title: The independently fractal nature of respiration and heart rate during exercise under normobaric and hyperbaric conditions.
abstract: To test the hypothesis that the fractal character of breathing and heart rate are independent, inter-breath intervals (IBI) and R-R intervals (RRI) were measured during rest and two levels of exercise at 1 and 2.8 ATA in a hyperbaric chamber in 18 male and female subjects (ages 19-74 years). Both RRI and IBI showed fractal properties. Fractal dimensions (D) for IBI were (mean +/- S.D.) 1.33 +/- 0.11, 1.29 +/- 0.12, 1.19 +/- 0.16 (rest, light and heavy exercise at 1ATA); 1.33 +/- 0.13, 1.25 +/- 0.13, 1.18 +/- 0.14 (same conditions at 2.8 ATA). Corresponding D for RRI were 1.19 +/- 0.11, 1.05 +/- 0.07 and 1.02 +/- 0.05 (1ATA); 1.20 +/- 0.10, 1.03 +/- 0.04 and 1.01 +/- 0.02 (2.8 ATA). The fractal dimension of each variable decreased with exercise and was unaffected by hyperbaric exposure. These two systems were not cross-correlated under any of the six conditions. During rest and light and moderate exercise at 1 and 2.8 ATA the results are consistent with heart rate variability and breathing rate variability being mutually independent of one another.
authors.affiliation: Mathematics Division, Army Research Office, Research Triangle Park, NC, and Physics Department, Duke University, Durham, NC, USA.
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: West
authors.forename: Lori A
authors.initials: LA
authors.lastname: Griffin
authors.forename: Heather J
authors.initials: HJ
authors.lastname: Frederick
authors.forename: Richard E
authors.initials: RE
authors.lastname: Moon
mesh_terms: D000328:Adult; D000368:Aged; D001274:Atmospheric Pressure; D018592:Cross-Over Studies; D004562:Electrocardiography / Q000379:methods; D015444:Exercise / Q000502:physiology*; D005260:Female; D017709:Fractals; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D006931:Hyperbaric Oxygenation; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D017711:Nonlinear Dynamics; D010101:Oxygen Consumption; D010807:Physical Endurance; D012119:Respiration; D012146:Rest / Q000502:physiology; D013997:Time Factors