Heart rate variability (HRV) describes variations of heart rate and is attributed to cyclic fluctuations in autonomic tone. The different methods of heart rate variability analysis allow for a non-invasive assessment of autonomic activity. This study analyzes the heart rate variability through both frequency domain methods and joint time-frequency domain methods which were executed through the LabVJEW graphical programming language. These algorithms were utilized to assess autonomic nervous system activity in Gulf War veterans with no health complaints versus Gulf War veterans with chronic fatigue syndrome. The heart rate variability analysis was obtained from acquired measurements of heart rate and blood pressure during periods of steady-state supine and standing positions. The subject populations as well as the physiological signals utilized in this study were obtained from the East Orange DVA Medical Center.

The results of this study indicate that there is no significant difference (p<.05) in autonomic nervous system activity, as assessed with low frequency/high frequency ratios, between Gulf War veterans with no health complaints versus Gulf War veterans with chronic fatigue syndrome. The results also indicate that there is no significant difference (p<.05) in the index of autonomic balance yielded from each of the LF/HF ratios obtained from the heart rate and blood pressure variabilities, respectively, versus the LF_{BP}/HF_{ECG}ratio.