Abstract
Purpose
Reduction of noise of breath-by-breath gas-exchange data is crucial to improve measurements. A recently described algorithm (“independent breath”), that neglects the contiguity in time of breaths, was tested.
Methods
Oxygen, carbon dioxide fractions, and ventilatory flow were recorded continuously over 26 min in 20 healthy volunteers at rest, during unloaded and moderate intensity cycling and subsequent recovery; oxygen uptake (\(\dot {V}{{\text{O}}_{\text{2}}}\)) was calculated with the “independent breath” algorithm (IND) and, for comparison, with three other “classical” algorithms. Average \(\dot {V}{{\text{O}}_{\text{2}}}\) and standard deviations were calculated for steady-state conditions; non-linear regression was run throughout the \(\dot {V}{{\text{O}}_{\text{2}}}\) data of the transient phases (ON and OFF), using a mono-exponential function.
Results
Comparisons of the different algorithms showed that they yielded similar average \(\dot {V}{{\text{O}}_{\text{2}}}\) at steady state (p = NS). The standard deviations were significantly lower for IND (post hoc contrasts, p < 0.001), with the slope of the relationship with the corresponding data obtained from “classical” algorithms being < 0.69. For both transients, the overall kinetics (evaluated as time delay + time constant) was significantly faster for IND (post hoc contrasts, p < 0.001). For the ON transient, the asymptotic standard errors of the kinetic parameters were significantly lower for IND, with the slope of the regression line with the corresponding values obtained from the “classical” algorithms being < 0.60.
Conclusion
The “independent breath” algorithm provided consistent average O2 uptake values while reducing the overall noise of about 30%, which might result in the halving of the required number of repeated trials needed to assess the kinetic parameters of the ON transient.
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Abbreviations
- ASE:
-
Asymptotic standard error
- AUC:
-
“Auchincloss” approach, i.e., the breath-by-breath alveolar gas-exchange algorithm according to Auchincloss et al. (1966)
- BTPS:
-
Body temperature pressure saturated
- EXP:
-
“expiration-only” approach, i.e., the breath-by-breath gas-exchange algorithm that uses information obtained during expiration and the Haldane transformation (Roecker et al. 2005; Ward 2018)
- FCO2, FN2, FO2 :
-
Instantaneous carbon dioxide, non-exchangeable gas at alveolar level (essentially nitrogen) and oxygen fractions
- FIO2, FIN2 :
-
Inspired oxygen and nitrogen ambient fractions
- IND:
-
“independent breath” approach, i.e., the breath-by-breath alveolar gas-exchange algorithm under investigation (Cettolo and Francescato 2018b)
- MANOVA:
-
Repeated measures multivariate analysis of variance
- MRTON, MRTOFF :
-
Mean response time of the ON and OFF kinetics, respectively
- RSS:
-
Residual sum of squares
- STPD:
-
Standard temperature pressure dry
- t :
-
Time
- t df :
-
t student value for a determined degree of freedom at a certain probability level
- TdON, TdOFF :
-
Time delay of the start of the ON and OFF kinetics, respectively
- t i, t e :
-
Starting times of inspiration and expiration, respectively; defined on the flow trace, where flow changes direction
- T ON, T OFF :
-
Start time of signal change of the ON and OFF transients, respectively, as obtained by the non-linear regression procedure
- \({t_x}\) :
-
Time of the end-expiratory exchanged gas fraction, defined on the FO2 trace
- t 1, t 2 :
-
Start and end times of the jth breath for the “independent breath” approach; defined on the FO2/FN2 trace
