Comparative Cross-sectional Study on Phasic Heart Rate Variability and Working Memory Among Young Adults.

CONTEXT

Heart rate variability (HRV) could be a promising early biomarker of cognitive impairment. A better understanding of reaction patterns between cardiovascular and cognitive functions can be helpful in predicting and preventing the manifestation of disease. Additionally, beneficial cardiovascular evidence for yoga is promising but lacks short-term (approximately one year) cross-sectional investigations.

OBJECTIVE

The study intended to investigate phasic HRV and its patterns of reaction in yoga practitioners and nonpractitioners, using rest and stress periods induced by cognitive tasks.

DESIGN

The research team designed a cross-sectional, controlled study.

SETTING

The study took place in the Cognitive Neuroscience Laboratory at Swami Vivekananda Yoga Anusandhana Samsthana (S-VYASA) in Bangalore, Karnataka, India.

PARTICIPANTS

Participants were 84 healthy male volunteers, 42 in the yoga group, the intervention group, and 42 in the nonyoga group, the control group.

OUTCOME MEASURES

Simultaneously the research team recorded both an autonomic measurement, an electrocardiogram (EKG), and a working memory (WM) task, the N-back task, to assess the effects of the two groups' reaction patterns on HRV and WM. The data included an average of a 5 min epoch for the baseline EKG and a 15 min epoch for the EKG during the N-back task. The research team recorded the HRV indices: (1) mean rhythm-to-rhythm (RR) intervals, (2) heart rate (HR), (3) standard deviation of RR intervals (STDRR), (4) root mean square of successive differences (RMSSD), (5) triangular interpolation of RR interval histogram (TINN), (6) percentage of successive normal sinus RR intervals >50 ms (pNN50), (7) number of adjacent N-N intervals over 50 ms (NN50), (8) low frequency (LF), (9) high frequency (HF), and (10) LF/HF ratio. The team compared the HRV indices to participants' reaction patterns while performing cognitive tasks.

RESULTS

In response to psychological stress, the yoga group had enhanced physiological activity, such as an increased cardiac activity, indicated during the task by a higher HR, NN50, and TINN and a lower RR, STDRR, pNN50, and RMSSD, indicating more flexibility. The control group had an increase only in HR and TINN and had a decreased RR. Simultaneously, the yoga group showed greater accuracy in the N-back task for WM compared to the control group.

CONCLUSIONS

The study revealed significant differences in phasic HRV and WM performance among the groups. The yoga group had higher phasic HRV indices with higher cognitive performance than the control group. This is the first study that has attempted to show that the cross-sectional differences in HRV indices between yoga practitioners and nonpractitioners exist at an early stage of life, where no disease has yet manifested. The research team suggest that incorporating yoga into daily life at a young age may yield a healthy life.