They were 12 normal, healthy male volunteers in the age range of 21 to 33 years (mean ± SD, 25.6 ± 3.1 years) who were familiar with both kapalabhati and nadisuddhi practices and had experience of the practices ranging from 6 months to 3 years (group average experience, 19.7 ± 12.8 months).
Design of the study : Recordings were made on separate days for the two different practices, maintaining the same time of recording of the day for each subject. The subject was seated in a dimly lit, sound attenuated chamber. Recordings, each lasting 5 min, were obtained before as well as immediately after each practice. The subject was seated in a comfortable sitting posture with the back straight, for both practices. The practices were performed at least 3 hours following the last meal.
The electrocardiogram was recorded using standard bipolar limb lead 1 configuration and an AC amplifier with 1.5 Hz high pass filter and 75 Hz low pass filter setting (Medicaid, Chandigarh, India). The ECG was digitized using a 12 bit analog-to-digital convertor (ADC) at a sampling rate of 500 Hz and stored on the hard disk of a PC/ AT 486 system COMPTECH (Bangalore, India) for analysis (6). The R waves were detected to obtain a point event series of successive R- R intervals, from which the beat to beat heart rate series was computed. The data recorded were visually inspected off-line and only noise free data were included for analysis.
Frequency domain analysis
The mean values were removed from the heart rate series to obtain the HRV series. The HRV power spectrum was obtained using fast Fourier transform analysis (FFT). The energy in HRV series of the following specific frequency bands was studied, viz., the very low frequency component (0.0- 0.05Hz), low frequency component (0.05- 0.15 Hz), and high frequency component (0.15-0.50 Hz). The low frequency and high frequency values were expressed as normalized units (7).
For the practice of rapid yoga breathing (kapalabhati), the subject was instructed to inhale deeply and start exhaling forcibly at the rate of 120 breath cycles per min (2.0Hz frequency). The rapid active exhalations are accomplished by rapid, forceful movements of the abdomen followed by passive, effortless inhalation. The duration of practice was prescribed as 1 min (8). Alternate nostril breathing (nadisuddhi pranayama) starts with exhalation through both nostrils, followed by closing the right nostril with the thumb of the right hand and inhaling slowly through the left nostril. After complete inhalation, the left nostril is closed with the little and ring fingers of the right hand followed by opening the right nostril and exhaling through it. The subject next inhales through the right nostril and then exhales through the left nostril. This forms one round of nadisuddhi pranayama. This was continued for fifteen minutes, which is the recommended duration of practice (8).
The values of derived parameters obtained before the practices and the ones obtained after the practices were compared using the t-test for paired data.