Effects of 10 Days 6 Degrees Head-Down Tilt on the Responses to FluidLoading and Lower Body Negative Pressure

Abstract

In an international collaborative project six normal male subjects were studied before, during, and after 10 days 6 degrees HDT. Fluid intake was controlled at 40 ml/(kg bw-day). Urine volume and body weight were determined daily. Fluid loading and LBNP were performed in all three phases of the study. Body weight diminishes by 2.6% because of fluid loss. Blood volume diminishes by 13%. The responses to fluid loading were similar in the three phases of the study. Sixty minutes after end of infusion only 5.5% of the infused saline remained in the intravascular compartment. Excess interstitial fluid was eliminated in the next 24 hs but a negative balance was recorded also in the following day. The compliance of the lower limbs expressed as the rate of limb volume change/unit LBNP change was increased at the end of the HDT phase and during the post HDT phase. The set point of intravascular volume was defended, as shown by the response to FL. HDT increased the compliance of the lower limbs.