Background. Unstimulated salivary flow rate (USFR) has a close relationship with the sympathetic-parasympathetic activities of the autonomic nervous system (ANS). The heart rate variability (HRV) allows knowing the balance between the sympathetic and parasympathetic activities of the ANS.

Objective: The objective of this work was to examine the relationship between USFR and the balance of sympathetic and parasympathetic activities of the ANS assessed by measuring HRV.

Materials and Methods: Fifty-six healthy subjects were studied divided into two groups according to a higher level (A) or lower (B) USFR. The USFR and the VFC were measured consecutively. The Pearson correlations of the variables of the intensity and frequency domains of the HRV with the values of the USFR of the whole group and either the groups with smaller or higher USFR were calculated. Values with p< 0.05 were considered statistically significant.

Results: The USFR of subjects with lower USFR correlated positively and significantly with PNN50 (p< 0.001), RMSSD (p< 0.001) and HF (p= 0.0183); and in a negative and significant way with the LF (p= 0.0182); while in the subjects of the total group and the group with higher USFR, it did not correlate significantly with the HRV parameters.

Conclusions: The results obtained allow us to propose that in healthy subjects with lower USFR, the sympathetic-parasympathetic activity relationship of the ANS plays a critical role in the control of USFR; while in subjects with greater USFR, other factors may have a role preponderant.

Keywords: non-stimulated salivary secretion, autonomic nervous system, heart rate variability.

1. Lima DLF, Carneiro SDRM, Barbosa FTS, Saintrain MVL, Moizan JAH, Doucet J. Salivary flow and xerostomia in older patients with type 2 diabetes mellitus. PLoS One. 2017; 12(8): e0180891.
2. Proctor GB, Carpenter GH. Salivary secretion: mechanism and neural regulation. Monogr Oral Sci. 2014; 24: 14-29.
3. Lees T, Shad-Kaneez F, Simpson AM, Nassif NT, Lin Y, Lal S. Heart rate variability as a biomarker for predicting stroke, post-stroke complications and functionality. Biomark Insights. 2018; 13: 1177271918786931.
4. Seely AJ, Macklem PT. Complex systems and the technology of variability analysis. Crit Care. 2004; 8(6): R367-84.
5. Rahman F, Pechnik S, Gross D, Sewell LT, Goldstein DS. Power Reflects Baroreflex Function, Not Cardiac Sympathetic Innervation. Clin Auton Res. 2011; 21(3): 133–141.
6. Shaffer F, McCraty R, Zerr CL. A healthy heart is not a metronome: an integrative review of the heart's anatomy and heart rate variability. Front Psychol. 2014; 5: 1040.
7. Garrett JR. The proper role of nerves in salivary secretion: a review. J Dent Res. 1987;66(2):387-97.
8. World Medical Association. World Medical Association Declaration of Helsinki: ethical principles for medical research involving human subjects. JAMA. 2013;310(20):2191-4
9. López-Jornet P, Bermejo-Fenoll A, Bagan-Sebastian JV, Pascual-Gomez E. Comparison of a new test for the measurement of resting whole saliva with the draining and the swab techniques. Braz Dent J. 1996;7(2):81-6.
10. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Circulation. 1996; 93(5): 1043-1065.
11. Rajendra Acharya U, Paul Joseph K, Kannathal N, Lim CM, Suri JS. Heart rate variability: a review. Med. Biol Eng Comput. 2006; 44: 1031-1051.
12. Emmelin N. Nerve interactions in salivaryglands. J Dent Res. 1987;66(2):509-17.
13. Shiba Y, Nitta E, Hirono C, Sugita M, Iwasa Y. Evaluation of mastication-induced change in sympatho-vagal balance through spectral analysis of heart rate variability. J Oral Rehabil. 2002; 29(10): 956-60.
14. Yildiz M, Doma S. Effect of spontaneous saliva swallowing on short-term heart rate variability (HRV) and reliability of HRV analysis. Clin PhysiolFunct Imaging. 2018;38(4):710-717.
15. Hocevar A, Tomsic M, Praprotnik S, Hojnik M, Kveder T, Rozman B. Parasympathetic nervous system dysfunction in primary Sjögren's syndrome. Ann Rheum Dis. 2003; 62(8): 702-4.
16. Koh JH, Kwok SK, Lee J, Park SH. Autonomic dysfunction in primary Sjogren's syndrome: a prospective cohort analysis of 154 Korean patients. Korean J Intern Med. 2017; 32(1): 165-173.
17. Berntson GG, Bigger JT Jr, Eckberg DL, Grossman P, Kaufmann PG, Malik M, Nagaraja HN, Porges SW, Saul JP, Stone PH, van der Molen MW. Heart rate variability: origins, methods, and interpretive caveats. Psychophysiology. 1997;34(6):623-48.
18. Billman GE. The LF/HF ratio does not accurately measure cardiac sympatho-vagal balance. Front Physiol. 2013; 4:26.
19. Pedersen AML, Sørensen CE, Proctor GB, Carpenter GH, Ekström J. Salivary secretion in health and disease. J Oral Rehabil. 2018;45 (9): 730-746.
20. Minagi HO, Ikai K, Araie T, Sakai M, Sakai T. Benefits of long-term pilocarpine due to increased muscarinic acetylcholine receptor 3 in salivary glands. Biochem Biophys Res Commun. 2018;503(2):1098-1102.

José Federico Rivas-Vilchis