represents the accommodated amount of volume by raising
venous pressure with 1 mmHg. In obstetrics, VC plays an important part. The
adaptation to pregnancy requires an increase in VC, which is reduced in women
who eventually develop preeclampsia.
In an earlier study, we developed 2 faster methods. However, those methods
turned out to have a high coefficient of reproducibility (CR) and coefficient
of variance (CV). Another fast method to measure VC is developed by Halliwill
et al. In this method cuff pressure is kept at 60 mmHg for 4 minutes, after
which the cuff is deflated with 1 mmHg/s. Halliwill also introduced a
non-invasive method to measure intravenous pressure. Unfortunately, we expect
this method to be inappropriate for applications in the obstetric field,
because of the increased capillary leakage in pregnancy and the used cuff
pressure of 60 mmHg is possibly not sub-diastolic in (pregnant) women.
Therefore, a comparison of these methods is needed to determine the best method
of measuring VC in women.
Besides, we would like to study the effect of orthostatic stress on venous
compliance and the best method to measure VC during orthostatic stress. We
expect a decrease in venous compliance when sympathetic activity increases
during head-up tilt. A decrease in venous compliance in this situation will
create a sufficient venous return and thus cardiac output.

To determine the best method of measuring venous compliance in women.
To determine the influence of orthostatic stress on venous compliance and the
best method to measure VC during orthostatic stress.

observational/validation study

There is a chance of imminent fainting at (mainly) 60 degrees head-up tilt,
which will resolve immediately after changing to supine position.
Besides, volunteers can experience irritation of the finger cuff (Finometer)
and cuff placed around the upper left arm (plethysmography). The amount of
mercury in the mercury-in-Silastic strain includes a negligibly risk for the
volunteers.
An intravenous catheter will be inserted in an antecubital vein, which has a
small chance of infection and/or haemorrhage on the place of insertion.