Nonlinear interaction of voluntary breathing and cardiovascular regulation.

To investigate the effects of voluntary breathing on respiratory sinus arrhythmia and nonlinearity of heart rate variability (HRV), two kinds of voluntary breathing, speech and breath-holding, were used. The results showed that both types of voluntary breathing diminished the high frequency component of HRV, but speech decreased, while breath-holding enhanced the nonlinearity of HRV as detected by the Volterra series method. This finding indicates that respiratory patterns have a variety of influences on cardiovascular regulation.