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Biomedical devices

Biomedical devices

Bioimpedance analyser tracks blood redistribution in spinning cosmonauts

15 May 2020 Tami Freeman
Borisenko Andrey Ivanovich

Microgravity is an unhealthy environment for the human body. Long-term exposure causes a decrease in bone density, loss of muscle mass and a shift of body fluids into the top half of the body, which can impact cardiovascular system function. From long stays aboard the International Space Station, to the future possibility of long-range space missions, it’s vital to address the health of astronauts and cosmonauts spending extended periods in space.

Early studies on rats showed that providing artificial gravity during a space flight reduced adverse health effects. This finding reinforced the idea that creating artificial gravity on board a space station, by use of rotation, could prevent health problems during space missions. As such, space agencies are developing and testing short-radius centrifuges (SRC) to create an optimal centrifuge model for use on space stations.

For research on Earth, an SRC can create similar effects on the human body to those generated by a centrifuge in orbit. A Russian research collaboration has now demonstrated the use of bioimpedance monitoring to detect and predict blood circulation changes during rotation on an SRC. The investigation is part of a large study at the Institute of Biomedical Problems of the Russian Academy of Sciences.

“Over several years, we have been developing portable bioimpedance analysers with a wide range of software intended both for independent work by cosmonauts aboard a spacecraft and for experimental studies simulating the effect of various space flight factors on Earth,” explains Svetlana Pavlovna Shchelykalina from Pirogov Russian National Research Medical University.

Blood redistribution

The study included nine healthy male volunteers, who underwent rotations in an SRC. The subjects lay on their backs in the centrifuge, with their heads 60 cm from the axis of rotation and their feet further away, thus creating acceleration along the body’s vertical axis in the direction of the legs.

During rotations, the researchers used their SPRUT-2 bioimpedance analyser to monitor the redistribution of participants’ body fluids, primarily blood. This technique works by evaluating the change in electrical resistance at a probing current frequency of 5 kHz, using electrodes placed on the subject’s head, arms and ankles. The setup enabled the team to measure resistance in various body regions: head and neck; thoracic (upper chest); abdominal (lower chest and abdomen); left and right legs; and left and right hands.

Shchelykalina and collaborators monitored each of the subjects during three different SRC rotation modes. Each mode included a 15 min acceleration phase, a constant plateau phase and a 15 min stop-down phase. For the first mode, the plateau phase comprised 30 min rotation at an acceleration of 2.05 standard Earth gravity (g). For the second and third modes, the plateau phases involved 30 min rotation at 2.47 g and 15 min rotation at 2.98 g, respectively.

The team recorded 21 completed tests, with four tests halted early as the subjects felt unwell. Measuring the electrical resistance of various body regions during rotation revealed that resistance of upper body regions – the head and neck, chest and abdomen – increased during the rotation, indicating a decrease in blood filling. Conversely, electrical resistance of the legs decreased, indicating increased blood filling.

This blood redistribution was independent of the rotation mode of during the first 30 minutes, and varied on average by 10% and -15% in head and legs regions, respectively. As the SRC slowed down, these changes in resistance reversed, although they did not have time to fully recover by the end of the rotation.

Cyclogram graphs

The maximum changes in resistance occurred at the end of the plateau phases. In the head region, the maximum increase ranged from 15.4% in the first rotation mode to 10.2% in the third mode. In the legs, the maximum decreases were -16.5% and -15.2% in the first mode, and -13.4% and -13.6% in the third.

Predicting fainting

The researchers separately analysed the four experiments halted for medical reasons. In one case, the subject lost consciousness. Here, they observed a sharp drop in resistance of the legs compared with the average, while resistance of the head region was similar to that seen in other subjects. The three subjects who felt ill but remained conscious did not exhibit any significant changes in resistance compared with successful test cases.

 The team suggest that it may therefore be possible to use bioimpedance monitoring to detect and predict blood circulation changes associated with syncopal states – in which loss of blood to the brain causes fainting.

“Syncopal states occur with a decrease in blood flow and blood filling in the vascular pools of the head and lungs, and an increase in blood filling of the legs,” explains study leader Galina Yur’evna Vassilieva from the Institute of Biomedical Problems. “Therefore, even a decrease in resistance in the legs can be a sufficiently reliable indirect predictor of the oncoming fainting.”

The researchers note that the high sensitivity demonstrated by their bioimpedance technology, with relatively high changes in resistance, shows potential for developing automated analysis algorithms similar to contour analysis.

“We are currently starting to test a new computer program designed specifically for bioimpedance observation during training on a short radius centrifuge,” Shchelykalina tells Physics World. “We hope to train the program to also recognize predictors of syncopal states.”

The research is published in Physiological Measurement.

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