Clinical Significance of Time-Domain Analysis of Heart Rate Variability in Burning Mouth Syndrome

Burning mouth syndrome (BMS) is characterized by oral burning or painful sensations without pathological changes; its real cause is unknown.  We previously reported that autonomic instability was probably associated with the pathogenesis of BMS based on the results of frequency analysis of heart rate variability (HRV) [1].  HRV is composed of time and frequency domains [2], although the significance of the time-domain analysis of HRV in BMS has not been discussed.  In this study we assessed the significance of the time-domain analysis, particularly in relation to autonomic instability. 

Patients were 22 Japanese females.  All patients received stellate ganglion near-infrared irradiation (SGR) once a week for 10 weeks.  The response to SGR was examined by time-domain analysis of HRV before and after every irradiation, and evaluated with visual analogue scale (VAS) representing tongue pain intensity.  The curative effects of SGR were assessed for the first and second half of the total treatment period, with each half consisting of 5 treatments in 5 weeks.  The 1st and 2nd VAS values were the mean values of VAS in each period.  It was defined as being therapeutically-effective, such that the 2nd VAS values was decreased by more than 50.0% compared to the 1st ones.  Statistical analyses were carried using the paired or unpaired Student’s t-test.  A value of P<0.05 was considered statistically significant. 

As a result, In 9 patients (40.9%), SGR was judged to be effective based on the differential between the 1st and 2nd VAS values.  No significant difference in the time domain was found between patients in the effective and ineffective group.  Then, we proposed several new parameters that were defined as the differences in previously established parameters between before and after irradiation.  The 1st D Mean HRT, representing the mean value of differential mean heart rate of the 1st half of the treatment period, was -0.8 ± 1.2 bpm, whereas the 2nd one was -1.8 ± 1.3 bpm in the effective group.  The 1st D Mean HRT was significantly higher than the 2nd one.  The 1st D RMSSD, representing the mean value of differential root mean square of successive NN interval differences of the 1st half of the treatment period, was -0.39 ± 4.70 ms, whereas the 2nd one was 2.89 ± 3.68 ms in the effective group.  The 1st D RMSSD was significantly lower than the 2nd one.  On the other hand, the 2nd D RMSSD was -0.82 ± 4.08 ms in the ineffective group; the 2nd D RMSSD in the effective group was significantly higher than that in the ineffective group. 

In conclusion, we found that our newly proposed parameters in the time domain, notably D Mean HRT and D RMSSD, were related to curative effects of SGR.  Based on these findings, we suggested that autonomic instability, particularly parasympathetic modulation associated with BMS, plays an important role in the pathogenic and healing process of BMS, because the parameters are considered indicative of parasympathetic responsiveness to SGR.  Therefore, time-domain analysis of HRV in BMS is very useful in follow-up of BMS and for determination of the therapeutic efficacy of SGR. 

All patients provided their informed consent after a full explanation of all procedures. 

The study was approved by an Institutional Review Board. 

References

[1] Momota Y, Takano H, et al. Frequency analysis of heart rate variability: a useful assessment tool of linearly polarized near-infrared irradiation to stellate ganglion area for burning mouth syndrome. Pain Med 2013; 14: 351-7. 

[2] Akselrod S, Gordon D, et al. Power spectrum analysis of heart rate fluctuation: a quantitative probe of beat-to-beat cardiovascular control. Science 1981; 213: 220-2.