A Unitized Regenerative Fuel Cell system uses heat pipes to convey waste heat from the fuel cell stack to the reactant storage tanks. The body network devices can be configured to support communication of status data, physiological information, alerts, control signals, and other information between one another. This aim is achieved by a heat insulation element according to the invention, in which the reinforcement mesh is arranged as a component of an abutment at a distance to the surface of the heat insulating board and in which the reinforcement mesh comprises a surface area which is smaller than the area of the surface of the heat insulating board. Operation indication LED lights are provided to indicate which of the two powers are in use, and if battery power is below acceptable levels. The breath test utilizes the measurement of expired 13C-labeled CO2 following the ingestion of a 13C-enriched glucose source. The respiratory shield is sized to be coupled with a respiratory device having a nasal air intake member so as to be positioned along an oral airflow axis.