Subjects were assessed in two separate sessions (i.e., RNB and BAW) at the same time of the day on different days. Each session consisted of 40 min of recording for each subject, with 30 min of a test period preceded and followed by two periods of 5 min each. During the test periods of the two sessions, two recordings each were obtained for RNB and for BAW, which were averaged for analysis. Baseline nostril patency was confirmed using a mirror to measure the right and left nostril vapour condensation patterns upon exhalation. With this method the condensation of vapour of the dominant nostril was larger and visible longer [10].

MLAEPs were recorded in the 100-ms, poststimulus time period without delay (Nicolet Bravo, USA), from both left and right symmetrical scalp sites referenced to the ipsilateral ear lobes (i.e., C3-A1 and C4-A2 respectively), with the ground electrode on the ventral surface of the left forearm. The preamplifier band-width was set at 10-1500 Hz and 1500 responses were averaged for each assessment. The rejection level was expressed as a percentage of the full-scale range of the analog-to-digital converter. This level was set at 90%. Binaural click stimuli of 50 ms duration and alternating polarity at the rate of 5 Hz were delivered through acoustically shielded earphones (Amplivox, UK). The threshold of hearing was noted for each subject and the intensity was kept at 60 dB above the normal hearing level (nHL) [average dB (nHL)±SD, 27.9±4.5 dB (nHL)].

 

Peak amplitudes of short latency wave V, and middle latency Na, Pa and Nb waves were measured from a zero DC baseline. Peak latency was measured from the time of click delivery. The auditory evoked potential components were described as follows: wave V was the maximum positive peak between 5 and 8 ms, and the Na wave was the maximum negative peak preceding the Pa wave, which is a positive component occurring between 25 and 32 ms. The Nb wave was taken as the first maximum negative component immediately following the Pa wave [11].

RNB is voluntary breathing through the right nostril, while the left nostril is kept occluded with gentle pressure from the ring and little fingers of the right hand (nasika mudra in Sanskrit) [12, 13]. Breathing is voluntarily regulated to be slow and deep with awareness of breathing. During BAW there was no voluntary manipulation of the nostrils, instead subjects breathed slowly and deeply, being aware of their breath, as for RNB.

 

Two factor analyses of variance [14] were performed to compare peak amplitudes of the MLAEP components recorded in the two sessions (Factor A, i.e., RNB sessions and BAW sessions). The test conditions (i.e., pre, during, post) constituted Factor B. Separate analyses were performed for MLAEPs recorded from symmetrical scalp sites on the left and right side. The Tukey test for multiple comparisons was used to detect significant differ- ences between group mean values. Similar analyses as mentioned in 1 above, were done for the peak latencies of the MLAEP components.