Heart rate variability as a measure of autonomic regulation of cardiac activity for assessing mental stress

Aim: The purpose of the study was to investigate the variations of autonomic regulation of cardiac activity during arithmetic stress test. Methods: We tested 245 healthy students with a mean age of 21.02 ± 0.17 years. The students were examining in the following sequence: recording of heart rate variability (HRV) (the marker of autonomic nervous system functioning) at rest (10 minutes), during mental arithmetic (10 minutes) and during the recovery (10 minutes). For the calculation, subjects were given a three-digit number and asked to count backward by sevens. (S. Jern et al., 1991). Results and Conclusions: During the mental arithmetic condition, the heart rate was reduced (Sign test (Z) = 9.85; p < 0.000001). HF component of HRV, which reflects only parasympathetic activity, decreased more during mental stress (Z = 3.76; p = 0.0002). The LF/HF ratio during stress was significantly higher than that in the rest period (Z = 5.85; p = 0.00002), indicating that sympathetic nerve activities during mental stress became predominant. Furthermore, VLF parameter, was significantly higher (Z = 3.12; p = 0.002) during the test than that at rest. pNN50 and RMSSD were lower during stress (respectively, Z = 6.49; p < 0.000001 and Z = 4.11; p < 0.00001), suggesting decreased sympathetic activity. During the mental arithmetic condition SD1 and SD1/SD2 were lower than that at rest (Z = 5.40; p < 0.000001 and Z = 7.66; p < 0.000001). SS and CCM parameters decreased more during mental stress (respectively, Z = 3.23; p < 0.000001 and Z = 7.33; p < 0.000001). All the studied HRV parameters approached the baseline level in the recovery phase. The main findings of this study suggest HRV analysis could be effective in automatically detecting functional status during mental stress.