Review articleModulatory effects of respiration
Introduction
Although cardiovascular variability arises from many different influences, probably the most consistent “external” modulator is breathing. Due to the highly complex organisation of breathing and the sophisticated respiratory responses to various stimuli, it is not surprising that the effects of respiration are complex, affecting cardiovascular variability at every level. Cardiovascular variability results from a number of associated factors, intrinsic, pseudo-rhythmic and transient.
Intrinsic rhythmicity at various frequencies had been described in the brainstem, in the efferent neurons and in the cardiac pacemaker cells. Rhythms of central origin modulate the cardiac pacemaker cells, producing oscillations in all frequency bands Koepchen et al., 1986, Shykoff et al., 1991, Malliani et al., 1991. Rhythms caused by the baroreflex may interact with rhythms generated in the brainstem De Boer et al., 1987, Bernardi et al., 1994a.
Pseudo-rhythmic phenomena include events that are often rhythmic but can change in frequency or show sudden changes in response to various stimuli; a typical example is respiration: respiratory pacemaker cells are located in the brainstem and generate a rhythm whose frequency and depth are primarily controlled by the central and peripheral chemoreflexes but can be easily varied by various factors such as exercise, stress, temperature and voluntary control, and more in general, by the two branches of the autonomic nervous system (Kitney and Rompelman, 1987).
The cardiovascular system is highly reactive to transient external stimuli; mechanical, gravitational, acoustic or thermal stimulation are only a few amongst many possible stimuli that can change the sympathetic–parasympathetic interaction Kitney and Rompelman, 1987, Bernardi et al., 1996. All these changes alter the frequency and depth of respiration, because of the need for an increase/decrease in ventilation as a consequence of associated stress/arousal.
Many different changes in respiration can be used to manipulate cardiovascular variability. The respiratory pattern is highly sensitive to voluntary changes; training of some aspects of respiratory function may temporarily or permanently influence cardiovascular modulation; therefore, is reasonable to suggest that manipulation of respiration may prove to be helpful in different physiologic and pathologic conditions. There is now growing evidence to support this view.
Section snippets
Respiratory sinus arrhythmia
Respiratory related variations in cardiovascular parameters are now increasingly studied not only as indices of autonomic activity but also because they convey information about pathophysiological processes and their prognosis. For example, chronic reduction of heart rate variability after myocardial infarction is a marker for subsequent sudden cardiac death Wolf et al., 1978, La Rovere et al., 1988. In healthy and in diabetic subjects, respiration related fluctuations in RR interval
Interaction between breathing rate and chemoreflex control of breathing
Since the discovery that dyspnea in heart failure is linked to a disturbed chemoreflex drive (Coats, 1997), the importance of the control of breathing through the chemoreflex is increasingly being recognised in the clinical field, and relatively simple methods, such as the rebreathing tests, have been applied in order to test the chemoreflex sensitivity to either oxygen or carbon dioxide Kronenberg et al., 1972, Rebuck and Campbell, 1974, Milic-Emili, 1975, Shaw et al., 1982, Chua and Coats,
The importance of manipulating breathing patterns in pathologic and physiologic conditions
The majority of groups studying cardiovascular autonomic control in various pathologic diseases did not consider the possibility that respiratory activity may vary and may be used as a compensating factor, at least in certain critical situations. A few studies (Lipsitz et al., 1998), however, indicate that changes in the respiratory pattern may help subjects affected by various diseases to cope with impending syncope or orthostatic hypotension. Full understanding of these spontaneous changes
Conclusions
Respiration is a powerful modulator of heart rate variability, and of reflex control systems. Abnormal respiratory modulation is often an early sign of autonomic dysfunction in a number of diseases. Manipulation of breathing pattern may provide beneficial effects not only of ventilatory efficiency, but also of cardiovascular and respiratory control in physiologic and pathologic conditions such as chronic heart failure. This opens a new area of future research in the better management of
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