The pNNx Heart Rate Variability Statistics: An Application to Neuroautonomic Dysfunction of Clozapine-Treated Subjects

Abstract

ObjectiveThe percentage of successive normal cardiac interbeat intervals greater than 50 msec (pNN50) is a widely used heart rate variability measure, which is useful in identifying the neuroautonomic dysfunction of psychiatric disorders. However, pNN50 is only one member of a larger family of pNNx statistics, where x is greater than 0 msec. The potential application of the general pNNx statistics has not yet been explored in the psychiatric field. The authors examined the pNNx statistics in clozapine-treated subjects and normal controls to evaluate the usefulness of the general pNNx statistics.MethodsSixty-one schizophrenic patients treated with clozapine and fifty-nine normal controls were evaluated. Probability values for the differences between the groups at each pNN value (range: pNN1-pNN100) were calculated using data obtained from a 30-minute electrocardiogram.ResultsThe conventional pNN50 and pNNx values with x<50 msec were all significantly lower in the patient group (p<0.05). The distinction between the two groups was more prominent at pNN values less than 50 msec than that observed at pNN50. The maximum separation between groups occurred at pNN5 (68.2±19.1 vs. 22.5±20.5, p<10-22).ConclusionThe pNNx with x<50 msec provided more robust discrimination between the groups than the conventional pNN50, suggesting the importance of analyzing very small variations of interbeat interval in discriminating normal and pathological heart rate patterns. The results also suggest that the general pNNx statistics may be applied and useful in evaluating the neuroautonomic dysfunction in patients treated with clozapine, complementing the traditionally computed pNN50 value.

Comparing cardiovascular load by heart rate variability (HRV) including pNNxx parameters with ratings of perceived medical intervention load (PMIL) in patients undergoing carotid endarterectomy or carotid artery stenting

“…Considering the effect sizes as well as the association with HF, pNN20, pNN25, and pNN30 seem more favorable than pNN50 and can be considered as indicators of vagal activity, however displaying higher effect sizes than pNN50 and HF. This advantage of using pNNxx statistics other than the traditional 50 ms threshold also supports findings in other research areas, such as fetal development [30], the impact of psychotropic medication on HRV in schizophrenic patients [23], flight phobia [9], and disturbed well-being [10]. The time domain parameter SDNN displayed the greatest Time × Intervention interaction effect and effect size, however indicating HR variability from unspecific origin.…”

“…In line with Mietus, et al [24], Kim, et al [23], and Trimmel [8,10] pNNxx thresholds around 25 ms mirrored subtle differences in HRV and in particular vagal activity that were less effectively captured by the usually applied 50 ms threshold. In the present investigation, pNN20, pNN25, and pNN30 showed the highest effect sizes, whereas parameters with lower (pNN05 and pNN10) or higher (pNN40 and pNN50) thresholds showed somewhat smaller effect sizes.…”

“…As the HRV parameter selection varies considerably between studies and different parameters have on the one hand shown to correlate substantially, but on the other hand have their unique contribution [8,10,13], the present study simultaneously considered a number of parameters. In this regard, several pNN thresholds (pNNxx) below the commonly used 50 ms threshold were examined, as they have been suggested to better discriminate between normal and various pathological conditions and to provide valuable information on the very short-term control of sinus rhythm dynamics [8,10,23,24]. As evidence is still poor whether pNN50 and pNN thresholds below 50 ms can be regarded as equivalent or not [23][24][25] and in how far they reflect vagal activity, the association between the pNNxx parameters and HF power was examined.…”

“…In this regard, several pNN thresholds (pNNxx) below the commonly used 50 ms threshold were examined, as they have been suggested to better discriminate between normal and various pathological conditions and to provide valuable information on the very short-term control of sinus rhythm dynamics [8,10,23,24]. As evidence is still poor whether pNN50 and pNN thresholds below 50 ms can be regarded as equivalent or not [23][24][25] and in how far they reflect vagal activity, the association between the pNNxx parameters and HF power was examined. Consequently, effect sizes were compared with regard to the Time × Intervention interaction in order to get a picture of the parameters' effect sizes.…”

A Robust Algorithm for Real-Time Peak Detection of Photoplethysmograms Using a Personal Computer Mouse

“…In fact, the percentage of pNN100 (two neighboring PPI values that have a difference of more than 100 ms) is approximately zero, which proves that PPI values that differ from adjacent normal PPI values by 100 ms or more are error peaks. The error peaks have to be checked and removed from the original PPG signal using an automatic method and a manual method (by visual inspection of all PPIs) [28]. In this method, observed results are the PPI values of the detected peaks, called x i .…”