Quantitative indicators of the Poincar'e plot of heart rate variability during breathing with imposed frequency

He study of nonlinear properties of the heart rate regulation system is an important direction of physiology of the autonomic nervous system. The aim of the study was to assess the effect of breathing with imposed frequency on heart rate variability using the Poincaré plot analysis. The study group consisted of 40 healthy volunteers (80% women). ECG was recorded during free breathing and breathing with imposed frequency at 6 breaths/min. The values of the Poincaré plot index (SD1, SD2, SD1/SD2, SS, Guzik’s index (GI), complex correlation measure (CCM)) were calculated. Breathing with imposed frequency caused an increase in the size of the point cloud (an increase in SD1, SD2, SS) and resulted in more elongated ellipse (a decrease in SD1/SD2). Reduction in GI during breathing with imposed frequency comhter of respiration is the dominant factor for phase asymmetry. The study found that the average CCM values obtained from records of breathing with imposed frequency were significantly lower than the ones obtained during free breathing. Breathing with imposed frequency causes changes in the attractor, an increase in asymmetry and a decrease in the complexity of the internal nonlinear dynamics of heart rate variability.