The possibility of using spectral indices of heart rate variability to improve the diagnostic value of cardiovascular autonomic function tests in rheumatoid arthritis patients.

To the Editor,

Our comment is related the paper by Javady Nejad et al. (1) where they reported cardiovascular autonomic control in 44 rheumatoid arthritis (RA) patients and 44 healthy subjects. Until now, the involvement of the autonomic nervous system in chronic systemic inflammatory disorders is disputable. Several authors reported significant differences in cardiovascular autonomic control in RA patients and healthy subjects: Refs. 3, 7, and 10-14 in the paper by Javady Nejad et al. (1).

The strong point of the cross-sectional study performed by Javady Nejad et al. (1) is the employment of a variety of cardiovascular autonomic function tests, namely, deep breathing with a frequency of 6 breaths per minute, active tilt test, Valsalva maneuver, and sustained handgrip. On the contrary to previous results, the authors found no difference between the RA patients and control subjects in their responses to the autonomic function tests. This important result requires an additional analysis. The ECG recording was performed by Nejad et al. (1) during all tests. Therefore, it is advisable to further explore the indicators of heart rate variability (HRV) (2) that may complement the classical interpretation of the cardiovascular autonomic function test results.

The response of heart autonomic control, which is studied by HRV, to external periodic disturbances (such as controlled breathing, controlled eye opening, etc.) is determined by a frequency-dependent phenomenon (3, 4). The external 0.1-Hz disturbance at a rate of six actions per minute is a powerful factor for baroreflex control that shows itself in healthy subjects as a resonance response in the low-frequency heart rate variations (3, 4). Moreover, a 0.1-Hz controlled breathing is potentially the main external factor for the study of barore-flex gain and its dysfunction. Thus, spectral analysis of HRV can supplement the results of the study conducted by Javady Nejad et al. (1). The controlled breathing can also be combined with a tilt test (3) to obtain useful additional information in the further study of cardiovascular autonomic control in RA patients.