- \(\dot {V}\) :
-
Respiratory flow at the mouth
- V L :
-
End-expiratory lung volume
- \(\dot {V}{{\text{O}}_2}^{{{\text{IND}}}}\), \(\dot {V}{{\text{O}}_2}^{{{\text{WES}}}}\), \(\dot {V}{{\text{O}}_2}^{{{\text{AUC}}}}\), and \(\dot {V}{{\text{O}}_2}^{{{\text{EXP}}}}\) :
-
Oxygen uptake calculated applying the “independent breath”, the “Wessel”, the “Auchincloss”, and the “expiration-only” approaches, respectively; all the data are expressed in STPD conditions
- \(\dot {V}{{\text{O}}_2}^{{\text{r}}}\) :
-
Baseline O2 uptake for the ON kinetic analysis
- \(\dot {V}{{\text{O}}_2}^{{{\text{ss}}}}\) :
-
Average steady-state O2 uptake for the OFF kinetic analysis
- WES:
-
“Wessel” approach, i.e., the breath-by-breath alveolar gas-exchange algorithm according to Wessel et al. (1979)
- \(\Delta \dot {V}{{\text{O}}_2}^{{{\text{rec}}}}\) :
-
Fall of oxygen uptake at the end of recovery
- \(\Delta \dot {V}{{\text{O}}_2}^{{{\text{ss}}}}\) :
-
Increase in oxygen uptake at steady state
- τ ON, τ OFF :
-
Time constant of the ON and OFF responses, respectively, as obtained by the non-linear regression procedure
References
Auchincloss JHJ, Gilbert R, Baule GH (1966) Effect of ventilation on oxygen transfer during early exercise. J Appl Physiol 21:810–818
Bates D, Watts D (1988) Nonlinear regression analysis and its applications. Wiley, New York
Beaver WL, Lamarra N, Wasserman K (1981) Breath-by-breath measurement of true alveolar gas exchange. J Appl Physiol 51:1662–1675
Benson A, Bowen T, Ferguson C, Murgatroyd S, Rossiter HB (2017) Data collection, handling and fitting strategies to optimize accuracy and precision of oxygen uptake kinetics estimation from breath-by-breath measurements. J Appl Physiol 123:227–242. https://doi.org/10.1152/japplphysiol.00988.2016
Bland JM, Altman DG (1986) Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1:307–310
Busso T, Robbins PA (1997) Evaluation of estimates of alveolar gas exchange by using a tidally ventilated nonhomogenous lung model. J Appl Physiol 82:1963–1971
Capelli C, Cautero M, di Prampero PE (2001) New perspectives in breath-by-breath determination of alveolar gas exchange in humans. Pflugers Arch 441:566–577
Capelli C, Cautero M, Pogliaghi S (2011) Algorithms, modelling and VO2 kinetics. Eur J Appl Physiol 111:331–342. https://doi.org/10.1007/s00421-010-1396-8
Cautero M, Beltrami AP, di Prampero PE, Capelli C (2002) Breath-by-breath alveolar oxygen transfer at the onset of step exercise in humans: methodological implications. Eur J Appl Physiol 88:203–213. https://doi.org/10.1007/s00421-002-0671-8
Cautero M, di Prampero PE, Capelli C (2003) New acquisitions in the assessment of breath-by-breath alveolar gas transfer in humans. Eur J Appl Physiol 90:231–241. https://doi.org/10.1007/s00421-003-0951-y
Cettolo V, Francescato MP (2015) Assessment of breath-by-breath alveolar gas exchange: an alternative view of the respiratory cycle. Eur J Appl Physiol 115:1897–1904. https://doi.org/10.1007/s00421-015-3169-x
Cettolo V, Francescato MP (2018a) Effects of abrupt changes in lung gas stores on the assessment of breath-by-breath gas exchange. Clin Physiol Funct Imaging 38:491–496. https://doi.org/10.1111/cpf.12444
Cettolo V, Francescato MP (2018b) Assessing breath-by-breath alveolar gas exchange: is the contiguity in time of breaths mandatory? Eur J Appl Physiol 118:1119–1130. https://doi.org/10.1007/s00421-018-3842-y
di Prampero PE, Lafortuna CL (1989) Breath-by-breath estimate of alveolar gas transfer variability in man at rest and during exercise. J Physiol 415:459–475
