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Am J Physiol Regul Integr Comp Physiol 289: R1618-R1624, 2005. First published August 4, 2005; doi:10.1152/ajpregu.00639.2004
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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Effect of inspiratory threshold loading on ventilatory kinetics during constant-load exercise

S. Keslacy,1 S. Matecki,1 J. Carra,2 F. Borrani,2 R. Candau,2 C. Prefaut,1 and M. Ramonatxo1

1Laboratoire de Physiologie des Interactions, Service Central de Physiologie Clinique, Hôpital Arnaud de Villeneuve; and 2Laboratoire Sport Performance, Université Montpellier I, Montpellier, France

Submitted 20 September 2004 ; accepted in final form 1 August 2005

Humoral factors play an important role in the control of exercise hyperpnea. The role of neuromechanical ventilatory factors, however, is still being investigated. We tested the hypothesis that the afferents of the thoracopulmonary system, and consequently of the neuromechanical ventilatory loop, have an influence on the kinetics of oxygen consumption (O2), carbon dioxide output (CO2), and ventilation (E) during moderate intensity exercise. We did this by comparing the ventilatory time constants ({tau}) of exercise with and without an inspiratory load. Fourteen healthy, trained men (age 22.6 ± 3.2 yr) performed a continuous incremental cycle exercise test to determine maximal oxygen uptake (O2 max = 55.2 ± 5.8 ml·min–1·kg–1). On another day, after unloaded warm-up they performed randomized constant-load tests at 40% of their O2 max for 8 min, one with and the other without an inspiratory threshold load of 15 cmH2O. Ventilatory variables were obtained breath by breath. Phase 2 ventilatory kinetics (O2, CO2, and E) could be described in all cases by a monoexponential function. The bootstrap method revealed small coefficients of variation for the model parameters, indicating an accurate determination for all parameters. Paired Student's t-tests showed that the addition of the inspiratory resistance significantly increased the {tau} during phase 2 of O2 (43.1 ± 8.6 vs. 60.9 ± 14.1 s; P < 0.001), CO2 (60.3 ± 17.6 vs. 84.5 ± 18.1 s; P < 0.001) and E (59.4 ± 16.1 vs. 85.9 ± 17.1 s; P < 0.001). The average rise in {tau} was 41.3% for O2, 40.1% for CO2, and 44.6% for E. The {tau} changes indicated that neuromechanical ventilatory factors play a role in the ventilatory response to moderate exercise.

neuromechanical ventilatory factors


Address for reprint requests and other correspondence: S. Keslacy, Laboratoire de Physiologie des Interactions, Service Central de Physiologie Clinique, Hôpital Arnaud de Villeneuve, 34295 Montpellier Cedex 5, France (e-mail: skeslacy{at}mail.med.upenn.edu)






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