The effects of paced respiration on cardiopulmonary responses to laboratory stressors

In an effort to evaluate the cardiovascular and respiratory responses to paced respiration, 35 young, male subjects were assigned at random to either a paced respiration or control group. Subjects were tested with a laboratory stress protocol for two sessions: all subjects had unregulated breathing rate during the first session whereas the second session was completed with breathing paced at 8 breaths/min for the paced group and unregulated once again for the unpaced group. Three tasks were used: a reaction time task, a mental arithmetic task, and a cold pressor task. It was discovered during testing that subjects could not adequately pace their breathing during mental arithmetic, so only data from the other two tasks and baseline were analysed. A variety of cardiopulmonary variables were measured, including cardiac output, heart rate, blood pressure, minute ventilation, respiratory rate, and respiratory sinus arrhythmia among others. Results using all subjects indicated few effects due to the pacing manipulation. Systolic and diastolic blood pressure were significantly lower during session 2 than session 1 for the paced subjects, whereas the unpaced group showed no such difference. Coupled with the larger stroke volumes seen by the paced group during session 2 relative to session 1, it was suggested that the pacing manipulation caused decreased peripheral resistance, perhaps due to decreased alpha-adrenergic stimulation as well as the biomechanical effects of slower inspiration. The pacing manipulation did not significantly affect the responses of cardiac output reactors to the reaction time and cold pressor tasks. Respiratory sinus arrhythmia was strongly affected by the pacing, but did not produce significant alterations in heart rate or cardiac output. Areas needing further research are discussed.