Changes in breath 13co2/12co2 during exercise of different
intensities.
Gautier, J. F., F. Pirnay, M. Lacroix, F. Mosora, A. J. Scheen, G.
Cathelineau, and P. J. Lefebvre.
Division of Diabetes, Nutrition and Metabolic Disorders, Department
of Medicine, Service of Social Medicine and Department of Biological
Physics and Biomechanics, University of Li[grave]ege, B-4000 LIEGE 1,
Belgium, and Service of Endocrinology, H[circumflex]opital Saint
-Louis, University of Paris 7, PARIS, France
APStracts 3:0195A, 1996.
The measurement of breath 13CO2/12CO2 is commonly used during exercise
to evaluate the oxidation rate of exogenous carbohydrates enriched in
13C. The aim of this study was to investigate whether exercise itself
affects the 13C/12C ratio in expired air CO2 in relation to exercise
intensity. The relative abundance of 13C and 12C in expired air CO2
was determined by isotope ratio mass spectrometry and expressed as
[delta]13C _ using Craig's formula and calibrated standards. Five
healthy young male European volunteers exercised on a treadmill after
an overnight fast during at least 105 min on four separate occasions
and in a randomized order. Work rates were performed at about 30 %,
45 %, 60 % and 75 % of their VO2max. [delta]13C in expired air CO2
and respiratory exchange ratio (RER) were determined every 15 or 30
min during exercise. At 30 and 45 % VO2max, a slight and non
statistically significant increase in [delta]13C levels was observed
at 30 min. In contrast, at 60 and 75 % VO2max, the rise was
statistically significant and averaged 0.83 o/oo and 0.99 o/oo
respectively. Average [delta]13C (between 0 and 105 min)
progressively increased with the intensity of exercise. Individual
values of [delta]13C and RER were positively correlated (r = 0.653, p
= 0.002) as well as values of [delta] 13C and endogenous
carbohydrates utilized (r = 0.752, p < 0.001). Factitious or
"pseudooxidation" of a 13C-enriched exogenous glucose load
(indeed non ingested) was calculated from the changes in expired air
[delta]13C. Over the whole period of exercise it was not
statistically significant at 30 and 45 % VO2max but attained 12.3 +/-
3.3 and 21.3 +/- 3.3 g/105 min at 60 and 75 % VO2max respectively.
Over the first 60 min of exercise, such "pseudooxidation" of
exogenous glucose was also significant at 30 and 45 % VO2max, i.e.
3.2 +/- 0.9 and 2.7 +/- 1.0 g/60 min respectively. In conclusion, by
modifying the mix of endogenous substrates oxidized, exercise at 60 %
VO2max and above significantly increases R-2 the 13C/12C ratio in
expired air CO2. At these intensities, this could lead to
overestimation of the oxidation of 13C-labeled substrates given
orally. At lower intensities of exercise, such overestimation is much
smaller and affects mainly the values recorded during the initial
part of the exercise bout.
Received 13 February 1995; accepted in final form 29 March 1996.
APS Manuscript Number A163-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96