Urine collection devices used in Space Shuttle missions have taken up too much space, have tended to leak, and have been cumbersome for men and impossible for women to use. The in-flight urine collection absorber (IUCA) was developed for the collection of small volumes of urine for metabolic studies involving stable (nonradioactive) isotopes such as deuterium (2H) and "heavy oxygen" (18O), which are used to study energy expenditure, water metabolism and body composition. The objectives of this hardware study were to evaluate potential effects of the absorbent filter on the analysis of these isotopes and to evaluate the ease of use of the IUCA by men and women in flight.
The IUCA is a small, conical piece of highly absorbent filter paper that can be placed in the Shuttles' urine-collection funnels. It is removed after a void and stored inside 2 resealable plastic bags. It weighs approximately 20 grams (g) empty and 35 g full. In evaluations on the ground, tap water spiked with known amounts of 2H and 18O was placed in IUCAs or in other urine-collection devices (UCDs). The samples were stored and weighed periodically to monitor evaporative losses. In addition, urine samples from 3 study subjects who had ingested water labeled with 2H and 18O were collected and stored in standard containers, urine collection bags, UCDs or IUCAs. The isotopes were analyzed by mass spectrometry. The IUCAs were also tested in flight by 5 astronauts (3 men and 2 women).
In the tests on the ground, evaporative losses from the IUCA were minimal and far less than from the UCD. Results of the isotope analyses were similar for the IUCA and the UCD. Collection of the urine with an IUCA rather than by one of the other methods made little difference in determinations of total energy expenditure and total body water. During flight the IUCA was able to collect samples of 11 to 13 milliliters, with no difference by gender. The results show that the IUCA is acceptable for collecting urine samples during flight for experiments involving stable isotopes, when urine volume measurements are not required. It can be used by men and women, even in constrained areas like the Shuttle middeck. It could also be used on the International Space Station.