Development of a lower body negative pressure box with an environmental control system for physiological studies

IntroductionA headward fluid shift occurs in microgravity due to the absence of hydrostatic gradients. Different countermeasures have been proposed to decrease related cardiovascular symptoms, like the application of lower body negative pressure (LBNP) in-flight. We have developed an LBNP box with an environmental control system. It aims at improving features of LBNP boxes currently used worldwide.MethodThe LBNP box is a cylindrical structure consisting of five carbon steel ribs wrapped with high pressure resistant and transparent vinyl. Inner and outer-wheeled trolleys were developed to safely, comfortably, and easily move the subject in and out of the box. A leather skirt is secured around the subject’s waist by an adjustable belt. The other end is secured between two wooden structures, which seal the open area of the LBNP box. An inlet and an outlet valves connect the external to the internal environments of the chamber. A tube system allows air to circulate gently in the box. Electronic sensors linked to a computer program are used to adjust the airflow keeping a pre-set negative pressure without changing humidity and temperature inside the box.ResultsThe LBNP box structure supported −100 mmHg for periods of 10 min. The trolley apparatus proved comfortable and improved the displacement and instrumentation of the subject. The sealing system was leakage-proof. The development of the micro-controller and the software interfaces was completed successfully. Air-pressure controller efficiently maintained the desired differential pressure.ConclusionThe improvements of the present LBNP box – comfortable and easy way of moving subjects in and out the box, the sealing mechanism, the well distributed airflow, and the computerized internal environment control system secondary to the input of electronic sensors – have substantially decreased the undesirable side-effects of uncontrolled environment conditions during rapid pressure changes, and increase test subjects’ comfort.