title: Influence of forced respiration on nonlinear dynamics in heart rate variability.
abstract: Although it is doubtful whether the normal sinus rhythm can be described as low-dimensional chaos, there is evidence for inherent nonlinear dynamics and determinism in time series of consecutive R-R intervals. However, the physiological origin for these nonlinearities is unknown. The aim of this study was to test whether the known nonlinear input from spontaneous respiration is a source for the nonlinearities in heart rate variability. Twelve healthy subjects were examined in supine position with 3-h electrocardiogram recordings during both spontaneous and forced respiration in accordance with a metronome set to 12 min(-1). Nonlinear dynamics were measured as the correlation dimension and the nonlinear prediction error. Complexity expressed as correlation dimension was unchanged from normal respiration, 9.1 +/- 0.5, compared with forced respiration, 9.3 +/- 0.6. Also, nonlinear determinism expressed as the nonlinear prediction error did not differ between spontaneous respiration, 32.3 +/- 3.4 ms, and forced respiration, 31.9 +/- 5.7. It is concluded that the origin of the nonlinear dynamics in heart rate variability is not a nonlinear input from the respiration into the cardiovascular oscillator. Additional studies are needed to elucidate the mechanisms behind the nonlinear dynamics in heart rate variability.
authors.affiliation: Department of Internal Medicine, Coronary Care Unit, Elsinore Hospital, Helsingor, Denmark.
authors.forename: J K
authors.initials: JK
authors.lastname: Kanters
authors.forename: M V
authors.initials: MV
authors.lastname: Højgaard
authors.forename: E
authors.initials: E
authors.lastname: Agner
authors.forename: N H
authors.initials: NH
authors.lastname: Holstein-Rathlou
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D017711:Nonlinear Dynamics; D012119:Respiration; D015656:Respiratory Mechanics; D016683:Supine Position; D013997:Time Factors