Orthostatic intolerance after space flight.

Physiologists have always been challenged by the adjustments of the human body to hostile environments. The set of papers in this issue of The Journal of Physiology (Cox et al. 2002; Ertl et al. 2002; Levine et al. 2002) fits into the tradition of the study of human responses to extreme physical circumstances. The Neurolab project represents a huge undertaking that required major contributions from many different collaborators, and the coordination of efforts at different institutions. The studies succeeded because of the dedication and years of work of the astronauts involved. The manuscripts present the fundamental findings from the first direct recordings of sympathetic vasoconstrictor nerves and noradrenaline kinetics in humans during microgravity. Despite the difficulties of performing such measurements on the space shuttle and the small numbers of astronauts involved, unique data are set forth that represent a major advance in our understanding of the physiology of space flight.