Heart Rate Variability as a Mental Workload Index

Abstract

In this study, we investigated relationship between task characteristics such as sensory intake and cardiovascular responses. Nineteen male participants were asked to perform a mental arithmetic task (MA) and a computerized mirror tracing (MT) task for five minutes each. In the MA task, participants were instructed to respond within five seconds by pressing the left or right mouse button. Therefore, this task includes a high time pressure (temporal restriction). In the MT task, participants were required to trace a zigzag pathway displayed on a PC screen by using a mouse. The horizontal and vertical control elements of the mouse were exchanged with each other. This task contains a sensory intake characteristic which induces parasympathetic dominance resulting in bradycardia. ECG and arterial blood pressure were continuously recorded during the two task blocks and before (PRE) and after (POST) resting periods of five minutes each. Heart rate variability indexes such as low frequency (LF) component, high frequency (HF) component and LF/HF ratio were derived. In the results, heart rate (HR) was considerably larger in the MA compared to PRE. On the contrary, the HR change was small in the MT, suggesting that the physiological response in MT is a pattern 2 type which is typically induced by a sensory intake task, although no significant difference was found between the two tasks. Systolic blood pressure (SBP) and Diastolic blood pressure (DBP) were higher in the MT than MA, but there was no significant difference between them. Both SBP and DBP were significantly higher in the task periods than resting periods. Significant differences were found only between PRE and MT, and PRE and POST in LF/HF which showed the highest value in POST, suggesting that the LF/HF ratio is not a reliable mental workload index.