Fowler WS (1948) Lung function studies. II. The respiratory dead space. J Appl Physiol 154:405–416. https://doi.org/10.1152/ajplegacy.1948.154.3.405
Francescato MP, Cettolo V, Bellio R (2014a) Assembling more O2 uptake responses: is it possible to merely stack the repeated transitions? Respir Physiol Neurobiol 200:46–49. https://doi.org/10.1016/j.resp.2014.06.004
Francescato M, Cettolo V, Bellio R (2014b) Confidence intervals for the parameters estimated from simulated O2 uptake kinetics: effects of different data treatments. Exp Physiol 99:187–195. https://doi.org/10.1113/expphysiol.2013.076208
Gimenez P, Busso T (2008) Implications of breath-by-breath oxygen uptake determination on kinetics assessment during exercise. Respir Physiol Neurobiol 162:238–241. https://doi.org/10.1016/j.resp.2008.07.004
Goldman E, Dzwonczyk R, Yadagani V (1986) Evaluation of four methods for estimating breath-by-breath exchange of O2 and CO2. IEEE Trans Biomed Eng BME 33:524–526
Golja P, Cettolo V, Francescato MP (2018) Calculation algorithms for breath-by-breath alveolar gas exchange: the unknowns! Eur J Appl Physiol 118:1869–1876. https://doi.org/10.1007/s00421-018-3914-z
Grønlund J (1984) A new method for breath-to-breath determination of oxygen flux across the alveolar membrane. Eur J Appl Physiol 52:167–172
Motulsky HJ, Ransnas LA (1987) Fitting curves to data using nonlinear regression: a practical and nonmathematical review. FASEB J 1:365–374
R Core Team (2015) R: a language and environment for statistical computing (vs. 3.2.2). R Foundation for Statistical Computing, Wien
Roberts CM, MacRae KD, Winning AJ, Adams L, Seed WA (1991) Reference values and prediction equations for normal lung function in a non-smoking white urban population. Thorax 46:643–650
Roecker K, Prettin S, Sorichter S (2005) Gas exchange measurements with high temporal resolution: the breath-by-breath approach. Int J Sports Med 26:S11–S18. https://doi.org/10.1055/s-2004-830506
Rossiter HB (2011) Exercise: kinetic considerations for gas exchange. Compr Physiol 1:203–244. https://doi.org/10.1002/cphy.c090010
Swanson G (1980) Breath-to breath considerations for gas exchange kinetics. In: Cerretelli P, Whipp BJ (eds) Exercise bioenergetics and gas exchange. Elsevier, Amsterdam, pp 211–222
Ward SA (2018) Open-circuit respirometry: real-time, laboratory-based systems. Eur J Appl Physiol 118:875–898. https://doi.org/10.1007/s00421-018-3860-9
Wessel H, Stout R, Bastanier C, Paul M (1979) Breath-by-breath variation of FRC: effect on VO2 and VCO2 measured at the mouth. J Appl Physiol Respir Environ Exerc Physiol 46:1122–1126
Wilmore JH, Costill DL (1973) Adequacy of the Haldane transformation in the computation of exercise VO2 in man. J Appl Physiol 35:85–89
Acknowledgements
Funding was provided by Università degli Studi di Udine—Dpt. of Medicine (2017).
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CV and FMP equally contributed in conception and design of the experiments; both performed the experiments, analysed the data, and wrote the paper. Both authors read and approved the final version of the manuscript.
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Communicated by I. Mark Olfert.
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Francescato, M.P., Cettolo, V. The “independent breath” algorithm: assessment of oxygen uptake during exercise. Eur J Appl Physiol 119, 495–508 (2019). https://doi.org/10.1007/s00421-018-4046-1
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DOI: https://doi.org/10.1007/s00421-018-4046-1