Poincaré Plot Indexes of Heart Rate Variability: Pattern II Responses and Mental Workload.

We investigated the difference in the Poincare plot indexes between Pattern I and Pattern II responses related to the sensory intake/rejection hypothesis. ECG s were recorded from 34 healthy participants during two resting periods and four mental tasks, i.e., mental arithmetic (MA), mirror tracing (MT), Embedded Figures Test (EFT), and Raven Progressive Matrix Test (RAVEN). MA tasks were performed in two conditions, i.e. machine-paced (MA-m) and self-paced (MA-s). The experimental procedure was divided into two sessions. Both began with a rest period and machine-paced MA task. In Session 1 this was followed by EFT and MT while in Session 2 this was followed by RAVEN and a self-paced MA task. NASA-TLX was used after each task to evaluate subjective mental workload. Mean RR interval, two parameters from Poincare plot, i.e. SD1 and SD2 were calculated. All indexes were standardized across eight blocks for each participant and were analyzed by repeated measures from ANOVA and the Tukey’s HSD method. In results, NASA-TLX scores in MA-m1, MAm2, and MT were significantly higher than in other tasks, and were lower in MA-s and RAVEN (p < .05). RRIs were longer in MT than in other blocks. Poincare plot parameters in MT showed distinctive changes in which SD1 was longer while SD2 was shorter. The combination of SD1 and SD2 in the Poincare plot may be useful in the evaluation of mental workload for tasks including a specific attribute such as sensory intake characteristics.