Respiration belt transducer

Respiration vital sign change was measured by a respiration belt transducer (BIOPAC system Inc, Goleta, CA, USA). The respiration belt was modified to function as a potentiometer, soldered in series with a 5 k ohm resistor that was powered by the 3.3 V power pin on the Arduino board. The voltage variation caused by the resistance change during each breath was measured by the HackEEG system as one of the biopotential channels. The respiration signal was filtered by a 5 Hz zero-phase low-pass filter in post-processing.
120 s after baseline recording, the subjects underwent a timed deep respiratory challenge. The timed respiratory challenge consisted of regular breathing (5 s inhale and 5 s exhale) that was carried out for 10 cycles. Post timed respiratory challenge data was then recorded for an additional 120 s. One subject’s respiratory data was excluded due to irrevocable data loss.

Twenty-five right-handed volunteers (10 female, age 26.3 ± 3.3 y [M ± SD]) participated in the control MEG study conducted at the Institute for Biomagnetism and Biosignal Analysis in Münster. All participants reported having no respiratory or neurological disease and gave written informed consent prior to all experimental procedures. The study was approved by the local ethics committee of the University of Münster (approval ID 2021-785-f-S). MEG recording parameters and procedures were identical to the original recordings described above. For each participant, we recorded two 6-min runs of resting state activity: In one run, participants were instructed to breathe naturally through their nose. Continuous monitoring via video ensured participants did indeed keep their mouth closed throughout the recording. In the other run, participants were instructed to breathe through their mouth while wearing a nose clip to prevent nasal breathing. The order of nasal and oral breathing was counterbalanced across participants. Again, we recorded the respiratory signal as thoracic circumference by means of a respiration belt transducer (BIOPAC Systems, Goleta, USA) placed around the participant’s chest. Individual respiration time courses were visually inspected for irregular breathing patterns such as breath holds or unusual breathing frequencies, but no such artefacts were detected.