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

Objective The 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. Methods Sixty-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. Results The conventional pNN50 and pNNx values with x