PDF version of COSPAR - Space Science Research in Canada Report

These data will be compared with the more detailed ground-basedmeasurements taken before and after the space mission. Hughson will useultrasound to determine the efficiency of the large vein that returns blood to theheart from the lower body. At the same time, he will be monitoring venous bloodpressure through a catheter in the right arm.Then he will then use a Lower Body Negative Pressure device to apply suction tothe lower body, which will shift blood out of the central region and back down tothe legs. “We can look at changes in the volume or size of the inferior vena cava,and we can look at the pressure to see how the pressure/volume relationshipchanges.”When someone comes back from space, the veins are more stretched or “floppy”than they were on Earth. “They hold a greater volume of blood at the samepressure,” said Hughson. “They don’t have good muscle tone to hold the bloodnear the heart so when you stand up, the blood could go away from the heart tothe lower part of the body. There’s less blood going up to the brain and you couldfaint.”What happens in the gut is also important. “It will hold a lot of volume, so youneed a system that very efficiently shuts down the blood flow going into thatregion,” said Hughson. “We’ll probably see less shutting down of the blood flowinto the gut region when you come back from space than you had beforehand.”This would mean it’s “hanging on to too much blood and once again, there’s lessblood coming back to the heart and therefore a poorer ability to regulate bloodpressure.”During the experiment, Hughson will monitor how much blood the heart ispumping out and how well the blood vessels are constricting. He wants todetermine how efficiently reflexes in the veins and arteries are controlling theconstriction. This “vascular resistance” serves as a kind of traffic cop, makingsure blood goes where it’s needed.“If you’re not putting out as much blood, you need to constrict the blood vesselsso the blood doesn’t go to the wrong place,” Hughson said. “You don’t want itgoing to the gut region or legs; you do want it going to the brain. If blood pressurestarts to fall, the blood vessels in the gut and the legs should constrict and theblood vessels to brain should dilate. We’ll be looking at how efficient the brainblood vessels are at dilating in response to a drop in blood pressure.”The number and complexity of the systems involved regulating blood pressuremeans that different kinds of countermeasures may be needed to prevent faintingproblems. One technique already used in space, called lower body negative31