hemodynamic effects of slow breathing: does the pattern matter beyond the rate?

purpose: patterned breathing allows standardized serial measurements of heart rate variability and baroreflex indices. the slow breathing augments these parameters, and regular exercises, including yoga breathing practices with even respiratory rates have long-term beneficial effects in cardiovascular diseases. the role of temporization of breathing phases, i.e. the ratio of expiration to inspiration, is not known. in order to characterize the hemodynamic and autonomic responses during varying breathing phases 27 volunteers performed three short breathing sessions at 6/minutes frequency with 5:5, 3:7 and 7:3 inspiration expiration ratios. results: the immediate responses in arterial pressure and heart rate were negligible. the time domain parameters of heart rate variability (sdrr, pnn50, rmssd) increased significantly with patterned breathing. so did the spontaneous baroreflex gain of increasing sequences (up-brs, from 12 ± 7 to 17 ± 10 ms/mmhg, p < 0.05), and the cross-spectral low frequency gain, the lf alpha (from 11 ± 7 to 15 ± 7 ms/mmhg, p < 0.05). none of these parameters differed significantly from each other while using any of tested inspiratory-expiratory patterns. conclusion: the major determinant of autonomic responses induced by slow patterned breathing is the breathing rate itself. from our observations, it follows that slow breathing exercises performed either with diagnostic or therapeutic purpose could be simplified, allowing more extensive investigations