An Acute Bout of a Controlled Breathing Frequency Lowers Sympathetic Neural Outflow but not Blood Pressure in Healthy Normotensive Subjects.

Controlled or paced breathing is often used as a stress reduction technique but the impact on blood pressure (BP) and sympathetic outflow have not been consistently reported. The purpose of this study was to determine whether a controlled breathing (12 breaths/min, CB) rate would be similar to an individual's spontaneous breathing (SB) rate. Secondly, would a CB rate of 12 breaths/min alter heart rate (HR), BP, and indices of muscle sympathetic nerve activity (MSNA). Twenty-one subjects (10 women, 11 men) performed two trials: SB, where the subject chose a comfortable breathing rate; and CB, where the subject breathed at a pace of 12 breaths/min. Each trial was 6 min during which respiratory waveforms, HR, BP (systolic, SBP; diastolic, DBP), and MSNA were recorded. During CB, the 6 min average breathing frequency (14±4 vs 12±1 breaths/min, P <0.05 for SB and CB, respectively), MSNA burst frequency (18±12 vs 14±10 bursts/min, P <0.01) and MSNA burst incidence (28±19 vs 21± 6 bursts/100 heart beats, P <0.01) were significantly lower than during SB. HR (66±9 vs 67±9 beats/min, P <0.05) was higher during CB. SBP (120±13 vs 121±15 mmHg, P =0.741), DBP (56±8 vs 57±9 mmHg, P =0.768), and MSNA total activity (166±94 vs 145±102 a.u./min, P =0.145) were not different between the breathing conditions. In conclusion, an acute reduction in breathing frequency such as that observed during CB elicited a decrease in indices of MSNA (burst frequency and incidence) with no change in BP.