A device for increasing, monitoring, and measuring perspiration water and solid loss at reduced ambient pressure, comprising a sealed chamber capable of maintaining less than atmospheric pressure for an extended period of time and a gasket-sealed door accessing the chamber. The chamber provides a controlled hypobaric environment for treatment of various medical conditions. Internal controls of ambient pressure inside, temperature, humidity, oxygen, CO2 and other environmental conditions within the chamber are included, as well as a mechanism for recovering perspiration water loss from an occupant of the chamber. Methods for determining the perspiration volume of water and solid loss experienced by an occupant in the chamber are also disclosed including a computer program for determining quantity of sweat produced by the occupant of the chamber on a continuous basis. An algorithm allowing for continuous calculations of sweat loss and fluid replacement requirements of the occupant of the chamber is disclosed.