HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 292/5/R1985    most recent 00792.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Fiamma, M.-N. Articles by Similowski, T. Search for Related Content PubMed PubMed Citation Articles by Fiamma, M.-N. Articles by Similowski, T.

ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Effects of hypercapnia and hypocapnia on ventilatory variability and the chaotic dynamics of ventilatory flow in humans

¹Université Pierre et Marie Curie-Paris, Paris; ²Assistance Publique, Hôpitaux de Paris, Groupe Hospitalier Pitié-Salpêtrière, Service Central d'Explorations Fonctionnelles Respiratoires, Paris; ³Université Joseph Fournier, Faculté de Médecine, Laboratoire TIMC/IMAG, Grenoble, France; ⁴Medical Research Division, Hamilton Medical AG, Bonaduz, Switzerland; and ⁵Assistance Publique, Hôpitaux de Paris, Groupe Hospitalier Pitié-Salpêtrière, Service de Pneumologie et Réanimation, Paris, France

Submitted 11 November 2006 ; accepted in final form 8 January 2007

In humans, lung ventilation exhibits breath-to-breath variability and dynamics that are nonlinear, complex, sensitive to initial conditions, unpredictable in the long-term, and chaotic. Hypercapnia, as produced by the inhalation of a CO₂-enriched gas mixture, stimulates ventilation. Hypocapnia, as produced by mechanical hyperventilation, depresses ventilation in animals and in humans during sleep, but it does not induce apnea in awake humans. This emphasizes the suprapontine influences on ventilatory control. How cortical and subcortical commands interfere thus depend on the prevailing CO₂ levels. However, CO₂ also influences the variability and complexity of ventilation. This study was designed to describe how this occurs and to test the hypothesis that CO₂ chemoreceptors are important determinants of ventilatory dynamics. Spontaneous ventilatory flow was recorded in eight healthy subjects. Breath-by-breath variability was studied through the coefficient of variation of several ventilatory variables. Chaos was assessed with the noise titration method (noise limit) and characterized with numerical indexes [largest Lyapunov exponent (LLE), sensitivity to initial conditions; Kolmogorov-Sinai entropy (KSE), unpredictability; and correlation dimension (CD), irregularity]. In all subjects, under all conditions, a positive noise limit confirmed chaos. Hypercapnia reduced breathing variability, increased LLE (P = 0.0338 vs. normocapnia; P = 0.0018 vs. hypocapnia), increased KSE, and slightly reduced CD. Hypocapnia increased variability, decreased LLE and KSE, and reduced CD. These results suggest that chemoreceptors exert a strong influence on ventilatory variability and complexity. However, complexity persists in the quasi-absence of automatic drive. Ventilatory variability and complexity could be determined by the interaction between the respiratory central pattern generator and suprapontine structures.

chaos; nonlinear analysis; respiratory control; breathing variability

This article has been cited by other articles:

				P. A. Robbins, B. Suki, J. J. Fredberg, F. E. Yates, J. H. T. Bates, T. Similowski, L. Glass, and A. J. E. Seely Being uncomfortable. J Appl Physiol, June 1, 2008; 104(6): 1848 - 1849. [Full Text] [PDF]

				N. A. Lever, E. G. Newall, and P. D. Larsen Differences in the characteristics of induced and spontaneous episodes of ventricular fibrillation Europace, November 1, 2007; 9(11): 1054 - 1058. [Abstract] [Full Text] [PDF]