Synchronization of Inhalation/Exhalation Ratio and Heart Rate Variability During Spontaneous Breathing: Discordance with LF/HF

In this study, we investigate the relationship between breathing patterns and cardiac autonomic nervous activity during spontaneous breathing. Electrocardiograms and respiratory signals were simultaneously monitored in six subjects for 5 minutes while in a seated position. The inhalation/exhalation ratio (i/e) was calculated, and its variance was compared with the heart rate variability index. The results showed that inhalation time tended to be longer than exhalation time, with the inhalation-to-exhalation ratio ranging from 1.074 to 1.423. Additionally, one subject exhibited an unusually slow respiratory cycle. The inhalation/exhalation ratio was not consistently associated with changes in the LF/HF ratio of heart rate variability, indicating individual differences. These findings suggest that while breathing patterns play a role in autonomic nervous system regulation and may have applications in stress and respiratory health management, there are limitations to these associations.