Yoga practice places particular emphasis on voluntary breath regulation, as this is traditionally believed to influence brain functions [1
]. In yoga practice there are several ways in which a practitioner may voluntarily modify their respiration, which includes changing the rate, depth, and breathing through the mouth, among other methods [2
Modifying the rate of breathing is the basis for a particular technique called kapalabhati
, which is a high frequency yoga breathing technique (with a breath rate of 1.0 to 2.0 Hz) [3
This high frequency yoga breathing (HFYB) technique could be expected to alter cardiac functioning, and indeed this was seen in a study on twenty-four volunteers who practiced the technique at the rate of 2.0 Hz for 15 minutes, analyzed as three, five minute periods [4
]. A 0.1 Hz rhythm was present in the record of R-R intervals and the blood pressure during the HFYB. The results were taken to support the hypothesis about the integrative role of cardiovascular and respiratory rhythms when the respiratory frequency is altered. The same authors further assessed the effects of the HFYB (at 2.0 Hz) as three, five minute periods, as in their other study, in seventeen advanced yoga practitioners [5
]. The EKG, respiration and blood pressure were recorded continuously during the three, five minute periods of HFYB, as well as before and after the practice. The beat to beat series of the R-R intervals as well as systolic and diastolic blood pressure were analyzed by a spectral analysis of the time series. All frequency bands of R-R interval variability were reduced in HFYB. These results as well as the changes in other variables point to decreased cardiac vagal modulation during HFYB. The changes in R-R interval variability, as well as in the blood pressure, were interpreted by the authors as suggestive of decreased cardiac vagal modulation during HFYB.
A comparable result was reported when twelve experienced practitioners practiced the HFYB technique at 2.0 Hz for one minute and a frequency domain analysis was carried out [6
]. Following one minute of HFYB there was a significant increase in the low frequency power and in the LF/HF ratio, while the HF power was significantly lower following the HFYB. The results suggested that the HFYB modifies the autonomic status by increasing sympathetic activity with reduced vagal activity.
The effect of HFYB on the cardiac autonomic control was hence reported to have comparable effects in two studies which differed in the duration of the practice i.e., fifteen minutes [5
] as compared to one minute [6
The same HFYB practice was shown to improve the performance in a cancellation task requiring both focused and selective attention [7
]. The participants here were forty-six medical students, forty-eight middle-aged adults (30 to 59 years), and sixteen older adults (all of whom were over 60 years of age). The HFYB was practiced at rates varying between 1.0 and 2.0 Hz, for 15 minutes.
Apart from the performance in a paper and pencil cancellation task [7
], the HFYB at 2.0 Hz for one minute also improved the performance in a P300 event related potential task [8
]. The P300 is an event related potential which is generated when attending to and differentiating between auditory stimuli [9
]. The P300 was recorded in two groups with fifteen participants in each group. One group practiced the HFYB at 2.0 Hz for one minute, while the other group practiced being aware of their breath, for the same duration of time. The P300 changed after both practices. A decreased latency of the P300 after the HFYB suggested a decrease in the time required to complete this attentional task. In contrast following breath awareness an increase in the P300 amplitude which was recorded, suggested that greater neural resources were needed to complete the task.
Attention and vigilance are associated with increased sympathetic modulation [10
]. Since HFYB (at 1.0 Hz and at 2.0 Hz) improved the performance in an attentional task [7
], the present study was undertaken to assess the effect of fifteen minutes (as three, five minute epochs) of the HFYB on heart rate variability with both time and frequency domain analysis, in a larger sample than was previously studied, i.e., in thirty-eight participants. All thirty-eight participants were assessed in two sessions. These were before, during, and after (i) HFYB and (ii) a comparable duration of breath awareness. Breath awareness was selected as the second technique practiced for two reasons, i.e., (i) breath awareness is believed to improve attention [7
] and hence may influence sympathetic modulation and (ii) breath awareness is a part of all yoga breathing techniques, including the HFYB (or kapalabhati
) studied here.