Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2002 Oct;88(4):378-80.
doi: 10.1136/heart.88.4.378.

The pNNx files: re-examining a widely used heart rate variability measure

J E Mietus  1 , C-K Peng, I Henry, R L Goldsmith, A L Goldberger
Affiliations

The pNNx files: re-examining a widely used heart rate variability measure

J E Mietus et al. Heart. 2002 Oct.

Abstract

Objective: To re-examine the standard pNN50 heart rate variability (HRV) statistic by determining how other thresholds compare with the commonly adopted 50 ms threshold in distinguishing physiological and pathological groups.

Design: Retrospective analysis of Holter monitor databases.

Subjects: Comparison of HRV data between 72 healthy subjects and 43 with congestive heart failure (CHF); between sleeping and waking states in the 72 healthy subjects; and between 20 young and 20 healthy elderly subjects.

Main outcome measures: Probability values for discriminating between groups using a family of pNN values ranging from pNN4 to pNN100.

Results: For all three comparisons, pNN values substantially less than 50 ms consistently provided better separation between groups. For the normal versus CHF groups, p < 10(-13) for pNN12 versus p < 10(-4) for pNN50; for the sleeping versus awake groups, p < 10(-21) for pNN12 versus p < 10(-10) for pNN50; and for the young versus elderly groups, p < 10(-6) for pNN28 versus p < 10(-4) for pNN50. In addition, for the subgroups of elderly healthy subjects versus younger patients with CHF, p < 0.007 for pNN20 versus p < 0.17 for pNN50; and for the subgroup of New York Heart Association functional class I-II CHF versus class III-IV, p < 0.04 for pNN10 versus p < 0.13 for pNN50.

Conclusions: pNN50 is only one member of a general pNNx family of HRV statistics. Enhanced discrimination between a variety of normal and pathological conditions is obtained by using pNN thresholds as low as 20 ms or less rather than the standard 50 ms threshold.

PubMed Disclaimer

Figures

Figure 1
Figure 1
(A) Mean pNN distributions, showing the mean percentage of successive NN interval increments greater than each given increment (pNN) versus the NN increment. pNN was calculated for each subject in the normal and congestive heart failure (CHF) groups over a 24 hour period and the resulting distributions were resampled at 2 ms intervals and smoothed using a five point moving window average. The means and standard deviations were then calculated for each group at each resampled point. The solid line indicates the mean values for the group of healthy subjects (n = 72); the dotted line indicates the mean values for the group with moderate to severe CHF (n = 43). The shaded bands represent 2 SEM for these data sets. (B) Mean pNN distribution differences. The difference between the means of the normal group and the CHF group shown in (A) is plotted as a solid line and the p values for the separation between groups at different NN increments are plotted as a dotted line. The most significant separation between the two groups is around x = 12 ms, not at the traditional x = 50 ms (vertical dashed line).
Figure 2
Figure 2
Comparison of (A) pNN50 with (B) pNN20 for subjects in the three primary comparison groups. Group means (*) and standard deviations are indicated alongside each data set. Probability (p) values computed using the Student's t test are indicated above each pair of comparison groups. The number of subjects in each group is given in parentheses below. More robust separation is obtained for pNN20 than pNN50 for each comparison. CHF, congestive heart failure; ELD, healthy elderly subjects; NML, healthy control subjects; SLP, healthy subjects during sleeping hours; WAK, healthy subjects during waking hours; YNG, healthy young subjects.
See this image and copyright information in PMC

References

    1. Ewing DJ, Neilson JMM, Travis P. New method for assessing cardiac parasympathetic activity using 24 hour electrocardiograms. Br Heart J 1984;52:396–402. - PMC - PubMed
    1. Bigger JT Jr, Kleiger RE, Fleiss JL, et al. Components of heart rate variability measured during healing of acute myocardial infarction. Am J Cardiol 1988;61:208–15. - PubMed
    1. Chakko S, Mulingtapang RF, Huikuri HV, et al. Alterations in heart rate variability and its circadian rhythm in hypertensive patients with left ventricular hypertrophy free of coronary artery disease. Am Heart J 1993;126:1364–72. - PubMed
    1. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Heart rate variability: standards of measurement, physiological interpretation, and clinical use. Circulation 1996;93:1043–65. - PubMed
    1. Tsuji H, Larson MG, Venditti FJ Jr, et al. Impact of reduced heart rate variability on risk for cardiac events. The Framingham Heart Study. Circulation 1996;94:2850–5. - PubMed

Publication types