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Effects of controlled breathing, mental activity and mental stress with or without verbalization on heart rate variability

Luciano Bernardi, MD^*, Joanna Wdowczyk-Szulc, MD, Cinzia Valenti, MD^*, Stefano Castoldi, BS^*, Claudio Passino, MD^*, Giammario Spadacini, MD^* and Peter Sleight, MD, FRCP

^* Department of Internal Medicine, IRCCS S. Matteo-University of Pavia, Pavia, Italy
Department of Cardiology, Gdansk, Poland
Department of Cardiovascular Medicine, John Radcliffe Hospital, Oxford, United Kingdom

View larger version (20K): [in a new window]   Figure 1 Effects of spontaneous and controlled breathing, reading (mentally or aloud), talking and mental stress (with or without verbalization) on respiratory frequency and on relative changes in minute ventilation (100% corresponds to minute ventilation during spontaneous breathing). Note that, in conditions associated with verbalization or mental stress, respiration is slowed down and falls into the LF band of RR interval (0.03–0.15 Hz). HF = high frequency; LF = low frequency. *p < 0.05; **p < 0.01; ***p < 0.001 versus spontaneous breathing; p < 0.05; p < 0.01; p < 0.001 versus silent reading; p < 0.05; p < 0.01; p < 0.001 versus controlled breathing; #p < 0.05; ##p < 0.01 versus mental stress aloud.

View larger version (23K): [in a new window]   Figure 2 Results (in normalized units, n.u.) of power spectrum analysis (PSA) of respiration and RR intervals (RR) during spontaneous and controlled breathing, reading (mentally or aloud), talking and mental stress (with or without verbalization). Note the inversion of the LF/HF ratio both in RR and respiration, mainly due to the increase in LF (white bars) as a consequence of slowing of breathing frequency or sympathetic activation (during mental stress), during reading aloud, free talking and mental stress, compared with spontaneous breathing. LF = low frequency, open bars; HF = high frequency, solid bars. *p < 0.05; **p < 0.01 versus spontaneous breathing; p < 0.05; p < 0.01; p < 0.001 versus silent reading; p < 0.05; p < 0.01; p < 0.001 versus controlled breathing.

View larger version (21K): [in a new window]   Figure 3 Power spectra of RR interval (RR) and respiration obtained in one subject during spontaneous breathing, free talking and mental stress aloud and silently. During free talking and mental stress aloud, the frequency of breathing decreases, but during mental stress aloud this fact cannot be totally responsible for the increase in the low frequency components in RR because of the evident decrease in respiratory power (i.e., decrease in tidal volume) and the lack of exact coincidence between the low frequency peaks in respiration and RR. Conversely, the increase in the low frequency components in RR during free talking can be explained, to a great extent, by the slowing of respiratory frequency (no decrease in respiratory power and tidal volume). a.u. = arbitrary units; ms = milliseconds.