Summary
Objectives:
The objectives of this paper were to present a method to extract the amplitude of RSA in the respiratory-phase domain, to compare that with subjective or objective indices of the MWL (mental workload), and to compare that with a conventional frequencyanalysis in terms of its accuracy during a mental arithmetic task.
Methods:
HRV (heart rate variability), ILV (instantaneous lung volume), and motion of the throat were measured under a mental arithmetic experiment and subjective and objective indices were also obtained. The amplitude of RSA was extracted in the respiratory-phase domain, and its correlation with the load level was compared with the results of the frequencydomain analysis, which is the standard analysis of the HRV.
Results:
The subjective and objective indices decreased as the load level increased, showing that the experimental protocol was appropriate. Then, the amplitude of RSA in the respiratory-phase domain also decreased with the increase in the load level. The results of the correlation analysis showed that the respiratory-phase domain analysis has higher negative correlations, −0.84 and −0.82, with the load level as determined bysimplecorrelation and rankcorrelation, respectively, than does frequencyanalysis, for which the correlations were found to be −0.54 and −0.63, respectively. In addition, it was demonstrated thatthe proposed method could be applied to the short-term extraction of RSA amplitude.
Conclusions:
We proposed a simple and effective method to extract the amplitude of the respiratory sinus arrhythmia (RSA) in the respiratory-phase domain and the results show that this method can estimate cardiac vagal activity more accurately than frequency analysis.
Keywords
Heart rate variability - Hilbert transform - respiratory phase - respiratory sinus arrhythmia