THE EFFECT OF POSTURAL CHANGE ON VASCULAR PERMEABILITY IN
HUMANS. S.A
Hope* and I.T. Meredith. Centre for Heart and Chest Research, Monash
University, Clayton, Victoria. The endothelium plays a central role in the control of
many vascular functions, including vascular tone, thrombosis and
permeability. Vascular responses to
endothelial stimuli occur over minutes.
We sought to examine the physiological changes in vascular permeability
as reflected by plasma colloid osmotic pressure (PCOP) in response to postural
changes in health. Venous blood was obtained from the arm of
30 healthy volunteers (14 male: 16 female, age 39 ± 10, mean ± SD) without
overt vascular disease after 20 minutes lying supine and a 5 minutes
standing. The plasma samples were analysed
using an Osmomat 050 Colloid Osmometer with a 10kDa molecular weight cut-off
membrane and 0.9% saline as the reference solution. PCOP measurements were shown to be
reproducible (coefficient of repeatability 0.4mmHg, coefficient of variation
0.7%). A consistent difference was
demonstrated between supine (25.8 ± 1.95) PCOP (p<0.001). The mean rise on standing was 1.9 mmHg
(range -0.4 - 6.4). Linear regression
analysis revealed a relationship between supine PCOP and height, body mass
index and age (p<0.05) and a trend towards a significant difference between
genders (p=0.052). PCOP in the erect
position was related to height and body surface area (p<0.05). Plasma colloid osmotic pressure, an index of vascular
permeability, is a dynamic physiological variable which alters with
posture. PCOP merits further
investigation as a dynamic marker of endothelial function in health and
disease.
