Astronaut Rhea Seddon wearing cardiovascular rebreathing unit (CRU) inside the orbiting Spacelab Life Sciences SLS-1 laboratory. SLS-1 was carried in the cargo bay of Shuttle Columbia during Mission STS-40 of 5-14 June 1991. Seddon is seen taking part in an experiment into cardiovascular conditioning both in-orbit and after return to Earth. The CRU is used to assess oxygen and CO2 flow in the body, cardiac output, total peripheral resistance to blood flow and lung function. Tests were conducted both at rest and during use of the exercise bicycle Seddon is sitting on. This was just one of the experiments in which the crew participated during the flight.