Isoprene and acetone concentration profiles during exercise on an ergometer
1 Innsbruck Medical University, Department of Operative Medicine, Anichstr. 35, A-6020 Innsbruck
2 Breath Research Unit of the Austrian Academy of Sciences, Dammstr. 22, A-6850 Dornbirn
3 Vorarlberg University of Applied Sciences, Hochschulstr. 1, A-6850 Dornbirn
4 University of Applied Sciences Technikum Wien, Höchstädtplatz 5, A-1200 Wien
5 Innsbruck Medical University, Department of Psychiatry, Anichstr. 35, A-6020 Innsbruck
6 Universität Wien, Fakultät für Mathematik, Nordbergstr. 15, A-1090 Wien
The basic requirement in real-time breath gas analysis is to implement an experimental setup allowing the fast quantification of volatile organic compounds (VOCs)
in exhaled breath as well as the acquisition of additional variables governing exhalation kinetics in a synchronized, reproducible and non-invasive way. A recording
station developed for efficient combination of proton transfer reaction mass spectrometer (PTR-MS) measurements with data reflecting the behavior of hemodynamic and
respiratory parameters is presented. Automatic sampling of exhaled breath is accomplished on the basis of measured respiratory flow: a flow-controlled shutter mechanism
guarantees that only end-tidal exhalation segments are drawn into the mass spectrometer for analysis. In particular, the suggested sampling procedure is applicable in other
mass spectrometric setups such as SIFT-MS.
Exhaled breath concentration profiles of two prototypic compounds, isoprene and acetone, during several exercise regimes are presented in Fig. 1, complementing earlier findings regarding the dynamic response of these compounds due to Senthilmohan et al. [1] and Karl et al. [2]. While isoprene tends to react very sensitively to changes in pulmonary ventilation and perfusion due to its lipophilic behavior and low Henry constant, hydrophilic acetone shows a rather stable behavior. The onset of exercise is accompanied by a drastic increase in breath isoprene concentration, usually by a factor of ~ 3-4 within about one minute. Due to a simultaneous increase in ventilation, the associated rise in molar flow, i.e., in the amount of isoprene exhaled per minute is even more pronounced, leading to a ratio between peak molar flow and molar flow at rest of ~ 11.
Figure 1. Representative profiles from a study subject during three workload scenarios:
- 5 min resting | 15 min exercise (75 W) | 3 min resting | 15 min exercise (75 W) | 12 min resting | 5 min exercise (75 W) | 5 min resting
- 5 min resting | 15 min exercise (75 W) | 12 min resting | 15 min exercise (75 W) | 3 min resting | 5 min exercise (75 W) | 5 min resting
- 5 min resting | 5 min supine position | 5 min resting | 5 min exercise (50 W) | 5 min exercise (100 W) | 5 min exercise (50 W) | 10 min resting
Our setup holds great potential in capturing continuous dynamics of non-polar, low-soluble VOCs over a wide measurement range. In particular, data appear to favor the hypothesis that short-term effects visible in breath isoprene levels are mainly caused by changes in pulmonary gas exchange patterns rather than fluctuations in endogenous synthesis.
[1] Senthilmohan et al. Redox Rep, 2000. 5(2-3): 151-3.
[2] Karl at al. J Appl Physiol, 2001. 91(2): 762-70.