Quantitative phase contrast images of flow within the rat vena cava in a 45° rat head down tilt (HDT) model of simulated microgravity

A magnetic resonance (MR) angiographic technique for noninvasive measurement of flow in the inferior vena cava was used to study flow changes in a HDT model of simulated microgravity. Quantitative phase contrast images of flow within the vena cava were obtained before (n=12) and after (n=12) a two week HDT protocol. Regional blood flow was determined by converting the intensity at the respective pixels into a corresponding flow. Average values for flow determined with MR angiography were 3.52 (S.E.M=0.05) mm³/sec before and 5.24 (S.E.M=0.05) mm³/sec after exposure to the HDT protocol. Post two week HDT flow increased 67% over the pre-HDT value. Using a paired t-test, a significant difference was found between flow values in the pre and post-HDT groups (p<0.004). We speculate that the changes in vena cava blood flow due to 45°. HDT may contribute to the overall changes observed in the cardiovascular System.