Sympathoinhibition in men during paced breathing at 0.25 Hz

This study tested the hypothesis that paced breathing (PB) would inhibit muscle sympathetic nerve activity (MSNA). Integrated MSNA (peroneal nerve) and hemodynamics were assessed in healthy young men (26 ± 2 years; n=8) while supine during spontaneous breathing over 2 to 5 minutes and then at 0.25 Hz for 4 minutes with a recovery period. Breathing rate was not different between spontaneous and PB (15.6 ± 2.0 vs 15.0 ± 0.5 breaths/minute). Compared to baseline, PB reduced (~25%) burst frequency (19 ± 7 vs 14 ± 8 bursts/minute, p<0.01) and incidence (35 ± 12 vs 27 ± 13 bursts/100 heart beats, p<0.01). These returned to baseline levels during recovery. Total MSNA, (mean burst amplitude x burst frequency) also was reduced with PB (2.5 ± 1.3 a.u.) compared with spontaneous breathing (3.3 ± 1.1 a.u.)(p<0.05). No differences were observed in heart rate, mean arterial pressure, burst amplitude, or stroke volume between conditions but cardiac output was higher (~10%) during PB (3.6 ± 0.9 L/min) versus baseline (4.0 ± 0.9 L/min)(p<0.05). Therefore, PB inhibited MSNA in a manner that was not accounted for by concurrent changes in blood pressure or cardiac output. Supported by CIHR and NSERC.