Statistics and graphs for heart rate variability : pNN50 or pNN20?

Two measures of heart rate variability, pNN50 and pNN20, are compared. A non-linear transformation of these measures is proposed, that is helpful in understanding their interrelationship. Provided a valid statistical test is employed, results from analysing pNN20 are likely to be equivalent to those from analysing pNN50. Arguments recently made by Mietus et al (2002 Heart 88 378–80) against the commonly used pNN50 are unconvincing.6 page(s