Isoprene and acetone concentration profiles during exercise on an ergometer

Area of Science:

• Physiological Measurement
• Analytical Chemistry
• Respiratory Physiology

Background:

• Volatile organic compounds (VOCs) in exhaled breath offer insights into physiological processes.
• Previous studies have shown dynamic responses of VOCs like isoprene and acetone during exercise.
• Understanding the kinetics of VOCs requires simultaneous measurement of respiratory parameters.

Purpose of the Study:

• To develop and validate a real-time system for simultaneous measurement of exhaled breath VOCs and physiological data.
• To investigate the dynamic changes in breath isoprene and acetone concentrations during exercise.
• To explore the relationship between VOC exhalation kinetics and physiological factors like ventilation and perfusion.

Main Methods:

• A real-time recording setup combining proton transfer reaction-mass spectrometry (PTR-MS) for VOC analysis with hemodynamic and respiratory monitoring.
• Implementation of continuous automatic sampling of end-tidal exhaled breath using a flow-controlled shutter mechanism.
• Acquisition of breath concentration profiles for isoprene and acetone during various exercise intensities.

Main Results:

• The system successfully captured dynamic changes in breath isoprene and acetone during exercise.
• Breath isoprene concentration increased significantly (3-4 fold) within 1 minute of exercise onset.
• Molar flow of isoprene showed a pronounced increase (approx. 11 fold) due to elevated ventilation during exercise.
• Hydrophilic acetone exhibited more stable breath concentrations compared to lipophilic isoprene.

Conclusions:

• The developed setup enables real-time capture of non-polar VOC dynamics and associated physiological factors.
• Short-term changes in breath isoprene levels during exercise are likely driven by pulmonary gas exchange alterations.
• The findings support the hypothesis that gas exchange patterns, rather than endogenous synthesis, primarily influence breath isoprene dynamics in the short term.