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Short‐term correlation properties of R–R interval dynamics at different exercise intensity levels
Author(s) -
Hautala Arto J.,
Mäkikallio Timo H.,
Seppänen Tapio,
Huikuri Heikki V.,
Tulppo Mikko P.
Publication year - 2003
Publication title -
clinical physiology and functional imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.608
H-Index - 67
eISSN - 1475-097X
pISSN - 1475-0961
DOI - 10.1046/j.1475-097x.2003.00499.x
Subject(s) - atropine , medicine , intensity (physics) , heart rate , cardiology , steady state (chemistry) , physical exercise , exercise intensity , exercise physiology , heart rate variability , correlation , endocrinology , mathematics , blood pressure , physics , chemistry , quantum mechanics , geometry
Summary Methods based on non‐linear heart rate (HR) dynamics have been suggested to probe features in HR behaviour that are not easily detected by the traditional HR variability indices. This study tested the hypothesis that analysis of correlation properties of R–R intervals provides useful information on HR fluctuation during exercise. High‐ (HF) and low‐frequency (LF) spectral components and a short‐term scaling exponent ( α 1 ) of HR variability, were analysed for nine healthy subjects at rest, during incremental and steady‐state exercise, during atropine infusion and during incremental exercise after atropine administration. During the incremental exercise test α 1 increased from rest to an intensity level of ∼40% of (from 1·07 ± 0·24 to 1·50 ± 0·25, P <0·001) and thereafter decreased linearly until the end of exercise (from 1·50 ± 0·25 to 0·38 ± 0·10, P <0·001). Atropine infusion increased the scaling exponent α 1 value from 0·91 ± 0·23 to 1·37 ± 0·31 ( P <0·001). During exercise after atropine infusion, a linear reduction was observed in the scaling exponent α 1 from 1·37 ± 0·23 to 0·25 ± 0·08 ( P <0·001). Analogous changes in α 1 were seen during long‐term steady‐state exercise compared to incremental exercise. Conventional HR variability indices did not show any significant changes during exercise at high exercise intensity levels. α 1 correlated with the LF/HF ratio at rest ( r = 0·90, P <0·001), but the correlation was weaker after atropine ( r = 0·71, P <0·05) and during exercise (e.g. r = 0·33, P = NS at the level of 40% of ). In conclusion, incremental exercise test until exhaustion results in bidirectional changes in correlation properties of R–R interval dynamics. These changes can be explained by the intensity of vagal and sympathetic input to the sinus node during the different intensity levels of exercise. Changes in α 1 values can be detected also in high intensity levels, when the conventional measures of HR variability can not be applied.