Use of intrinsic modes in biology: Examples of indicial response of pulmonary blood pressure to ± step hypoxia

Wei Huang, Zheng Shen, Norden E. Huang, Yuan Cheng Fung

Research output: Contribution to journalArticlepeer-review

79 Scopus citations

Abstract

Recently, a new method to analyze biological nonstationary stochastic variables has been presented. The method is especially suitable to analyze the variation of one biological variable with respect to changes of another variable. Here, it is illustrated by the change of the pulmonary blood pressure in response to a step change of oxygen concentration in the gas that an animal breathes. The pressure signal is resolved into the sum of a set of oscillatory intrinsic mode functions, which have zero 'local mean,' and a final nonoscillatory mode. With this device, we obtain a set of 'mean trends,' each of which represents a 'mean' in a definitive sense, and together they represent the mean trend systematically with different degrees of oscillatory content. Correspondingly, the oscillatory content of the signal about any mean trend can be represented by a set of partial sums of intrinsic mode functions. When the concept of 'indicial response function' is used to describe the change of one variable in response to a step change of another variable, we now have a set of indicial response functions of the mean trends and another set of indicial response functions to describe the energy or intensity of oscillations about each mean trend. Each of these can be represented by an analytic function whose coefficients can be determined by a least-squares curve-fitting procedure. In this way, experimental results are stated sharply by analytic functions.

Original languageEnglish
Pages (from-to)12766-12771
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume95
Issue number22
DOIs
StatePublished - 27 Oct 1998

Keywords

  • Fourier spectrum
  • Hilbert spectrum
  • Nonlinear oscillations
  • Nonstationary
  • Stochastic process

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