DOI 10.4306/pi.2009.6.4.294 The pNNx Heart Rate Variability Statistics:

ObjectiveaaThe percentage of successive normal cardiac interbeat intervals greater than 50 msec (pNN50) is a widely used heart rate variability measure, which is useful in identify-ing 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. MethodsaaSixty-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. ResultsaaThe conventional pNN50 and pNNx values with x<50 msec were all signifi-cantly 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)