Metabolic monitoring and assessment of anaerobic threshold by means of breath biomarkers.

Volatile breath constituents such as acetone and ammonia have been linked to dextrose, fat, and protein metabolism. Non-invasive breath analysis, therefore, may be used for metabolic monitoring, identification of fuel sources actually used for energy production and determination of the anaerobic threshold (AT). This study was intended to assess correlations between exhaled volatile organic compound (VOC) concentrations, metabolism, and physiological parameters. In addition, we tried to find out whether AT could be determined by means of non-invasive analysis of VOCs in breath. Exhaled concentrations of acetone, ammonia, and isoprene were determined in 21 healthy volunteers under controlled ergometric exercise by means of continuous real time Proton Transfer Reaction Mass Spectrometry (PTR-MS). In parallel, spiro-ergometric parameters (O-2, CO2, respiratory rate and minute ventilation) and hemodynamic data such as heart rate were recorded. AT was determined from serum lactate, by means of respiratory exchange rate and by means of exhaled acetone concentrations. Exhaled acetone concentrations mirrored exercise induced changes of dextrose metabolism and lipolysis. Bland-Altman statistics showed good agreement between lactate threshold, respiratory compensation point (RCP), and determination of AT by means of exhaled acetone. Exhaled ammonia concentration seemed to be linked to protein metabolism and changes of pH under exercise. Isoprene concentrations showed a close correlation to cardiac output and minute ventilation. Breath biomarkers represent a promising alternative for metabolic monitoring under exercise as they can be determined non-invasively and continuously. In addition, these markers may add complementary information on biochemistry, energy production and fuel consumption