Abstract
Purpose
Breath-by-breath (BbB) determination of the O2 flux at alveolar level implies the identification of the start and end points of each respiratory cycle; Grønlund defined them as the times in two successive breaths showing equal expiratory gas fractions. Alternatively, the start and end points of each breath might be linked to the ratio between the exchangeable and non-exchangeable gases. The alternative algorithm is described and evaluated with respect to the algorithm proposed by Grønlund.
Methods
Oxygen and carbon dioxide fractions, and ventilatory flow at the mouth were continuatively recorded in 20 subjects over 6 min at rest and during a cycloergometer exercise including 4 increasing intensities lasting 6 min each. Alveolar BbB oxygen uptake was calculated from the gas and flow traces by means of the two methods at stake.
Results
Total number of analysed breaths was 14,257. The data obtained with the two methods were close to the identity line (average slope 0.998 ± 0.004; R > 0.994; n > 334 in all subjects). Average difference between the O2 uptake data obtained by the two methods amounted to −0.27 ± 1.29 mL/min, whilst the standard deviation of the differences was 11.5 ± 4.6 mL/min. The relative percentage difference was independent from the O2 uptake and showed an average bias amongst subjects close to zero (−0.06 ± 0.15 %).
Conclusions
The alternative timing of the respiratory cycle provided congruent O2 uptake data and made the identification of the start and end points of each breath more robust without introducing systematic errors.
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Abbreviations
- BbB:
-
Breath-by-breath
- FO2 :
-
Oxygen fraction at the mouth
- \({\text{FO}}_{ 2}^{\text{A}}\) :
-
Oxygen fraction at alveolar level
- FN2 :
-
Nitrogen fraction at the mouth
- \({\text{FN}}_{ 2}^{\text{A}}\) :
-
Nitrogen fraction at alveolar level
- \(\Delta v^{\text{A}}\) :
-
Variation of the alveolar gas volume
- \(\Delta v{\text{O}}_{ 2i}^{\text{S}}\) :
-
Variation of pulmonary oxygen stores
- OG:
-
Original Grønlund’s algorithm
- SG:
-
Simplified Grønlund’s algorithm
- STPD:
-
Standard temperature pressure dry
- t 1 :
-
Starting time of the ith breath
- t 2 :
-
Final time of the ith breath defined on the FO2 trace or on the FO2/FN2 trace
- t 3 :
-
Final time of the ith breath defined on the FN2 trace
- \(v_{i - 1}^{\text{A}}\) :
-
Alveolar volume at the beginning of the ith breath
- \(v{\text{N}}_{ 2}^{\text{A}}\) :
-
Volume of nitrogen exchanged at alveolar level
- \(v{\text{O}}_{ 2}^{\text{A}}\) :
-
Volume of oxygen taken up at alveolar level
- \(v{\text{O}}_{ 2}^{\text{M}}\) :
-
Volume of oxygen exchanged at the mouth
- \(\dot{V}{\text{CO}}_{ 2}^{\text{A}}\) :
-
Alveolar carbon dioxide release
- \(\dot{V}{\text{O}}_{ 2}^{\text{A}}\) :
-
Alveolar oxygen uptake
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Acknowledgments
This work was supported by the Department of Medical and Biological Sciences funding of the University of Udine to M. Pia Francescato.
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Communicated by Susan Hopkins.
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Cettolo, V., Francescato, M.P. Assessment of breath-by-breath alveolar gas exchange: an alternative view of the respiratory cycle. Eur J Appl Physiol 115, 1897–1904 (2015). https://doi.org/10.1007/s00421-015-3169-x
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DOI: https://doi.org/10.1007/s00421-015-3169-x