title: Cardiorespiratory coupling: common rhythms in cardiac, sympathetic, and respiratory activities.
abstract: Cardiorespiratory coupling is an encompassing term describing more than the well-recognized influences of respiration on heart rate and blood pressure. Our data indicate that cardiorespiratory coupling reflects a reciprocal interaction between autonomic and respiratory control systems, and the cardiovascular system modulates the ventilatory pattern as well. For example, cardioventilatory coupling refers to the influence of heart beats and arterial pulse pressure on respiration and is the tendency for the next inspiration to start at a preferred latency after the last heart beat in expiration. Multiple complementary, well-described mechanisms mediate respiration's influence on cardiovascular function, whereas mechanisms mediating the cardiovascular system's influence on respiration may only be through the baroreceptors but are just being identified. Our review will describe a differential effect of conditioning rats with either chronic intermittent or sustained hypoxia on sympathetic nerve activity but also on ventilatory pattern variability. Both intermittent and sustained hypoxia increase sympathetic nerve activity after 2 weeks but affect sympatho-respiratory coupling differentially. Intermittent hypoxia enhances sympatho-respiratory coupling, which is associated with low variability in the ventilatory pattern. In contrast, after constant hypobaric hypoxia, 1-to-1 coupling between bursts of sympathetic and phrenic nerve activity is replaced by 2-to-3 coupling. This change in coupling pattern is associated with increased variability of the ventilatory pattern. After baro-denervating hypobaric hypoxic-conditioned rats, splanchnic sympathetic nerve activity becomes tonic (distinct bursts are absent) with decreases during phrenic nerve bursts and ventilatory pattern becomes regular. Thus, conditioning rats to either intermittent or sustained hypoxia accentuates the reciprocal nature of cardiorespiratory coupling. Finally, identifying a compelling physiologic purpose for cardiorespiratory coupling is the biggest barrier for recognizing its significance. Cardiorespiratory coupling has only a small effect on the efficiency of gas exchange; rather, we propose that cardiorespiratory control system may act as weakly coupled oscillator to maintain rhythms within a bounded variability.
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, Case Western Reserve University, Cleveland, OH, USA; Department of Neurosciences, Case Western Reserve University, Cleveland, OH, USA. Electronic address: thomas.dick@cwru.edu.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Dick
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, Case Western Reserve University, Cleveland, OH, USA.
authors.forename: Yee-Hsee
authors.initials: YH
authors.lastname: Hsieh
authors.affiliation: Department of Neurosciences, Case Western Reserve University, Cleveland, OH, USA.
authors.forename: Rishi R
authors.initials: RR
authors.lastname: Dhingra
authors.affiliation: Department of Physiological Sciences, University of Florida, Gainesville, FL, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Baekey
authors.affiliation: Department of Neurosciences, Case Western Reserve University, Cleveland, OH, USA.
authors.forename: Roberto F
authors.initials: RF
authors.lastname: Galán
authors.affiliation: Department of Physiology, Michigan State University, East Lansing, MI, USA.
authors.forename: Erica
authors.initials: E
authors.lastname: Wehrwein
authors.affiliation: Department of Molecular Pharmacology and Physiology, University of South Florida, Tampa, FL, USA.
authors.forename: Kendall F
authors.initials: KF
authors.lastname: Morris
mesh_terms: D000818:Animals; D006439:Hemodynamics; D006801:Humans; D010507:Periodicity; D051381:Rats; D012143:Respiratory Physiological Phenomena; D013564:Sympathetic Nervous System / Q000502:physiology*
keywords: neural control of heart rate; neural control of respiration; neural control of sympathetic nerve activity; weakly coupled oscillators
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