Time-frequency analysis of cardio-respiratory response to mental task execution

Heart rate, heart rate variability (HRV), and respiratory effort have been proposed in numerous studies with the goal of correlating physiological parameters with mental workload. Aim of this study was to analyze the cardio-respiratory response to a mental task (Sternberg Task) from a single lead ambulatory ECG recording, in healthy subjects. Under no assumptions on stationarity, HRV was analyzed in the time-frequency domain by means of the Hilbert Huang Transform (HHT). A surrogate respiratory signal was also extracted from the ECG recording, by means of an established principal component analysis (PCA) based method, and its spectrum was analyzed. A sharp decrease in low frequency (LF) components of HRV during the execution of the mental task with respect to the resting intervals was generally observed. In some subjects, an increase in the peak-power respiratory rate was also observed during task execution.