The movement of fluid from the vascular compartment to the interstitial space during standing is a well-established phenomenon in healthy subjects. The resulting decrease in plasma volume causes hemoconcentration of various component of the blood (Hct, Hb, protein, etc.). Some 10 to 20 minutes need to elapse before an apparent dynamic equilibrium can be attained. Patients with orthostatic intolerance (Oi) of unknown cause have delayed development of orthostatic symptoms after standing. Therefore, the purpose of this study was to determine the dynamic plasma volume changes upon standing in Ol patients compared to healthy subjects. We assessed postural changes in plasma volume in 14 patients with Ol and 11 healthy subjects before and for up to 60 min following assumption of upright posture using the Evans blue dye method for baseline absolute plasma volume, together with monitoring of serial hematocrit and total nrotpin for Kiihemient relative volume rhanoes Healthy subjects reduced the plasma volume 12% (range: 10-18%) while patients with OI reduced their plasma volume 21% (range: 15-27%) (p <0.003). OI patients required 24 minutes for their orthostatic plasma volume to plateau, whereas normal subjects only required 12 minutes (0.002). These data indicate that profound dynamic changes in plasma volume occur with the assumption of the upright posture in patients with OI. This dynamic orthostatic hypovolemia correlates with the development of symptoms in OI and may offer new insight into the mechanisms of orthostatic symptoms in this and in other diseases.
|Journal||Journal of Investigative Medicine|
|State||Published - 1996|