ABSTRACT
Heart rate variability (HRV) is a simple technique which helps to assess the alterations in cardiac autonomic activity in healthy and diseased individuals. It is performed in various research centers using different hardwares and softwares. Hence, HRV reports generated from these centers cannot be compared unless their HRV data acquisition systems and the HRV analysis softwares correlate or agree with each other. In this study, Intra-class correlation coefficient test was done to see the extent of correlation among three HRV analysis softwares used by researchers in India, namely, (1). Kubios HRV version 2.0, Department of Physics, University of Kuopio, Finland, (2). HRV soft 1.1 Version, Autonomic Function Laboratory, Department of Physiology, All India Institute Of Medical Sciences (AIIMS), New Delhi and (3). Nevrokard aHRV 12.0.0. (Medistar Inc., Slovenia). Following standard guidelines, five minutes ECG data was acquired from twenty six healthy volunteers in supine, sitting and standing positions. The R-R intervals were computed from the ECG data and was subjected to short-term HRV analysis using the above three softwares. Statistical analysis revealed a highly significantly (p<0.001) perfect positive correlation (ICC values > 0.8) among the three softwares for both time domain and frequency domain parameters in the three different positions. Hence, it may be proposed that the interpretation of short-term HRV reports generated by the three softwares, across laboratories, can be equated.
ABSTRACT
Studies show that yogic type of breathing exercises reduces the spontaneous respiratory rate. However, there are no conclusive studies on the effects of breathing exercise on heart rate variability. We investigated the effects of non-yogic breathing exercise on respiratory rate and heart rate variability. Healthy subjects (21-33 years, both genders) were randomized into the intervention group (n=18), which performed daily deep breathing exercise at 6 breaths/min (0.1 Hz) for one month, and a control group (n=18) which did not perform any breathing exercise. Baseline respiratory rate and short-term heart rate variability indices were assessed in both groups. Reassessment was done after one month and the change in the parameters from baseline was computed for each group. Comparison of the absolute changes [median (inter-quartile ranges)] of the parameters between the intervention and control group showed a significant difference in the spontaneous respiratory rate [intervention group –2.50 (–4.00, –1.00), control group 0.00 (–1.00, 1.00), cycles/min, P<0.001], mean arterial pressure [intervention group –0.67 (–6.67, 1.33), control group 0.67 (0.00, 6.67), mmHg, (P<0.05)], high frequency power [intervention group 278.50 (17.00, 496.00), control group –1.00 (–341.00, 196.00), ms2 P<0.05] and sum of low and high frequency powers [intervention group 512.00 (–73.00, 999.00), control group 51.00 (–449.00, 324.00), ms2, P<0.05]. Neither the mean of the RR intervals nor the parameters reflecting sympatho-vagal balance were significantly different across the groups. In conclusion, the changes produced by simple deep slow breathing exercise in the respiratory rate and cardiac autonomic modulation of the intervention group were significant, when compared to the changes in the control group. Thus practice of deep slow breathing exercise improves heart rate variability in healthy subjects, without altering their cardiac autonomic balance. These findings have implications in the use of deep breathing exercises to improve cardiac autonomic control in subjects known to have reduced heart rate variability.
ABSTRACT
Background. Heart rate variability measures are reported to be altered in patients with various diseases, implying related abnormality of cardiac autonomic function. Could associated anxiety-induced mental stress, invariably present in all patients, contribute to these alterations? To address this question, we compared heart rate variability parameters computed from students during university examinations, a known cause of mental stress, with those computed during holidays when students are mentally relaxed. We felt that the changes in heart rate variability, if any, could be attributed to mental stress alone. Methods. We compared short-term heart rate variability parameters computed from 5-minute electrocardiogram recordings during supine rest in 18 healthy students, along with recordings of respiratory rate and blood pressure, during university examinations and holidays. Results. The mean of all the RR intervals was significantly lower, while the mean arterial pressure was significantly higher at the time of examinations. Measures of total variability, namely standard deviation of the normal-to-normal RR intervals and total spectral power, were significantly reduced during examinations. Low frequency normalized units (LF nu), high frequency (HF) nu and the LF/HF ratio were not significantly different. Conclusion. The decreased mean RR interval indicates an overall increase in heart rate or cardiac sympatho-excitation during examinations. This is associated with a decrease in total heart rate variability at the time of mental stress. None of the parameters indicative of the ratio of the extent of modulation of cardiac sympathetic to parasympathetic activity were different. These findings may be useful when interpreting measures of heart rate variability in patients.