title: Quantitative beat-to-beat analysis of heart rate dynamics during exercise.
abstract: Beat-to-beat heart rate (HR) dynamics were studied by plotting each R-R interval as a function of the previous R-R interval (Poincaré plot) during incremental doses of atropine followed by exercise for 10 subjects and during exercise without autonomic blockade for 31 subjects. A quantitative two-dimensional vector analysis of a Poincaré plot was used by measuring separately the standard deviation of instantaneous beat-to-beat R-R interval variability (SD1) and the standard deviation of continuous long-term R-R interval variability (SD2) as well as the SD1/SD2 ratio. Quantitative Poincaré measures were compared with linear measures of HR variability (HRV) and with approximate entropy (ApEn) at rest and during exercise. A linear progressive reduction was observed in SD1 during atropine administration, and it remained almost at the zero level during exercise after a parasympathetic blockade. Atropine resulted in more variable changes in SD2 and the SD1/SD2 ratio, but during exercise after parasympathetic blockade, a progressive increase was observed in the SD1/SD2 ratio until the end of exercise. The SD1/SD2 ratio had no significant correlations with the frequency domain measures of HRV. However, the SD1/SD2 ratio had a modest correlation with ApEn at rest (r = -0.69, P < 0.001), but not during exercise (r = 0.27, P = NS). All measures of vagal modulation of HR decreased progressively until the ventilatory threshold level was reached, when sympathetic activation was reflected as changes in the SD1/SD2 ratio. These results show that quantitative two-dimensional vector analysis of a Poincaré plot can provide useful information on vagal modulation of R-R interval dynamics during exercise that are not easily detected by linear summary measures of HRV or by ApEn.
authors: Merikoski Rehabilitation and Research Center, University of Oulu, Finland.
authors: M P
authors: MP
authors: Tulppo
authors: T H
authors: TH
authors: Mäkikallio
authors: T E
authors: TE
authors: Takala
authors: T
authors: T
authors: Seppänen
authors: H V
authors: HV
authors: Huikuri
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold; D001285:Atropine / Q000494:pharmacology; D015444:Exercise; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D010276:Parasympatholytics / Q000494:pharmacology; D012146:Rest
chemical_list: D010276:Parasympatholytics; D001285:Atropine