Table 1.

Mathematical expressions used to simulate constant gravitational stress

Gravitational Effect	Expression
Hydrostatic pressure, mmHg	Ph,n = ρgchn
Intrathoracic pressure, mmHg	$P_{\text{th}}=P_{{\text{th}}_0}-3.5\frac{g_{\text{c}}}{g_{\text{E}}}$
Maximal blood volume lost from intravascular volume, mL	$V_{\text{max}}=300\frac{g_{\text{c}}}{g_{\text{E}}}$

P_h,n, hydrostatic pressure in compartment n; ρ, density of blood (7.95 mmHg/s²/m²); g_c, gravitational acceleration in constant gravity field; h_n, effective vertical length of compartment n (defined as half of the anatomical vertical length, except of the leg compartments where the effective length is assumed to be one third of the anatomical vertical length); P_th, intrathoracic pressure; $P_{{\text{th}}_{\text{0}}}$, nominal intrathoracic pressure (−4 mmHg); g_E, gravitational acceleration on Earth (9.81 m/s²); V_max, maximal blood volume lost from intravascular volume into the interstitial space.