The relationship between HRV and parasympathetic effect is best described by a function in which there is an ascending limb where HRV increases as parasympathetic effect increases until it reaches a plateau level; HRV then decreases as parasympathetic effect increases. Because there is marked interindividual variation in this relationship, differences in HRV between individuals may reflect differences in this relationship and/or differences in autonomic effects.

No abstract

Within the acceptable noise range for SAECG, lower noise results in longer QRSd and larger variance, suggesting that more accurate recordings may have less reproducibility. The random timing of noise relative to signal results in the distribution/variance of repeated measurements. Statistical strategies may be used to reduce some of this variance and may enhance the diagnostic utility of SAECG.

No abstract

These data confirm that HRV reflects the character of parasympathetic modulation of the heart rate rather than parasympathetic tone per se. Furthermore, this study identifies two distinct physiologic explanations for the finding of low HRV, namely, diminished vagal discharge and resistance of cardiac muscarinic receptors to vagal discharge. Further delineation of the relationships between parasympathetic tone and HRV will allow for better understanding of the pathophysiologic derangements associated with low HRV.