Adaptive responses of heart rate regulation during functional tests with breath holding

BACKGROUND: Synchronization of biorhythms in living organisms is of particular interest to researchers from the standpoint of adaptation theory. AIM: To study the characteristics of the response of regulatory influences on heart rhythm during tests with voluntary breath holding during inhalation and exhalation. MATERIAL AND METHODS: The study sample included 21 randomly selected students (9 males, 12 females) aged 20.64±1.14 years with body weight 67.19±12.98 kg, height 172.29±7.63 cm. All subjects were divided into three groups (I, II, III) according to the classification by N.I. Shlyk (2009), which is based on the predominance of central or autonomic circuits of heart rhythm regulation. A fivefold sequential ECG recording was conducted using the hardware-software complex “Varicard 3.0” with the subject seated after a five-minute rest: 1 — baseline state; 2 — voluntary breath holding during inhalation; 3 — resting state; 4 — voluntary breath holding during exhalation; 5 — resting state. Using the “Varicard 3.0” system, a mathematical analysis of heart rhythm was performed, taking into account statistical parameters of heart rhythm and indices of spectral frequency analysis. RESULTS: During the period of breath holding, heart rate variability decreased, while at rest it increased in all groups. In group I, after a breath-hold test during the rest period, eutonia was observed according to spectral analysis (HF=LF). Statistical analysis in this group demonstrated an increase in the contribution of the parasympathetic component to heart rate variability (RMSSD, pNN50, SDNN, CV), signifying the prerequisites for increased heart rate variability. In group II, after breath-holding tests, a slight decrease in sympathetic activity was observed. A tense pattern of autonomic regulation was observed during the exhalation breath-hold test, which may indicate a reduced functional state of the regulatory systems. Group III was characterized by a sharp increase in sympathetic activation in the test with breath holding during inhalation, followed by a soft correction during breath holding during exhalation, which can be regarded as an adequate response of the body to the load. At rest, after the test, the regulation pattern returned to the original one with a moderate predominance of parasympathetic activity and, accordingly, a more favorable level of heart rate variability for the body. CONCLUSION: Adaptive reactions of the heart rate variability are manifested by an increase in sympathetic activation, which, subsequently, during normal breathing, is replaced by a compensatory activation of the parasympathetic division of the autonomous nervous system. Although reactions are unidirectional, the severity can vary across the groups.