Influence of higher respiratory rate on SDNN heart rate variability and heart rate in healthy subjects

Reduced standard deviation of R-R intervals (SDNN), elevated heart rate (HR) and respiratory rate (RR) are noted in poor prognosis of cardiovascular disease. But is there association between these three parameters is not clear. To investigate the influence of RR on HR and SDNN in healthy subjects. In 10 healthy subjects, SDNN and HR was calculated from electrocardiogram tracing recorded from lead II in supine position while breathing at 12, 15 and 20 respiratory cycles/per minute for one minute duration. Statistical analysis was done by ANOVA/Kruskal -Wallis test followed by multiple comparisons. Association between two continues variables were measured by Pearson Correlation Coefficient test. p value < 0.05 considered significant. HR was higher while breathing at 20 cycles compared to 12 cycles/minute (p < 0.05). There was no difference in HR while breathing at 15 cycles compared to 12 and 20 cycles/minute. There was no significant difference SDNN while breathing at 12, 15 and 20 cycles/minute. There was no correlation between HR and SDNN while breathing at 12, 15 and 20 cycles/minute. Higher respiratory rate may influence heart rate but not SDNN.