ORIGINAL ARTICLE

European Journal of Applied Physiology

, Volume 83, Issue 4, pp 402-408

First online:

Analysis of end-tidal and arterial PCO2 gradients using a breathing model

  • H. BenallalAffiliated withLaboratoire de Physiologie et Physiopathologie de l'Exercice et Handicap – GIP Exercice, Centre Hospitalier Universitaire de Saint-Etienne, Pavillon 12 Hôpital de Saint-Jean Bonnefonds, 42055 Saint-Etienne Cedex 2, France e-mail: benallai@univ-st-etienne.fr Tel.: +33-477127985; Fax: +33-477127229
  • , T. BussoAffiliated withLaboratoire de Physiologie et Physiopathologie de l'Exercice et Handicap – GIP Exercice, Université Jean Monnet, Faculté de Médecine, Saint-Etienne, 15 rue Ambroise Paré, 42023 Saint-Etienne Cedex 2, France

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Abstract

The aim of this paper was to analyse the difference between end-tidal carbon dioxide tension (P ETCO2) and arterial carbon dioxide tension (P aCO2) at rest and during exercise using a homogeneous lung model that simulates the cyclic feature of breathing. The model was a catenary two-compartment model that generated five non-linear first-order differential equations and two equations for gas exchange. The implemented mathematical modelling described variations in CO2 and O2 compartmental fractions and alveolar volume. The model also included pulmonary capillary gas exchange. Ventilatory experimental data were obtained from measurements performed on a subject at rest and during four 5-min bouts of exercise on a cycle ergometer at 50, 100, 150 and 200 W, respectively. Analysis of the P ETCO2-P aCO2 difference between experimental and sinusoidally adjusted ventilatory flow profiles at rest and during exercise showed that the model produced similar values in P ETCO2-P aCO2 for different respiratory flow dynamics (P ≅ 0.75). The model simulations allowed us to study the effects of metabolic, circulatory and respiratory parameters on P ETCO2-P aCO2 at rest and during exercise. During exercise, metabolic CO2 production, O2 uptake and cardiac output affected significantly the P ETCO2-P aCO2 difference from the 150-W workload (P < 0.001). The pattern of breathing had a significant effect on the P ETCO2-P aCO2 difference. The mean (SD) P ETCO2-P aCO2 differences simulated using experimental profiles were 0.80 (0.95), 1.65 (0.40), 2.40 (0.20), 3.30 (0.30) and 4.90 (0.20) mmHg, at rest and during exercise at 50, 100, 150 and 200 W, respectively. The relationship between P ETCO2-P aCO2 and tidal volume was similar to data published by Jones et al. (J Appl Physiol 47: 954–960, 1979).

Key words Respiratory cycle Exercise Fluctuating alveolar gas composition Cardiac output Gas exchange