The Influence of Breathing Exercises on the Heart Rate Variability Parameters of Female Medical Students

We studied the influence of breathing exercises (BEs) with a paced rhythm on the dynamics of heart rate variability (HRV) parameters in order to study the nature of adaptive processes in the body of girls with different initial levels of total HRV. Heart rate (HR), the temporal indicators SDNN, mNN, RMSSD, pNN50, the spectral parameters TP, HF and HFnu, LF and LFnu, LF/HF, as well as the sympathovagal balance index (SBI) and the stress index (SI), were evaluated. According to the SDNN level, individuals with conditionally low and conditionally high total HRV levels were identified—the LV (40 (31; 47) ms) and HV (64 (58; 70) ms) groups. At rest, HRV parameters in HV girls were significantly higher than in the LV subgroup. After BEs, a significant increase in SDNN and TP was observed in the LV subgroup against the background of a decrease in HF and HFnu and an increase in LF and LFnu, and the LF/HF ratio after BEs increased by 80%. In HV girls after BEs, a 6% increase in heart rate, but not in the total HRV parameters was recorded; a decrease in HF and HFnu was compensated for by an increase in LFnu; as a result, the LF/HF ratio increased significantly almost 1.5-fold compared to the rest level. In LV girls, the SBI and SI values were 2.6–2.7 times higher than in the HV subgroup. After BEs, a 24 and 19% decrease in SBI and SI was observed in the LV, but not in the HV subgroup. Thus, the adaptation of the work of the heart to BEs occurred in a similar way in LV and HV individuals; however, it differed in different adaptation costs of such an effort for LV and HV subjects.