Quantitative phase contrast images to quantitate flow in a rat model of microgravity

A magnetic resonance angiographic (MRA) technique for noninvasive measurement of flow in the inferior vena cava (IVC) was used to study blood flow changes in a simulated microgravity model. Microgravity was simulated in adult male Fischer 344 rats (n = 12, with each rat acting as its own control) using a tail harness to elevate the hindquarters, producing a non-weight bearing hindlimb (NWH) model. Quantitative phase contrast images of flow within the IVC were obtained initially and after a 2-week NWH protocol. Inferior vena cava blood flow was determined by converting the intensity at the respective magnetic resonance pixels into a corresponding flow by Doppler techniques. Average values for flow determined with MR angiography were 351.8 (SEM = 49) mm3 x s(-1) initially and 524.5 (SEM = 46) mm3 x s(-1) after exposure to 2 weeks of the NWH protocol. Post 2-week NWH flow increased 49.1% over the initial NWH value. Using a paired t-test, a significant difference was found between the rats' IVC flow values in the initial and post-NWH groups (p < 0.004). The changes in IVC blood flow due to 45 degrees NWH may contribute to the overall changes observed in the cardiovascular system during simulated microgravity.