Karen Sharwood - April 01, 2002: Physiology 101 - The physiological testing for the cardiovascular control experiment started last week and is now well underway. The testing itself is relatively simple (and relatively boring for Mark), but it has been designed so that Mark will easily be able to repeat it while in space. The test consists of three different parts: an orthostatic tolerance test, a cardiovascular exercise test and a recovery test.
The orthostatic tolerance test is separated into two parts – 10 minutes of lying and 10 minutes of standing. The aim of this test is to monitor the changes in blood pressure and heart rate with the introduction of gravity.
While we are lying down, the blood is evenly distributed throughout the body, which simulates gravity as closely as possible while on Earth. As soon as we stand up, because of the presence of gravity, all of the blood rushes down to our legs and there is a drop in our blood pressure as the body does not expect the sudden change in posture. This causes the dizziness that we sometimes feel when standing up quickly.
The brain immediately detects that there is a decrease in the amount of blood being returned to it as well as to the heart, and responds immediately by tightening the blood vessels in our legs, thereby forcing more blood back to the heart. At the same time, heart rate also increases so as to move more blood around the body. All of these changes happen within seconds of standing, which can be seen on the Polar heart rate graph. This test will be a primary focus of the study, as we are interested to see whether this response of the brain and the cardiovascular system will be affected by space flight where there will be no need for these changes to occur.
The cardiovascular-response test is performed on a stationary cycle ergometer. The bicycle we are using for pre- and post-flight testing is an exact replica of the equipment that is onboard the ISS. The test consists of exercise bouts that each last two minutes and are of increasing intensity. Each exercise session is separated by one minute of rest, which can be seen on the heart-rate graph. The heart rate increases as intensity increases because more muscles are needed by the body to continue producing a constant force against an increasing resistance. As more muscle fibres are recruited, there is an increased need for blood and oxygen to reach them and therefore the heart will need to beat harder to reach them all.
We then measure 10 minutes of recovery to determine how long it takes for the cardiovascular system to return to resting values. Through all three of these tests, we measure heart-rate continuously and blood pressure at specific times during each component.
I wanted to use the same equipment that would be used on the ISS so that we would be able to compare data captured on board to the pre- and post flight data as closely as possible. After months of negotiating and battling with ECG equipment and data, we found out that the Institute for Biomedical Problems (IMBP) has the exact equipment used on board as well as a smaller portable system they use more regularly and that they were cool with us using. The Russians have been incredibly cautious during any of Mark’s physical training and are always pedantic about monitoring cardiovascular and physiological response so they requested that they use the Gamma One ECG equipment, which is also used on board the ISS. So, picture this: a Polar heart rate monitor, the on-board ECG equipment, the IMBP ECG system and the Gamma One ECG … er, just in case anything went wrong. Geez, Mark may as well have been wired up to the ISS itself (heh heh heh).
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