Entropy measures of heart rate variation in conscious XXXX .

@entity235 @entity551 @entity3897 @entity1169
Our goal was to determine the contributions of sympathetic and parasympathetic activity to entropy measures of heart rate variability (HRV). We compared our results with two commonly used methods to analyze HRV: standard deviation (SDNN) and power spectral analysis (HF norm). Beat-by-beat analysis of R-R intervals was performed in conscious @entity235 . The R-R intervals were analyzed with approximate entropy (ApEn) and entropy of symbolic dynamics (SymDyn) to assess the effects of reducing system complexity. This was achieved by pharmacologically inhibiting sympathetic, parasympathetic, and total autonomic nervous system regulation of heart rate. Three conditions were examined: rest, standing, and systemic @entity551 . At rest or standing, sympathetic inhibition ( @entity1169 ) had no effect on ApEn or SymDyn, whereas parasympathetic ( @entity3897 ) and combined ( @entity1169 + @entity3897 ) inhibition reduced both entropy measures to near zero. Systemic @entity551 reduced both entropy measures in intact @entity235 . When @entity551 was induced after sympathetic inhibition, ApEn was increased compared with @entity551 alone, whereas parasympathetic inhibition with @entity551 resulted in near-zero ApEn. Changes in the entropy measures of HRV were directionally similar to changes in SDNN and HF norm. These results indicate that the entropy of R-R intervals reflects parasympathetic modulation of heart rate.
