New perspectives in breath-by-breath determination of alveolar gas exchange in humans

Abstract

Alveolar gas transfer over a given breath (i) was determined in ten subjects at rest and during steady-state cycling at 60, 90 or 120 W as the sum of volume of gas transferred at the mouth plus the changes of the alveolar gas stores. This is given by the gas fraction (FA) change at constant volume plus the volume change (deltaVAi) at constant fraction i.e. VAi-1(FAi-FAi-1)+FAi x deltaVAi, where VAi-1 is the end-expiratory volume at the beginning of the breath. These quantities, except for VAi-1, can be measured on a single-breath (breath-by-breath) basis and VAi-1 set equal to the subject's functional residual capacity (FRC, Auchincloss model). Alternatively, the respiratory cycle can be defined as the interval elapsing between two equal expiratory gas fractions in two successive breaths (Grønlund model G). In this case, Ft1 = Ft2 and thus the term VAi-1 (FAi-FAi-1) vanishes. In the present study, average alveolar O2 uptake (VO2,A) and CO2 output (VCO2,A) were equal in both approaches whereby the mean signal-to-noise ratio (S/N) was 40% larger in G. Other approaches yield steady state S/N values equal to that obtained in G, although they are based on the questionable assumption that the inter-breath variability of alveolar gas transfer is minimal. It is concluded that the only promising approach for assessing "true" single-breath alveolar gas transfer is that originally proposed by Grønlund.

Simultaneous determination of the kinetics of cardiac output, systemic O2 delivery, and lung O2 uptake at exercise onset in men

“…The alignment of the traces was corrected for the time delay between the flowmeter and the mass spectrometer. Breath-by-breath V O2 and CO2 output (V CO2) were then computed by means of the Grønlund's algorithm (8). A software specifically written under the Labview developing environment was used.…”

Phase I dynamics of cardiac output, systemic O2 delivery, and lung O2 uptake at exercise onset in men in acute normobaric hypoxia

“…The alignment of traces was corrected for the time delay between the flowmeter and the mass spectrometer. Breath-by-breath V O2 and CO2 output (V CO2) were then computed off-line by means of a modified version of Grønlund's algorithm (9). Software purposely written under the Labview developing environment (Labview 5.0; National Instruments, Austin, TX) was used.…”

“…Software purposely written under the Labview developing environment (Labview 5.0; National Instruments, Austin, TX) was used. The characteristics and physiological implications of Grønlund's algorithm are widely discussed elsewhere (9,11,27).…”

Relating pulmonary oxygen uptake to muscle oxygen consumption at exercise onset: in vivo and in silico studies

“…This volume rate of pulmonary oxygen uptake at the mouth differs from the volume exchange rate at the alveolar-capillary level. To provide a more precise dynamic description related to the alveolar gas exchange, a different algorithm could be used (Capelli et al 2001;Cautero et al 2005). However, even if the response times τ V O 2p were overestimated by 30% (Cautero et al 2003), the differences of the dynamic responses among VO 2p , VO 2m and UO 2m during exercise would still be significant.…”